17.OpenGL--替换纹理图像的全部或一部分

• 理论基础 
  和修改原有纹理相比，创建新纹理的开销更大。我们主要使用glTexSubImage*和glCopyTexSubImage*()来修改纹理，前者用于替换的纹理来源外部读取，后者替换的纹理来源自身帧缓冲区。

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• 实例代码

#include "GLTools.h"#ifdef __APPLE__#include <glut/glut.h>#else#define FREEGLUT_STATIC#include <GL/glut.h>#endif#define checkImageWidth 64#define checkImageHeight 64#define subImageWidth 45#define subImageHeight 45static GLubyte checkImage[checkImageHeight][checkImageWidth][4];static GLubyte subImage[subImageHeight][subImageWidth][4];static GLuint texName;//纹理数据(黑白相间的棋盘和蓝色区域)void makeCheckImages(void){    int i, j, c;    for (i = 0; i < checkImageHeight; i++) {        for (j = 0; j < checkImageWidth; j++) {            c = ((((i&0x8)==0)^((j&0x8))==0))*255;            checkImage[i][j][0] = (GLubyte) c;            checkImage[i][j][1] = (GLubyte) c;            checkImage[i][j][2] = (GLubyte) c;            checkImage[i][j][3] = (GLubyte) 255;        }    }    for (i = 0; i < subImageHeight; i++) {        for (j = 0; j < subImageWidth; j++) {            subImage[i][j][0] = (GLubyte) 0;            subImage[i][j][1] = (GLubyte) 0;            subImage[i][j][2] = (GLubyte) 255;            subImage[i][j][3] = (GLubyte) 255;        }    }}void init(void){    glClearColor (0.0, 0.0, 0.0, 0.0);    glShadeModel(GL_FLAT);    glEnable(GL_DEPTH_TEST);    makeCheckImages();    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);    glGenTextures(1, &texName);    glBindTexture(GL_TEXTURE_2D, texName);    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, checkImageWidth, checkImageHeight,                 0, GL_RGBA, GL_UNSIGNED_BYTE, checkImage);}void display(void){    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    glEnable(GL_TEXTURE_2D);    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);    glBindTexture(GL_TEXTURE_2D, texName);    glBegin(GL_QUADS);    glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);    glTexCoord2f(0.0, 1.0); glVertex3f(-2.0, 1.0, 0.0);    glTexCoord2f(1.0, 1.0); glVertex3f(0.0, 1.0, 0.0);    glTexCoord2f(1.0, 0.0); glVertex3f(0.0, -1.0, 0.0);    glTexCoord2f(0.0, 0.0); glVertex3f(1.0, -1.0, 0.0);    glTexCoord2f(0.0, 1.0); glVertex3f(1.0, 1.0, 0.0);    glTexCoord2f(1.0, 1.0); glVertex3f(2.41421, 1.0, -1.41421);    glTexCoord2f(1.0, 0.0); glVertex3f(2.41421, -1.0, -1.41421);    glEnd();    glFlush();    glDisable(GL_TEXTURE_2D);}void reshape(int w, int h){    glViewport(0, 0, (GLsizei) w, (GLsizei) h);    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 30.0);    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    glTranslatef(0.0, 0.0, -3.6);}void keyboard (unsigned char key, int x, int y){    switch (key) {        case 's':        case 'S':            //指定当前活动的纹理            glBindTexture(GL_TEXTURE_2D, texName);            /*用subImage纹理替换原纹理的(12,12)至            (subImageWidth,subImageHeight)区域*/            glTexSubImage2D(GL_TEXTURE_2D, 0, 12, 12,             subImageWidth, subImageHeight,             GL_RGBA,GL_UNSIGNED_BYTE, subImage);            glutPostRedisplay();            break;        case 'r':        case 'R':            glBindTexture(GL_TEXTURE_2D, texName);            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,             checkImageWidth, checkImageHeight, 0,             GL_RGBA,GL_UNSIGNED_BYTE, checkImage);            glutPostRedisplay();            break;        case 27:            exit(0);            break;        default:            break;    }}int main(int argc, char** argv){    glutInit(&argc, argv);    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);    glutInitWindowSize(250, 250);    glutInitWindowPosition(100, 100);    glutCreateWindow(argv[0]);    init();    glutDisplayFunc(display);    glutReshapeFunc(reshape);    glutKeyboardFunc(keyboard);    glutMainLoop();    return 0; }
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