'''OpenGL extension ARB.framebuffer_object
This module customises the behaviour of the
OpenGL.raw.GL.ARB.framebuffer_object to provide a more
Python-friendly API
Overview (from thespec import
ARB_framebuffer_object is an extension intended to address the following
goals:
- Reflect FBO-related functionality found in the OpenGL 3.0 specification.
- Integrate multiple disjoint extensions into a single ARB extension.
These extensions are:
EXT_framebuffer_object
EXT_framebuffer_blit
EXT_framebuffer_multisample
EXT_packed_depth_stencil
- Where appropriate, relax some of the constraints expressed by previous
FBO-related extensions. In particular the requirement of matching
attachment dimensions and component sizes has been relaxed, to allow
implementations the freedom to support more flexible usages where
possible.
ARB_framebuffer_object defines an interface for drawing to rendering
destinations other than the buffers provided to the GL by the
window-system.
In this extension, these newly defined rendering destinations are
known collectively as "framebuffer-attachable images". This
extension provides a mechanism for attaching framebuffer-attachable
images to the GL framebuffer as one of the standard GL logical
buffers: color, depth, and stencil. (Attaching a
framebuffer-attachable image to the accum logical buffer is left for
a future extension to define). When a framebuffer-attachable image
is attached to the framebuffer, it is used as the source and
destination of fragment operations as described in Chapter 4.
By allowing the use of a framebuffer-attachable image as a rendering
destination, this extension enables a form of "offscreen" rendering.
Furthermore, "render to texture" is supported by allowing the images
of a texture to be used as framebuffer-attachable images. A
particular image of a texture object is selected for use as a
framebuffer-attachable image by specifying the mipmap level, cube
map face (for a cube map texture), and layer (for a 3D texture)
that identifies the image. The "render to texture" semantics of
this extension are similar to performing traditional rendering to
the framebuffer, followed immediately by a call to CopyTexSubImage.
However, by using this extension instead, an application can achieve
the same effect, but with the advantage that the GL can usually
eliminate the data copy that would have been incurred by calling
CopyTexSubImage.
This extension also defines a new GL object type, called a
"renderbuffer", which encapsulates a single 2D pixel image. The
image of renderbuffer can be used as a framebuffer-attachable image
for generalized offscreen rendering and it also provides a means to
support rendering to GL logical buffer types which have no
corresponding texture format (stencil, accum, etc). A renderbuffer
is similar to a texture in that both renderbuffers and textures can
be independently allocated and shared among multiple contexts. The
framework defined by this extension is general enough that support
for attaching images from GLobjectsotherthantextures import
renderbuffers could be added by layered extensions.
To facilitate efficient switching between collections of
framebuffer-attachable images, this extension introduces another new
GL object, called a framebuffer object. A framebuffer object
contains the state that defines the traditional GL framebuffer,
including its set of images. Prior to this extension, it was the
window-system which defined and managed this collection of images,
traditionally by grouping them into a "drawable". The window-system
API's would also provide a function (i.e., wglMakeCurrent,
glXMakeCurrent, aglSetDrawable, etc.) to bind a drawable with a GL
context (as is done in the WGL_ARB_pbuffer extension). In this
extension however, this functionality is subsumed by the GL and the
GL provides the function BindFramebufferARB to bind a framebuffer
object to the current context. Later, the context can bind back to
the window-system-provided framebuffer in order to display rendered
content.
Previous extensions that enabled rendering to a texture have been
much more complicated. One example is the combination of
ARB_pbuffer and ARB_render_texture, both of which are window-system
extensions. This combination requires calling MakeCurrent, an
operation that may be expensive, to switch between the window and
the pbuffer drawables. An application must create one pbuffer per
renderable texture in order to portably use ARB_render_texture. An
application must maintain at least one GL context per texture
format, because each context can only operate on a single
pixelformat or FBConfig. All of these characteristics make
ARB_render_texture both inefficient and cumbersome to use.
