Graphics Reference
In-Depth Information
Let's now look at some examples that demonstrate how to use framebuffer
objects. Example 12-2 demonstrates how to render to texture using
framebuffer objects. In this example, we draw to a texture using a
framebuffer object. We then use this texture to draw a quad to the
window system-provided framebuffer (i.e., the screen). Figure 12-2 shows
the generated image.
Example 12-2
Render to Texture
GLuint framebuffer;
GLuint depthRenderbuffer;
GLuint texture;
GLint texWidth = 256, texHeight = 256;
GLint maxRenderbufferSize;
glGetIntegerv ( GL_MAX_RENDERBUFFER_SIZE, &maxRenderbufferSize);
// check if GL_MAX_RENDERBUFFER_SIZE is >= texWidth and texHeight
if ( ( maxRenderbufferSize <= texWidth ) ||
( maxRenderbufferSize <= texHeight ) )
{
// cannot use framebuffer objects, as we need to create
// a depth buffer as a renderbuffer object
// return with appropriate error
}
// generate the framebuffer, renderbuffer, and texture object names
glGenFramebuffers ( l, &framebuffer );
glGenRenderbuffers ( l, &depthRenderbuffer );
glGenTextures ( l, &texture );
// bind texture and load the texture mip level 0
// texels are RGB565
// no texels need to be specified as we are going to draw into
// the texture
glBindTexture ( GL_TEXTURE_2D, texture );
glTexImage2D ( GL_TEXTURE_2D, O, GL_RGB, texWidth, texHeight, 0,
GL_RGB, GL_UNSIGNED_SHORT_5_6_5, NULL );
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,
GL_CLAMP_TO_EDGE );
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,
GL_CLAMP_TO_EDGE );
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
GL_LINEAR );
