从一个texture读出rgba数据
int iBytesPerRow = iWidth * 4;
unsigned char *baseAddress = malloc(iBytesPerRow * iHeight);
GLuint fboID;
glGenFramebuffers(1, &fboID);
glBindFramebuffer(GL_FRAMEBUFFER, fboID);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, inputTexture, 0);
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glReadPixels(0, 0, iWidth, iHeight, GL_RGBA, GL_UNSIGNED_BYTE, baseAddress);
glDeleteFramebuffer(1, &fboID);
将rgba写入一个texture
GLuint texture;
glActiveTexture(GL_TEXTURE1);
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width , height, 0, format, GL_UNSIGNED_BYTE, buffer);
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
