OpenSG Users ()

Michael Raab | 8 Jun 2012 10:51

OpenSG1.8 - Problem with BlendChunk

Hi all,

we have a problem with the OpenSG Blendchunk implementation. We are trying to render a geometry that has
blend equation set to FUNC_ADD. The graphic chip is either onBoard Intel or ATI. It seems that GL extension
glBlendEquationEXT is not supported by these chips. OpenSG throws a warning that indicates that the
extension is not supported. However I'm not sure if this extension is necessary when using FUNC_ADD.
Please find attached a test geometry..

Thanks,
Michael
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Carsten Neumann | 8 Jun 2012 16:08

Re: OpenSG1.8 - Problem with BlendChunk

Hello Michael,

On 06/08/2012 03:51 AM, Michael Raab wrote:
> we have a problem with the OpenSG Blendchunk implementation. We are trying to render a geometry that has
blend equation set to FUNC_ADD. The graphic chip is either onBoard Intel or ATI. It seems that GL extension
glBlendEquationEXT is not supported by these chips. OpenSG throws a warning that indicates that the
extension is not supported. However I'm not sure if this extension is necessary when using FUNC_ADD.

as far as I can tell glBlendEquationEXT is introduced by
http://www.opengl.org/registry/specs/EXT/blend_minmax.txt
With subsequent extensions
- http://www.opengl.org/registry/specs/EXT/blend_subtract.txt
- http://www.opengl.org/registry/specs/EXT/blend_logic_op.txt

adding additional blending equations (GL_FUNC_ADD is just the OpenGL
default blending equation: C' = clamp((Cs * S) + (Cd * D), 0.0, 1.0).

If you need additive blending you can leave _sfBlendEquation set to
GL_NONE (which is functionally equivalent to GL_FUNC_ADD anyway) and set
_sfSrcFactor = GL_ONE and _sfDestFactor = GL_ONE.

Cheers,
Carsten

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