OpenGL extension EXT.framebuffer_multisample
This module customises the behaviour of the
OpenGL.raw.GL.EXT.framebuffer_multisample to provide a more
Overview (from the spec)
This extension extends the EXT_framebuffer_object framework to
enable multisample rendering.
The new operation RenderbufferStorageMultisampleEXT() allocates
storage for a renderbuffer object that can be used as a multisample
buffer. A multisample render buffer image differs from a
single-sample render buffer image in that a multisample image has a
number of SAMPLES that is greater than zero. No method is provided
for creating multisample texture images.
All of the framebuffer-attachable images attached to a framebuffer
object must have the same number of SAMPLES or else the framebuffer
object is not "framebuffer complete". If a framebuffer object with
multisample attachments is "framebuffer complete", then the
framebuffer object behaves as if SAMPLE_BUFFERS is one.
In traditional multisample rendering, where
DRAW_FRAMEBUFFER_BINDING_EXT is zero and SAMPLE_BUFFERS is one, the
GL spec states that "the color sample values are resolved to a
single, displayable color each time a pixel is updated." There are,
however, several modern hardware implementations that do not
actually resolve for each sample update, but instead postpones the
resolve operation to a later time and resolve a batch of sample
updates at a time. This is OK as long as the implementation behaves
"as if" it had resolved a sample-at-a-time. Unfortunately, however,
honoring the "as if" rule can sometimes degrade performance.
In contrast, when DRAW_FRAMEBUFFER_BINDING_EXT is an
application-created framebuffer object, MULTISAMPLE is enabled, and
SAMPLE_BUFFERS is one, there is no implicit per-sample-update
resolve. Instead, the application explicitly controls when the
resolve operation is performed. The resolve operation is affected
by calling BlitFramebufferEXT (provided by the EXT_framebuffer_blit
extension) where the source is a multisample application-created
framebuffer object and the destination is a single-sample
framebuffer object (either application-created or window-system
This design for multisample resolve more closely matches current
hardware, but still permits implementations which choose to resolve
a single sample at a time. If hardware that implementes the
multisample resolution "one sample at a time" exposes
EXT_framebuffer_multisample, it could perform the implicit resolve
to a driver-managed hidden surface, then read from that surface when
the application calls BlitFramebufferEXT.
Another motivation for granting the application explicit control
over the multisample resolve operation has to do with the
flexibility afforded by EXT_framebuffer_object. Previously, a
drawable (window or pbuffer) had exclusive access to all of its
buffers. There was no mechanism for sharing a buffer across
multiple drawables. Under EXT_framebuffer_object, however, a
mechanism exists for sharing a framebuffer-attachable image across
several framebuffer objects, as well as sharing an image between a
framebuffer object and a texture. If we had retained the "implicit"
resolve from traditional multisampled rendering, and allowed the
creation of "multisample" format renderbuffers, then this type of
sharing would have lead to two problematic situations:
* Two contexts, which shared renderbuffers, might perform
competing resolve operations into the same single-sample buffer
with ambiguous results.
* It would have introduced the unfortunate ability to use the
single-sample buffer as a texture while MULTISAMPLE is ENABLED.
By using the BlitFramebufferEXT from EXT_framebuffer_blit as an
explicit resolve to serialize access to the multisampled contents
and eliminate the implicit per-sample resolve operation, we avoid
both of these problems.
The official definition of this extension is available here:
|EXTENSION_NAME = 'GL_EXT_framebuffer_multisample'|
GL_FRAMEBUFFER_INCOMPLETE_MULTISAMPLE_EXT = GL_FRAMEBUFFER_INCOMPLETE_MULTISAMPLE_EXT
GL_MAX_SAMPLES_EXT = GL_MAX_SAMPLES_EXT
GL_RENDERBUFFER_SAMPLES_EXT = GL_RENDERBUFFER_SAMPLES_EXT
__file__ = '/home/mcfletch/pylive/OpenGL/GL/EXT/framebuffer_multisample.pyc'
__name__ = 'OpenGL.GL.EXT.framebuffer_multisample'
__package__ = 'OpenGL.GL.EXT'
glRenderbufferStorageMultisampleEXT = <OpenGL.platform.baseplatform.glRenderbufferStorageMultisampleEXT object at 0x6514690>