7.3 Modulative Shadows
Modulative shadows work by darkening an already rendered scene with a fixed colour. First, the scene is rendered normally containing all the objects which will be shadowed, then a modulative pass is done per light, which darkens areas in shadow. Finally, objects which do not receive shadows are rendered.
There are 2 modulative shadow techniques; stencil-based (See section 7.1 Stencil Shadows : SHADOWTYPE_STENCIL_MODULATIVE) and texture-based (See section 7.2 Texture-based Shadows : SHADOWTYPE_TEXTURE_MODULATIVE). Modulative shadows are an inaccurate lighting model, since they darken the areas of shadow uniformly, irrespective of the amount of light which would have fallen on the shadow area anyway. However, they can give fairly attractive results for a much lower overhead than more 'correct' methods like 7.4 Additive Light Masking, and they also combine well with pre-baked static lighting (such as pre-calculated lightmaps), which additive lighting does not. The main thing to consider is that using multiple light sources can result in overly dark shadows (where shadows overlap, which intuitively looks right in fact, but it's not physically correct) and artifacts when using stencil shadows (See section The Silhouette Edge).
Shadow Colour
The colour which is used to darken the areas in shadow is set by SceneManager::setShadowColour; it defaults to a dark grey (so that the underlying colour still shows through a bit).
Note that if you're using texture shadows you have the additional option of using Integrated Texture Shadows rather than being forced to have a separate pass of the scene to render shadows. In this case the 'modulative' aspect of the shadow technique just affects the colour of the shadow texture.
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