Thread: Z-buffer problem (?)

  1. #1
    Registered User
    Join Date
    Oct 2001

    Z-buffer problem (?)

    I have implemented Z-buffer algorithm but sometimes I get weird results, ie visibility is not solved correctly. My Z-buffer algorithm works like that:

    -------Step 0:
    Initialize Z-buffer with smallest possible negative numbers
    Initialize frame buffer to background colour

    -------Step 1:

    Projection of all polygons to 2D:

    x_2d = x_3d
    y_2d = y_3d

    (ie projection to xy plane, z coordinates are ommited, more in the remarks section)

    ------Step 2 (for each 2d polygon - ie for each projection)

    Scan conversion of the 2d polygon -> for each pixel of that polygon:

    calculate z-value: z=-(a*x2d + b*x2d + d)/ c
    a, b, c, d are taken from the equation of the plane in which the original 3d polygon lies - and a, b, c are coordinates of the 3d polygon's normal (calculated as P1P2 x P1P3 where P1, P2, P3 are vertices of the 3d polygon)

    compare z-buffer w/ z-value, update z-buffer and frame buffer if z-value > z-buffer[x2d, y2d]

    -------Step 3

    Write frame buffer to screen


    1) I am be unable to project polygons to 2d in a different way than by ommiting z-coordinates because the expression for calculating the z-value in Step 2 wouldn't work in different case, I think

    2) Moreover - from the same reason - I am unable to do any transformations and eg. have [0;0] in the middle of the screen


    Where (on the internet) can I find a complete, accurate, step-by-step description of the z-buffer algorithm, with all the necessary expression, equations etc. and perhaps some sample code in C/C++/Pascal or VB? Everything I have found do far are vague descriptions with weird pseudo-code, there is not a word about when I work with 3d polygon, when with its 2d projection etc. - only John Carmack could understand that))))

    Is anything described in my implementation wrong?

    Thank you very much

  2. #2
    Normal vector Carlos's Avatar
    Join Date
    Sep 2001
    this might help:

    A search on google for "Z-buffer AND visibility AND algorithm AND source code" might be helpful
    Last edited by Carlos; 01-28-2003 at 08:01 AM.

  3. #3
    Registered User
    Join Date
    Oct 2001
    I've just tried your search phrase in Google and I've found this page:

    This is exactly what I was looking for!

    Thank you!!

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