BiasSurface: Further revised the internal design of this component

In this iteration vertex illumination is fully decoupled from the
"surface", whose main job now is tracking changes and routing through
update notifications from sources to vertexes.

The next step is separating the illumination form the surface so it
can again be managed with an external buffer (the difference being
that now these are thinking VertexIllum instances).

doomsday/client/include/render/biassurface.h

@@ -20,6 +20,7 @@
 #ifndef DENG_RENDER_SHADOWBIAS_SURFACE_H
 #define DENG_RENDER_SHADOWBIAS_SURFACE_H
 
+#include <de/Error>
 #include <de/Vector>
 
 #include "MapElement"
@@ -33,6 +34,10 @@ class BiasTracker;
  */
 class BiasSurface
 {
+public:
+    /// An unknown light contributor was referenced @ingroup errors
+    DENG2_ERROR(UnknownContributorError);
+
 public:
     /**
      * Construct a new surface.
@@ -58,16 +63,30 @@ class BiasSurface
 
     void updateAfterMove();
 
+    /**
+     * Returns a light source contributor by @a index.
+     */
+    BiasSource &contributor(int index) const;
+
+    /**
+     * Determine the earliest time in milliseconds that an affecting source
+     * was changed/deleted.
+     */
+    uint timeOfLatestContributorUpdate() const;
+
     /**
      * Perform lighting for the supplied geometry. It is assumed that this
      * geometry has the @em same number of vertices as the bias surface.
      *
-     * @param vertCount  Number of vertices to be lit.
-     * @param positions  World coordinates for each vertex.
-     * @param colors     Final lighting values will be written here.
+     * @param surfaceNormal  Normal of the surface being lit.
+     * @param biasTime       Current time in milliseconds for bias.
+     * @param vertCount      Number of vertices to be lit.
+     * @param positions      World coordinates for each vertex.
+     * @param colors         Final lighting values will be written here.
      */
-    void lightPoly(de::Vector3f const &surfaceNormal, int vertCount,
-                   struct rvertex_s const *positions, struct ColorRawf_s *colors);
+    void lightPoly(de::Vector3f const &surfaceNormal, uint biasTime,
+                   int vertCount, struct rvertex_s const *positions,
+                   struct ColorRawf_s *colors);
 
 private:
     DENG2_PRIVATE(d)