GLSL下几个简单的Shader （转载）

在ShaderDesigner下编Shader是最为方便的，但这里先用OpenGL下的编程来举例

转载自 http://blog.csdn.net/boksic

这几个Shader的实际效果：

1.最简单的固定单色Shader

Vertex Shader

坐标经过投影矩阵变换：vTrans = projection * modelview * incomingVertex

void main()
{
    gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix * gl_Vertex;
}

或者更简单的方式，使用ftransform函数

void main()
{
    gl_Position = ftransform();
}

Fragment Shader

赋予像素一个固定值的颜色

void main()
{
    gl_FragColor = vec4(0.4,0.4,0.8,1.0);
}

2.颜色Shader

在OpenGL程序当中使用 glColor函数指定颜色时，接收该颜色值的Shader

例如OpenGL程序当中画一个红色茶壶：

glColor3f(1, 0, 0);
glutSolidTeapot(1);

glColor在Shader当中总共涉及四个值

attribute vec4 gl_Color;

varying vec4 gl_FrontColor; // writable on the vertex shader
varying vec4 gl_BackColor; // writable on the vertex shader

varying vec4 gl_Color; // readable on the fragment shader

流程如下：

OpenGL程序使用glColor函数后，将颜色值以attribute gl_Color的形式传给了Vertex Shader, Vertext Shader接受到后开始计算gl_FontColor和gl_BackColor,而在Fragment Shader则会接受到一个由FontColor和BackColor插值计算出来的varying gl_Color(注意：该gl_Color与Vertex Shader当中的不同)，因而可以基于gl_Color开始计算gl_FragColor

Vertex Shader

void main()
{
    gl_FrontColor = gl_Color;
    gl_Position = ftransform();
}

Fragment Shader

void main()
{
    gl_FragColor = gl_Color;
}

3.动态变形Shader

随着时间变动，改变渲染坐标。关键在于如何把OpenGl的变量传递给Shader

比如在OpenGL中设定一个时间变量time,初始化为0，每次渲染时增加0.1:

float t = 0;
void renderScene(void) {
...
    t += 0.001;
}

那么将其传递给Shader需要做的是:

1.在初始化阶段使用glGetUniformLocation获取Shader里变量的存取位置

2.在渲染阶段使用glUniform给该存取位置变量赋值

GLint loc;
float t = 0;
void renderScene(void) {
...
    glUniform1f(loc, t);
    t += 0.001;
}
void setShaders() {
...
 glUseProgram(p);
    loc = glGetUniformLocation(p, "time");
}

最后在shader中使用时声明一下即可使用（本例当中让图形沿x轴3d翻转）

Vertex Shader

uniform float time;
void main()
{
    gl_FrontColor = gl_Color;

    vec4 v = vec4(gl_Vertex);
        v.y=v.y*cos(time)+v.y*sin(time);
        v.z=-v.y*sin(time)+cos(time)*v.z;
    gl_Position = gl_ModelViewProjectionMatrix * v;
}

Fragment Shader

void main()
{

    gl_FragColor = gl_Color;
}

 

4.Lambert Shader

Lambert模型下的Shader,只考虑漫反射，反射强度正比于入射光与法线方向的夹角余弦值:Io= Ld*Md*cosθ

Ld是散射光颜色(gl_LightSource[0].diffuse)，Md是材质散射系数(gl_FrontMaterial.diffuse),夹角余弦cosθ可由正规化的法线向量（normal）和入射光向量(lightDir)点乘得到。

OpenGL当中可以对材质和光照的属性进行设置

float lpos[4] = { 1, 0.5, 1, 0 };
float lAmb[4] = { 0.2, 0.5, 1.0, 1 };
float lDif[4] = { 0.2, 1.0, 1.0, 1 };
float lSpe[4] = { 1.0, 1.0, 1.0, 1 };
    glLightfv(GL_LIGHT0, GL_POSITION, lpos);
    glLightfv(GL_LIGHT0, GL_AMBIENT, lAmb);
    glLightfv(GL_LIGHT0, GL_DIFFUSE, lDif);
    glLightfv(GL_LIGHT0, GL_SPECULAR, lSpe);

