《Temporal AA , SMAA and MSAA》

Temporal AA

Temporal AA主要是为了修复场景帧率小于运动物体运动速度的锯齿问题，当帧率太低时候，运动的物体就会一卡一卡，为了避免这种造成的锯齿，原理上帧率刷新速度应该大于两倍运动速度才行。TXAA就是为了修复这种情况。比如高速旋转的轮子用这种AA就会有很好的效果。

伪代码：

For each image frame:
        For each object in the frame:
                Calculate the temporal transformation function for each dynamic attribute
                Determine the areas the object covers during the filtered interval
        For each pixel:
                Determine which objects are covering this pixel at some time in the sampled interval
                Determine the subintervals of time during which each object projects onto this pixel
                Perform hidden surface removal by removing subintervals of occluded objects
                Determine pixel intensity function based on the remaining subintervals and the object's temporal transformation function
        Filter resulting pixel intensity function

上面伪代码中最后一步提到的“temporal transformation function”简单指代一个和物体改变相关的函数，比如，在一帧内物体移动到位置。

一些object的属性比如形状，颜色，位置等作为分析并不是很有效率，如果要使用，它们的值之间需要进行插值，利用B-Splines或者简单的线性插值。

TXAA对于非常简单的物体（比如圆盘）可以在image space，对于特别复杂的几何体，就需要在object space之内进行以上算法的估算。

这种AA在实现的时候，可能会依赖motion vector buffer或者前一帧的变换矩阵来找到上一帧像素对应位置，然后做一些blur。

 

wiki的解释：

https://en.wikipedia.org/wiki/Temporal_anti-aliasing

 

关于UE4的Temporal AA的解释：

https://de45xmedrsdbp.cloudfront.net/Resources/files/TemporalAA_small-59732822.pdf

---

 

SMAA

SMAA(Subpixel Morphological Antialiasing) 是目前效果和效率相对最好的AA方法，基于MLAA的寻边算法，相比于传统的MSAA的耗费大，TXAA(tmporal AA)，FXAA造成比较糊的效果，SMAA是AA算法首选。 

https://github.com/iryoku/smaa

/**
 * Copyright (C) 2013 Jorge Jimenez (jorge@iryoku.com)
 * Copyright (C) 2013 Jose I. Echevarria (joseignacioechevarria@gmail.com)
 * Copyright (C) 2013 Belen Masia (bmasia@unizar.es)
 * Copyright (C) 2013 Fernando Navarro (fernandn@microsoft.com)
 * Copyright (C) 2013 Diego Gutierrez (diegog@unizar.es)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is furnished to
 * do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software. As clarification, there
 * is no requirement that the copyright notice and permission be included in
 * binary distributions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */


/**
 *                  _______  ___  ___       ___           ___
 *                 /       ||   \/   |     /   \         /   \
 *                |   (---- |  \  /  |    /  ^  \       /  ^  \
 *                 \   \    |  |\/|  |   /  /_\  \     /  /_\  \
 *              ----)   |   |  |  |  |  /  _____  \   /  _____  \
 *             |_______/    |__|  |__| /__/     \__\ /__/     \__\
 * 
 *                               E N H A N C E D
 *       S U B P I X E L   M O R P H O L O G I C A L   A N T I A L I A S I N G
 *
 *                         http://www.iryoku.com/smaa/
 *
 * Hi, welcome aboard!
 * 
 * Here you'll find instructions to get the shader up and running as fast as
 * possible.
 *
 * IMPORTANTE NOTICE: when updating, remember to update both this file and the
 * precomputed textures! They may change from version to version.
 *
 * The shader has three passes, chained together as follows:
 *
 *                           |input|------------------·
 *                              v                     |
 *                    [ SMAA*EdgeDetection ]          |
 *                              v                     |
 *                          |edgesTex|                |
 *                              v                     |
 *              [ SMAABlendingWeightCalculation ]     |
 *                              v                     |
 *                          |blendTex|                |
 *                              v                     |
 *                [ SMAANeighborhoodBlending ] <------·
 *                              v
 *                           |output|
 *
 * Note that each [pass] has its own vertex and pixel shader. Remember to use
 * oversized triangles instead of quads to avoid overshading along the
 * diagonal.
 *
 * You've three edge detection methods to choose from: luma, color or depth.
 * They represent different quality/performance and anti-aliasing/sharpness
 * tradeoffs, so our recommendation is for you to choose the one that best
 * suits your particular scenario:
 *
 * - Depth edge detection is usually the fastest but it may miss some edges.
 *
 * - Luma edge detection is usually more expensive than depth edge detection,
 *   but catches visible edges that depth edge detection can miss.
 *
 * - Color edge detection is usually the most expensive one but catches
 *   chroma-only edges.
 *
 * For quickstarters: just use luma edge detection.
 *
 * The general advice is to not rush the integration process and ensure each
 * step is done correctly (don't try to integrate SMAA T2x with predicated edge
 * detection from the start!). Ok then, let's go!
 *
 *  1. The first step is to create two RGBA temporal render targets for holding
 *     |edgesTex| and |blendTex|.
 *
 *     In DX10 or DX11, you can use a RG render target for the edges texture.
 *     In the case of NVIDIA GPUs, using RG render targets seems to actually be
 *     slower.
 *
 *     On the Xbox 360, you can use the same render target for resolving both
 *     |edgesTex| and |blendTex|, as they aren't needed simultaneously.
 *
 *  2. Both temporal render targets |edgesTex| and |blendTex| must be cleared
 *     each frame. Do not forget to clear the alpha channel!
 *
 *  3. The next step is loading the two supporting precalculated textures,
 *     'areaTex' and 'searchTex'. You'll find them in the 'Textures' folder as
 *     C++ headers, and also as regular DDS files. They'll be needed for the
 *     'SMAABlendingWeightCalculation' pass.
 *
 *     If you use the C++ headers, be sure to load them in the format specified
 *     inside of them.
 *
 *     You can also compress 'areaTex' and 'searchTex' using BC5 and BC4
 *     respectively, if you have that option in your content processor pipeline.
 *     When compressing then, you get a non-perceptible quality decrease, and a
 *     marginal performance increase.
 *
 *  4. All samplers must be set to linear filtering and clamp.
 *
 *     After you get the technique working, remember that 64-bit inputs have
 *     half-rate linear filtering on GCN.
 *
 *     If SMAA is applied to 64-bit color buffers, switching to point filtering
 *     when accesing them will increase the performance. Search for
 *     'SMAASamplePoint' to see which textures may benefit from point
 *     filtering, and where (which is basically the color input in the edge
 *     detection and resolve passes).
 *
 *  5. All texture reads and buffer writes must be non-sRGB, with the exception
 *     of the input read and the output write in
 *     'SMAANeighborhoodBlending' (and only in this pass!). If sRGB reads in
 *     this last pass are not possible, the technique will work anyway, but
 *     will perform antialiasing in gamma space.
 *
 *     IMPORTANT: for best results the input read for the color/luma edge 
 *     detection should *NOT* be sRGB.
 *
 *  6. Before including SMAA.h you'll have to setup the render target metrics,
 *     the target and any optional configuration defines. Optionally you can
 *     use a preset.
 *
 *     You have the following targets available: 
 *         SMAA_HLSL_3
 *         SMAA_HLSL_4
 *         SMAA_HLSL_4_1
 *         SMAA_GLSL_3 *
 *         SMAA_GLSL_4 *
 *
 *         * (See SMAA_INCLUDE_VS and SMAA_INCLUDE_PS below).
 *
 *     And four presets:
 *         SMAA_PRESET_LOW          (%60 of the quality)
 *         SMAA_PRESET_MEDIUM       (%80 of the quality)
 *         SMAA_PRESET_HIGH         (%95 of the quality)
 *         SMAA_PRESET_ULTRA        (%99 of the quality)
 *
 *     For example:
 *         #define SMAA_RT_METRICS float4(1.0 / 1280.0, 1.0 / 720.0, 1280.0, 720.0)
 *         #define SMAA_HLSL_4
 *         #define SMAA_PRESET_HIGH
 *         #include "SMAA.h"
 *
 *     Note that SMAA_RT_METRICS doesn't need to be a macro, it can be a
 *     uniform variable. The code is designed to minimize the impact of not
 *     using a constant value, but it is still better to hardcode it.
 *
 *     Depending on how you encoded 'areaTex' and 'searchTex', you may have to
 *     add (and customize) the following defines before including SMAA.h:
 *          #define SMAA_AREATEX_SELECT(sample) sample.rg
 *          #define SMAA_SEARCHTEX_SELECT(sample) sample.r
 *
 *     If your engine is already using porting macros, you can define
 *     SMAA_CUSTOM_SL, and define the porting functions by yourself.
 *
 *  7. Then, you'll have to setup the passes as indicated in the scheme above.
 *     You can take a look into SMAA.fx, to see how we did it for our demo.
 *     Checkout the function wrappers, you may want to copy-paste them!
 *
 *  8. It's recommended to validate the produced |edgesTex| and |blendTex|.
 *     You can use a screenshot from your engine to compare the |edgesTex|
 *     and |blendTex| produced inside of the engine with the results obtained
 *     with the reference demo.
 *
 *  9. After you get the last pass to work, it's time to optimize. You'll have
 *     to initialize a stencil buffer in the first pass (discard is already in
 *     the code), then mask execution by using it the second pass. The last
 *     pass should be executed in all pixels.
 *
 *
 * After this point you can choose to enable predicated thresholding,
 * temporal supersampling and motion blur integration:
 *
 * a) If you want to use predicated thresholding, take a look into
 *    SMAA_PREDICATION; you'll need to pass an extra texture in the edge
 *    detection pass.
 *
 * b) If you want to enable temporal supersampling (SMAA T2x):
 *
 * 1. The first step is to render using subpixel jitters. I won't go into
 *    detail, but it's as simple as moving each vertex position in the
 *    vertex shader, you can check how we do it in our DX10 demo.
 *
 * 2. Then, you must setup the temporal resolve. You may want to take a look
 *    into SMAAResolve for resolving 2x modes. After you get it working, you'll
 *    probably see ghosting everywhere. But fear not, you can enable the
 *    CryENGINE temporal reprojection by setting the SMAA_REPROJECTION macro.
 *    Check out SMAA_DECODE_VELOCITY if your velocity buffer is encoded.
 *
 * 3. The next step is to apply SMAA to each subpixel jittered frame, just as
 *    done for 1x.
 *
 * 4. At this point you should already have something usable, but for best
 *    results the proper area textures must be set depending on current jitter.
 *    For this, the parameter 'subsampleIndices' of
 *    'SMAABlendingWeightCalculationPS' must be set as follows, for our T2x
 *    mode:
 *
 *    @SUBSAMPLE_INDICES
 *
 *    | S# |  Camera Jitter   |  subsampleIndices    |
 *    +----+------------------+---------------------+
 *    |  0 |  ( 0.25, -0.25)  |  float4(1, 1, 1, 0)  |
 *    |  1 |  (-0.25,  0.25)  |  float4(2, 2, 2, 0)  |
 *
 *    These jitter positions assume a bottom-to-top y axis. S# stands for the
 *    sample number.
 *
 * More information about temporal supersampling here:
 *    http://iryoku.com/aacourse/downloads/13-Anti-Aliasing-Methods-in-CryENGINE-3.pdf
 *
 * c) If you want to enable spatial multisampling (SMAA S2x):
 *
 * 1. The scene must be rendered using MSAA 2x. The MSAA 2x buffer must be
 *    created with:
 *      - DX10:     see below (*)
 *      - DX10.1:   D3D10_STANDARD_MULTISAMPLE_PATTERN or
 *      - DX11:     D3D11_STANDARD_MULTISAMPLE_PATTERN
 *
 *    This allows to ensure that the subsample order matches the table in
 *    @SUBSAMPLE_INDICES.
 *
 *    (*) In the case of DX10, we refer the reader to:
 *      - SMAA::detectMSAAOrder and
 *      - SMAA::msaaReorder
 *
 *    These functions allow to match the standard multisample patterns by
 *    detecting the subsample order for a specific GPU, and reordering
 *    them appropriately.
 *
 * 2. A shader must be run to output each subsample into a separate buffer
 *    (DX10 is required). You can use SMAASeparate for this purpose, or just do
 *    it in an existing pass (for example, in the tone mapping pass, which has
 *    the advantage of feeding tone mapped subsamples to SMAA, which will yield
 *    better results).
 *
 * 3. The full SMAA 1x pipeline must be run for each separated buffer, storing
 *    the results in the final buffer. The second run should alpha blend with
 *    the existing final buffer using a blending factor of 0.5.
 *    'subsampleIndices' must be adjusted as in the SMAA T2x case (see point
 *    b).
 *
 * d) If you want to enable temporal supersampling on top of SMAA S2x
 *    (which actually is SMAA 4x):
 *
 * 1. SMAA 4x consists on temporally jittering SMAA S2x, so the first step is
 *    to calculate SMAA S2x for current frame. In this case, 'subsampleIndices'
 *    must be set as follows:
 *
 *    | F# | S# |   Camera Jitter    |    Net Jitter     |   subsampleIndices   |
 *    +----+----+--------------------+-------------------+----------------------+
 *    |  0 |  0 |  ( 0.125,  0.125)  |  ( 0.375, -0.125) |  float4(5, 3, 1, 3)  |
 *    |  0 |  1 |  ( 0.125,  0.125)  |  (-0.125,  0.375) |  float4(4, 6, 2, 3)  |
 *    +----+----+--------------------+-------------------+----------------------+
 *    |  1 |  2 |  (-0.125, -0.125)  |  ( 0.125, -0.375) |  float4(3, 5, 1, 4)  |
 *    |  1 |  3 |  (-0.125, -0.125)  |  (-0.375,  0.125) |  float4(6, 4, 2, 4)  |
 *
 *    These jitter positions assume a bottom-to-top y axis. F# stands for the
 *    frame number. S# stands for the sample number.
 *
 * 2. After calculating SMAA S2x for current frame (with the new subsample
 *    indices), previous frame must be reprojected as in SMAA T2x mode (see
 *    point b).
 *
 * e) If motion blur is used, you may want to do the edge detection pass
 *    together with motion blur. This has two advantages:
 *
 * 1. Pixels under heavy motion can be omitted from the edge detection process.
 *    For these pixels we can just store "no edge", as motion blur will take
 *    care of them.
 * 2. The center pixel tap is reused.
 *
 * Note that in this case depth testing should be used instead of stenciling,
 * as we have to write all the pixels in the motion blur pass.
 *
 * That's it!
 */

