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Hardware Acceleration of Line Stipple Rendering Using Texture Maps

IP.com Disclosure Number: IPCOM000009706D
Publication Date: 2002-Sep-11
Document File: 3 page(s) / 59K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that uses a one-dimensional texture map to render lines with stipple patterns. Benefits include enabling the hardware to accelerate line stipple rendering even when the hardware cannot provide support for this feature.

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Hardware Acceleration of Line Stipple Rendering Using
Texture Maps

Disclosed is a method that uses a one-dimensional texture map to render lines with stipple patterns. Benefits include enabling the hardware to accelerate line stipple rendering even when the hardware cannot provide support for this feature.

Background

Typically, drawing patterned lines in graphics hardware is done by using a line stipple pattern.

The stipple pattern consists of a sequence of 0s and 1s. Each time a pixel is generated for a line, a stipple counter is incremented so that the next pixel looks up the next 0 or 1. If the stipple pattern has a 0, the pixel is not drawn. If the stipple pattern has a 1, the pixel is drawn.

Drawing lines using the line stipple pattern is an operation that can be provided by the graphics hardware; however, certain hardware architectures make is very difficult to support this feature.

These architectures may require primitives to progress in a certain screen direction (e.g. from top to bottom), or they may use techniques such as zone rendering, where the primitives are rendered by completely rendering one small zone before moving to the next zone.

General Description

Line stipple patterns use a pattern and a� factor. The pattern is a sequence of 0’s and 1’s which describe the pattern of pixels that are “killed” (when bit is 0) or drawn (when bit is 1). The factor is a count that is used to modify the effective line stipple by causing each bit in line stipple to be used “factor” times. The line stipple pattern is 16 bits. The factor is limited to the range [1,256]. The line stipple pattern is a circular pattern with a starting point. Additionally, when two connected lines are drawn, the line stipple pattern continues from the first line to the next line (i.e. the line stipple pattern can start anywhere within the 16 bit pattern).

The disclosed method creates a texture map that represents the line stipple pattern together with the repeat factor. Figure 1 shows a replication factor of 2, where A, B, C and D represent either 0 or 1. Computing the texture coordinates that use this replicated stipple pattern is relatively easy. There are minor issues associated with correct sampling of the textures which can be handled by adjusting the texture coordinates based on the s...