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Thread: The order in which a model vertexes are loaded, influences the performances?

  1. #11
    Member Regular Contributor
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    Jul 2012
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    429
    Quote Originally Posted by GClements View Post
    If a draw call renders multiple primitives which modify a given pixel, the pixel's value at the end of the draw call must be that resulting from the last primitive which included that pixel.

    If depth tests are enabled, the rendering order still matters in cases where both primitives have the same depth value for the pixel (if the depth comparison is GL_LESS or GL_GREATER, the second primitive will fail the test and the value from the first primitive will be used; if the comparison is GL_LEQUAL or GL_GEQUAL, the second primitive will pass the depth test and the value from the second primitive will be used).

    Additionally, depth tests and blending involve a read-modify-write operation on the framebuffer. For each primitive, the value read must be that written by the preceding primitive.

    But if two primitives can easily be determined not to overlap, then none of this matters. The two primitives can be rendered in either order or in parallel, which may allow for higher utilisation of the GPU.
    Really interesting. And since the OP uses point size, this happens even more often (square of the pixel size).

  2. #12
    Junior Member Newbie
    Join Date
    Jan 2016
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    15
    I add another important detail.
    I have a LOD manager, that subdivides a model in 8^x cubes (here x=3, 512 cubes) and render them based on the distance of the camera from each of these cubes.

    While ordering and loading the vertex data in the cubes the same problem appeared, slowing down during rendering.
    I made a try and set only the high level lod to be rendered: that is the LOD model. By shuffling the order in which the draws were called for each subcubes I had no substantial changes...
    Again seems like the order of the data in the VBO made the difference????!!!!

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