Hello,

   I'am now working on some bitmap based grass, bush etc. I'am trying to 
place a lot of rectangles with bitmap grass patches on the groud. 
Bitmaps are partially transparent. The result is, that I have a lot of 
rectangles on every ray hittng the ground, so I must set very high 
max_trace_level to render it correctly...

My idea is to create some "masked_polygon", or to add a "mask" into the 
polygon and use this mask when determing, if some ray hits the polygon. 
When the ray hits completely transparent part of the polygon, consider 
it as "no hit" and return hits only with full opaque or semi-transparent 
parts. Something like

#declare BitmapPig = pigment {
   image_map {png "something.png"}
}

polygon {
   5, <0, 0>, <1, 0>, <1, 1>, <0, 1>, <0, 0>
   mask {BitmapPig}
   pigment {BitmapPig}
}

This will remove the neccesasrity of high max_trace_level and I think, 
that it can be faster, than shooting new ray from every hitted, but 
completely transparent part of polygons.

What do you think about this?

Regards

Vaclav

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