体积雾(dx9)

1.什么是体积雾?

这个问题通过图片来解答再合适不过了，下面是本文利用体积雾做的一个结果

所谓体积雾：顾名思义就是被限制了形状的雾，本文表述如何通过ImageProcess(图象处理)的方式实现体积雾。

2.常规雾原理

雾效最终体现在雾颜色与场景色的混合上。决定雾的浓度的关键就在这个混合因子上。下面我们给出公式.

float4 finalColor = factor * fogColor + ( 1 - factor) * sceneColor; ( !提取公因式,减少计算量)

= factor( fogColor - sceneColor) + sceneColor; ( factor>=0 && factor<=1)

(雾化公式) finalColor ：混合后颜色

sceneColor：场景象素色

factor ：混合因子

3.体积雾原理

雾效关键在于如何求得每个场景可见象素点的混合因子！

float factor = fogDepth / ( fogEnd - fogStart);

也就是视点与目标象素点的距离上雾所占的距离 fogDepth。根据Z Buffer,我们可以获取每帧每个象素到视点的距离。

于是，我们同样可以通过渲染FogVolume的正面与反面的深度到两张贴图上。这样我们就可以根据当前场景深度信息以及前面的两张贴图，获得FogDepth,

4.实现步骤

1.首先渲染所有场景物体, 此处我们需要FrameBuffer, 与 Z Buffer信息

2.渲染所有物模型的背面的深度到一张纹理上

3.渲染所有雾模型的正面的尝试到一张纹理上

4.利用场景的ZBuffer信息, 雾的两张深度纹理, 雾参数处理场景的FrameBuffer

5.具体步骤

1.获取场景的ZBuffer, 与 FrameBuffer

因为dx9无法直接获取场景的ZBuffer信息，所以我们要采用别的方式，

1.把所有的场景多渲染一次，把深度信息渲染到一张纹理上;

2.使用MultiRenderTarget 渲染场景的同时把深度信息保存到一张纹理上

下面我们只介绍MultiRenderTarget的方式。

MultiRenderTarget 是 Ps 2.0 即支持的渲染方式。其实现方法比较简单，只需更改PS( pixel shader)的返回值

例(这里使用使用两个RenderTarget)：

   struct PS_OUTPUT
   {
        float4   Target0 : COLOR0;
        float4   Target1 : COLOR1;
    };

硬件支持的RenderTarget数可以通过 D3DCaps.NumSimultaneousRTs 查看，一般显卡：4

代码部分：

  // 设置多RenderTarget
  g_pDevice->SetRenderTarget( 0, m_pMainRenderTarget);
  g_pDevice->SetRenderTarget( 1, m_pDepthTexture->GetSurface());

// 渲染调用代码

g_pDevice->SetRenderTarget( 0, m_pMainRenderTarget);
g_pDevice->SetRenderTarget( 1, NULL);

注意：使用MultiRenderTarget 不能开启反锯齿

// 拷贝FrameBuffer到一张动态纹理上

IDirect3DSurface9* pSurface = NULL;
g_pDevice->GetRenderTarget( 0, &pSurface);

// copy back buffer into refraction map texture
g_pDevice->StretchRect( pSurface, 0, m_pTextureSrc->GetSurface(), 0, D3DTEXF_NONE);

SAFE_RELEASE( pSurface);

2.渲染所有物模型的背面的深度到一张纹理上
3.渲染所有雾模型的正面的尝试到一张纹理上

4最后利用所有的数据更改FrameBuffer

Shader 代码：

uniform float2 g_fogParam; // x: fogStart y: fogEnd
uniform float3 g_fogColor; // FogColor

// vertexInput
struct VS_INPUT
{
float3 Position : POSITION0;
float2 Texcoord : TEXCOORD0;
};

// Vertex OutPut
struct VS_OUTPUT
{
float4 Position : POSITION;
float2 Texcoord : TEXCOORD1;
};

// Vertex Shader
VS_OUTPUT VS(VS_INPUT In)
{
VS_OUTPUT Out;

Out.Position = float4(In.Position, 1.0f);
Out.Texcoord = In.Texcoord;

return Out;
}

texture texSrc;
texture texSceneDepth;
texture texFogFront;
texture texFogBack;

// 纹理采样
sampler2D RGBSampler = sampler_state
{
texture = <texSrc>;
};

sampler2D DepthSampler = sampler_state
{
texture = <texSceneDepth>;
};

sampler2D FogFrontSampler = sampler_state
{
texture = <texFogFront>;
};

sampler2D FogBackSampler = sampler_state
{
texture = <texFogBack>;
};

