Optimizing a graphics rendering pipeline using early Z-mode

• US 20070257905A1
• Filed: 05/08/2006
• Published: 11/08/2007
• Est. Priority Date: 05/08/2006
• Status: Active Grant

• Current Assignee: NVIDIA Corporation
• Original Assignee: NVIDIA Corporation
• Inventors: Molnar, Steven, French, Mark, Kilgariff, Emmett, Steiner, Walter, Voorhies, Douglas, Weitkemper, Adam
• Granted Patent: US 8,933,933 B2
• Time in Patent Office: Days
• US Class Current: 345/419
• CPC Class Codes: G06T 15/005 General purpose rendering architectures
• CPC Class Codes: G06T 15/405 using Z-buffer

Abstract

One embodiment of the present invention sets forth an architecture for optimizing graphics rendering efficiency by advancing the Z-test operation prior to pixel shading whenever possible. The current rendering state, as maintained by the setup engine, determines whether advancing the Z-test function above the shader engine for “early” Z-testing is possible or whether the Z-test function should be deferred until after shading operations for “late” Z-testing. Data is dynamically routed to each processing engine in the pipeline, so that the appropriate data flow for either early Z or late Z is dynamically constructed, as determined by the current rendering state. Efficiency is gained by relieving the shader engine of unnecessary work whenever possible by discarding pixels before they enter the shader engine. The same functional units are utilized in both early Z and late Z configurations, minimizing any additional hardware required for implementation.

Claims

1. A configurable graphics rendering pipeline for processing graphics primitives, the graphics rendering pipeline comprising:

a setup engine configured to determine whether processing should proceed in early Z-mode or late Z-mode;

a raster engine configured to receive a geometry primitive from the setup engine and convert the geometry primitive into at least one pixel primitive;

a shader engine configured to perform shading operations on pixels associated with the at least one pixel primitive;

a Z-raster operations (ZROP) unit configured to compute Z-data for each of the pixels;

a Z-resolve engine configured to determine, for each pixel, whether the pixel is to be kept or discarded based on the Z-data associated with the pixel; and

a pre-raster operations (PROP) unit configured to modify a data flow path between the shader engine and the ZROP unit to support both early Z-mode and late Z-mode,

wherein the pixels associated with the at least one pixel primitive are processed first by the ZROP unit and the Z-resolve engine and then by the shader engine when the graphics rendering pipeline is configured for early Z-mode, and the pixels are processed first by the shader engine and then by the ZROP unit and the Z-resolve engine when the graphics rendering pipeline is configured for late Z-mode.

2. The graphics rendering pipeline of claim 1, wherein the setup engine is configured to evaluate a rendering state associated with the geometry primitive to determine whether a change from early Z-mode to late Z-mode or from late Z-mode to early Z-mode should be made.

3. The graphics rendering pipeline of claim 2, wherein the setup engine includes a hysteresis counter that tracks the number of geometry primitives presented to the setup engine while the graphics rendering pipeline is configured for late Z-mode.

4. The graphics rendering pipeline of claim 3, wherein a hysteresis count is set to a count value, and the hysteresis count is advanced each time the setup engine receives a new geometry primitive while the graphics rendering pipeline is configured for late Z-mode.

5. The graphics rendering pipeline of claim 4, wherein the setup engine is permitted to switch the graphics rendering pipeline configuration to early Z-mode when the hysteresis count equals a trigger value.

6. The graphics rendering pipeline of claim 2, wherein the set up engine is configured to execute a flush operation prior to switching from early Z-mode to late Z-mode or from late Z-mode to early Z-mode.

7. The graphics rendering pipeline of claim 6, wherein the setup engine is configured to instruct the PROP unit to modify the data flow path between the shader engine and the ZROP unit to switch from early Z-mode to late Z-mode or from late Z-mode to early Z-mode.

