一个简单的GLSL Shader例子

本例子选自OpenGL Shading Language中的第一个Shader例子，使用颜色平滑地表示一个表面的温度。温度及其颜色的范围在应用程序中进行设置。
//先看顶点着色器temp.vert：
uniform float CoolestTemp;
uniform float TempRange;
attribute float VertexTemp;//每个定点都对应一个温度值
varying float Temperature;//传递到片段处理器进行后续处理
void main(void)
{
//进行插值
Temperature = (VertexTemp - CoolestTemp) / TempRange;
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
}
//片段着色器temp.frag：
uniform vec3 CoolestColor;
uniform vec3 HottestColor;
varying float Temperature;
void main(void)
{
//通过温度值寻找一个相应的颜色，位于最冷和最热之间
vec3 color = mix(CoolestColor, HottestColor,Temperature);
gl_FragColor = vec4(color,1.0);
}
下面看看如何将着色器和应用程序进行链接（第一步是创建着色器对象，指定着色器源代码，进行编译，并程序对象和着色器进行绑定和链接），同时指定了一些一致变量的值
/*public*/
int installShaders(const GLchar *Vertex, const GLchar *Fragment)
{
GLint vertCompiled, fragCompiled;
// status values
GLint linked;
// Create a vertex shader object and a fragment shader object
VertexShaderObject = glCreateShader(GL_VERTEX_SHADER);
FragmentShaderObject = glCreateShader(GL_FRAGMENT_SHADER); /
/ Load source code strings into shaders
glShaderSource(VertexShaderObject, 1, &Vertex, NULL);
glShaderSource(FragmentShaderObject, 1, &Fragment, NULL);
// Compile the brick vertex shader, and print out
// the compiler log file.
glCompileShader(VertexShaderObject);
glGetShaderiv(VertexShaderObject, GL_COMPILE_STATUS, &vertCompiled);
// Compile the brick vertex shader, and print out
// the compiler log file.
glCompileShader(FragmentShaderObject);
glGetShaderiv(FragmentShaderObject, GL_COMPILE_STATUS, &fragCompiled);
if (!vertCompiled || !fragCompiled)
return 0;
// Create a program object and attach the two compiled shaders
ProgramObject = glCreateProgram();
glAttachShader(ProgramObject, VertexShaderObject);
glAttachShader(ProgramObject, FragmentShaderObject);
// Link the program object and print out the info log
glLinkProgram(ProgramObject);
glGetProgramiv(ProgramObject, GL_LINK_STATUS, &linked);
if (!linked)
return 0;
// Install program object as part of current state
glUseProgram(ProgramObject);
// Set up initial uniform values
glUniform1f(glGetUniformLocation(ProgramObject, "CoolestTemp"), 0.0f);
glUniform1f(glGetUniformLocation(ProgramObject, "TempRange"), 1.0f);
glUniform3f(glGetUniformLocation(ProgramObject, "CoolestColor"), 0.0, 0.0, 1.0);
glUniform3f(glGetUniformLocation(ProgramObject, "HottestColor"), 1.0, 0.0, 0.0);
return 1;
}
这其中用到了一些读取外部着色器代码的函数，顶点着色器后缀自定义为.vert，片段着色器自定义为.frag，我们也可以将着色器放在程序中存储在一个字符串中。
//Shader related functions static int shaderSize(char *fileName, EShaderType shaderType)
{
//返回顶点着色器或者片段着色器的大小
char name[100];
strcpy(name, fileName);
switch (shaderType)
{
case EVertexShader:
strcat(name, ".vert");
break;
case EFragmentShader:
strcat(name, ".frag");
break;
default:
printf("ERROR: unknown shader file type ");
exit(1);
break;
}
int count = -1;
// Open the file, seek to the end to find its length
int fd = _open(name, _O_RDONLY);
if (fd != -1)
{
count = _lseek(fd, 0, SEEK_END) + 1;
_close(fd);
}
return count;
}
static int readShader(char *fileName, EShaderType shaderType, char *shaderText, int size)
{
// Reads a shader from the supplied file and returns the shader in the
// arrays passed in.
Returns 1 if successful, 0 if an error occurred.
// The parameter size is an upper limit of the amount of bytes to read.
// It is ok for it to be too big.
FILE *fh;
char name[100];
int count;
strcpy(name, fileName);
switch (shaderType)
{
case EVertexShader:
strcat(name, ".vert");
break;
case EFragmentShader:
strcat(name, ".frag");
break;
default:
printf("ERROR: unknown shader file type ");
exit(1);
break;
}
// Open the file
fh = fopen(name, "r");
if (!fh)
return -1;
// Get the shader from a file.
fseek(fh, 0, SEEK_SET);
count = (int) fread(shaderText, 1, size, fh);
shaderText[count] = '