Draw shape shadows using index buffer

src/Preload/Render.hs

@@ -96,6 +96,7 @@ preloadRender = do
     bindVertexArrayObject $= Just shPosVAOname
     bindBuffer ArrayBuffer $= Just shVBOname
     setupVertexAttribPointer 0 3 7 0
+    bindBuffer ElementArrayBuffer $= Just shEBOname
     let shPosColVAO = VAO { _vao = shPosColVAOname, _vaoVBO = shVBO }
         shPosVAO    = VAO { _vao = shPosVAOname,    _vaoVBO = shVBO }
     -- lighting shaders
@@ -107,6 +108,16 @@ preloadRender = do
     lightingLineShadowShad
         <- makeShader "lighting/lineShadow" [vert,geom,frag] [3] ELinesAdjacency
                 >>= addUniforms ["lightPos"]
+    silEBOname <- genObjectName
+    silEBOptr <- mallocArray numDrawableElements
+    -- it may be important to bind this while the correct VAO is bound
+    bindBuffer ElementArrayBuffer $= Just silEBOname
+    bufferData ElementArrayBuffer $=
+        ( fromIntegral $ glushortSize * numDrawableElements
+        , nullPtr
+        , StreamDraw
+        )
+    let silEBO = EBO {_ebo = silEBOname, _eboPtr = silEBOptr}
 -- 2D draw shaders
     bslist <- makeShader "dualTwoD/basic"   [vert,frag] [3,4]   ETriangles 
     bslista <- makeShader "dualTwoD/basic"   [vert,frag] [3,4]   ETriangles 
@@ -181,6 +192,7 @@ preloadRender = do
         { _pictureShaders = shadV
         , _shapeShader = bslista {_shadVAO = shPosColVAO }
         , _shapeEBO = shEBO
+        , _silhouetteEBO = silEBO
         , _lightingCapShader        = lightingCapShad { _shadVAO = shPosVAO }
         , _lightingLineShadowShader = lightingLineShadowShad
         , _lightingOccludeShader    = wsShad    {_shadVAO = wpVAO}