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faseidman

OpenGL ES - Discussion/Problems Thread

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I'm pretty new at this, but after having played around with OpenGL ES for a little bit, I'm struck by what looks like some handicaps: 1. You can't call glGetIntegerv with either GL_MODELVIEW_MATRIX or GL_PROJECTION_MATRIX or GL_TEXTURE_MATRIX. Huh? I ran into this trying to implement billboarding for a particle system, which I don't think is possible to do without knowing the world matrix. 2. Point sprites seem to have a maximum size of 1, at least in the default setup. Why on earth have point sprites with a maximum size of 1? Anyone else having issues with ES?

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Original post by faseidman
1. You can't call glGetIntegerv with either GL_MODELVIEW_MATRIX or GL_PROJECTION_MATRIX or GL_TEXTURE_MATRIX. Huh? I ran into this trying to implement billboarding for a particle system, which I don't think is possible to do without knowing the world matrix.
This is a limitation of OpenGL ES 1.0. Dynamic states can't be queried. For matrices, you can get around this by using the OES_query_matrix extension. This extension is optional, but it's supported in the QUALCOMM implementation (I'm the one who wrote it, actually).
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Original post by faseidman
2. Point sprites seem to have a maximum size of 1, at least in the default setup. Why on earth have point sprites with a maximum size of 1?
You mean points? Point sprites aren't supported in 1.0.

We didn't support a point size other than 1 because doing so requires that antialiasing, and we didn't want to do that in a software implementation. However, the phones that contest entries will run on will have some hardware support, and I believe that sizes greater than 1 will be supported.

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Thanks for clarifying that about point sprites. I read something about point sprite support on khronos' website, so I assumed it was implemented here.

As for the worldview matrix thing, would that be portable to a cell phone then if it's supported by QUALCOMM? It would be great if I could use it, but if it's going to cause a problem I'd rather do something that I know is going to work.

Thanks for your help.

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Original post by faseidman
Thanks for clarifying that about point sprites. I read something about point sprite support on khronos' website, so I assumed it was implemented here.
They were added in 1.1, which was announced at SIGGRAPH last week. There aren't really any 1.1 implementations available yet, though.
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Original post by faseidman
As for the worldview matrix thing, would that be portable to a cell phone then if it's supported by QUALCOMM? It would be great if I could use it, but if it's going to cause a problem I'd rather do something that I know is going to work.
It's as portable as any OpenGL extension. In other words, as long as you check for the extension before using it, and provide a backup plan if it's not there, it'll be portable.

For the purposes of this contest, though, the OES_query_matrix extension will be fully supported on the platforms used for judging, so feel free to use it.

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Thanks man, you rock.

Is the call slow? I read somewhere today that reading things back from the graphics hardware is a very slow operation. If that's true I'd rather just keep a copy of the world stack in memory.

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