Graphics Reference
In-Depth Information
window system-provided drawables. Framebuffer objects, therefore,
provide a better and more efficient method for rendering to a texture or
an off-screen surface.
The framebuffer objects API supports the following operations:
• Creating framebuffer objects using OpenGL ES commands only
• Creating and using multiple framebuffer objects within a single
EGL context—that is, without requiring a rendering context per
framebuffer
• Creating off-screen color, depth, or stencil renderbuffers and textures,
and attaching these to a framebuffer object
• Sharing color, depth, or stencil buffers across multiple framebuffers
• Attaching textures directly to a framebuffer as color or depth, thereby
avoiding the need to do a copy operation
• Copying between framebuffers and invalidating framebuffer contents
In this section, we describe what renderbuffer and framebuffer objects are,
explain how they differ from window system-provided drawables, and
consider when to use a renderbuffer instead of a texture.
A
renderbuffer object
is a 2D image buffer allocated by the application.
The renderbuffer can be used to allocate and store color, depth, or stencil
values and can be used as a color, depth, or stencil attachment in a
framebuffer object. A renderbuffer is similar to an off-screen window
system-provided drawable surface, such as a pbuffer. A renderbuffer,
however, cannot be directly used as a GL texture.
A
framebuffer object
(FBO) is a collection of color, depth, and stencil textures
or render targets. Various 2D images can be attached to the color attachment
point in the framebuffer object. These include a renderbuffer object that
stores color values, a mip level of a 2D texture or a cubemap face, a layer of a
2D array textures, or even a mip level of a 2D slice in a 3D texture. Similarly,
various 2D images containing depth values can be attached to the depth
attachment point of an FBO. These can include a renderbuffer, a mip level
of a 2D texture, or a cubemap face that stores depth values. The only 2D
image that can be attached to the stencil attachment point of an FBO is a
renderbuffer object that stores stencil values.
