3D graphics rendering system for performing Z value clamping in near-Z range to maximize scene resolution of visually important Z components

• US 6,618,048 B1
• Filed: 11/28/2000
• Issued: 09/09/2003
• Est. Priority Date: 10/28/1999
• Status: Active Grant

• Current Assignee: Nintendo Company Limited
• Original Assignee: Nintendo Company Limited
• Inventors: Leather, Mark M.
• Primary Examiner(s): Zimmerman, Mark
• Assistant Examiner(s): Nguyen, Kimbinh T.
• Application Number:
  US09/726,223
• Time in Patent Office: 1,015 Days
• Field of Search: 345/419, 345/421, 345/422, 345/427, 345/428, 345/506, 345/620, 345/627
• US Class Current: 345/422
• CPC Class Codes: G06T 15/405 using Z-buffer

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. The graphics pipeline performs Z-buffering and optionally provides memory efficient full scene anti-aliasing (FSAA). When the anti-aliasing rendering mode is selected, Z value bit compression is performed to more efficiently make use of the available Z buffer memory. A Z-clamping arrangement is used to improve the precision of visually important Z components by clamping Z values to zero of pixels that fall within a predetermined Z-axis range near the Z=0 eye/camera (viewport) plane. This allows a Z-clipping plane to be used very close to the eye/camera plane—to avoid undesirable visual artifacts produced when objects rendered near to the eye/camera plane are clipped—while preserving Z value precision for the remaining depth of the scene. In an example implementation, a Z value compression circuit provided in the graphics pipeline is enhanced to effectuate Z-clamping within the predetermined range of Z values. The enhanced circuitry includes an adder for left-shifting an input Z value one or more bits prior to compression and gates for masking out the most significant non-zero shifted bits to zero.

Claims

1. In a 3D graphics rendering system, a method of performing Z buffering, comprising:

establishing a first clipping plane, znear, at a Z-axis position very near to the Z=0 plane and a second clipping plane, zfar, at a Z-axis position very far from the z=0 plane;

establishing a Z-axis value clamping plane, znear2, at z=znear2=znear*(1<

<

n), wherein “

n”

is a predetermined integer value that sets a position of the znear2 clamping plane relative to the znear plane and effectively provides a predetermined z value resolution for a portion of a rendered scene that lies between the znear2 plane and the zfar plane;

performing conventional Z-buffering for pixels having z values where znear2<

z<

zfar; and

clamping z values to a predetermined value for pixels where znear≦

z≦

znear2, wherein pixel data corresponding to clamped z values is written to a display frame buffer in a first to last rendered order.

2. The graphics system of claim 1 wherein the predetermined value for clamped Z values is zero.

3. In a 3D graphics rendering system including a processor and a separate graphics processing pipeline having transformation and lighting circuitry, the pipeline performing Z buffering, an arrangement included within the graphics pipeline for providing Z value compression and selectable Z value clamping, comprising:

a priority encoder and a shifter, wherein said priority encoder provides a shift value to said shifter for performing a binary value compression operation; and

an adder including bit masking circuitry, said adder connected between the priority encoder and the shifter,

wherein said adder is used to selectably increase a shift value provided by the priority encoder to said shifter during a Z value compression operation to effectively clamp Z values within a selectable predetermined range.

4. The graphics system of claim 3 wherein said predetermined Z value is zero.

5. The graphics system of claim 3 wherein said predetermined range of Z values is determined by a Z clipping plane, znear, defined at a predetermined Z-axis position very near to the z=0 plane and a Z clamping plane, znear2, defined at z=znear2=znear*(1<

<

n), where “

n”

is equal to an integer value indicative of a selected increase in shift value provided to said priority encoder.

6. In a 3D graphics rendering system including a processor and a separate graphics processing pipeline, the pipeline performing full scene anti-aliasing with Z-value compression, a method for selectably setting a predetermined Z value resolution for a portion of a rendered scene, comprising:

shifting a binary Z-value one or more bit positions prior to performing Z value compression, wherein the amount of shifting determines a range of Z values near a Z=0 plane for which Z values are clamped to a predetermined value.

7. In a graphics processing system that renders and displays images at least in part in response to polygon vertex attribute data including Z-value binary data stored in an associated memory, a Z value compression processing circuit portion embodied in hardware, comprising:

a priority encoder,

a shifter, and

an adder connected between the priority encoder and the shifter, wherein the adder may be used to selectably increase a value provided by said priority encoder to said shifter for shifting the Z-value binary data an additional predetermined number of bit positions during a compression operation to effectuate a clamping of Z values that are within a predetermined range of Z values to a predetermined value.