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] = ''; 
if (ferror(fh)) 
count = 0; 
fclose(fh); 
return count; 
}

/*public*/ 
int readShaderSource(char *fileName, GLchar **vertexShader, GLchar **fragmentShader) 
{ 
int vSize, fSize; 
// // Allocate memory to hold the source of our shaders. 
vSize = shaderSize(fileName, EVertexShader); 
fSize = shaderSize(fileName, EFragmentShader); 
if ((vSize == -1) || (fSize == -1)) 
{ 
printf("Cannot determine size of the shader %s ", fileName); return 0; 
} 
*vertexShader = (GLchar *) malloc(vSize); 
*fragmentShader = (GLchar *) malloc(fSize); 
// // Read the source code // 
if (!readShader(fileName, EVertexShader, *vertexShader, vSize)) 
{ 
printf("Cannot read the file %s.vert ", fileName); 
return 0; 
} 
if (!readShader(fileName, EFragmentShader, *fragmentShader, fSize)) 
{ 
printf("Cannot read the file %s.frag ", fileName); 
return 0; 
} 
return 1; 
} 
这里我们只绘制一个简单的三角形，需要为每个顶点指定一个属性值，代表其温度值，着色器中我们对其进行了读取并插值。对于复杂的图形，应当使用顶点数组进行指定。 
static void display(void) 
{ 
glLoadIdentity(); 
glTranslatef(0.0, 0.0, -5.0); 
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//查询定点着色器属性变量VertexTemp，并对它进行设置，每个定点需要指定一个属性 
GLint tempLoc = glGetAttribLocationARB(ProgramObject, "VertexTemp"); 
glBegin(GL_TRIANGLES); 
glVertexAttrib1f(tempLoc, 0.0f); 
glVertex3f(1.0f,0.0f,0.0f); 
glVertexAttrib1f(tempLoc, 0.5f); 
glVertex3f(-1.0f,0.0f,0.0f); 
glVertexAttrib1f(tempLoc, 1.0f); 
glVertex3f(0.0f,1.0f,0.0f); 
glEnd(); 
glFlush(); 
glutSwapBuffers(); 
} 
运行效果如下：

   
整个程序如下： 
 

#include

#include

#include

#include

#include

#define GLEW_STATIC 1

#include

#include

#include

 

//窗口句柄

static GLint window;

 

GLuint ProgramObject = 0;                            //程序对象

GLuint VertexShaderObject = 0;                   //顶点着色器对象

GLuint FragmentShaderObject = 0;    //片段着色器对象

 

//Shader类型

typedef enum {

    EVertexShader,

         EFragmentShader,

} EShaderType;

 

//用来检查OpenGL版本，需要GLSL 2.0支持

void getGlVersion( int *major, int *minor )

{

    constchar* verstr = (constchar*)glGetString( GL_VERSION );

    if( (verstr == NULL) || (sscanf( verstr, "%d.%d", major, minor ) != 2) )

    {

        *major = *minor = 0;

        fprintf( stderr, "Invalid GL_VERSION format!!! " );

    }

}

 

staticvoid display(void)

{

    glLoadIdentity();

    glTranslatef(0.0, 0.0, -5.0);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

 

         //查询定点着色器属性变量VertexTemp，并对它进行设置，每个定点需要指定一个属性

         GLint tempLoc = glGetAttribLocationARB(ProgramObject, "VertexTemp");

         glBegin(GL_TRIANGLES);

                   glVertexAttrib1f(tempLoc, 0.0f);        

                   glVertex3f(1.0f,0.0f,0.0f);

                   glVertexAttrib1f(tempLoc, 0.5f);

                   glVertex3f(-1.0f,0.0f,0.0f);

                   glVertexAttrib1f(tempLoc, 1.0f);

                   glVertex3f(0.0f,1.0f,0.0f);

         glEnd();

    glFlush();

    glutSwapBuffers();

}

 

staticvoid reshape(int wid, int ht)

{

    float vp = 0.8f;

    float aspect = (float) wid / (float) ht;

        

    glViewport(0, 0, wid, ht);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    //glOrtho(-1.0, 1.0, -1.0, 1.0, -10.0, 10.0);

    glFrustum(-vp, vp, -vp / aspect, vp / aspect, 3, 10.0);

         glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

}

 

 

//Shader related functions

staticint 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;

}

 

 

staticint 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] = '';

 

    if (ferror(fh))

        count = 0;

 

    fclose(fh);

    return count;

}

 

 

/*public*/

int readShaderSource(char *fileName, GLchar **vertexShader, GLchar **fragmentShader)

{

    int vSize, fSize;

 

    //

    // Allocate memory to hold the source of our shaders.

    //

    vSize = shaderSize(fileName, EVertexShader);

    fSize = shaderSize(fileName, EFragmentShader);

 

    if ((vSize == -1) || (fSize == -1))

    {

        printf("Cannot determine size of the shader %s ", fileName);

        return 0;

    }

 

    *vertexShader = (GLchar *) malloc(vSize);

    *fragmentShader = (GLchar *) malloc(fSize);

 

    //

    // Read the source code

    //

    if (!readShader(fileName, EVertexShader, *vertexShader, vSize))

    {

        printf("Cannot read the file %s.vert ", fileName);

        return 0;

    }

 

    if (!readShader(fileName, EFragmentShader, *fragmentShader, fSize))

    {

        printf("Cannot read the file %s.frag ", fileName);

        return 0;

    }

 

    return 1;

}

 

 

/*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;

}

 

/******************************************************************************/

/*

/* Main

/*

/******************************************************************************/

int main( int argc, char **argv )

{

    int success = 0;

    int gl_major, gl_minor;

    GLchar *VertexShaderSource, *FragmentShaderSource;

        

    glutInit( &argc, argv );

    glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);

    glutInitWindowSize(500, 500);

    window = glutCreateWindow( "Temperature Shader");

        

    glutDisplayFunc(display);

    glutReshapeFunc(reshape);

        

    // Initialize the "OpenGL Extension Wrangler" library

    glewInit();

        

    // Make sure that OpenGL 2.0 is supported by the driver

    getGlVersion(&gl_major, &gl_minor);

    printf("GL_VERSION major=%d minor=%d ", gl_major, gl_minor);

        

    if (gl_major < 2)

    {

        printf("GL_VERSION major=%d minor=%d ", gl_major, gl_minor);

        printf("Support for OpenGL 2.0 is required for this demo...exiting ");

        exit(1);

    }

        

    readShaderSource("temp", &VertexShaderSource, &FragmentShaderSource);

    success = installShaders(VertexShaderSource, FragmentShaderSource);

        

    if (success)

        glutMainLoop();

   

    return 0;

}