Shadow mapping in a low cost graphics system

• US 6,664,962 B1
• Filed: 11/28/2000
• Issued: 12/16/2003
• Est. Priority Date: 08/23/2000
• Status: Active Grant

• Current Assignee: Nintendo Company Limited
• Original Assignee: Nintendo Company Limited
• Inventors: Hirose, Kazuki, Komsthoeft, Matthew, Ockenden, K. Michael, Yasumoto, Yoshitaka
• Primary Examiner(s): Zimmerman, Mark
• Assistant Examiner(s): Nguyen, Kimbinh T.
• Application Number:
  US09/722,421
• Time in Patent Office: 1,113 Days
• Field of Search: 345/426, 345/421, 345/422, 345/419, 345/420, 345/582, 345/589, 345/427, 345/473
• US Class Current: 345/426
• CPC Class Codes: G06T 15/04 Texture mapping
• CPC Class Codes: G06T 15/60 Shadow generation

Abstract

A graphics system including a custom graphics and audio processor produces exciting 2D and 3D graphics and surround sound. The system includes a graphics and audio processor including a 3D graphics pipeline and an audio digital signal processor. Full-scene shadow mapping can be performed by having the lighting hardware calculate distance using a distance attenuation function. If more precision is desirable, texture coordinate generating hardware can be used to calculate texture coordinates that index into a ramp texture lookup storing precision distance values. A unique ramp texture providing redundant values can be used to eliminate ramp texture lookup errors.

Claims

1. A shadow mapping method comprising:

generating texture coordinates representing a distance between a light and a surface;

mapping a ramp texture in response to the texture coordinates to obtain a precision depth; and

using the precision depth in a shadow mapping comparison.

2. The method of claim 1 wherein the ramp texture comprises a two-dimensional texture including redundant entries.

3. The method of claim 1 wherein the ramp texture comprises a two-dimensional texture including unused entries.

4. The method of claim 1 wherein the ramp texture includes redundant entries.

5. The method of claim 1 wherein the generating step includes:

transforming a vertex position into light space by taking into account the depth range of a scene.

6. The method of claim 1 further including rendering a shadow map into an embedded frame buffer, and copying out said shadow map into a shadow map texture for use in said shadow mapping comparison.

7. The method of claim 1 further including performing a front face culled rendering to generate a shadow map for said shadow mapping comparison.

8. The system of claim 1 wherein said ramp texture provides a linearly increasing ramp function.

9. The system of claim 1 wherein said ramp texture provides a continuous ramp function from a minimum value to a maximum value.

10. The method of claim 1 wherein said ramp texture provides a linearly increasing ramp function.

11. The method of claim 1 wherein said ramp texture provides a continuous ramp function from a minimum value to a maximum value.

12. A graphics pipeline including:

a texture coordinate generator that generates a pair of texture coordinates s, t that together encode the distance from a surface to a light;

a texture mapper that maps a ramp texture in response to said texture coordinates to provide a depth value; and

a comparator that compares said depth value with a shadow map.

13. In a graphics pipeline including an embedded frame buffer, a shadow mapping technique including:

rendering a scene into the embedded frame buffer, and

copying embedded frame buffer contents into a shadow map texture for use in a shadow mapping depth comparison.

14. A technique as in claim 13 wherein said rendering step comprises rendering depth values into an embedded z buffer.

15. A technique as in claim 13 wherein said rendering step comprises rendering object ID values into an embedded color frame buffer.