在ShaderDesigner下編Shader是最爲方便的,但這裏先用OpenGL下的編程來舉例
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這幾個Shader的實際效果:
1.最簡單的固定單色Shader
Vertex Shader
座標經過投影矩陣變換:vTrans = projection * modelview * incomingVertex
void main()
{
gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix * gl_Vertex;
}
或者更簡單的方式,使用ftransform函數void main()
{
gl_Position = ftransform();
}
Fragment Shader
賦予像素一個固定值的顏色
void main()
{
gl_FragColor = vec4(0.4,0.4,0.8,1.0);
}
2.顏色Shader
在OpenGL程序當中使用 glColor函數指定顏色時,接收該顏色值的Shader
例如OpenGL程序當中畫一個紅色茶壺: glColor3f(1, 0, 0);
glutSolidTeapot(1);
glColor在Shader當中總共涉及四個值
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函數後,將顏色值以attribute gl_Color的形式傳給了Vertex Shader, Vertext Shader接受到後開始計算gl_FontColor和gl_BackColor,而在Fragment Shader則會接受到一個由FontColor和BackColor插值計算出來的varying gl_Color(注意:該gl_Color與Vertex Shader當中的不同),因而可以基於gl_Color開始計算gl_FragColor
Vertex Shader
void main()
{
gl_FrontColor = gl_Color;
gl_Position = ftransform();
}
Fragment Shader
void main()
{
gl_FragColor = gl_Color;
}
3.動態變形Shader
隨着時間變動,改變渲染座標。關鍵在於如何把OpenGl的變量傳遞給Shader
比如在OpenGL中設定一個時間變量time,初始化爲0,每次渲染時增加0.1:
float t = 0;
void renderScene(void) {
...
t += 0.001;
}
那麼將其傳遞給Shader需要做的是:
1.在初始化階段使用glGetUniformLocation獲取Shader裏變量的存取位置
2.在渲染階段使用glUniform給該存取位置變量賦值
GLint loc;
float t = 0;
void renderScene(void) {
...
glUniform1f(loc, t);
t += 0.001;
}
void setShaders() {
...
glUseProgram(p);
loc = glGetUniformLocation(p, "time");
}
最後在shader中使用時聲明一下即可使用(本例當中讓圖形沿x軸3d翻轉)
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,只考慮漫反射,反射強度正比於入射光與法線方向的夾角餘弦值:Io= Ld*Md*cosθ
Ld是散射光顏色(gl_LightSource[0].diffuse),Md是材質散射係數(gl_FrontMaterial.diffuse),夾角餘弦cosθ可由正規化的法線向量(normal)和入射光向量(lightDir)點乘得到。
OpenGL當中可以對材質和光照的屬性進行設置
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;
/* 法線向量 */
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);/* 散射項 */
diffuse = gl_FrontMaterial.diffuse * gl_LightSource[0].diffuse;
gl_FrontColor = NdotL * diffuse;gl_Position = ftransform();
}
Fragment Shader
void main()
{
gl_FragColor = gl_Color;
}
如果再考慮上環境散射項,那麼OpenGL中使用glLightfv來設定環境光
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.法線Shader
將法線方向映射到顏色空間中,可用於生成法線貼圖
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();
}