HSR & Z-Buffer

Fall 2009 revised 2

HSR (Hidden Surface Removal)

• Painters algorithm– Depth-sorting; Back-to-front rendering– Sort based on some points on the polygon

Painter’s algorithm (cont)

• Cannot resolve this:– No correct ordering to draw these polygons

Fall 2009 revised 4

HSR (cont)• Z-buffer Algorithm

– For each pixel, we keep track of the corresponding depth or distance.– This is called the z-buffer.– If a new object is drawn, only replace the pixels in the frame-buffer if

the new pixel’s value is less than the pixel’s value in the z-buffer.

Fall 2009 revised 5

Z-BufferNote: OpenGL has 0 at the near end and 1 at the far end

near

far