1. 黃聰賢

2. Light Position Mesh Polygon Shadow Polygon

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

4.  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

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

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

7. light

8.  Why? +1 +1-1 =0

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

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