Screen space effects utilizing the alpha channel and the alpha buffer

• US 6,603,482 B1
• Filed: 01/31/2000
• Issued: 08/05/2003
• Est. Priority Date: 01/31/2000
• Status: Expired due to Term

• Current Assignee: Rockwell Collins Simulation and Training Solutions, LLC (Rtx Corporation)
• Original Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Inventors: Tidwell, Reed P.
• Primary Examiner(s): Tung, Kee M.
• Application Number:
  US09/494,597
• Time in Patent Office: 1,282 Days
• Field of Search: 345/501, 345/545, 345/503, 345/426, 345/581, 345/589, 345/592, 345/530, 345/539, 345/591, 345/549, 345/629
• US Class Current: 345/592
• CPC Class Codes: G06T 15/005 General purpose rendering architectures

Abstract

A method for using the alpha channel to generate screen space effects in a high fidelity, real time, computer graphics simulation system. The first step is providing a rendering engine with an alpha processing channel, a frame buffer that includes an alpha memory, and a post processor. Next, screen effect data is processed through the alpha channel. The third step is storing screen effect data in the alpha buffer memory. Then the screen effect data is applied to the frame buffer color data using the post processor. The primary screen effects that are desired to be generated through the alpha channel are double buffered overlays, accurate night scene rendering and edge blending attenuation at channel boundaries. Night scene rendering features include range attenuated slewable own-ship light lobes, non-attenuation of point lights and luminous polygons, and ambient lighting.

Claims

1. A method for using a graphics accelerator for screen effects in a real time simulation system, comprising the steps of:

(a) providing a rendering engine with an alpha channel, and a frame buffer having an alpha memory and a post processor;

(b) storing screen effect data in the alpha memory; and

(c) applying the screen effect data using the post processor to frame buffer color data.

2. The method as in claim 1 wherein step (b) of storing the screen effect data further comprises the step of processing the screen effect data through the alpha channel.

3. The method as in claim 1 wherein the step of storing screen effect data includes rendering at least one own-ship lighting lobe screen effect and storing the at least one own-ship lighting lobe in the alpha memory.

4. The method as in claim 1 wherein the step of storing the screen effect data further comprises loading the screen effect data from a bitmap.

5. The method as in claim 1 further comprising the step of applying a range attenuation to the screen effect based on a range of each pixel.

6. The method as in claim 5 including calculating the range of each pixel by interpolating from a range for each vertex using the alpha channel.

7. The method as in claim 5 including loading the range of each pixel as a constant and storing the range for each pixel while it is being rendered.

8. The method as in claim 1 wherein the step of storing screen effect data includes storing a lighting pattern.

9. The method as in claim 8 further comprising applying a range attenuation to an own-ship light lobe pattern based on a range calculated at each pixel of each polygon through the alpha processor while the polygon is being rendered.

10. The method as in claim 1 wherein the step of storing the screen effect data includes identifying point lights and luminous objects and avoiding applying an own-ship light lobe pattern to the point lights and luminous objects.

11. The method as in claim 10 wherein the luminous objects are luminous polygons.

12. A graphics accelerator with a frame buffer, used in a real time simulation system, comprising:

(a) an alpha processing channel;

(b) an alpha memory coupled to the alpha processing channel, wherein screen effect data rendered in the alpha processing channel is stored in the alpha memory and then applied to the frame buffer; and

(c) a post processor wherein screen effects are applied to frame buffer color data.

13. The graphics accelerator as in claim 12 wherein the screen effect data is a double buffered overlay.

14. The graphics accelerator of claim 13 wherein the overlay consists of a color index and an overlay alpha factor by which an overlay color is blended with frame buffer color data.

15. The graphics accelerator of claim 13 wherein the overlay alpha factor is processed through the alpha channel.

16. The graphics accelerator of claim 13 wherein the overlay alpha factor is stored in the alpha memory of the frame buffer.

17. The graphics accelerator as in claim 12 wherein the screen effect data simulates own-ship lights.

18. The graphics accelerator as in claim 12 wherein the alpha memory contains a plurality of pixels and an own-ship lighting pattern is defined by X and Y location.

19. The graphics accelerator as in claim 12 wherein the screen effect data is edge blending attenuation patterns.

20. The graphics accelerator as in claim 12, wherein the alpha memory further comprises a plurality of subpixels and a luminous bit corresponding to each subpixel to define subpixels taken by luminous polygons and point lights.

21. The graphics accelerator as in claim 12, wherein the alpha memory further comprises a plurality of pixels and subpixels and an inverse range field corresponding to each pixel.

22. The graphics accelerator as in claim 12, wherein the alpha memory further comprises a plurality of pixels and subpixels and an edge blending value is stored for each pixel.

23. A method for simulating night scenes and own-ship lighting using a graphics accelerator with a frame buffer, comprising:

(a) storing a ship mounted lighting pattern in an alpha memory of the frame buffer;

(b) generating range values for pixels based on a range calculated for vertices of a polygon and interpolated through the alpha channel when the polygon is rendered;

(c) processing the range values and applying range attenuation to the own-ship lighting pattern as a post process to the frame buffer when pixels are scanned out of the frame buffer for display; and

(d) avoiding attenuation of point lights and luminous polygons by checking a luminous bit stored in the alpha memory at a subpixel level and not attenuating the respective subpixels.

24. The method as in claim 23 further comprising the step of adjusting the ambient lighting independent of the ship mounted lighting pattern intensity.

25. The method as described in claim 23 wherein the step of processing the range thorough an alpha processing channel further comprises processing the range values through the alpha channel to derive a double buffered range value for each pixel.

26. The method as described in claim 23 wherein the step of adjusting the ambient lighting further includes multiplying the lobe pattern by a scale factor and adding an offset.

27. The method as described in claim 23 further comprising double buffering the ship mounted lighting pattern to allow for smooth simulation of lobe movement.

28. The method as described in claim 23 further comprising loading the ship mounted lighting pattern as a pre-rendered bitmap.

29. The method as described in claim 23 further comprising rendering the own-ship lighting pattern through the alpha channel.