Light: Support for specularmap

The specular map is embedded in the alpha component of texture.
Alpha value of 1. means no specular, alpha of 0. means 100% specular.

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@14786 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/graphics/callbacks.cpp

@@ -348,6 +348,8 @@ void LightBlendProvider::OnSetConstants(IMaterialRendererServices *srv, int)
     srv->setVertexShaderConstant("specular", &tex, 1);
     tex = 2;
     srv->setVertexShaderConstant("ambient_occlusion", &tex, 1);
+    tex = 3;
+    srv->setVertexShaderConstant("specular_map", &tex, 1);
 }
 
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