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Occlusion culling in a complex isometric engine?

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I'm making (with Game Maker, I'm not a good programmer) an isometric tile-based engine, which features 3D terrain map by assigning a "height" value to each tile, and shifting them up accordingly. So, it's basically 2D, there is no perspective correction, and the objects are sprites, just as Tactics Ogre. While I have no problem in making a TO-like engine, mine has two major differences. First, movement is NOT tile-based; second, I want to avoid limitations in the size of the objects (a building or a large creature would span several tiles). Both of these complicate dramatically the criteria for sorting the order in which the images are drawn, so I can't use simple equations for that (for example, depth = -Y). I looked around in the 3D graphics tutorials and read about some methods: sorting polygons by distance (imprecise in this case), pixelwise z-buffering (out of question! GM does everything in software) and BSP tree... I have to make some algorithm and run it in realtime... any suggestions? EDIT If I understood correctly what frustum culling is (removal of polygons outside of the viewing cone?) it's not an issue. The terrain is made of "blocks", that are made of the upper facet and the two vertical facets; the other 3 aren't drawn at all. If I draw the tiles and the objects based on their Y position on the map, the tiles are drawn correctly but the object sprites are partially occluded by the tiles they stand on (this happens when object.y < tile.y. I tried several formulas but I think it's probably impossible to solve the problem with an equation. [edited by - medioman80 on August 13, 2003 9:56:54 PM]

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Guest Anonymous Poster
Are you sure you need to invest in the time and energy to create an occlusion-culling algorithm? I''d just live with the frustrum-culling for now and see how good your framerate is. You might not even need to worry about it.

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