黃聰賢

Light Position Mesh Polygon Shadow Polygon

 Clear color buffer and stencil buffer  Render the scene with ambient only

 Mask color buffer and depth buffer  Enable back face culling  Increase stencil value if depth test is passed  Draw shadow polygons Stencil value = 1 Stencil value = 0

 Mask color buffer and depth buffer  Enable front face culling  Decrease stencil value if depth test is passed  Draw shadow polygons Stencil value = = 0 Stencil value = +1

 Clear depth buffer  Set stencil pass condition ◦ Equal to zero  Render the scene with full lighting Ambient only

light

 Why? =0

 How? Edge A Edge B light n n n n front back Edge C n back n

Front n Back n Ensure shadow polygons face outside. ab a' b' a b a' c c