Pixel shading system

• US 6,147,690 A
• Filed: 02/06/1998
• Issued: 11/14/2000
• Est. Priority Date: 02/06/1998
• Status: Expired due to Term

• Current Assignee: Rockwell Collins Simulation and Training Solutions, LLC
• Original Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Inventors: Cosman, Michael A.
• Primary Examiner(s): Zimmerman, Mark
• Assistant Examiner(s): Sealey, Lance W.
• Application Number:
  US09/020,171
• Time in Patent Office: 1,012 Days
• Field of Search: 345/422, 345/431, 345/434, 345/443, 345/505, 345/502, 345/523, 345/191
• US Class Current: 345/592
• CPC Class Codes: G06T 11/40 Filling a planar surface by adding surface attributes, e.g. colour or texture
• CPC Class Codes: G06T 15/405 using Z-buffer
• CPC Class Codes: G06T 15/503 Blending, e.g. for anti-aliasing
• CPC Class Codes: G06T 15/80 Shading

Abstract

A method and an apparatus for improved pixel shading. The method of the present invention is based upon the notion of allowing multiple polygons to contribute to the net transmittance effect of a single pixel. This is accomplished by providing a new multi-sample data structure which can store visual attributes for each polygon, sorting all the transparent polygons in a front-to-back arrangement, processing the transparent polygon records and then the opaque polygon records by accumulating the net effect of the transmittance of all polygons being sampled in a pixel, and applying the color attributes to the net effect of transmittance, thereby decoupling color from the calculations for determining transmittance.

Claims

1. A method for improved pixel shading using multi-sampling to thereby obtain more accurate pixel rendering, said method comprising the steps of:

(1) providing a multi-sampling data structure capable of storing attributes for each transparent and opaque polygon in a pixel;

(2) processing the transparent polygons in sorted order and the opaque polygons to thereby accumulate a net effect of transmittance of all the transparent polygons in the pixel if present; and

(3) processing each opaque polygon after any transparent polygons that overlap the opaque polygon.

2. The method as defined in claim 1 wherein the step of providing a new multi-sampling data structure further comprises the step of enabling more than one polygon in the sample to affect transmittance thereof, wherein the new data structure includes sufficient memory space for storing for each polygon its visual attributes and the samples in which the polygon can appear.

3. The method as defined in claim 1 wherein the step of processing the polygons to thereby accumulate a net effect of transmittance further comprises the step of combining polygon transmittances in hardware for each sample.

4. The method as defined in claim 1 wherein the step of processing the polygons to thereby accumulate a net effect of transmittance further comprises the step of processing a plurality of samples from each pixel by receiving as input a polygon transmittance signal and a plurality of polygon sample mask bits, and for generating as an output signal a plurality of sample residual transmittance signals.

5. The method as defined in claim 4 wherein the method further comprises the step of receiving and summing the plurality of sample residual transmittance signals, and generating an output signal representing a pixel residual transmittance for each pixel.

6. The method as defined in claim 5 wherein the method further comprises the step of obtaining a pixel shade by multiplying the pixel residual transmittance of each pixel by a plurality of polygon color attributes.

7. The method as defined in claim 6 wherein the step of obtaining a pixel shade by applying the polygon color attributes to the net effect of transmittance further comprises using one multiply-accumulator for each color to be combined in the pixel.

8. The method as defined in claim 1 wherein the method further comprises the step of calculating the pixel transmissiveness at a sample level.

9. The method as defined in claim 1 wherein the method further comprises the step of waiting until the net effect of transmittance is determined for a pixel before applying color attributes.

10. The method as defined in claim 1 wherein the method further comprises the step of determining the net effect of transmittance as a function of a total number of polygons in a pixel, and not of a total number of samples in the pixel.

11. The method as defined in claim 1 wherein the method further comprises the step of obtaining correct pixel shading without scene degradation for pixels disposed behind any combination of transmissive polygons.

12. The method as defined in claim 1 wherein the method further comprises the step of including only a closest opaque polygon after determining the net transmittance effect.

13. The method as in claim 1, wherein the step of processing the transparent polygons further comprises allowing multiple winning transparent polygons for each pixel sub-sample.

14. A method for improved pixel shading using multi-sampling to thereby obtain more accurate pixel rendering said method comprising the steps of:

(1) providing a multi-sampling data structure capable of storing attributes for each transparent and opaque polygon in a pixel;

(2) processing the transparent and the opaque polygons to thereby accumulate a net effect of transmittance of all the transparent polygons in the pixel if present, and of all the opaque polygons in the pixel; and

(3) obtaining correctly rendered results for all combinations of transmissive polygons except where at least two transmissive polygons interpenetrate.

