一种是直观的使用glGetTexImage,然后获取数据到内存再贴上去，这种方法很慢

另一种是使用FBO，将纹理附加到FBO，然后用glCopyTexSubImage2D,不涉及跟内存交换数据，速度飞快。

方法一：获取纹理再拷贝

1. unsigned char * data = new unsigned char[normal_texture.width*normal_texture.Hight*4];

2. glBindTexture(GL_TEXTURE_2D,src_id);

3. glGetTexImage(GL_TEXTURE_2D,0,GL_RGBA,GL_UNSIGNED_BYTE,data);

4. glBindTexture(GL_TEXTURE_2D,dest_id);

5. glTexSubImage2D(GL_TEXTURE_2D,0,0,0,width,height,GL_RGBA,GL_UNSIGNED_BYTE,data);

6. glBindTexture(GL_TEXTURE_2D,0);

第二种方法：FBO拷贝

1. GLuint fbo;

2. glGenFramebuffers(1,&fbo);

3. /// bind the FBO

4. glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo);

5. /// attach the source texture to the fbo

6. glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,

7. GL_TEXTURE_2D, src_id, 0);

8. /// bind the destination texture

9. glBindTexture(GL_TEXTURE_2D, dest_id);

10. /// copy from framebuffer (here, the FBO!) to the bound texture

11. glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, width,height);

12. /// unbind the FBO

13. glBindFramebuffer(GL_FRAMEBUFFER, 0);

14. glBindTexture(GL_TEXTURE_2D,0);