Z buffer

Z buffer

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  A. K. Biswas,Dept. Of Computer Apllication, B.I.T., Durg 1 COMPUTER GRAPHICSCOMPUTER GRAPHICS Visible Surface DetectionVisible Surface Detection (Z-Buffer/Depth Buffer)(Z-Buffer/Depth Buffer)
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  A. K. Biswas,Dept. Of Computer Apllication, B.I.T., Durg 2 DEPTH-BUFFER METHODDEPTH-BUFFER METHOD  Compares surface depth values throughout a scene for each pixel position on the projection plane  Usually applied to scenes only containing polygons  Fast approach due to easy depth values computation  Also often called the z-buffer method (x2, y2) & z2 (x3, y3) & z3 (x1, y1) & z1  (x1, y1), (x2, y2) & (x3, y3) are the pixel positions of surfaces S1, S2, and S3 respectively.  z1, z2 and z3 defines the depth values (distance) of surfaces S1, S2, and S3 respectively from the View Plane
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  A. K. Biswas,Dept. Of Computer Apllication, B.I.T., Durg 3 DEPTH-BUFFER METHOD (Cont…)DEPTH-BUFFER METHOD (Cont…) 1. Initialise the depth buffer and frame buffer so that for all buffer positions (x, y) depthBuff(x, y) = 1.0 frameBuff(x, y) = bgColour 2. Process each polygon in a scene, one at a time – For each projected (x, y) pixel position of a polygon, calculate the depth z (if not already known) – If z < depthBuff(x, y), compute the surface colour at that position and set depthBuff(x, y) = z frameBuff(x, y) = surfColour(x, y)  After all surfaces are processed depthBuff and frameBuff will store correct values
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  A. K. Biswas,Dept. Of Computer Apllication, B.I.T., Durg 4 DEPTH CALCULATIONDEPTH CALCULATION
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  ExampleExample A. K. Biswas,Dept. Of Computer Apllication, B.I.T., Durg 5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 1 6 6 6 6 6 6 1 1 6 6 6 6 6 1 1 1 6 6 6 6 1 1 1 1 6 6 6 1 1 1 1 1 6 6 1 1 1 1 1 1 6 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 6 6 6 6 6 6 6 1 6 6 6 6 6 6 1 1 6 6 6 6 6 1 1 1 6 6 6 6 1 1 1 1 6 6 6 1 1 1 1 1 6 6 1 1 1 1 1 1 6 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Surface-1 Depth Buffer Depth Buffer Frame Buffer
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  ExampleExample A. K. Biswas,Dept. Of Computer Apllication, B.I.T., Durg 6 6 6 6 6 6 6 6 1 6 6 6 6 6 6 1 1 6 6 6 6 6 1 1 1 6 6 6 6 1 1 1 1 6 6 6 7 1 1 1 1 6 6 7 7 7 1 1 1 6 7 7 7 7 7 1 1 1 1 1 1 1 1 1 1 6 6 6 6 6 6 6 1 6 6 6 6 6 6 1 1 6 6 6 6 6 1 1 1 6 6 6 6 1 1 1 1 6 6 6 1 1 1 1 1 6 6 1 1 1 1 1 1 6 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 7 1 1 1 1 1 1 1 7 1 1 1 1 1 1 7 1 1 1 1 1 7 1 1 1 1 7 1 1 1 7 1 1 1 1 1 1 1 1 1 1 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 6 6 6 6 6 6 6 1 6 6 6 6 6 6 1 1 6 6 6 6 6 1 1 1 6 6 6 6 1 1 1 1 6 6 6 1 1 1 1 1 6 6 1 1 1 1 1 1 6 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Surface-2Depth Buffer Depth Buffer Frame Buffer
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  A. K. Biswas,Dept. Of Computer Apllication, B.I.T., Durg 7 Iterative Calculations (cont…)Iterative Calculations (cont…) top scan line bottom scan line y scan line y - 1 scan line x x’
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  A. K. Biswas,Dept. Of Computer Apllication, B.I.T., Durg 8 DISADVANTAGES OF DEPTH BUFFERDISADVANTAGES OF DEPTH BUFFER This method only find out one visible surface at each pixel position that means it deals with only Opaque surface. 1 2 3 4 5 6 1 Red 2 Red 3 Green 4 Blue 5 Green 6 Red