//-----------------------------------------------------------------------------
// SMAA Presets

/**
 * Note that if you use one of these presets, the following configuration
 * macros will be ignored if set in the "Configurable Defines" section.
 */

#if defined(SMAA_PRESET_LOW)
#define SMAA_THRESHOLD 0.15
#define SMAA_MAX_SEARCH_STEPS 4
#define SMAA_DISABLE_DIAG_DETECTION
#define SMAA_DISABLE_CORNER_DETECTION
#elif defined(SMAA_PRESET_MEDIUM)
#define SMAA_THRESHOLD 0.1
#define SMAA_MAX_SEARCH_STEPS 8
#define SMAA_DISABLE_DIAG_DETECTION
#define SMAA_DISABLE_CORNER_DETECTION
#elif defined(SMAA_PRESET_HIGH)
#define SMAA_THRESHOLD 0.1
#define SMAA_MAX_SEARCH_STEPS 16
#define SMAA_MAX_SEARCH_STEPS_DIAG 8
#define SMAA_CORNER_ROUNDING 25
#elif defined(SMAA_PRESET_ULTRA)
#define SMAA_THRESHOLD 0.05
#define SMAA_MAX_SEARCH_STEPS 32
#define SMAA_MAX_SEARCH_STEPS_DIAG 16
#define SMAA_CORNER_ROUNDING 25
#endif

//-----------------------------------------------------------------------------
// Configurable Defines

/**
 * SMAA_THRESHOLD specifies the threshold or sensitivity to edges.
 * Lowering this value you will be able to detect more edges at the expense of
 * performance. 
 *
 * Range: [0, 0.5]
 *   0.1 is a reasonable value, and allows to catch most visible edges.
 *   0.05 is a rather overkill value, that allows to catch 'em all.
 *
 *   If temporal supersampling is used, 0.2 could be a reasonable value, as low
 *   contrast edges are properly filtered by just 2x.
 */
#ifndef SMAA_THRESHOLD
#define SMAA_THRESHOLD 0.1
#endif

/**
 * SMAA_DEPTH_THRESHOLD specifies the threshold for depth edge detection.
 * 
 * Range: depends on the depth range of the scene.
 */
#ifndef SMAA_DEPTH_THRESHOLD
#define SMAA_DEPTH_THRESHOLD (0.1 * SMAA_THRESHOLD)
#endif

/**
 * SMAA_MAX_SEARCH_STEPS specifies the maximum steps performed in the
 * horizontal/vertical pattern searches, at each side of the pixel.
 *
 * In number of pixels, it's actually the double. So the maximum line length
 * perfectly handled by, for example 16, is 64 (by perfectly, we meant that
 * longer lines won't look as good, but still antialiased).
 *
 * Range: [0, 112]
 */
#ifndef SMAA_MAX_SEARCH_STEPS
#define SMAA_MAX_SEARCH_STEPS 16
#endif

