|
'''OpenGL extension APPLE.row_bytes |
|
|
|
This module customises the behaviour of the |
|
OpenGL.raw.GL.APPLE.row_bytes to provide a more |
|
Python-friendly API |
|
|
|
Overview (from the spec) |
|
|
|
The APPLE_row_bytes extension was developed to relax the limitations |
|
within GL regarding the packing and unpacking of pixel data from |
|
arbitrary arrangements in memory. |
|
|
|
Prior to this extension, similar, albeit more restrictive, functionality |
|
existed in GL using pixel storage modes for unpacking, packing, and |
|
alignment. The limitation of the existing mechanism lies primarily in how |
|
packing or unpacking of data is specified with pixel atomicity rather than |
|
basic machine units. To some extent, this pixel granularity can be |
|
overcome using pixel storage modes GL_UNPACK_ALIGNMENT and |
|
GL_PACK_ALIGNMENT. Both of these parameters are specified in basic |
|
machine units but their range of possible values is restricted and even |
|
then they do not allow for the packing and unpacking of pixel data in a |
|
fully arbitrary manner. |
|
|
|
Consider this simple example: |
|
|
|
Consider a column of pixels in memory. The pixels are of GL_RGB |
|
format and GL_UNSIGNED_BYTE type resulting in 3 bytes per pixel. |
|
Now consider that this column of pixel data was arranged in memory |
|
such that each row of the image (in this case each pixel) has two |
|
bytes padding or space between them. |
|
|
|
Each row of 1 pixel then has 5 bytes. An attempting to express this |
|
memory arrangement with existing pixel storage semantics would |
|
naturally start with a GL_UNPACK_ROW_LENGTH of 1 because there is |
|
one pixel per row. However, no valid value of GL_UNPACK_ALIGNMENT, |
|
1, 2, 4, or 8, will allow the proper row padding to express this |
|
memory arrangement. |
|
|
|
The official definition of this extension is available here: |
|
http://www.opengl.org/registry/specs/APPLE/row_bytes.txt |
|
''' |
|
from OpenGL import platform, constant, arrays |
|
from OpenGL import extensions, wrapper |
|
import ctypes |
|
from OpenGL.raw.GL import _types, _glgets |
|
from OpenGL.raw.GL.APPLE.row_bytes import * |
|
from OpenGL.raw.GL.APPLE.row_bytes import _EXTENSION_NAME |
|
|
|
def glInitRowBytesAPPLE(): |
|
'''Return boolean indicating whether this extension is available''' |
|
from OpenGL import extensions |
|
return extensions.hasGLExtension( _EXTENSION_NAME ) |
|
|
|
|
|
|