ARB_framebuffer_object, on the other hand, is both simpler to use
and more efficient than ARB_render_texture. The
ARB_framebuffer_object API is contained wholly within the GL API and
has no (non-portable) window-system components. Under
ARB_framebuffer_object, it is not necessary to create a second GL
context when rendering to a texture image whose format differs from import
that of the window. Finally, unlike the pbuffers of
ARB_render_texture, a single framebuffer object can facilitate
rendering to an unlimited number of texture objects.
This extension differs from EXT_framebuffer_objectbysplittingthe import
framebuffer object binding point into separate DRAW and READ
bindings (incorporating functionality introduced by
EXT_framebuffer_blit). This allows copying directly from one import
framebuffer to another. In addition, a new high performance blit
function is added to facilitate these blits and perform some data
conversion where allowed.
This extension also enables usage of multisampling in conjunction with
renderbuffers (incorporating functionality from import
EXT_packed_depth_stencil), as follows:
The new operation RenderbufferStorageMultisample() allocates
storage for a renderbuffer object that can be used as a multisample
buffer. A multisample render buffer image differs from a import
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 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 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 BlitFramebuffer 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 provided).
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 implements the
multisample resolution "one sample at a time" exposes
ARB_framebuffer_object, it could perform the implicit resolve
to a driver-managed hidden surface, then read from thatsurfacewhen import
the application calls BlitFramebuffer.
Another motivation for granting the application explicit control
over the multisample resolve operation has to do with the
flexibility afforded by ARB_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 ARB_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 traditionalmultisampledrenderingallowedthe import
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.
Using BlitFramebuffer 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.
This extension also enables usage of packed depth-stencil formats in
renderbuffers (incorporating functionality from import
EXT_packed_depth_stencil), as follows:
Many OpenGL implementations have chosen to interleave the depth and
stencil buffers into one buffer, often with 24 bits of depth
precision and 8 bits of stencil data. 32 bits is more than is
needed for the depth buffer much of the time; a 24-bit depth buffer,
on the other hand, requires that reads and writes of depth data be
unaligned with respect to power-of-two boundaries. On the other
hand, 8 bits of stencil data is more than sufficient for most
applications, so it is only natural to pack the two buffers into a
single buffer with both depth and stencil data. OpenGL never
provides direct access to the buffers, so the OpenGL implementation
can provide an interface to applications where it appears the one
merged buffer is composed of two logical buffers.
One disadvantage of this scheme is that OpenGL lacks any means by
which this packed data can be handled efficiently. For example,
when an application reads from thebitdepthbufferusingthe import
type GL_UNSIGNED_SHORT will lose 8 bits of data, while
GL_UNSIGNED_INT has 8 too many. Both require expensive format
conversion operations. A 24-bit format would be no more suitable,
because it would also suffer from theunalignedmemoryaccessesthat import
made the standalone 24-bit depth buffer an unattractive proposition
in the first place.
Many applications, such as parallel rendering applications, may also
wish to draw to or read back from boththedepthstencilbuffers import
at the same time. Currently this requires two separate operations,
reducing performance. Since the buffers are interleaved, drawing to
or reading from bothshouldbenomoreexpensivethanusingjust import
one; in some cases, it may even be cheaper.
This extension provides a new data format, GL_DEPTH_STENCIL,
that can be used with the glDrawPixels, glReadPixels, and
glCopyPixels commands, as well as a packed data type,
GL_UNSIGNED_INT_24_8, that is meant to be used with
GL_DEPTH_STENCIL. No other data types are supported with
GL_DEPTH_STENCIL. If ARB_depth_texture or SGIX_depth_texture is
supported, GL_DEPTH_STENCIL/GL_UNSIGNED_INT_24_8 data can
also be used for textures; this provides a more efficient way to
supply data for a 24-bit depth texture.