/**
 * SMAA_MAX_SEARCH_STEPS_DIAG specifies the maximum steps performed in the
 * diagonal pattern searches, at each side of the pixel. In this case we jump
 * one pixel at time, instead of two.
 *
 * Range: [0, 20]
 *
 * On high-end machines it is cheap (between a 0.8x and 0.9x slower for 16 
 * steps), but it can have a significant impact on older machines.
 *
 * Define SMAA_DISABLE_DIAG_DETECTION to disable diagonal processing.
 */
#ifndef SMAA_MAX_SEARCH_STEPS_DIAG
#define SMAA_MAX_SEARCH_STEPS_DIAG 8
#endif

/**
 * SMAA_CORNER_ROUNDING specifies how much sharp corners will be rounded.
 *
 * Range: [0, 100]
 *
 * Define SMAA_DISABLE_CORNER_DETECTION to disable corner processing.
 */
#ifndef SMAA_CORNER_ROUNDING
#define SMAA_CORNER_ROUNDING 25
#endif

/**
 * If there is an neighbor edge that has SMAA_LOCAL_CONTRAST_FACTOR times
 * bigger contrast than current edge, current edge will be discarded.
 *
 * This allows to eliminate spurious crossing edges, and is based on the fact
 * that, if there is too much contrast in a direction, that will hide
 * perceptually contrast in the other neighbors.
 */
#ifndef SMAA_LOCAL_CONTRAST_ADAPTATION_FACTOR
#define SMAA_LOCAL_CONTRAST_ADAPTATION_FACTOR 2.0
#endif

/**
 * Predicated thresholding allows to better preserve texture details and to
 * improve performance, by decreasing the number of detected edges using an
 * additional buffer like the light accumulation buffer, object ids or even the
 * depth buffer (the depth buffer usage may be limited to indoor or short range
 * scenes).
 *
 * It locally decreases the luma or color threshold if an edge is found in an
 * additional buffer (so the global threshold can be higher).
 *
 * This method was developed by Playstation EDGE MLAA team, and used in 
 * Killzone 3, by using the light accumulation buffer. More information here:
 *     http://iryoku.com/aacourse/downloads/06-MLAA-on-PS3.pptx 
 */
#ifndef SMAA_PREDICATION
#define SMAA_PREDICATION 0
#endif

/**
 * Threshold to be used in the additional predication buffer. 
 *
 * Range: depends on the input, so you'll have to find the magic number that
 * works for you.
 */
#ifndef SMAA_PREDICATION_THRESHOLD
#define SMAA_PREDICATION_THRESHOLD 0.01
#endif

/**
 * How much to scale the global threshold used for luma or color edge
 * detection when using predication.
 *
 * Range: [1, 5]
 */
#ifndef SMAA_PREDICATION_SCALE
#define SMAA_PREDICATION_SCALE 2.0
#endif

/**
 * How much to locally decrease the threshold.
 *
 * Range: [0, 1]
 */
#ifndef SMAA_PREDICATION_STRENGTH
#define SMAA_PREDICATION_STRENGTH 0.4
#endif

/**
 * Temporal reprojection allows to remove ghosting artifacts when using
 * temporal supersampling. We use the CryEngine 3 method which also introduces
 * velocity weighting. This feature is of extreme importance for totally
 * removing ghosting. More information here:
 *    http://iryoku.com/aacourse/downloads/13-Anti-Aliasing-Methods-in-CryENGINE-3.pdf
 *
 * Note that you'll need to setup a velocity buffer for enabling reprojection.
 * For static geometry, saving the previous depth buffer is a viable
 * alternative.
 */
#ifndef SMAA_REPROJECTION
#define SMAA_REPROJECTION 0
#endif

/**
 * SMAA_REPROJECTION_WEIGHT_SCALE controls the velocity weighting. It allows to
 * remove ghosting trails behind the moving object, which are not removed by
 * just using reprojection. Using low values will exhibit ghosting, while using
 * high values will disable temporal supersampling under motion.
 *
 * Behind the scenes, velocity weighting removes temporal supersampling when
 * the velocity of the subsamples differs (meaning they are different objects).
 *
 * Range: [0, 80]
 */
#ifndef SMAA_REPROJECTION_WEIGHT_SCALE
#define SMAA_REPROJECTION_WEIGHT_SCALE 30.0
#endif

/**
 * On some compilers, discard cannot be used in vertex shaders. Thus, they need
 * to be compiled separately.
 */
#ifndef SMAA_INCLUDE_VS
#define SMAA_INCLUDE_VS 1
#endif
#ifndef SMAA_INCLUDE_PS
#define SMAA_INCLUDE_PS 1
#endif

//-----------------------------------------------------------------------------
// Texture Access Defines

#ifndef SMAA_AREATEX_SELECT
#if defined(SMAA_HLSL_3)
#define SMAA_AREATEX_SELECT(sample) sample.ra
#else
#define SMAA_AREATEX_SELECT(sample) sample.rg
#endif
#endif

#ifndef SMAA_SEARCHTEX_SELECT
#define SMAA_SEARCHTEX_SELECT(sample) sample.r
#endif

#ifndef SMAA_DECODE_VELOCITY
#define SMAA_DECODE_VELOCITY(sample) sample.rg
#endif

//-----------------------------------------------------------------------------
// Non-Configurable Defines

#define SMAA_AREATEX_MAX_DISTANCE 16
#define SMAA_AREATEX_MAX_DISTANCE_DIAG 20
#define SMAA_AREATEX_PIXEL_SIZE (1.0 / float2(160.0, 560.0))
#define SMAA_AREATEX_SUBTEX_SIZE (1.0 / 7.0)
#define SMAA_SEARCHTEX_SIZE float2(66.0, 33.0)
#define SMAA_SEARCHTEX_PACKED_SIZE float2(64.0, 16.0)
#define SMAA_CORNER_ROUNDING_NORM (float(SMAA_CORNER_ROUNDING) / 100.0)

//-----------------------------------------------------------------------------
// Porting Functions

#if defined(SMAA_HLSL_3)
#define SMAATexture2D(tex) sampler2D tex
#define SMAATexturePass2D(tex) tex
#define SMAASampleLevelZero(tex, coord) tex2Dlod(tex, float4(coord, 0.0, 0.0))
#define SMAASampleLevelZeroPoint(tex, coord) tex2Dlod(tex, float4(coord, 0.0, 0.0))
#define SMAASampleLevelZeroOffset(tex, coord, offset) tex2Dlod(tex, float4(coord + offset * SMAA_RT_METRICS.xy, 0.0, 0.0))
#define SMAASample(tex, coord) tex2D(tex, coord)
#define SMAASamplePoint(tex, coord) tex2D(tex, coord)
#define SMAASampleOffset(tex, coord, offset) tex2D(tex, coord + offset * SMAA_RT_METRICS.xy)
#define SMAA_FLATTEN [flatten]
#define SMAA_BRANCH [branch]
#endif
#if defined(SMAA_HLSL_4) || defined(SMAA_HLSL_4_1)
SamplerState LinearSampler { Filter = MIN_MAG_LINEAR_MIP_POINT; AddressU = Clamp; AddressV = Clamp; };
SamplerState PointSampler { Filter = MIN_MAG_MIP_POINT; AddressU = Clamp; AddressV = Clamp; };
#define SMAATexture2D(tex) Texture2D tex
#define SMAATexturePass2D(tex) tex
#define SMAASampleLevelZero(tex, coord) tex.SampleLevel(LinearSampler, coord, 0)
#define SMAASampleLevelZeroPoint(tex, coord) tex.SampleLevel(PointSampler, coord, 0)
#define SMAASampleLevelZeroOffset(tex, coord, offset) tex.SampleLevel(LinearSampler, coord, 0, offset)
#define SMAASample(tex, coord) tex.Sample(LinearSampler, coord)
#define SMAASamplePoint(tex, coord) tex.Sample(PointSampler, coord)
#define SMAASampleOffset(tex, coord, offset) tex.Sample(LinearSampler, coord, offset)
#define SMAA_FLATTEN [flatten]
#define SMAA_BRANCH [branch]
#define SMAATexture2DMS2(tex) Texture2DMS<float4, 2> tex
#define SMAALoad(tex, pos, sample) tex.Load(pos, sample)
#if defined(SMAA_HLSL_4_1)
#define SMAAGather(tex, coord) tex.Gather(LinearSampler, coord, 0)
#endif
#endif
#if defined(SMAA_GLSL_3) || defined(SMAA_GLSL_4)
#define SMAATexture2D(tex) sampler2D tex
#define SMAATexturePass2D(tex) tex
#define SMAASampleLevelZero(tex, coord) textureLod(tex, coord, 0.0)
#define SMAASampleLevelZeroPoint(tex, coord) textureLod(tex, coord, 0.0)
#define SMAASampleLevelZeroOffset(tex, coord, offset) textureLodOffset(tex, coord, 0.0, offset)
#define SMAASample(tex, coord) texture(tex, coord)
#define SMAASamplePoint(tex, coord) texture(tex, coord)
#define SMAASampleOffset(tex, coord, offset) texture(tex, coord, offset)
#define SMAA_FLATTEN
#define SMAA_BRANCH
#define lerp(a, b, t) mix(a, b, t)
#define saturate(a) clamp(a, 0.0, 1.0)
#if defined(SMAA_GLSL_4)
#define mad(a, b, c) fma(a, b, c)
#define SMAAGather(tex, coord) textureGather(tex, coord)
#else
#define mad(a, b, c) (a * b + c)
#endif
#define float2 vec2
#define float3 vec3
#define float4 vec4
#define int2 ivec2
#define int3 ivec3
#define int4 ivec4
#define bool2 bvec2
#define bool3 bvec3
#define bool4 bvec4
#endif