// Pixel Shader
float4 PS(VS_OUTPUT In) : COLOR
{
float depth = tex2D( DepthSampler, In.Texcoord).r;
float fogFront = tex2D( FogFrontSampler, In.Texcoord).r;
float fogBack = tex2D( FogBackSampler, In.Texcoord).r;

float dis = 0.f;

if( depth > fogBack)
dis = fogBack - fogFront;
else if( depth > fogFront)
dis = depth - fogFront;

float factor = max(( dis - g_fogParam.x), 0.f) / ( g_fogParam.y - g_fogParam.x);

float3 rgb = tex2D(RGBSampler, In.Texcoord);
float3 color = rgb + factor * ( g_fogColor - rgb);

return float4( color, 1.f);
}

technique technique0
{
pass p0
{
  VertexShader = compile vs_3_0 VS();
  PixelShader = compile ps_3_0 PS();
}
}

另：为了减少判断量, 需把所有的图片 Clear为黑色

Please help to write shaders for volumetric fog. I have an error. But I do not know where.

float4x4 g_wvp;
//depth.vsh  m_pFogShaderDepth
void vs_depth( inout float4 pos   : POSITION  ,
                 out float  depth : TEXCOORD0 )
{
    pos = mul( pos, g_wvp );
    depth = pos.z;
}

//depth.psh  m_pFogShaderDepth
float4 ps_depth( in float depth : TEXCOORD0 ) : COLOR
{
    return float4( depth, 0.f, 0.f, 0.f );
}

    sampler2D s_fog_back;
    sampler2D s_fog_front;
    sampler2D s_scene_depth;

//fog.ps  m_pPixShader
float4 Main_ps( in float2 tex : TEXCOORD0 ) : COLOR
{

    float fog_back    = tex2D( s_fog_back    , tex ).r;
    float fog_front   = tex2D( s_fog_front   , tex ).r;
    float scene_depth = tex2D( s_scene_depth , tex ).r;

    float k = fog_back - fog_front;
    k -= fog_back - clamp( scene_depth, 0, fog_back );

    return float4(0.5f,0.5f,0.5f, k*0.5f );
}

Code C++

p_d3d_Device->SetRenderState(D3DRS_CULLMODE, D3DCULL_CW);

    p_d3d_Device->SetTexture(0,m_pEndFogTexture);
//********************************
    D3DXMATRIX V;
    TheCamera.getViewMatrix(&V);

    D3DXMATRIX matRes;
    //matRes=mxWorld*mxView*mxProj;
    matRes=mxWorld*V*mxProj;

    VertShaderConstTable->SetMatrix(p_d3d_Device, MatrixHandle, &matRes);
    //------------------------------
    p_d3d_Device->SetPixelShader( NULL );
    //reverse the culling order to get the back side


    p_d3d_Device->SetRenderState( D3DRS_ZFUNC , D3DCMP_GREATER  );

    p_d3d_Device->Clear(NULL, NULL, D3DCLEAR_TARGET| D3DCLEAR_ZBUFFER , D3DCOLOR_ARGB(0, 0, 0, 0), 0.0, 0);

    p_d3d_Device->SetRenderState(D3DRS_CULLMODE, D3DCULL_CW);

    p_d3d_Device->SetTexture(0,m_pEndFogTexture);

    p_d3d_Device->SetVertexShader( m_pFogShaderDepth );



    for( DWORD i=0; i<g_dwNumMaterials; i++ )
     {
     m_pMeshFloor->DrawSubset( i );
     }

    p_d3d_Device->SetRenderState(D3DRS_CULLMODE, D3DCULL_CCW);

    p_d3d_Device->SetTexture(1,m_pStartFogTexture);


    p_d3d_Device->SetVertexShader( m_pFogShaderDepth );

    for( DWORD i=0; i<g_dwNumMaterials; i++ )
     {
     m_pMeshFloor->DrawSubset( i );
     }
    p_d3d_Device->SetRenderState( D3DRS_CULLMODE,         D3DCULL_NONE );

    p_d3d_Device->SetVertexShader( NULL);
    p_d3d_Device->SetPixelShader( m_pPixShader );



    for( DWORD i=0; i<g_dwNumMaterials; i++ )
     {
     m_pMeshFloor->DrawSubset( i );
     }




    //---------------------------------
    p_d3d_Device->SetRenderState( D3DRS_ALPHABLENDENABLE, FALSE);
   //**********************************

    p_d3d_Device->EndScene ();
    p_d3d_Device->Present (NULL, NULL, NULL, NULL);

as a result I have displayed a blue cube, textured very wrong, on a gray background. Read the article Russian programmer http://timai-ru.blogspot.com/

posted @ 2011-02-23 17:47 oayx 阅读(3763) 评论(1) 编辑收藏举报

刷新页面返回顶部

oayx

体积雾(dx9)

公告