Graphics Reference
In-Depth Information
Chapter 12
In this chapter, we describe what framebuffer objects are, how applications
can create them, and how applications can use them for rendering to an
off-screen buffer or rendering to a texture. We start by discussing why we
need framebuffer objects. We then introduce framebuffer objects and new
object types they add to OpenGL ES, and explain how they differ from the
EGL surfaces described in Chapter 3, “An Introduction to EGL.” We go on
to discuss how to create framebuffer objects; explore how to specify color,
depth, and stencil attachments to a framebuffer object; and then provide
examples that demonstrate rendering to a framebuffer object. Last but not
least, we discuss performance tips and tricks that can help ensure good
performance when using framebuffer objects.
A rendering context and a drawing surface need to be first created and
made current before any OpenGL ES commands can be called by an
application. The rendering context and the drawing surface are usually
provided by the native windowing system through an API such as EGL.
Chapter 3 describes how to create an EGL context and surface and how
to attach them to a rendering thread. The rendering context contains
the appropriate state required for correct operation. The drawing surface
provided by the native windowing system can be a surface that will be
displayed on the screen, referred to as the window system-provided
framebuffer, or it can be an off-screen surface, referred to as a pbuffer.
The calls to create the EGL drawing surfaces let you specify the width and