#if !defined(SMAA_HLSL_3) && !defined(SMAA_HLSL_4) && !defined(SMAA_HLSL_4_1) && !defined(SMAA_GLSL_3) && !defined(SMAA_GLSL_4) && !defined(SMAA_CUSTOM_SL)
#error you must define the shading language: SMAA_HLSL_*, SMAA_GLSL_* or SMAA_CUSTOM_SL
#endif

//-----------------------------------------------------------------------------
// Misc functions

/**
 * Gathers current pixel, and the top-left neighbors.
 */
float3 SMAAGatherNeighbours(float2 texcoord,
                            float4 offset[3],
                            SMAATexture2D(tex)) {
    #ifdef SMAAGather
    return SMAAGather(tex, texcoord + SMAA_RT_METRICS.xy * float2(-0.5, -0.5)).grb;
    #else
    float P = SMAASamplePoint(tex, texcoord).r;
    float Pleft = SMAASamplePoint(tex, offset[0].xy).r;
    float Ptop  = SMAASamplePoint(tex, offset[0].zw).r;
    return float3(P, Pleft, Ptop);
    #endif
}

/**
 * Adjusts the threshold by means of predication.
 */
float2 SMAACalculatePredicatedThreshold(float2 texcoord,
                                        float4 offset[3],
                                        SMAATexture2D(predicationTex)) {
    float3 neighbours = SMAAGatherNeighbours(texcoord, offset, SMAATexturePass2D(predicationTex));
    float2 delta = abs(neighbours.xx - neighbours.yz);
    float2 edges = step(SMAA_PREDICATION_THRESHOLD, delta);
    return SMAA_PREDICATION_SCALE * SMAA_THRESHOLD * (1.0 - SMAA_PREDICATION_STRENGTH * edges);
}

/**
 * Conditional move:
 */
void SMAAMovc(bool2 cond, inout float2 variable, float2 value) {
    SMAA_FLATTEN if (cond.x) variable.x = value.x;
    SMAA_FLATTEN if (cond.y) variable.y = value.y;
}

void SMAAMovc(bool4 cond, inout float4 variable, float4 value) {
    SMAAMovc(cond.xy, variable.xy, value.xy);
    SMAAMovc(cond.zw, variable.zw, value.zw);
}


#if SMAA_INCLUDE_VS
//-----------------------------------------------------------------------------
// Vertex Shaders

/**
 * Edge Detection Vertex Shader
 */
void SMAAEdgeDetectionVS(float2 texcoord,
                         out float4 offset[3]) {
    offset[0] = mad(SMAA_RT_METRICS.xyxy, float4(-1.0, 0.0, 0.0, -1.0), texcoord.xyxy);
    offset[1] = mad(SMAA_RT_METRICS.xyxy, float4( 1.0, 0.0, 0.0,  1.0), texcoord.xyxy);
    offset[2] = mad(SMAA_RT_METRICS.xyxy, float4(-2.0, 0.0, 0.0, -2.0), texcoord.xyxy);
}

/**
 * Blend Weight Calculation Vertex Shader
 */
void SMAABlendingWeightCalculationVS(float2 texcoord,
                                     out float2 pixcoord,
                                     out float4 offset[3]) {
    pixcoord = texcoord * SMAA_RT_METRICS.zw;

    // We will use these offsets for the searches later on (see @PSEUDO_GATHER4):
    offset[0] = mad(SMAA_RT_METRICS.xyxy, float4(-0.25, -0.125,  1.25, -0.125), texcoord.xyxy);
    offset[1] = mad(SMAA_RT_METRICS.xyxy, float4(-0.125, -0.25, -0.125,  1.25), texcoord.xyxy);

    // And these for the searches, they indicate the ends of the loops:
    offset[2] = mad(SMAA_RT_METRICS.xxyy,
                    float4(-2.0, 2.0, -2.0, 2.0) * float(SMAA_MAX_SEARCH_STEPS),
                    float4(offset[0].xz, offset[1].yw));
}

/**
 * Neighborhood Blending Vertex Shader
 */
void SMAANeighborhoodBlendingVS(float2 texcoord,
                                out float4 offset) {
    offset = mad(SMAA_RT_METRICS.xyxy, float4( 1.0, 0.0, 0.0,  1.0), texcoord.xyxy);
}
#endif // SMAA_INCLUDE_VS

#if SMAA_INCLUDE_PS
//-----------------------------------------------------------------------------
// Edge Detection Pixel Shaders (First Pass)

/**
 * Luma Edge Detection
 *
 * IMPORTANT NOTICE: luma edge detection requires gamma-corrected colors, and
 * thus 'colorTex' should be a non-sRGB texture.
 */
float2 SMAALumaEdgeDetectionPS(float2 texcoord,
                               float4 offset[3],
                               SMAATexture2D(colorTex)
                               #if SMAA_PREDICATION
                               , SMAATexture2D(predicationTex)
                               #endif
                               ) {
    // Calculate the threshold:
    #if SMAA_PREDICATION
    float2 threshold = SMAACalculatePredicatedThreshold(texcoord, offset, SMAATexturePass2D(predicationTex));
    #else
    float2 threshold = float2(SMAA_THRESHOLD, SMAA_THRESHOLD);
    #endif

    // Calculate lumas:
    float3 weights = float3(0.2126, 0.7152, 0.0722);
    float L = dot(SMAASamplePoint(colorTex, texcoord).rgb, weights);

    float Lleft = dot(SMAASamplePoint(colorTex, offset[0].xy).rgb, weights);
    float Ltop  = dot(SMAASamplePoint(colorTex, offset[0].zw).rgb, weights);

    // We do the usual threshold:
    float4 delta;
    delta.xy = abs(L - float2(Lleft, Ltop));
    float2 edges = step(threshold, delta.xy);

    // Then discard if there is no edge:
    if (dot(edges, float2(1.0, 1.0)) == 0.0)
        discard;

    // Calculate right and bottom deltas:
    float Lright = dot(SMAASamplePoint(colorTex, offset[1].xy).rgb, weights);
    float Lbottom  = dot(SMAASamplePoint(colorTex, offset[1].zw).rgb, weights);
    delta.zw = abs(L - float2(Lright, Lbottom));

    // Calculate the maximum delta in the direct neighborhood:
    float2 maxDelta = max(delta.xy, delta.zw);

    // Calculate left-left and top-top deltas:
    float Lleftleft = dot(SMAASamplePoint(colorTex, offset[2].xy).rgb, weights);
    float Ltoptop = dot(SMAASamplePoint(colorTex, offset[2].zw).rgb, weights);
    delta.zw = abs(float2(Lleft, Ltop) - float2(Lleftleft, Ltoptop));

    // Calculate the final maximum delta:
    maxDelta = max(maxDelta.xy, delta.zw);
    float finalDelta = max(maxDelta.x, maxDelta.y);

    // Local contrast adaptation:
    edges.xy *= step(finalDelta, SMAA_LOCAL_CONTRAST_ADAPTATION_FACTOR * delta.xy);

    return edges;
}

/**
 * Color Edge Detection
 *
 * IMPORTANT NOTICE: color edge detection requires gamma-corrected colors, and
 * thus 'colorTex' should be a non-sRGB texture.
 */
float2 SMAAColorEdgeDetectionPS(float2 texcoord,
                                float4 offset[3],
                                SMAATexture2D(colorTex)
                                #if SMAA_PREDICATION
                                , SMAATexture2D(predicationTex)
                                #endif
                                ) {
    // Calculate the threshold:
    #if SMAA_PREDICATION
    float2 threshold = SMAACalculatePredicatedThreshold(texcoord, offset, predicationTex);
    #else
    float2 threshold = float2(SMAA_THRESHOLD, SMAA_THRESHOLD);
    #endif