GLfloat ambient  [] = { 0.1f, 0.1f, 0.1f, 1.0f};
GLfloat diffuse  [] = { 1.0f, 0.0f, 0.0f, 1.0f};
GLfloat specular [] = { 1.0f, 1.0f, 1.0f, 1.0f};
GLfloat shininess[] = { 0.0f};
glMaterialfv(GL_FRONT, GL_AMBIENT, ambient);
glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuse);
glMaterialfv(GL_FRONT, GL_SPECULAR, specular);
glMaterialfv(GL_FRONT, GL_SHININESS, shininess);

Vertex Shader

void main() {

    vec3 normal, lightDir;
    vec4 diffuse;
    float NdotL;
    /* 法线向量 */
    normal = normalize(gl_NormalMatrix * gl_Normal);
    /* 入射光向量*/
    lightDir = normalize(vec3(gl_LightSource[0].position));   /* cosθ */
NdotL = max(dot(normal, lightDir), 0.0);/* 散射项 */
diffuse = gl_FrontMaterial.diffuse * gl_LightSource[0].diffuse;

  gl_FrontColor = NdotL * diffuse;gl_Position = ftransform();
}

 

Fragment Shader

 

void main()
{
    gl_FragColor = gl_Color;
}

如果再考虑上环境散射项，那么OpenGL中使用glLightfv来设定环境光

float lpos[4] = { 1, 0.5, 1, 0 };
float lAmb[4] = { 0.2, 0.5, 1, 1 };
void renderScene(void) {
...
    glLightfv(GL_LIGHT0, GL_POSITION, lpos);
    glLightfv(GL_LIGHT0, GL_AMBIENT, lAmb);
...
}

 

Vertex Shader

void main()
{
    vec3 normal, lightDir;
    vec4 diffuse, ambient, globalAmbient;
    float NdotL;

    normal = normalize(gl_NormalMatrix * gl_Normal);
    lightDir = normalize(vec3(gl_LightSource[0].position));
    NdotL = max(dot(normal, lightDir), 0.0);
    diffuse = gl_FrontMaterial.diffuse * gl_LightSource[0].diffuse;
    /* Compute the ambient and globalAmbient terms */

    ambient = gl_FrontMaterial.ambient * gl_LightSource[0].ambient;
    globalAmbient = gl_LightModel.ambient * gl_FrontMaterial.ambient;
    gl_FrontColor =  NdotL * diffuse + globalAmbient + ambient;

    gl_Position = ftransform();
}

 

5.Blinn-Phong Shader

Phong光照模型，考虑反射成分(specular项)。其中Shininess在OpenGL中材质可用glMaterialfv进行设置

void main()
{
    vec3 normal, lightDir;
    vec4 diffuse, ambient, globalAmbient,specular;
    float NdotL;float NdotHV;

    normal = normalize(gl_NormalMatrix * gl_Normal);
    lightDir = normalize(vec3(gl_LightSource[0].position));
    NdotL = max(dot(normal, lightDir), 0.0);
    diffuse = gl_FrontMaterial.diffuse * gl_LightSource[0].diffuse;
    /* Compute the ambient and globalAmbient terms */

    ambient = gl_FrontMaterial.ambient * gl_LightSource[0].ambient;
    globalAmbient = gl_LightModel.ambient * gl_FrontMaterial.ambient;

        /* compute the specular term if NdotL is  larger than zero */
    if (NdotL > 0.0) {

        // normalize the half-vector, and then compute the
        // cosine (dot product) with the normal
        NdotHV = max(dot(normal, gl_LightSource[0].halfVector.xyz),0.0);
        specular = gl_FrontMaterial.specular * gl_LightSource[0].specular *
                pow(NdotHV,gl_FrontMaterial.shininess);
    }


    gl_FrontColor =  NdotL * diffuse + globalAmbient + ambient +specular;

    gl_Position = ftransform();
}

6.法线Shader

将法线方向映射到颜色空间中，可用于生成法线贴图

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