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Posts Tagged ‘GSoC’

Opacity Shadow Maps artifacts

Opacity shadow maps can suffer from sever artifacts if not “enough” maps are generated. The artifacts are caused by the fact that new points, without shadow information, are introduced by each opacity map. Below you can see the grass from CS rendered using only 15 opacity maps (the diagonal lines perpendicular to the light’s direction are the artifacts, in case they weren’t obvious enough 🙂 ):

The limit is 15 because, at the moment, the textures are passed as an array of sampler2D and only 16 (15 opacity + 1 material) textures can be used in one shader on my video card, NVIDIA GeForce 9500M GS. However, 4 times more maps can be generated if every channel of every texture is used, yielding 60 maps (but only 14 textures):

As can be seen from the above picture the artifacts are now slightly less visible (more but smaller), so increasing the number of maps is one way of trying to remove these artifacts. Another (smarter) way is by aligning the opacity maps with the geometry, using information from a depth map, as described in deep opacity maps (DOM). This is what I plan to implement for the second part of GSoC. Here is how DOM should improve the rendering:

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Another year, another blog

So this is my second year at both Google Summer of Code (GSoC) and Crystal Space (CS) after the last year’s project, which you can find at: http://hairrendering.wordpress.com/.

This year I plan to implement “Real-Time Volumetric Shadows for Dynamic Objects”, by adding a new render manager in CS.

This idea came to me while trying to figure out why my hair rendering didn’t look as good as advertised by other demos, such as NVIDIA Nalu. The reason is that my hair plugin lacked self-shadowing and so I studied how this can be implemented by doing an Individual Study Option at my university, regarding “Rendering real-time self-shadowed dynamic hair”. You can find my presentation here.

For this project I plan to implement Opacity Shadow Maps (OSM) for starters and then implement some more advanced techniques, such as Fourier Opacity Mapping (FOM) and/or improve the OSM by using a different sorting algorithm.

If you would like to view the implementation, as it progress, you can check out via SVN the CS selfshadow branch (no account needed). Also, if you experience problems compiling CS, you can read this post here (it’s a little bit old, but it should do the trick).