Recent advances in computer performance have enabled graphic systems to provide more realistic graphical images using personal computers, home video game computers, handheld devices, and the like. In such graphic systems, a number of procedures are executed to “render” or draw graphic primitives to the screen of the system. A “graphic primitive” is a basic component of a graphic picture, such as a point, line, polygon, or the like. Rendered images are formed with combinations of these graphic primitives. Many procedures may be utilized to perform 3-D graphics rendering.
Specialized graphics processing units (e.g., GPUs, etc.) have been developed to optimize the computations required in executing the graphics rendering procedures. The GPUs are configured for high-speed operation and typically incorporate one or more rendering pipelines. Each pipeline includes a number of hardware-based functional units that are optimized for high-speed execution of graphics instructions/data, where the instructions/data are fed into the front end of the pipeline and the computed results emerge at the back end of the pipeline. The hardware-based functional units, cache memories, firmware, and the like, of the GPU are optimized to operate on the low-level graphics primitives (e.g., comprising “points”, “lines”, “triangles”, etc.) and produce real-time rendered 3-D images.
The real-time rendered 3-D images are generated using raster display technology. Raster display technology is widely used in computer graphics systems, and generally refers to the mechanism by which the grid of multiple pixels comprising an image are influenced by the graphics primitives. For each primitive, a typical rasterization system generally steps from pixel to pixel and determines whether or not to “render,” or write a given pixel into a frame buffer or pixel map, as per the contribution of the primitive. This, in turn, determines how to write the data to the display buffer representing each pixel.
Various traversal algorithms and various rasterization methods have been developed for computing from a graphics primitive based description to a pixel based description (e.g., rasterizing pixel to pixel per primitive) in a way such that all pixels within the primitives comprising a given 3-D scene are covered. For example, some solutions involve generating the pixels in a unidirectional manner. Such traditional unidirectional solutions involve generating the pixels row-by-row in a constant direction. This requires that the sequence shift across the primitive to a starting location on a first side of the primitive upon finishing at a location on an opposite side of the primitive.
Other traditional methods involve stepping pixels in a local region following a space filling curve such as a Hilbert curve. The coverage for each pixel is evaluated to determine if the pixel is inside the primitive being rasterized. This technique does not have the large shifts (which can cause inefficiency in the system) of the unidirectional solutions, but is typically more complicated to design than the unidirectional solution.
Once the primitives are rasterized into their constituent pixels, these pixels are then processed in pipeline stages subsequent to the rasterization stage where the rendering operations are performed. Typically, these rendering operations involve reading the results of prior rendering for a given pixel from the frame buffer, modifying the results based on the current operation, and writing the new values back to the frame buffer. For example, to determine if a particular pixel is visible, the distance from the pixel to the camera is often used. The distance for the current pixel is compared to the closest previous pixel from the frame buffer, and if the current pixel is visible, then the distance for the current pixel is written to the frame buffer for comparison with future pixels. Similarly, rendering operations that assign a color to a pixel often blend the color with the color that resulted from previous rendering operations. Generally, rendering operations assign a color to each of the pixels of a display in accordance with the degree of coverage of the primitives comprising a scene. The per pixel color is also determined in accordance with texture map information that is assigned to the primitives, lighting information, and the like.
A problem exists however with the ability of prior art 3-D rendering architectures to scale to handle the increasingly complex 3-D scenes of today's applications. Many of these applications require the ability to efficiently implement complex screen coloring and rendering effects in real-time, such as, for example, complex OpenVG (Open Vector Graphics) screen effects. Additional applications require the ability to accurately draw complex objects or characters in real-time whether the character will ultimately result on screen or not, and the ability to accurately simulate “lens flare” type effects for bright light sources.
With computer screens now commonly having screen resolutions of 1920×1200 pixels or larger, traditional methods of increasing 3-D rendering performance to handle increasingly demanding applications are problematic. For example, increasing clock speed to improve performance has negative side effects, such as increasing power consumption and increasing the heat produced by the GPU integrated circuit die. Other methods for increasing performance, such as incorporating large numbers of parallel execution units for parallel execution of GPU operations have negative side effects such as increasing integrated circuit die size, decreasing yield of the GPU manufacturing process, increasing power requirements, and the like.
Thus, a need exists for a rasterization process that can scale as graphics application needs require and provide added performance without incurring penalties such as increased power consumption and/or reduced fabrication yield.