Raytraced Shadows Problem
- by Mat
Hey There!
I've got a problem with shadowrays in my raytracer.
Please have a look at the following two pictures
3D sMax:
My Raytracer:
The scene is lit by a very bright light, shining from the back. It's so bright that there is no gradient in the shading, just either white or dark (due to the overexposure).
both images were rendered using 3DStudioMax and both use the exact same geometry, just in one case the normals are interpolated across the triangles.
Now consider the red dot on the surface. In the case of the unsmoothed version, it lies in a dark area. this means that the light source is not visible from this triangle, since it's facing away from it.
In the smoothed version however, it lies in the lit area, because the interpolated normal would suggest, that the light would be visible at that point (although the actual geometry of the triangle is facing away from the lightsource).
My problem now is when raytraced shadows come in. if a shadowray is shot into the scene, from the red dot, to test whether the light-source is visible or not (to determine shadowing), the shadowray will return an intersection, independent of whether normals are interpolated or not (because intersections only depend on the geometry). Therefore the pixel would be shaded dark.
3dsamx is handling the case correctly - the rendered image was generated with Raytraced shadows turned on. However, my own Raytracer runs exactly into this problem when i turn on raytraced shadows (in my raytracer, the point is dark in both cases, because raytraced shadows determine the point lying in the shadow), and i don't know how to solve it.
I hope someone knows this problem and how to deal with it..
thanks!