15. A method for improved pixel shading using multi-sampling to thereby obtain more accurate pixel rendering of transparent and opaque polygons, said method comprising the steps of:

(1) providing a new multi-sampling data structure capable of storing attributes for each polygon in a pixel;

(2) sorting all the transparent polygons in the pixel in a front-to-back order; and

(3) processing the polygons to thereby accumulate a net effect of transmittance of all the transparent polygons in the pixel if present, and of the opaque polygons in the pixel.

16. A method for processing pixel samples to thereby determine a transmittance effect by a polygon on a pixel, said method comprising the steps of:

(1) receiving a polygon transmittance value if the polygon claims a sample;

(2) storing the polygon transmittance value in a residual transmittance register when it is a first polygon being processed; and

(3) accumulating a residual transmittance value in the residual transmittance register by multiplying each subsequent polygon transmittance value received as input, by a current residual transmittance value to attenuate each of the subsequent polygon transmittance values which is then transmitted as the output signal.

17. The method as defined in claim 16 wherein the method further comprises the step of repeating the process for all polygons which claim the sample to thereby determine the net effect of transmittance by all the polygons on the pixel.

18. A pixel shading system which includes utilizing a net effect of transmittance from one or more polygons to thereby render improved pixel shading, wherein the system calculates transmittance from a plurality of samples for each pixel, said system comprising:

a means for processing a plurality of samples from each pixel by receiving as input a polygon transmittance signal and a plurality of polygon sample mask bits, and for generating as an output signal a plurality of sample residual transmittance signals;

a means for receiving and summing the plurality of sample residual transmittance signals and for generating an output signal representing a pixel residual transmittance for each pixel;

a means for obtaining a pixel shade by multiplying the pixel residual transmittance of each pixel by a plurality of polygon color attributes;

a means for accumulating a plurality of pixels shades for each of the polygons which are present in the pixel; and

wherein the means for processing a plurality of samples from each pixel further comprises a plurality of pixel sample processors, wherein each processor receives a unique polygon sample mask bit.

19. The pixel shading system as defined in claim 18 wherein the means for receiving and summing the plurality of sample residual transmittance signals further comprises a pixel sample processor output summation network.

20. The pixel shading system as defined in claim 18 wherein the means for obtaining a pixel shade further comprises:

a first shade multiplier which multiplies the pixel residual transmittance by a red polygon color component of a current polygon;

a second shade multiplier which multiples the pixel residual transmittance by a green polygon color component of the current polygon; and

a third shade multiplier which multiples the pixel residual transmittance by a blue polygon color component of the current polygon.

21. The pixel shading system as defined in claim 18 wherein a total number of the plurality of pixel sample processors is equal to a total number of possible pixel samples.

22. The pixel shading system as defined in claim 18 wherein the system further comprises a means for clearing memory in the plurality of pixel sample processors.

23. The pixel shading system as defined in claim 18 wherein each of the plurality of pixel sample processors further comprises a processing means for receiving a first polygon transmittance value if the first polygon claims the sample, storing the first polygon transmittance value, and receiving subsequent polygon transmittance values for other polygons which claim the sample, and wherein each of the subsequent polygon transmittance values attenuates a residual transmittance value of the sample until all transparent polygons which claim the sample are processed.

24. The pixel shading system as defined in claim 23 wherein the processing means further comprises:

a first switch which receives as inputs a current polygon transmittance value and an identity value, wherein the first switch passes the current polygon transmittance if a sample mask bit of a current polygon is present in a pixel sample;

a sample residual transmittance register;

a second switch which receives as inputs a sample residual transmittance signal from the sample residual transmittance register from a previous polygon in the pixel sample and an identity value, wherein the second switch passes the sample residual transmittance signal if the current polygon is not a first polygon evaluated in the sample;

a multiplier which receives output from the first switch and the second switch, and which transmits an output signal to the sample residual transmittance register; and

a third switch which receives as inputs the output from the second switch and a null value, said third switch passing the output of the second switch if the sample mask bit of the current polygon is present.

25. A method for improved pixel shading using sub-sampling to thereby obtain more accurate pixel rendering, said method comprising the steps of:

(1) providing a multi-sampling data structure capable of storing attributes for each transparent and opaque polygon which affect a pixel and the pixel'"'"'s associated sub-samples;

(2) processing the transparent polygons in sorted order and the opaque polygons to thereby accumulate a net effect of transmittance of all the transparent polygons in the pixel, wherein each sub-sample is influenced by more than one polygon associated with that sub-sample.