GL_DEPTH_STENCIL data, when passed through the pixel path,
undergoes both depth and stencil operations. The depth data is
scaled and biased by the current GL_DEPTH_SCALE and GL_DEPTH_BIAS,
while the stencil data is shifted and offset by the current
GL_INDEX_SHIFT and GL_INDEX_OFFSET. The stencil data is also put
through the stencil-to-stencil pixel map.
glDrawPixels of GL_DEPTH_STENCIL data operates similarly to that
of GL_STENCIL_INDEX data, bypassing the OpenGL fragment pipeline
entirely, unlike the treatment of GL_DEPTH_COMPONENT data. The
stencil and depth masks are applied, as are the pixel ownership and
scissor tests, but all other operations are skipped.
glReadPixels of GL_DEPTH_STENCIL data reads back a rectangle
from boththedepthstencilbuffers. import
glCopyPixels of GL_DEPTH_STENCIL data copies a rectangle from import
both the depth and stencil buffers. Like glDrawPixels, it applies
both the stencil and depth masks but skips the remainder of the
OpenGL fragment pipeline.
glTex[Sub]Image[1,2,3]D of GL_DEPTH_STENCIL data loads depth and
stencil data into a depth_stencil texture. glGetTexImage of
GL_DEPTH_STENCIL data can be used to retrieve depth and stencil
data from adepthstenciltexture. import
In addition, a new base internal format, GL_DEPTH_STENCIL, can
be used by both texture images and renderbuffer storage. When an
image with a DEPTH_STENCIL internal format is attached to both
the depth and stencil attachment points of a framebuffer object,
then it becomes both the depth and stencil
buffers of the framebuffer. This fits nicely with hardware that
interleaves both depth and stencil data into a single buffer. When
a texture with DEPTH_STENCIL data is bound for texturing, only
the depth component is accessible through the texture fetcher. The
stencil data can be written with TexImage or CopyTexImage, and can
be read with GetTexImage. When a DEPTH_STENCIL image is
attached to the stencil attachment of the bound framebuffer object,
the stencil data can be accessed through any operation that reads
from writestotheframebuffersstencilbuffer. import
The official definition of this extension is available here:
http://www.opengl.org/registry/specs/ARB/framebuffer_object.txt
'''
from OpenGL import platform,constants,constant,arrays
from OpenGL import extensions,wrapper
from OpenGL.GL import glget
import ctypes
from OpenGL.raw.GL.ARB.framebuffer_object import *
### END AUTOGENERATED SECTION
from OpenGL.lazywrapper import lazy
glGenFramebuffers = wrapper.wrapper(glGenFramebuffers).setOutput(
'framebuffers',
lambda x: (x,),
'n')
glGenRenderbuffers = wrapper.wrapper(glGenRenderbuffers).setOutput(
'renderbuffers',
lambda x: (x,),
'n')
@lazy( glDeleteFramebuffers )
def glDeleteFramebuffers( baseOperation, n, framebuffers=None ):
"""glDeleteFramebuffers( framebuffers ) -> None
"""
if framebuffers is None:
framebuffers = arrays.GLuintArray.asArray( n )
n = arrays.GLuintArray.arraySize( framebuffers )
return baseOperation( n, framebuffers )
# Setup the GL_UNSIGNED_INT_24_8 image type
from OpenGL import images
from OpenGL.constants import GL_UNSIGNED_INT
images.TYPE_TO_ARRAYTYPE[ GL_UNSIGNED_INT_24_8 ] = GL_UNSIGNED_INT
images.TIGHT_PACK_FORMATS[ GL_UNSIGNED_INT_24_8 ] = 4
# The extensions actually use the _EXT forms, which is a bit confusing
# for users, IMO.
GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS = constant.Constant( 'GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS', 0x8CD9 )
GL_FRAMEBUFFER_INCOMPLETE_FORMATS = constant.Constant( 'GL_FRAMEBUFFER_INCOMPLETE_FORMATS', 0x8CDA )
GL_FRAMEBUFFER_UNSUPPORTED = constant.Constant( 'GL_FRAMEBUFFER_UNSUPPORTED', 0x8CDD )
|