    // Calculate color deltas:
    float4 delta;
    float3 C = SMAASamplePoint(colorTex, texcoord).rgb;

    float3 Cleft = SMAASamplePoint(colorTex, offset[0].xy).rgb;
    float3 t = abs(C - Cleft);
    delta.x = max(max(t.r, t.g), t.b);

    float3 Ctop  = SMAASamplePoint(colorTex, offset[0].zw).rgb;
    t = abs(C - Ctop);
    delta.y = max(max(t.r, t.g), t.b);

    // We do the usual threshold:
    float2 edges = step(threshold, delta.xy);

    // Then discard if there is no edge:
    if (dot(edges, float2(1.0, 1.0)) == 0.0)
        discard;

    // Calculate right and bottom deltas:
    float3 Cright = SMAASamplePoint(colorTex, offset[1].xy).rgb;
    t = abs(C - Cright);
    delta.z = max(max(t.r, t.g), t.b);

    float3 Cbottom  = SMAASamplePoint(colorTex, offset[1].zw).rgb;
    t = abs(C - Cbottom);
    delta.w = max(max(t.r, t.g), t.b);

    // Calculate the maximum delta in the direct neighborhood:
    float2 maxDelta = max(delta.xy, delta.zw);

    // Calculate left-left and top-top deltas:
    float3 Cleftleft  = SMAASamplePoint(colorTex, offset[2].xy).rgb;
    t = abs(C - Cleftleft);
    delta.z = max(max(t.r, t.g), t.b);

    float3 Ctoptop = SMAASamplePoint(colorTex, offset[2].zw).rgb;
    t = abs(C - Ctoptop);
    delta.w = max(max(t.r, t.g), t.b);

    // Calculate the final maximum delta:
    maxDelta = max(maxDelta.xy, delta.zw);
    float finalDelta = max(maxDelta.x, maxDelta.y);

    // Local contrast adaptation:
    edges.xy *= step(finalDelta, SMAA_LOCAL_CONTRAST_ADAPTATION_FACTOR * delta.xy);

    return edges;
}

/**
 * Depth Edge Detection
 */
float2 SMAADepthEdgeDetectionPS(float2 texcoord,
                                float4 offset[3],
                                SMAATexture2D(depthTex)) {
    float3 neighbours = SMAAGatherNeighbours(texcoord, offset, SMAATexturePass2D(depthTex));
    float2 delta = abs(neighbours.xx - float2(neighbours.y, neighbours.z));
    float2 edges = step(SMAA_DEPTH_THRESHOLD, delta);

    if (dot(edges, float2(1.0, 1.0)) == 0.0)
        discard;

    return edges;
}

//-----------------------------------------------------------------------------
// Diagonal Search Functions

#if !defined(SMAA_DISABLE_DIAG_DETECTION)

/**
 * Allows to decode two binary values from a bilinear-filtered access.
 */
float2 SMAADecodeDiagBilinearAccess(float2 e) {
    // Bilinear access for fetching 'e' have a 0.25 offset, and we are
    // interested in the R and G edges:
    //
    // +---G---+-------+
    // |   x o R   x   |
    // +-------+-------+
    //
    // Then, if one of these edge is enabled:
    //   Red:   (0.75 * X + 0.25 * 1) => 0.25 or 1.0
    //   Green: (0.75 * 1 + 0.25 * X) => 0.75 or 1.0
    //
    // This function will unpack the values (mad + mul + round):
    // wolframalpha.com: round(x * abs(5 * x - 5 * 0.75)) plot 0 to 1
    e.r = e.r * abs(5.0 * e.r - 5.0 * 0.75);
    return round(e);
}

float4 SMAADecodeDiagBilinearAccess(float4 e) {
    e.rb = e.rb * abs(5.0 * e.rb - 5.0 * 0.75);
    return round(e);
}

/**
 * These functions allows to perform diagonal pattern searches.
 */
float2 SMAASearchDiag1(SMAATexture2D(edgesTex), float2 texcoord, float2 dir, out float2 e) {
    float4 coord = float4(texcoord, -1.0, 1.0);
    float3 t = float3(SMAA_RT_METRICS.xy, 1.0);
    while (coord.z < float(SMAA_MAX_SEARCH_STEPS_DIAG - 1) &&
           coord.w > 0.9) {
        coord.xyz = mad(t, float3(dir, 1.0), coord.xyz);
        e = SMAASampleLevelZero(edgesTex, coord.xy).rg;
        coord.w = dot(e, float2(0.5, 0.5));
    }
    return coord.zw;
}

float2 SMAASearchDiag2(SMAATexture2D(edgesTex), float2 texcoord, float2 dir, out float2 e) {
    float4 coord = float4(texcoord, -1.0, 1.0);
    coord.x += 0.25 * SMAA_RT_METRICS.x; // See @SearchDiag2Optimization
    float3 t = float3(SMAA_RT_METRICS.xy, 1.0);
    while (coord.z < float(SMAA_MAX_SEARCH_STEPS_DIAG - 1) &&
           coord.w > 0.9) {
        coord.xyz = mad(t, float3(dir, 1.0), coord.xyz);

        // @SearchDiag2Optimization
        // Fetch both edges at once using bilinear filtering:
        e = SMAASampleLevelZero(edgesTex, coord.xy).rg;
        e = SMAADecodeDiagBilinearAccess(e);

        // Non-optimized version:
        // e.g = SMAASampleLevelZero(edgesTex, coord.xy).g;
        // e.r = SMAASampleLevelZeroOffset(edgesTex, coord.xy, int2(1, 0)).r;

        coord.w = dot(e, float2(0.5, 0.5));
    }
    return coord.zw;
}

/** 
 * Similar to SMAAArea, this calculates the area corresponding to a certain
 * diagonal distance and crossing edges 'e'.
 */
float2 SMAAAreaDiag(SMAATexture2D(areaTex), float2 dist, float2 e, float offset) {
    float2 texcoord = mad(float2(SMAA_AREATEX_MAX_DISTANCE_DIAG, SMAA_AREATEX_MAX_DISTANCE_DIAG), e, dist);

    // We do a scale and bias for mapping to texel space:
    texcoord = mad(SMAA_AREATEX_PIXEL_SIZE, texcoord, 0.5 * SMAA_AREATEX_PIXEL_SIZE);

    // Diagonal areas are on the second half of the texture:
    texcoord.x += 0.5;

    // Move to proper place, according to the subpixel offset:
    texcoord.y += SMAA_AREATEX_SUBTEX_SIZE * offset;

    // Do it!
    return SMAA_AREATEX_SELECT(SMAASampleLevelZero(areaTex, texcoord));
}

/**
 * This searches for diagonal patterns and returns the corresponding weights.
 */
float2 SMAACalculateDiagWeights(SMAATexture2D(edgesTex), SMAATexture2D(areaTex), float2 texcoord, float2 e, float4 subsampleIndices) {
    float2 weights = float2(0.0, 0.0);

    // Search for the line ends:
    float4 d;
    float2 end;
    if (e.r > 0.0) {
        d.xz = SMAASearchDiag1(SMAATexturePass2D(edgesTex), texcoord, float2(-1.0,  1.0), end);
        d.x += float(end.y > 0.9);
    } else
        d.xz = float2(0.0, 0.0);
    d.yw = SMAASearchDiag1(SMAATexturePass2D(edgesTex), texcoord, float2(1.0, -1.0), end);

    SMAA_BRANCH
    if (d.x + d.y > 2.0) { // d.x + d.y + 1 > 3
        // Fetch the crossing edges:
        float4 coords = mad(float4(-d.x + 0.25, d.x, d.y, -d.y - 0.25), SMAA_RT_METRICS.xyxy, texcoord.xyxy);
        float4 c;
        c.xy = SMAASampleLevelZeroOffset(edgesTex, coords.xy, int2(-1,  0)).rg;
        c.zw = SMAASampleLevelZeroOffset(edgesTex, coords.zw, int2( 1,  0)).rg;
        c.yxwz = SMAADecodeDiagBilinearAccess(c.xyzw);

        // Non-optimized version:
        // float4 coords = mad(float4(-d.x, d.x, d.y, -d.y), SMAA_RT_METRICS.xyxy, texcoord.xyxy);
        // float4 c;
        // c.x = SMAASampleLevelZeroOffset(edgesTex, coords.xy, int2(-1,  0)).g;
        // c.y = SMAASampleLevelZeroOffset(edgesTex, coords.xy, int2( 0,  0)).r;
        // c.z = SMAASampleLevelZeroOffset(edgesTex, coords.zw, int2( 1,  0)).g;
        // c.w = SMAASampleLevelZeroOffset(edgesTex, coords.zw, int2( 1, -1)).r;

