look up table

Graphics and GPU Programming Programming

Started by takis July 01, 2005 10:16 AM

2 comments, last by superpig 18 years, 9 months ago

150

Author

July 01, 2005 10:16 AM

Hello, I am simulating corrosion with particles. I adjust the color of a particle according to his life time. If a particle is dead, it get black and i use alpha channel to simulate holes in the surface. But how can i use a lookup table, to find colors according to the life time of a particle? I got the colors from real life images of corrosion. According to his lifetime i have to choose one of them. How longer a particle lives, how darker brown it get.

superpig

1,826

July 01, 2005 11:26 AM

The easiest way to do it is to use a 1D texture. You create your lookup table as a texture 1 pixel high by N pixels across, going from initial time at the left to 'maximum' time at the right (the end of your table). When rendering, divide the life of your particle by the maximum time represented by your texture, and use the resulting 0..1 value as a texture coordinate. You get interpolation between neighbouring entries for free which can be quite nice.

Richard "Superpig" Fine - saving pigs from untimely fates - Microsoft DirectX MVP 2006/2007/2008/2009
"Shaders are not meant to do everything. Of course you can try to use it for everything, but it's like playing football using cabbage." - MickeyMouse

takis

150

Author

July 01, 2005 01:24 PM

If i understand it correctly: i just have to put my N colors in an 1xN array.

superpig

1,826

July 01, 2005 02:00 PM

Yup, basically. That's all a texture really is, after all - an array of colours.

look up table

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