[图形学] Chp18 OpenGL表面纹理函数

　　以2D表面为例展示纹理贴图，用opengl设置一个2D纹理，颜色存储在32*32*3的数组中，对应的纹理坐标为0<=s, t<=1.0. 画出几个正方形表面，分别以GL_CLAMP(纹理坐标大于1或小于0都被规范到1和0)，GL_REPEAT（类似平铺，超过0或1的部分忽略整数位进行贴图），GL_MODULATE（纹理颜色与对象颜色相乘）, GL_REPLACE(纹理颜色替换对象颜色)几种形式进行贴图。

 #include <GLUT/GLUT.h>

 GLsizei winWidht = , winHeight = ;

 void init (void)
 {
     glClearColor(1.0, 1.0, 1.0, 0.0);

     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
     gluOrtho2D(-, , -, );
 }

 void xyCoords (void)
 {
     glBegin(GL_LINES);
     glColor3f(0.0, 0.0, 0.0);
     glVertex2i(-, );
     glVertex2i(, );
     glVertex2i(, -);
     glVertex2i(, );
     glEnd();
 }

 void lineTextureMapping (void)
 {
     GLint k;
     GLubyte texLine [];

     for (k = ; k <= ; k +=) {
         texLine [*k] = ;
         texLine [*k+] = ;
         texLine [*k+] = ;
         texLine [*k+] = ;
     }

     for (k = ; k <= ; k +=) {
         texLine [*k] = ;
         texLine [*k+] = ;
         texLine [*k+] = ;
         texLine [*k+] = ;
     }

     glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
     glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

     glTexImage1D(GL_TEXTURE_1D, , GL_RGBA, , , GL_RGBA, GL_UNSIGNED_BYTE, texLine);
     glEnable(GL_TEXTURE_1D);

     glColor3f(1.0, 1.0, 1.0);
     glBegin(GL_LINES);
     glTexCoord1f(0.25);
     glVertex2f(-4.5, 4.0);
     glTexCoord1f(1.0);
     glVertex2f(-4.5, -4.0);
     glEnd();

     glDisable(GL_TEXTURE_1D);
 }

 void surfaceTextureMapping (void)
 {
     GLint k, j;
     GLubyte texArray [][][];

     for (k = ; k < ; k++) {
         for (j = ; j < ; j++) {
             texArray [k][j][] =  - k*j/;
             texArray [k][j][] =  + k*j/;
             texArray [k][j][] = ;
             texArray [k][j][] = ;
         }
     }

     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
     glTexImage2D(GL_TEXTURE_2D, , GL_RGBA, , , , GL_RGBA, GL_UNSIGNED_BYTE, texArray);
     glEnable(GL_TEXTURE_2D);

     glColor3f(0.5, 0.5, 0.5); // 与纹理值相乘，因此会发暗
     glBegin(GL_QUADS);
     glTexCoord2f(0.0, 0.0);
     glVertex2f(0.0, 0.0);
     glTexCoord2f(3.0, 0.0);
     glVertex2f(3.0, 0.0);
     glTexCoord2f(3.0, 3.0);
     glVertex2f(3.0, 3.0);
     glTexCoord2f(0.0, 3.0);
     glVertex2f(0.0, 3.0);
     glEnd();

     glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
     glColor3f(0.5, 0.5, 0.5); // 替换为纹理颜色，则不会像前一个图案那样发暗
     glBegin(GL_QUADS);
     glTexCoord2f(0.0, 0.0);
     glVertex2f(-4.0, -4.0);
     glTexCoord2f(1.0, 0.0);
     glVertex2f(-1.0, -4.0);
     glTexCoord2f(1.0, 1.0);
     glVertex2f(-1.0, -1.0);
     glTexCoord2f(0.0, 1.0);
     glVertex2f(-4.0, -1.0);
     glEnd();
     glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

     // 不允许纹理坐标超过1，因此小于0的设为0，大于1的设为1
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
     glColor3f(1.0, 1.0, 1.0);
     glBegin(GL_QUADS);
     glTexCoord2f(0.0, 0.0);
     glVertex2f(-4.0, 0.0);
     glTexCoord2f(, 0.0);
     glVertex2f(-1.0, 0.0);
     glTexCoord2f(, );
     glVertex2f(-1.0, 3.0);
     glTexCoord2f(0.0, );
     glVertex2f(-4.0, 3.0);
     glEnd();
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

     glDisable(GL_TEXTURE_2D);
 }

 void displayFcn (void)
 {
     glClear(GL_COLOR_BUFFER_BIT);

 //    lineTextureMapping();
     surfaceTextureMapping();
     xyCoords();

     glFlush();
 }

 void winReshapeFcn (GLint newWidth, GLint newHeight)
 {
     glViewport(, , newWidth, newHeight);
 }

 int main(int argc, char * argv[])
 {
     glutInit(&argc, argv);
     glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
     glutInitWindowSize(winWidht, winHeight);
     glutInitWindowPosition(, );
     glutCreateWindow("texture mapping");

     init();
     glutDisplayFunc(displayFcn);
     glutReshapeFunc(winReshapeFcn);
     glutMainLoop();

     return ;
 }