        // Merge crossing edges at each side into a single value:
        float2 cc = mad(float2(2.0, 2.0), c.xz, c.yw);

        // Remove the crossing edge if we didn't found the end of the line:
        SMAAMovc(bool2(step(0.9, d.zw)), cc, float2(0.0, 0.0));

        // Fetch the areas for this line:
        weights += SMAAAreaDiag(SMAATexturePass2D(areaTex), d.xy, cc, subsampleIndices.z);
    }

    // Search for the line ends:
    d.xz = SMAASearchDiag2(SMAATexturePass2D(edgesTex), texcoord, float2(-1.0, -1.0), end);
    if (SMAASampleLevelZeroOffset(edgesTex, texcoord, int2(1, 0)).r > 0.0) {
        d.yw = SMAASearchDiag2(SMAATexturePass2D(edgesTex), texcoord, float2(1.0, 1.0), end);
        d.y += float(end.y > 0.9);
    } else
        d.yw = float2(0.0, 0.0);

    SMAA_BRANCH
    if (d.x + d.y > 2.0) { // d.x + d.y + 1 > 3
        // Fetch the crossing edges:
        float4 coords = mad(float4(-d.x, -d.x, d.y, d.y), SMAA_RT_METRICS.xyxy, texcoord.xyxy);
        float4 c;
        c.x  = SMAASampleLevelZeroOffset(edgesTex, coords.xy, int2(-1,  0)).g;
        c.y  = SMAASampleLevelZeroOffset(edgesTex, coords.xy, int2( 0, -1)).r;
        c.zw = SMAASampleLevelZeroOffset(edgesTex, coords.zw, int2( 1,  0)).gr;
        float2 cc = mad(float2(2.0, 2.0), c.xz, c.yw);

        // Remove the crossing edge if we didn't found the end of the line:
        SMAAMovc(bool2(step(0.9, d.zw)), cc, float2(0.0, 0.0));

        // Fetch the areas for this line:
        weights += SMAAAreaDiag(SMAATexturePass2D(areaTex), d.xy, cc, subsampleIndices.w).gr;
    }

    return weights;
}
#endif

//-----------------------------------------------------------------------------
// Horizontal/Vertical Search Functions

/**
 * This allows to determine how much length should we add in the last step
 * of the searches. It takes the bilinearly interpolated edge (see 
 * @PSEUDO_GATHER4), and adds 0, 1 or 2, depending on which edges and
 * crossing edges are active.
 */
float SMAASearchLength(SMAATexture2D(searchTex), float2 e, float offset) {
    // The texture is flipped vertically, with left and right cases taking half
    // of the space horizontally:
    float2 scale = SMAA_SEARCHTEX_SIZE * float2(0.5, -1.0);
    float2 bias = SMAA_SEARCHTEX_SIZE * float2(offset, 1.0);

    // Scale and bias to access texel centers:
    scale += float2(-1.0,  1.0);
    bias  += float2( 0.5, -0.5);

    // Convert from pixel coordinates to texcoords:
    // (We use SMAA_SEARCHTEX_PACKED_SIZE because the texture is cropped)
    scale *= 1.0 / SMAA_SEARCHTEX_PACKED_SIZE;
    bias *= 1.0 / SMAA_SEARCHTEX_PACKED_SIZE;

    // Lookup the search texture:
    return SMAA_SEARCHTEX_SELECT(SMAASampleLevelZero(searchTex, mad(scale, e, bias)));
}

/**
 * Horizontal/vertical search functions for the 2nd pass.
 */
float SMAASearchXLeft(SMAATexture2D(edgesTex), SMAATexture2D(searchTex), float2 texcoord, float end) {
    /**
     * @PSEUDO_GATHER4
     * This texcoord has been offset by (-0.25, -0.125) in the vertex shader to
     * sample between edge, thus fetching four edges in a row.
     * Sampling with different offsets in each direction allows to disambiguate
     * which edges are active from the four fetched ones.
     */
    float2 e = float2(0.0, 1.0);
    while (texcoord.x > end && 
           e.g > 0.8281 && // Is there some edge not activated?
           e.r == 0.0) { // Or is there a crossing edge that breaks the line?
        e = SMAASampleLevelZero(edgesTex, texcoord).rg;
        texcoord = mad(-float2(2.0, 0.0), SMAA_RT_METRICS.xy, texcoord);
    }

    float offset = mad(-(255.0 / 127.0), SMAASearchLength(SMAATexturePass2D(searchTex), e, 0.0), 3.25);
    return mad(SMAA_RT_METRICS.x, offset, texcoord.x);

    // Non-optimized version:
    // We correct the previous (-0.25, -0.125) offset we applied:
    // texcoord.x += 0.25 * SMAA_RT_METRICS.x;

    // The searches are bias by 1, so adjust the coords accordingly:
    // texcoord.x += SMAA_RT_METRICS.x;

    // Disambiguate the length added by the last step:
    // texcoord.x += 2.0 * SMAA_RT_METRICS.x; // Undo last step
    // texcoord.x -= SMAA_RT_METRICS.x * (255.0 / 127.0) * SMAASearchLength(SMAATexturePass2D(searchTex), e, 0.0);
    // return mad(SMAA_RT_METRICS.x, offset, texcoord.x);
}

float SMAASearchXRight(SMAATexture2D(edgesTex), SMAATexture2D(searchTex), float2 texcoord, float end) {
    float2 e = float2(0.0, 1.0);
    while (texcoord.x < end && 
           e.g > 0.8281 && // Is there some edge not activated?
           e.r == 0.0) { // Or is there a crossing edge that breaks the line?
        e = SMAASampleLevelZero(edgesTex, texcoord).rg;
        texcoord = mad(float2(2.0, 0.0), SMAA_RT_METRICS.xy, texcoord);
    }
    float offset = mad(-(255.0 / 127.0), SMAASearchLength(SMAATexturePass2D(searchTex), e, 0.5), 3.25);
    return mad(-SMAA_RT_METRICS.x, offset, texcoord.x);
}

float SMAASearchYUp(SMAATexture2D(edgesTex), SMAATexture2D(searchTex), float2 texcoord, float end) {
    float2 e = float2(1.0, 0.0);
    while (texcoord.y > end && 
           e.r > 0.8281 && // Is there some edge not activated?
           e.g == 0.0) { // Or is there a crossing edge that breaks the line?
        e = SMAASampleLevelZero(edgesTex, texcoord).rg;
        texcoord = mad(-float2(0.0, 2.0), SMAA_RT_METRICS.xy, texcoord);
    }
    float offset = mad(-(255.0 / 127.0), SMAASearchLength(SMAATexturePass2D(searchTex), e.gr, 0.0), 3.25);
    return mad(SMAA_RT_METRICS.y, offset, texcoord.y);
}

float SMAASearchYDown(SMAATexture2D(edgesTex), SMAATexture2D(searchTex), float2 texcoord, float end) {
    float2 e = float2(1.0, 0.0);
    while (texcoord.y < end && 
           e.r > 0.8281 && // Is there some edge not activated?
           e.g == 0.0) { // Or is there a crossing edge that breaks the line?
        e = SMAASampleLevelZero(edgesTex, texcoord).rg;
        texcoord = mad(float2(0.0, 2.0), SMAA_RT_METRICS.xy, texcoord);
    }
    float offset = mad(-(255.0 / 127.0), SMAASearchLength(SMAATexturePass2D(searchTex), e.gr, 0.5), 3.25);
    return mad(-SMAA_RT_METRICS.y, offset, texcoord.y);
}

/** 
 * Ok, we have the distance and both crossing edges. So, what are the areas
 * at each side of current edge?
 */
float2 SMAAArea(SMAATexture2D(areaTex), float2 dist, float e1, float e2, float offset) {
    // Rounding prevents precision errors of bilinear filtering:
    float2 texcoord = mad(float2(SMAA_AREATEX_MAX_DISTANCE, SMAA_AREATEX_MAX_DISTANCE), round(4.0 * float2(e1, e2)), dist);
    
    // We do a scale and bias for mapping to texel space:
    texcoord = mad(SMAA_AREATEX_PIXEL_SIZE, texcoord, 0.5 * SMAA_AREATEX_PIXEL_SIZE);

    // Move to proper place, according to the subpixel offset:
    texcoord.y = mad(SMAA_AREATEX_SUBTEX_SIZE, offset, texcoord.y);

    // Do it!
    return SMAA_AREATEX_SELECT(SMAASampleLevelZero(areaTex, texcoord));
}

