Hi Allen,
Allen Bierbaum wrote:
> We have an application where we dynamically add geometry and textures at
> runtime. We load the data into memory in a background thread and that seems
> to be working correctly. But when the new data gets added to the scene
> graph, we seem to be suffering a very significant drop in performance (pause
> for .5 - 1.0 seconds).
That sounds very long. How big are your textures? Do you only upload one
at a time or a larger number of them?
> I am still trying to track down the details inside
> OpenSG, but I suspect it is the time spent on texture upload and texture
> object creation before the texture is used.
>
> I am assuming that OpenSG does something like this:
>
> - Once a new material is added to geometry and that new material has a new
> texture
> - The next time the geometry is rendered, the material is activated
> - This causes opensg to:
> - Create a texture object
> - Upload the image into the texture object
> - Activate that object to render the geometry
>
Texture objects are only created if needed, but generally yes.
> This is a very simplistic explaination and I have not looked at the code in
> detail but this seems to be the behavior and would follow the OpenGL
> conventions.
>
> In any case, I suspect that the delay between uploading the image and using
> it is there the system performance is suffering.
>
> Now this may be more of an OpenGL question then anything, but is it possible
> to put a few frames delay between uploading the texture into the texture
> object, and the first time the texture is used? Said another way, is there
> a way for the system to upload the texture into the graphics hardware in the
> background before the data is actually needed for rendering?
>
Rumor has it that the drivers can do that, but I haven't spent a lot of
time confirming it. You could do it by validating the TextureChunk
before putting it into a Material. You'd need access to the GLId, which
is internal right now. It might make sense to add an externally callable
validate() call to the TC to allow that.
But in general .5-1 sec sounds very long for uploading a texture. Are
you using compressed texture formats like a DXT by chance? Unless you
store compressed data in the image, that data will have to be compressed
on upload, and that can take quite a bit of time.
Hope it helps
Dirk
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