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c-mos

question to occlusion culling

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c-mos    129
Hello, at the moment my volume rendering is without any performance improvements. So I want to use an octree. The knots hold information about the alpha value. If its zero then this knot is not visible and the texcoords of the vertices of this non-visible knot wont be send to the shader. But there is one problem. There will be sub-boxes in the octree that are visible but they are occluded by visible boxes infront of them. At this time, the vertices of all visible boxes will be send to the shader. So I need a way to find out what are the front boxes and what boxes are occluded. Somewhere I read that the octree has to be sorted front to back each time the view direction changes. But I dont understand why to sort front to back. When I've created the octree and sampled the knots with the transfer function i set each sub-box to visible or non-visible. They have their position. And when I sort front to back, that would mix it al up. And parts will be rendered that are not visible and visible parts will be not rendered. regards, c-mos

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Einar89    144
I think what you heard about are BSP trees, which are not the same thing. They draw the scene back to front.
Why send the alpha value to the shader, when it`s easier and a lot faster to simply not draw the content of those boxes.
Octrees are used for frustrum culling, not for occlusion culling. You would have to use a more sophisticated algorithm for that:)

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c-mos    129
It is used for volume rendering (gpu raycasting). So the volume is divided into smaller sub volumes. They have to be sorted in a front to back manner. the alpha value decides wether the sob volume will be raycasted or not. I dont understand why to sort the octree.

regards,
c-mos

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