Difference: GMT_4YP_25_2 (1 vs. 2)
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14 Apr 2025 - gmt11
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| More efficient alternatives have been proposed, the most well known being dual-paraboloid mapping, which involves only two renders to two rectangular depth textures. This is efficient, but the issues with this technique (non-linear transformation of depths which causes distortion if the triangles are too large, and introduces discontinuities at the seam of each map; and a very varying resolution across the shadow range) have limited it's practical value. Alternatively, tetrahedron mapping sticks to linear transformations, but requires four renders and still has somewhat variable resolution. | ||||||||
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| < < | This project will investigate a new technique which only requires two renders but creates depth maps which are similar to rectangular-based pyramids, effectively surrounding the point light with an irregular octahedron. The transformation is linear, so there is no need to use small triangles exceptwhere triangles span multiple top or bottom faces of the octahedron. The shadow rendering is pretty good even without fixing this: but it should be trivial to fix by splitting such triangles in a geometry shader, which would result in perfect shadow maps which only depend on resolution: and even this can be controlled by careful positioning of the apex of the octahedra (you can see it is off-centre in the images above). Using a geometry shader to split triangles may even make it possible to use a single render with very little increase in triangle count. | |||||||
| > > | This project will investigate a new technique which only requires two renders but creates depth maps which are similar to rectangular-based pyramids, effectively surrounding the point light with an irregular octahedron. The transformation is linear, so there is no need to use small triangles except where triangles span multiple top or bottom faces of the octahedron. The shadow rendering is pretty good even without fixing this: but it should be trivial to fix by splitting such triangles in a geometry shader, which would result in perfect shadow maps which only depend on resolution: and even this can be controlled by careful positioning of the apex of the octahedra (you can see it is off-centre in the images above). Geometry shaders are notoriously inefficient, but this may be a good use for one: indeed it should also make it possible to use a single render with very little increase in triangle count. | |||||||
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| < < | This should interest anyone who enjoys computer graphics and wants the chance to implement and compare different shadow techniques and rigourously explore the practical consequences of each. It would be ideal for someone with some experience of computer graphics and shaders in particular already (particularly opengl, and GLSL) but would also work for anyone who is keen to learn. | |||||||
| > > | This should interest anyone who enjoys computer graphics and wants the chance to implement and compare different shadow techniques and rigorously explore the practical consequences of each. It would be ideal for someone with some experience of computer graphics and shaders in particular already (particularly opengl, and GLSL) but would also work for anyone who is keen to learn. | |||||||
| Click here for other medical imaging projects offered by Graham Treece. | ||||||||
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