//-----------------------------------------------------------------------------
// Corner Detection Functions

void SMAADetectHorizontalCornerPattern(SMAATexture2D(edgesTex), inout float2 weights, float4 texcoord, float2 d) {
    #if !defined(SMAA_DISABLE_CORNER_DETECTION)
    float2 leftRight = step(d.xy, d.yx);
    float2 rounding = (1.0 - SMAA_CORNER_ROUNDING_NORM) * leftRight;

    rounding /= leftRight.x + leftRight.y; // Reduce blending for pixels in the center of a line.

    float2 factor = float2(1.0, 1.0);
    factor.x -= rounding.x * SMAASampleLevelZeroOffset(edgesTex, texcoord.xy, int2(0,  1)).r;
    factor.x -= rounding.y * SMAASampleLevelZeroOffset(edgesTex, texcoord.zw, int2(1,  1)).r;
    factor.y -= rounding.x * SMAASampleLevelZeroOffset(edgesTex, texcoord.xy, int2(0, -2)).r;
    factor.y -= rounding.y * SMAASampleLevelZeroOffset(edgesTex, texcoord.zw, int2(1, -2)).r;

    weights *= saturate(factor);
    #endif
}

void SMAADetectVerticalCornerPattern(SMAATexture2D(edgesTex), inout float2 weights, float4 texcoord, float2 d) {
    #if !defined(SMAA_DISABLE_CORNER_DETECTION)
    float2 leftRight = step(d.xy, d.yx);
    float2 rounding = (1.0 - SMAA_CORNER_ROUNDING_NORM) * leftRight;

    rounding /= leftRight.x + leftRight.y;

    float2 factor = float2(1.0, 1.0);
    factor.x -= rounding.x * SMAASampleLevelZeroOffset(edgesTex, texcoord.xy, int2( 1, 0)).g;
    factor.x -= rounding.y * SMAASampleLevelZeroOffset(edgesTex, texcoord.zw, int2( 1, 1)).g;
    factor.y -= rounding.x * SMAASampleLevelZeroOffset(edgesTex, texcoord.xy, int2(-2, 0)).g;
    factor.y -= rounding.y * SMAASampleLevelZeroOffset(edgesTex, texcoord.zw, int2(-2, 1)).g;

    weights *= saturate(factor);
    #endif
}

//-----------------------------------------------------------------------------
// Blending Weight Calculation Pixel Shader (Second Pass)

float4 SMAABlendingWeightCalculationPS(float2 texcoord,
                                       float2 pixcoord,
                                       float4 offset[3],
                                       SMAATexture2D(edgesTex),
                                       SMAATexture2D(areaTex),
                                       SMAATexture2D(searchTex),
                                       float4 subsampleIndices) { // Just pass zero for SMAA 1x, see @SUBSAMPLE_INDICES.
    float4 weights = float4(0.0, 0.0, 0.0, 0.0);

    float2 e = SMAASample(edgesTex, texcoord).rg;

    SMAA_BRANCH
    if (e.g > 0.0) { // Edge at north
        #if !defined(SMAA_DISABLE_DIAG_DETECTION)
        // Diagonals have both north and west edges, so searching for them in
        // one of the boundaries is enough.
        weights.rg = SMAACalculateDiagWeights(SMAATexturePass2D(edgesTex), SMAATexturePass2D(areaTex), texcoord, e, subsampleIndices);

        // We give priority to diagonals, so if we find a diagonal we skip 
        // horizontal/vertical processing.
        SMAA_BRANCH
        if (weights.r == -weights.g) { // weights.r + weights.g == 0.0
        #endif

        float2 d;

        // Find the distance to the left:
        float3 coords;
        coords.x = SMAASearchXLeft(SMAATexturePass2D(edgesTex), SMAATexturePass2D(searchTex), offset[0].xy, offset[2].x);
        coords.y = offset[1].y; // offset[1].y = texcoord.y - 0.25 * SMAA_RT_METRICS.y (@CROSSING_OFFSET)
        d.x = coords.x;

        // Now fetch the left crossing edges, two at a time using bilinear
        // filtering. Sampling at -0.25 (see @CROSSING_OFFSET) enables to
        // discern what value each edge has:
        float e1 = SMAASampleLevelZero(edgesTex, coords.xy).r;

        // Find the distance to the right:
        coords.z = SMAASearchXRight(SMAATexturePass2D(edgesTex), SMAATexturePass2D(searchTex), offset[0].zw, offset[2].y);
        d.y = coords.z;

        // We want the distances to be in pixel units (doing this here allow to
        // better interleave arithmetic and memory accesses):
        d = abs(round(mad(SMAA_RT_METRICS.zz, d, -pixcoord.xx)));

        // SMAAArea below needs a sqrt, as the areas texture is compressed
        // quadratically:
        float2 sqrt_d = sqrt(d);

        // Fetch the right crossing edges:
        float e2 = SMAASampleLevelZeroOffset(edgesTex, coords.zy, int2(1, 0)).r;

        // Ok, we know how this pattern looks like, now it is time for getting
        // the actual area:
        weights.rg = SMAAArea(SMAATexturePass2D(areaTex), sqrt_d, e1, e2, subsampleIndices.y);

        // Fix corners:
        coords.y = texcoord.y;
        SMAADetectHorizontalCornerPattern(SMAATexturePass2D(edgesTex), weights.rg, coords.xyzy, d);

        #if !defined(SMAA_DISABLE_DIAG_DETECTION)
        } else
            e.r = 0.0; // Skip vertical processing.
        #endif
    }

    SMAA_BRANCH
    if (e.r > 0.0) { // Edge at west
        float2 d;

        // Find the distance to the top:
        float3 coords;
        coords.y = SMAASearchYUp(SMAATexturePass2D(edgesTex), SMAATexturePass2D(searchTex), offset[1].xy, offset[2].z);
        coords.x = offset[0].x; // offset[1].x = texcoord.x - 0.25 * SMAA_RT_METRICS.x;
        d.x = coords.y;

        // Fetch the top crossing edges:
        float e1 = SMAASampleLevelZero(edgesTex, coords.xy).g;

        // Find the distance to the bottom:
        coords.z = SMAASearchYDown(SMAATexturePass2D(edgesTex), SMAATexturePass2D(searchTex), offset[1].zw, offset[2].w);
        d.y = coords.z;

        // We want the distances to be in pixel units:
        d = abs(round(mad(SMAA_RT_METRICS.ww, d, -pixcoord.yy)));

        // SMAAArea below needs a sqrt, as the areas texture is compressed 
        // quadratically:
        float2 sqrt_d = sqrt(d);

        // Fetch the bottom crossing edges:
        float e2 = SMAASampleLevelZeroOffset(edgesTex, coords.xz, int2(0, 1)).g;

        // Get the area for this direction:
        weights.ba = SMAAArea(SMAATexturePass2D(areaTex), sqrt_d, e1, e2, subsampleIndices.x);

        // Fix corners:
        coords.x = texcoord.x;
        SMAADetectVerticalCornerPattern(SMAATexturePass2D(edgesTex), weights.ba, coords.xyxz, d);
    }

    return weights;
}

//-----------------------------------------------------------------------------
// Neighborhood Blending Pixel Shader (Third Pass)

float4 SMAANeighborhoodBlendingPS(float2 texcoord,
                                  float4 offset,
                                  SMAATexture2D(colorTex),
                                  SMAATexture2D(blendTex)
                                  #if SMAA_REPROJECTION
                                  , SMAATexture2D(velocityTex)
                                  #endif
                                  ) {
    // Fetch the blending weights for current pixel:
    float4 a;
    a.x = SMAASample(blendTex, offset.xy).a; // Right
    a.y = SMAASample(blendTex, offset.zw).g; // Top
    a.wz = SMAASample(blendTex, texcoord).xz; // Bottom / Left

    // Is there any blending weight with a value greater than 0.0?
    SMAA_BRANCH
    if (dot(a, float4(1.0, 1.0, 1.0, 1.0)) < 1e-5) {
        float4 color = SMAASampleLevelZero(colorTex, texcoord);

        #if SMAA_REPROJECTION
        float2 velocity = SMAA_DECODE_VELOCITY(SMAASampleLevelZero(velocityTex, texcoord));

        // Pack velocity into the alpha channel:
        color.a = sqrt(5.0 * length(velocity));
        #endif

        return color;
    } else {
        bool h = max(a.x, a.z) > max(a.y, a.w); // max(horizontal) > max(vertical)

        // Calculate the blending offsets:
        float4 blendingOffset = float4(0.0, a.y, 0.0, a.w);
        float2 blendingWeight = a.yw;
        SMAAMovc(bool4(h, h, h, h), blendingOffset, float4(a.x, 0.0, a.z, 0.0));
        SMAAMovc(bool2(h, h), blendingWeight, a.xz);
        blendingWeight /= dot(blendingWeight, float2(1.0, 1.0));

        // Calculate the texture coordinates:
        float4 blendingCoord = mad(blendingOffset, float4(SMAA_RT_METRICS.xy, -SMAA_RT_METRICS.xy), texcoord.xyxy);

