I suspect that this may be normal behaviour rather than a driver issue. The fact that you're seeing this kind of video RAM usage at all with client arrays indicates that the geometry is being cached in video RAM. So you specify the arrays and draw, all good. Then you change the color array and now you've got two copies cached - the original (which the driver is presumably keeping around in case you need to go back to it) and the new. After a while, if you haven't gone back to the original, the driver decides to throw out it's old copy.
You may be able to control some of this behaviour with some use of GL_EXT_compiled_vertex_array, or you may be better off not using a vertex array for your constant color case (just glColor4f it instead).
Strange Video Memory Increase
Author
Thanks, I'll check out the GL_EXT_compiled _vertex_array. I get the same problem when I have varied colours
at the vertex and just change the values to say RGB ->RBG. Basically, any change to the colour array causes
the problem.
I appreciate all your comments gentlemen.
Pretty much this. For the most part, the driver knows best. If your changing values in your submitted data, it's highly likely the driver is simply caching the data, without releasing the old buffer immediately.mhagain, on 28 Mar 2013 - 12:50, said:
I suspect that this may be normal behaviour rather than a driver issue. The fact that you're seeing this kind of video RAM usage at all with client arrays indicates that the geometry is being cached in video RAM. So you specify the arrays and draw, all good. Then you change the color array and now you've got two copies cached - the original (which the driver is presumably keeping around in case you need to go back to it) and the new. After a while, if you haven't gone back to the original, the driver decides to throw out it's old copy.
You may be able to control some of this behaviour with some use of GL_EXT_compiled_vertex_array, or you may be better off not using a vertex array for your constant color case (just glColor4f it instead).
This is not uncommon to see in windows either. In short, i'd recommend not worrying about what the driver is doing, unless it's actually causing a problem.
Well I think it is a problem for him as he said that when he changes the value, his graphics card's memory usage shoots up from 600M to 1G and then it starts to lag. If the driver is caching the data, then he would need to find a way to remove the values he's editing from the cache.
The problem is in the "idea" to store 600MB in a single vertex array and transfer it in each draw call. That is not the way to go. I guess the performace is terrible if the data is not cached. The driver is probably trying to save performance by caching data and that's the problem. It could be solved by making smaller buffers.
The only real way to handle this that I can think of is to use two different fragment shaders, one with the constant colour as a uniform. From the looks of the OP's sample code he's not using shaders at all, but running on prehistoric hardware shouldnt be a problem here; the kind of hardware that can handle this volume of data will always have shaders available anyway.
ah, i missed where he said it was lagging, my bad.Well I think it is a problem for him as he said that when he changes the value, his graphics card's memory usage shoots up from 600M to 1G and then it starts to lag. If the driver is caching the data, then he would need to find a way to remove the values he's editing from the cache.
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