Abstract: In a computer graphic system a method and apparatus for dynamically maintaining an overflow flag in a multi-layer buffer. A circuit for maintaining an overflow signal is provided. This circuit is provided new pixel data from the computer system and old pixel data from a memory and in response dynamically asserts or de-asserts the overflow signal. An increment and decrement generator, which is coupled to the new overflow generator, is provided a new overflow signal and an old overflow signal and in response generates an increment signal and a decrement signal. An overflow tracking circuit, which is coupled to the increment and decrement generator, is provided. The overflow tracking circuit uses the increment and decrement signals to maintain an overflow count value.

Abstract: A method and apparatus for generating pixel shading values in a computer controlled display system. Generally, the apparatus is embodied in a rendering pipeline, where each stage of the pipeline performs a particular pixels shading function, so that pixels are shaded in a distributed and direct fashion. The method of the present invention includes the steps of: deriving a pixel interpolation value from an object description, providing a first and second shading parameters and the pixel interpolation value to a first shader, generating the first shading value for the pixel, providing second and third shading parameters and the pixel interpolation value to a second shader and generating second shading value for the pixel.

Abstract: A rendering device for providing 3-D graphics rendering in a computer system. A hardware scanline rendering approach is utilized. Using a hardware scanline rendering approach the bandwidth requirements between a system frame buffer and the rendering device are minimized. The minimization of bandwidth requirement allows for the rendering device to be used with existing computer system designs while keeping design changes at a minimum. The result is that for a given desired performance of a combined computer system and rendering device, the cost of both the computer system without the rendering device, and the cost of the rendering device itself may be reduced. The rendering device is generally comprised of a bus attachment for coupling to the system bus of the computer system; a scanline rendering device and a scanout device for transferring the scanline of shaded pixel values to the system frame buffer.

Abstract: A method and apparatus for approximating a value distributed between two endpoints. The method and apparatus are embodied in a rendering device for calculating pixel shading values for the display of 3-D graphical images. The method approximates a function P(w)=(1-w)A+wB, where w is a provided interpolation weight between 0 and 1, A is a first endpoint value and B is a second endpoint value. The method causes exact evaluation for the cases where P(0)=A and P(1)=B.

Abstract: A method and apparatus for simultaneously rendering multiple scanlines. Using a scanline approach to rendering, multiple scanlines may be rendered simultaneously through the use of parallel rendering means. The rendering of multiple scanlines in parallel is enabled by creating scanline independence. Scanline independence is achieved by interpolation through direct evaluation of object information. During the rendering process each of the rendering means vertically interpolates to identify a span corresponding to the scanline being rendered. A span is identified by it's X, Y coordinates on a scanline. The scanline being rendered provides the Y-coordinate.