Attribute blending system for composing computer-graphic images from objects

A computer graphies system according to claim 6 wherein said contending polygons have attributes to represent obscurity and said equation further includes parameters O.sub.A and O.sub.B representative of said obscurity of said forward polygon and said rearward polygon, respectively, as follows:

• A.sub.M =[(.alpha..sub.A /.alpha..sub.M)-.alpha..sub.0 RO.sub.B ]A.sub.A +[(.alpha..sub.A /.alpha..sub.M)-.alpha..sub.0 (1-R)O.sub.A ]A.sub.B
• 9. A computer graphics system according to claim 6 wherein said combined pixel coverage .alpha..sub.M and said excess pixel coverage .alpha..sub.0 are defined in accordance with the equations:
• .alpha..sub.M =.alpha..sub.A +.alpha..sub.B, if .alpha..sub.M>
• 1, then .alpha..sub.M =1
• .alpha..sub.0 =(.alpha..sub.A /.alpha..sub.M)+(.alpha..sub.B
• /.alpha..sub.M)-1, if .alpha..sub.0 <0 then .alpha..sub.n =0 10. A computer graphics system according to claim 1 wherein said means for computing blended attribute pixel data signals implements a filter
• function centered on said pixel for computing said blended attribute. 11. For use in conjunction with a computer graphics display apparatus including a frame buffer, a process for providing picture element (pixel) signals to the frame buffer for an anti-aliased display of polygons that are defined as located at various depths along a depth dimension in a pyramid of vision (model space), the pyramid of vision being defined by a view point having at least one ray associated with a pixel of said display, said ray passing through certain of said contending polygons at various points of said polygons, said contending polygons having attributes contending for said pixel, said display being defined in two dimensional space within said pyramid of vision, and further having a determined coarseness parameter indicated in the depth dimension, said process including the steps of:
• providing representative signals for each of, a forward contending polygon and a rearward contending polygon, in the depth dimension of model space, said forward contending polygon having a forward point along said ray in said depth dimension, said rearward contending polygon having a rearward point along said ray in said depth dimension;
• determining representative signals for the distance in said depth dimension between said forward point and said rearward point in model space;
• providing representative signals for said coarseness parameter in model space;
• computing blended attribute pixel data signals, said blended attribute pixel data being a blended attribute between said forward and rearward polygons, by correlating said representative signals for the distance in said depth dimension between said forward and said rearward points with signals representative of said coarseness parameter;
• and
• storing said blended attribute pixel data signals in said frame buffer for
• driving a computer graphics display. 12. A computer graphics process according to claim 11 wherein said contending polygons have attributes to represent color and said computing step computes a blended attribute of
• color. 13. A computer graphics process according to claim 11 wherein said contending polygons have attributes to represent obscurity and said
• computing step computes a blended attribute of obscurity. 14. A computer graphics process according to claim 11 wherein said contending polygons have attributes to represent depth and said computing step computes a
• blended attribute of depth. 15. A computer graphics process according to claim 11 further comprising a step of conditionally actuating said computing step for computing blended attribute pixel data signals
• controlled by said distance in relation to said coarseness parameter. 16. A computer graphics process according to claim 11 wherein said step of computing blended attribute pixel data signals computes said blended attribute pixel data signals in accordance with the equation:
• A.sub.M =[(.alpha..sub.A /.alpha..sub.M)-.alpha..sub.0 R]A.sub.A +[(.alpha..sub.B /.alpha..sub.M)-.alpha..sub.0 (1-R)]A.sub.R
• where A.sub.M is said blended attribute for said pixel, .alpha..sub.A represents pixel coverage of said forward point of said forward polygon, .alpha..sub.B represents pixel coverage of said rearward point of said rearward polygon, .alpha..sub.M represents a combined pixel coverage of said rearward and forward points, .alpha..sub.0 represents excess of said combined pixel coverage beyond capacity of said pixel, A.sub.A represents said attribute of said forward polygon and A.sub.B represents said attribute of said rearward polygon, and R represents said correlated
• distance. 17. A computer graphics process according to claim 16 wherein said correlated distance R is defined in accordance with the equation:
• ##EQU2## where Z.sub.B represents position of said rearward point along said ray in said depth dimension, Z.sub.A represents position of said forward point
• along said ray, and .DELTA.Z represents said coarseness parameter. 18. A computer graphics process according to claim 16 wherein said contending polygons have attributes to represent obscurity and said equation further includes parameters O.sub.A and O.sub.B representative of said obscurity of said forward polygon and said rearward polygon, respectively, as follows:
• A.sub.M =[(.alpha..sub.A /.alpha..sub.M)-.alpha..sub.0 RO.sub.B ]A.sub.A +[(.alpha..sub.B /.alpha..sub.M)-.alpha..sub.0 (1-R)O.sub.A ]A.sub.B.
• 19. A computer graphics process according to claim 16 wherein said combined pixel coverage .alpha..sub.M and said excess pixel coverage .alpha..sub.0 are defined in accordance with the equations:
• .alpha..sub.M =.alpha..sub.A +.alpha..sub.B, if .alpha..sub.M >1, then .alpha..sub.M =1
• .alpha..sub.0 =(.alpha..sub.M /.alpha..sub.M)+(.alpha..sub.B
• /.alpha..sub.M)-1, if .alpha..sub.0 <0 then .alpha..sub.B =0 20. A computer graphics process according to claim 11 wherein said step of computing blended attribute pixel data signals implements a filter function centered on said pixel for computing said blended attribute.