Hello,
I’m rendering compositions into a pixel buffer context with floating
point pixels on Leopard.
glGetBooleanv (GL_COLOR_FLOAT_APPLE, ...) returns true, and the
accuracy of the output images is OK, but on some hardware, blending
modes Over and Add of Billboards and Sprites don’t work. They just
copy.
Also, anti-aliasing doesn't work on some hardware with floating
point pixels.
Support for ARB_half_float_pixel, ARB_texture_float (as well as the
APPLE etc. variants) is entirely hardware dependent. The ATI Radeon
X1600 (i.e. R5xx) GPU listed below only supports floating point
blending for 16-bit per (R, G, B, A) component (64-bit) FP targets.
The parameters to use for this (assuming the renderer in question
exports this extension) would be:
GL_RGBA16F_ARB = internalFormat
GL_RGBA = format
GL_HALF_FLOAT_ARB = type
You can query those extensions via:
GLboolean ARB_half_float_pixel_supported =
gluCheckExtension("GL_ARB_half_float_pixel",
glGetString(GL_EXTENSIONS));
GLboolean ARB_texture_float_supported =
gluCheckExtension("GL_ARB_texture_float",
glGetString(GL_EXTENSIONS));
Note that this will not tell you whether or not a renderer offers
hardware (blending, filtering) support for all of the included
internalFormat, type parameters
defined through these extensions. Currently there isn't a way (through
the GL API or otherwise) to query such support at runtime.
Also keep in mind that texture filtering for these targets isn't
supported on this renderer. (i.e. GL_TEXTURE_MIN_FILTER and
GL_TEXTURE_MAG_FILTER should be set to
GL_NEAREST). If you want higher quality filtering support you will
need to implement this manually via the programmable fragment pipeline.
As an example this problem occurs with a X1600 graphics card on an
iMac with MacOS 10.5.1.
Is there a way to estimate by software, when blending and anti
aliasing are supported correctly with float pixels?
Thanks,
Eberhard Ammelt
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