GLSL下几个简单的Shader
在ShaderDesigner下编Shader是最为方便的，但这里先用OpenGL下的编程来举例
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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
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
void main()
{
vec3 normal;
normal = normalize(gl_NormalMatrix * gl_Normal);
gl_FrontColor = (vec4(normal.x,normal.y,normal.z,1.0)+1)/2;
gl_Position = ftransform();
}