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access OpenGL thextures storage memory

ElixirElixir Member Posts: 5
Hallo!

After registering some texture in OpenGL, i have its handle. Can i use (and how) this handle for texture reading/writing ? Maybe exists some other ways (without handle using)? Can i access to memory that was allocated for texture?

Thank you.

Comments

  • CroWCroW Member Posts: 348
    hmm,never tried that,but it should be possible.you can use glGetTexImage-function to obtain bitmap-pixel-data and glTexImage to set it.however you should use this calls as less as possible because textures are stored in videocard-memory and cpu-access to video-memory is very slow.
  • ElixirElixir Member Posts: 5
    Thank you for your responce.
    Why cpu-access to video-memory is very slow? And if it's true then how OpenGL access to video memory? Can i do it as well as OpenGL? What do you think about it?


  • CroWCroW Member Posts: 348
    the videomemory is located on your graphics-card,every read/write operation must pass data through wether agp or on older cards throgugh pci-bus.this is always slower as access to main-memory.however,gpu (the mainprocessor on modern graphicscards) access is much faster because the gpu doesnt need to use the agp-bus to read/write data.

    opengl-driver for your graphics-hardware will try to reduce bus-usage by holding as much textur/vertex data in graphiccards memory as possible and let the gpu do all the rendering/drawing work.
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