CompuServe Messages

Robert: Yes, use as grassy a material as you like. Regardless of whether you want to use the Global Shadow parms or the Local, "because [shadow maps] are made of up of bitmaps, the resolution [shadow map size] you use for each shadow-casting bitmap inversely affects the accuracy of the shadow and the rendering time. Thus, the higher the resolution, the more accurate the shadow, but the slower the rendering time." – page 7-160 "Map size – Used for shadow maps only, this sets the size, in pixels-squared, of the shadow depth bitmap. The map size requirements depend primarily upon the DISTANCE of the light source to the object, and secondarily upon the rendering output resolution. If the shadow map appears too coarse, increase the map size. The bitmap used by the shadow maps must fill the area covered by the falloff of the spotlight. Thus, the wider the falloff, the coarser the shadow appears." – page 7-162 "Map Sample Range – Used for shadow maps only, the Sample Range determines how much area within the shadow is averaged. This affects the size of the soft edge of the shadow and is roughly similar to the falloff of a spotlight. Small values reduce the area that is averaged, effectively bringing the edge of the shadow inward, which produces sharp-edged shaodws with more aliasing. There are three basic situations to watch out for: Values less than 3 can produce coarse-edged shadows, which you can offset by increasing the Map Size. Values greater than 5 can produce streaking and moire patterns, and require increased Bias values or a larger Map Size." – page 7-163 Another thing not _directly_ mentioned, is the fact that the greater the number of objects/faces in the scene (ie that the light can see) the worse the shadow will look. In fact, with a too small map size, shadows of smaller objects can disappear entirely because they are essentially spread too thin! So, make the map size as large as you can (but remember that , say, a 3500 line map takes something like 50Mb of RAM), and keep the sample range low. Make the spotlight as close to the objects it's illuminating as possible, and you may need to use an array of overlapping lights to get broader coverage at a closer range. In this case, each shadow map can be smaller, as it "sees" less. Dave