8. A computer system configured to process graphics primitives, the computer system comprising:

a memory; and

a processing unit that includes a configurable graphics rendering pipeline having;

a setup engine configured to determine whether processing should proceed in early Z-mode or late Z-mode;

a raster engine configured to receive a geometry primitive from the setup engine and convert the geometry primitive into at least one pixel primitive;

a shader engine configured to perform shading operations on pixels associated with the at least one pixel primitive;

a Z-raster operations (ZROP) unit configured to compute Z-data for each of the pixels;

a Z-resolve engine configured to determine, for each pixel, whether the pixel is to be kept or discarded based on the Z-data associated with the pixel; and

a pre-raster operations (PROP) unit configured to modify a data flow path between the shader engine and the ZROP unit to support both early Z-mode and late Z-mode,

wherein the pixels associated with the at least one pixel primitive are processed first by the ZROP unit and the Z-resolve engine and then by the shader engine when the graphics rendering pipeline is configured for early Z-mode, and the pixels are processed first by the shader engine and then by the ZROP unit and the Z-resolve engine when the graphics rendering pipeline is configured for late Z-mode.

9. The computing system of claim 8, wherein the setup engine is configured to evaluate a rendering state associated with the geometry primitive to determine whether a change from early Z-mode to late Z-mode or from late Z-mode to early Z-mode should be made.

10. The computing system of claim 9, wherein the setup engine includes a hysteresis counter that tracks the number of geometry primitives presented to the setup engine while the graphics rendering pipeline is configured for late Z-mode.

11. The computing system of claim 10, wherein a hysteresis count is set to a count value, and the hysteresis count is advanced each time the setup engine receives a new geometry primitive while the graphics rendering pipeline is configured for late Z-mode.

12. The computing system of claim 11, wherein the setup engine is permitted to switch the graphics rendering pipeline configuration to early Z-mode when the hysteresis count equals a trigger value.

13. The computing system of claim 9, wherein the set up engine is configured to execute a flush operation prior to switching from early Z-mode to late Z-mode or from late Z-mode to early Z-mode.

14. The computing system of claim 13, wherein the setup engine is configured to instruct the PROP unit to modify the data flow path between the shader engine and the ZROP unit to switch from early Z-mode to late Z-mode or from late Z-mode to early Z-mode.

15. A method for switching the configuration of a graphics rendering pipeline between early Z-mode and late Z-mode, the method comprising:

receiving a geometry primitive;

determining whether the graphics rendering pipeline is configured for early Z-mode or for late Z-mode;

determining whether to switch the configuration of the graphics rendering pipeline from early Z-mode to late Z-mode or from late Z-mode to early Z-mode; and

executing a flush operation to complete in-progress work in the graphics rendering pipeline, if the configuration of the graphics rendering pipeline is to be switched.

16. The method of claim 15, further comprising the step of advancing a hysteresis count upon receiving the geometry primitive, if the graphics rendering pipeline is determined to be configured for late Z-mode.

17. The method of claim 16, wherein the step of determining whether to switch the configuration of the graphics rendering pipeline comprises determining whether the hysteresis count is equal to a trigger value, if the graphics rendering pipeline is determined to be configured for late Z-mode.

18. The method of claim 17, further comprising the step of switching the configuration of the graphics rendering pipeline to early Z-mode by modifying a data flow path through the graphics rendering pipeline so that pixel primitives are transmitted to a Z-raster operations (ZROP) unit and a Z-resolve engine before being transmitted to a shader engine.

19. The method of claim 15, wherein the step of determining whether to switch the configuration of the graphics rendering pipeline comprises evaluating a rendering state associated with the geometry primitive.

20. The method of claim 15, wherein the graphics rendering pipeline is configured for early Z-mode, and further comprising the step of switching the configuration to late Z-mode by modifying a data flow path through the graphics rendering pipeline so that pixel primitives are transmitted to a shader engine before being transmitted to a Z-raster operations (ZROP) unit and a Z-resolve engine.