Casting shadows from a point light used to be difficult compared to spot lights before the days of DirectX 10. Similar to spot light shadow map, the point light shadow map has to cover the entire area affected by the light. Cube-map textures seem like a natural candidate for this task, but they could not be used properly with DirectX 9 due to two problems.
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Cube maps can be thought of as six 2D textures, one texture for each face of the cube. Cube maps are great for representing information around a center point, which in this recipe, is the point light's center.
The first problem was memory. A point light with the same range as a spot light will need six times the amount of memory to cast shadows of the same quality due to the cube map's six faces. This may have been acceptable if that memory could have been reused for both point and spot light shadows, but there was no way to do that.
Problem number two had to do with the lack of hardware PCF support. When implementing...