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 45
static 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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