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'''OpenGL extension KHR.blend_equation_advanced
This module customises the behaviour of the
OpenGL.raw.GLES2.KHR.blend_equation_advanced to provide a more
Python-friendly API
Overview (from the spec)
This extension adds a number of "advanced" blending equations that can be
used to perform new color blending operations, many of which are more
complex than the standard blend modes provided by unextended OpenGL. This
extension provides two different extension string entries:
- KHR_blend_equation_advanced: Provides the new blending equations, but
guarantees defined results only if each sample is touched no more than
once in any single rendering pass. The command BlendBarrierKHR() is
provided to indicate a boundary between passes.
- KHR_blend_equation_advanced_coherent: Provides the new blending
equations, and guarantees that blending is done coherently and in API
primitive order. An enable is provided to allow implementations to opt
out of fully coherent blending and instead behave as though only
KHR_blend_equation_advanced were supported.
Some implementations may support KHR_blend_equation_advanced without
supporting KHR_blend_equation_advanced_coherent.
In unextended OpenGL, the set of blending equations is limited, and can be
expressed very simply. The MIN and MAX blend equations simply compute
component-wise minimums or maximums of source and destination color
components. The FUNC_ADD, FUNC_SUBTRACT, and FUNC_REVERSE_SUBTRACT
multiply the source and destination colors by source and destination
factors and either add the two products together or subtract one from the
other. This limited set of operations supports many common blending
operations but precludes the use of more sophisticated transparency and
blending operations commonly available in many dedicated imaging APIs.
This extension provides a number of new "advanced" blending equations.
Unlike traditional blending operations using the FUNC_ADD equation, these
blending equations do not use source and destination factors specified by
BlendFunc. Instead, each blend equation specifies a complete equation
based on the source and destination colors. These new blend equations are
used for both RGB and alpha components; they may not be used to perform
separate RGB and alpha blending (via functions like
BlendEquationSeparate).
These blending operations are performed using premultiplied source and
destination colors, where RGB colors produced by the fragment shader and
stored in the framebuffer are considered to be multiplied by alpha
(coverage). Many of these advanced blending equations are formulated
where the result of blending source and destination colors with partial
coverage have three separate contributions: from the portions covered by
both the source and the destination, from the portion covered only by the
source, and from the portion covered only by the destination. Such
equations are defined assuming that the source and destination coverage
have no spatial correlation within the pixel.
In addition to the coherency issues on implementations not supporting
KHR_blend_equation_advanced_coherent, this extension has several
limitations worth noting. First, the new blend equations are not
supported while rendering to more than one color buffer at once; an
INVALID_OPERATION will be generated if an application attempts to render
any primitives in this unsupported configuration. Additionally, blending
precision may be limited to 16-bit floating-point, which could result in a
loss of precision and dynamic range for framebuffer formats with 32-bit
floating-point components, and in a loss of precision for formats with 12-
and 16-bit signed or unsigned normalized integer components.
The official definition of this extension is available here:
http://www.opengl.org/registry/specs/KHR/blend_equation_advanced.txt
'''
from OpenGL import platform, constant, arrays
from OpenGL import extensions, wrapper
import ctypes
from OpenGL.raw.GLES2 import _types, _glgets
from OpenGL.raw.GLES2.KHR.blend_equation_advanced import *
from OpenGL.raw.GLES2.KHR.blend_equation_advanced import _EXTENSION_NAME
def glInitBlendEquationAdvancedKHR():
'''Return boolean indicating whether this extension is available'''
from OpenGL import extensions
return extensions.hasGLExtension( _EXTENSION_NAME )
### END AUTOGENERATED SECTION
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