Z - buffer algorithm

Z - buffer algorithm

Fig.3.3. Z- buffer algorithm

In Z-buffering, the depth of ‘Z’value is verified against available depth value. If the present pixel is behind the pixel in the Z-buffer, the pixel is eliminated, or else it is shaded and its depth value changes the one in the Z-buffer. Z-buffering helps dynamic visuals easily, and is presently introduced effectively in graphics hardware.

·        Depth buffering is one of the easiest hidden surface algorithms

·        It keeps follow of the space to nearest object at every pixel position.

·       Initialized to most negative z value.

·        when image being drawn, if its z coordinate at a position is higher than z buffer value, it is drawn, and new z coordinate value is stored; or else, it is not drawn

·        If a line in three dimensional is being drawn, then the middle z values are interpolated: linear interpolation for polygons, and can calculate z for more difficult surfaces.

Algorithm: loop on y;

loop on x;

zbuf[x,y] = infinity;

loop on objects

{

loop on y within y range of this object

{

loop on x within x range of this scan line of this object

{

if z(x,y) < zbuf[x,y] compute z of this object at this pixel & test zbuf[x,y] = z(x,y) update z-buffer

image[x,y] = shade(x,y) update image (typically RGB)

}

}

}

Basic operations:

1.    compute y range of an object

2.    compute x range of a given scan line of an object

3.    Calculate intersection point of a object with ray through pixel position (x,y).