        // We exploit bilinear filtering to mix current pixel with the chosen
        // neighbor:
        float4 color = blendingWeight.x * SMAASampleLevelZero(colorTex, blendingCoord.xy);
        color += blendingWeight.y * SMAASampleLevelZero(colorTex, blendingCoord.zw);

        #if SMAA_REPROJECTION
        // Antialias velocity for proper reprojection in a later stage:
        float2 velocity = blendingWeight.x * SMAA_DECODE_VELOCITY(SMAASampleLevelZero(velocityTex, blendingCoord.xy));
        velocity += blendingWeight.y * SMAA_DECODE_VELOCITY(SMAASampleLevelZero(velocityTex, blendingCoord.zw));

        // Pack velocity into the alpha channel:
        color.a = sqrt(5.0 * length(velocity));
        #endif

        return color;
    }
}

//-----------------------------------------------------------------------------
// Temporal Resolve Pixel Shader (Optional Pass)

float4 SMAAResolvePS(float2 texcoord,
                     SMAATexture2D(currentColorTex),
                     SMAATexture2D(previousColorTex)
                     #if SMAA_REPROJECTION
                     , SMAATexture2D(velocityTex)
                     #endif
                     ) {
    #if SMAA_REPROJECTION
    // Velocity is assumed to be calculated for motion blur, so we need to
    // inverse it for reprojection:
    float2 velocity = -SMAA_DECODE_VELOCITY(SMAASamplePoint(velocityTex, texcoord).rg);

    // Fetch current pixel:
    float4 current = SMAASamplePoint(currentColorTex, texcoord);

    // Reproject current coordinates and fetch previous pixel:
    float4 previous = SMAASamplePoint(previousColorTex, texcoord + velocity);

    // Attenuate the previous pixel if the velocity is different:
    float delta = abs(current.a * current.a - previous.a * previous.a) / 5.0;
    float weight = 0.5 * saturate(1.0 - sqrt(delta) * SMAA_REPROJECTION_WEIGHT_SCALE);

    // Blend the pixels according to the calculated weight:
    return lerp(current, previous, weight);
    #else
    // Just blend the pixels:
    float4 current = SMAASamplePoint(currentColorTex, texcoord);
    float4 previous = SMAASamplePoint(previousColorTex, texcoord);
    return lerp(current, previous, 0.5);
    #endif
}

//-----------------------------------------------------------------------------
// Separate Multisamples Pixel Shader (Optional Pass)

#ifdef SMAALoad
void SMAASeparatePS(float4 position,
                    float2 texcoord,
                    out float4 target0,
                    out float4 target1,
                    SMAATexture2DMS2(colorTexMS)) {
    int2 pos = int2(position.xy);
    target0 = SMAALoad(colorTexMS, pos, 0);
    target1 = SMAALoad(colorTexMS, pos, 1);
}
#endif

//-----------------------------------------------------------------------------
#endif // SMAA_INCLUDE_PS

import "shaders/modules/graphics/smaa/SMAA.h"

vertex
{
    in
    {
        float4 clipCoord_quadCoord;
        float4 uv0_uv1;
        float4 uv0Min_uv0Max;
        float4 uv1Min_uv1Max;
    }

    out
    {
        float2 uv;
        float4 offsets[2];
    }

    main(out float4 position : MR_Position)
    {
        float4 pos = float4(In.clipCoord_quadCoord.xy, 0,1);
        Out.uv = In.uv0_uv1.xy;
        SMAANeighborhoodBlendingVS(pos, position, Out.uv, Out.offsets);
    }
}

pixel
{
    in
    {
        float2 uv;
        float4 offsets[2];
    }

    MR_Sampler2D colorTex : MR_Texture0 { filter = linear, wrap = clamp };
    MR_Sampler2D blendTex : MR_Texture1 { filter = linear, wrap = clamp };

    main(out float4 outColor : MR_Color)
    {
        outColor = SMAANeighborhoodBlendingPS(In.uv, In.offsets, colorTex, blendTex);

    @ifdef GFX_SMAA_BLEND_SRGB
        outColor = pow(outColor, vec4(1.0/2.2));
    @endif
    }
}

import "shaders/modules/graphics/smaa/SMAA.h"

vertex
{
    in
    {
        float4 clipCoord_quadCoord;
        float4 uv0_uv1;
        float4 uv0Min_uv0Max;
        float4 uv1Min_uv1Max;
    }

    out
    {
        float2 uv;
        float2 pixcoord;
        float4 offsets[3];
    }

    main(out float4 position : MR_Position)
    {
        float4 pos = float4(In.clipCoord_quadCoord.xy, 0,1);
        Out.uv = In.uv0_uv1.xy;
        SMAABlendingWeightCalculationVS(pos, position, Out.uv, Out.pixcoord, Out.offsets);
    }
}

pixel
{
    in
    {
        float2 uv;
        float2 pixcoord;
        float4 offsets[3];
    }

    MR_Sampler2D edgesTex : MR_Texture0 { filter = linear, wrap = clamp };
    MR_Sampler2D areaTex { texture = "textures/AreaTexDX9.dds",    filter = linear, wrap = clamp };
    MR_Sampler2D searchTex { texture = "textures/SearchTex.dds", filter = point, wrap = clamp };
    
    main(out float4 outColor : MR_Color)
    {
        outColor = SMAABlendingWeightCalculationPS(In.uv, In.pixcoord, In.offsets, edgesTex, areaTex, searchTex, int4(0,0,0,0));
    }
}

import "shaders/modules/graphics/smaa/SMAA.h"

vertex
{
    in
    {
        float4 clipCoord_quadCoord;
        float4 uv0_uv1;
        float4 uv0Min_uv0Max;
        float4 uv1Min_uv1Max;
    }

    out
    {
        float2 uv;
        float4 offsets[3];
    }

    main(out float4 position : MR_Position)
    {
        float4 pos = float4(In.clipCoord_quadCoord.xy, 0,1);
        Out.uv = In.uv0_uv1.xy;
        SMAAEdgeDetectionVS(pos, position, Out.uv, Out.offsets);
    }
}

pixel
{
    in
    {
        float2 uv;
        float4 offsets[3];
    }

    MR_Sampler2D colorTex : MR_Texture0 { filter = linear, wrap = clamp };
    
    @ifdef SMAA_PREDICATION
        MR_Sampler2D depthbuffer : MR_DepthTexture { filter = linear, wrap = clamp };
    @endif
    @ifdef GFX_SMAA_DEPTH_EDGE_DETECTION
        MR_Sampler2D depthbuffer : MR_DepthTexture { filter = linear, wrap = clamp };
    @endif

    main(out float4 outColor : MR_Color)
    {
    @ifdef GFX_SMAA_DEPTH_EDGE_DETECTION
        outColor = SMAADepthEdgeDetectionPS(In.uv, In.offsets, depthbuffer);
    @endif
    @ifdef GFX_SMAA_LUMA_EDGE_DETECTION
        @ifdef SMAA_PREDICATION
            outColor = SMAALumaEdgeDetectionPS(In.uv, In.offsets, colorTex, depthbuffer);
        @else
            outColor = SMAALumaEdgeDetectionPS(In.uv, In.offsets, colorTex);
        @endif
    @endif
    @ifdef GFX_SMAA_COLOR_EDGE_DETECTION
        @ifdef SMAA_PREDICATION
            outColor = SMAAColorEdgeDetectionPS(In.uv, In.offsets, colorTex, depthbuffer);
        @else
            outColor = SMAAColorEdgeDetectionPS(In.uv, In.offsets, colorTex);
        @endif
    @endif
    }
}

 

UE4支持SMAA版本:

https://github.com/inequation/UnrealEngine/tree/SMAA-4.12

---

 

MSAA

名字很像的MSAA（Multi-Sampling AA）是硬件AA，只是在光栅化阶段（VS与PS之间的线性插值过程），判断一个三角形是否被像素覆盖的时候会计算多个覆盖样本（Coverage sample），但是在pixel shader着色阶段计算像素颜色的时候每个像素还是只计算一次。例如下图是4xMSAA，三角形只覆盖了4个coverage sample中的2个。所以这个三角形需要生成一个fragment在pixel shader里着色，只不过生成的fragment还是在像素中央（位置，法线等信息插值到像素中央）然后只运行一次pixel shader，最后得到的结果在resolve阶段会乘以0.5，因为这个三角形只cover了一半的sample。现代所有GPU都在硬件上实现了这个算法，而且在shading的运算量远大于光栅化的今天，这个方法远比SSAA快很多。

 

MSAA与deferred rendering不怎么兼容，因为用deferred shading的时候场景都先被光栅化到GBuffer上了，不直接做shading。