Graphics Reference
In-Depth Information
OpenGL ES 3.0 adds many new features related to off-screen rendering to
framebuffer objects:
• Multiple render targets (MRTs)—Allow the application to render
simultaneously to several color buffers at one time. With MRTs, the
fragment shader outputs several colors, one for each attached color
buffer. MRTs are used in many advanced rendering algorithms, such as
deferred shading.
• Multisample renderbuffers—Enable the application to render to off-
screen framebuffers with multisample anti-aliasing. The multisample
renderbuffers cannot be directly bound to textures, but they can
be resolved to single-sample textures using the newly introduced
framebuffer blit.
• Framebuffer invalidation hints—Many implementations of OpenGL
ES 3.0 are based on GPUs that use tile-based rendering (TBR;
explained in the
Framebuffer Invalidation
section in Chapter 12).
It is often the case that TBR incurs a significant performance cost
when having to unnecessarily restore the contents of the tiles for
further rendering to a framebuffer. Framebuffer invalidation gives
the application a mechanism to inform the driver that the contents
of the framebuffer are no longer needed. This allows the driver
to take optimization steps to skip unnecessary restore operations
on the tiles. Such functionality is very important to achieve
peak performance in many applications, especially those that do
significant amounts of off-screen rendering.
• New blend equations—The min/max functions are supported in
OpenGL ES 3.0 as a blend equation.
OpenGL ES 3.0 is backward compatible with OpenGL ES 2.0. This means
that just about any application written to use OpenGL ES 2.0 will run on
implementations of OpenGL ES 3.0. There are some very minor changes
to the later version that will affect a small number of applications in terms
of backward compatibility. Namely, framebuffer objects are no longer
shared between contexts, cubemaps are always filtered using seamless
filtering, and there are minor changes in the way signed fixed-point
numbers are converted to floating-point numbers.
