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A Method of increasing the Window ID Planes without increasing the WAT

IP.com Disclosure Number: IPCOM000100016D
Original Publication Date: 2005-Mar-15
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Abstract

In a Unix* graphics environment, it's possible to display different pixel types on the screen at the same time. In other words, the user might have an 8 bit color depth window on top of a 24 bit color depth window. The mechanism to do this is built into the graphics card. This article describes a method to allow more pixel types on the screen at the same time than previously done.

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A Method of increasing the Window ID Planes without increasing the WAT

One way to achieve multiple pixel types on the screen at the same time is to use a separate piece of memory on the graphics card so every entry corresponds to a pixel on the screen. This piece of memory called Window ID Planes stores a Window ID (WID) for every pixel on the screen. The WID is an index into the Window Attribute Table (WAT). The WAT is a table which the RAMDAC uses to determine how to display a particular pixel. The WAT contains pixel attributes such a pixel type, colormap slot, gamma, etc. This allows multiple pixel interpretations on the display at the same time. For instance, a user can have a 24 bit depth window and an 8 bit depth window on the display at the same time. Yet, Window ID planes are a limited resource. If the graphic adapter supports 4 bits for the Window ID Planes, then the WAT can have only 16 entries, thus 16 different pixel interpretations can be displayed on the screen at the same time. Increasing the number bits for the Window ID Planes increases the size of the WAT which also increases the cost associated to provide more memory on the graphics card. There needed to be a way to increase the number of Window ID Planes without increasing the size of the WAT.

Instead of the Window ID Planes containing an index into the WAT, the Window ID Planes will be used by the RAMDAC to transmit the correct pixel interpretation to the display directly (i.e. bypass the WAT pixel interpretations). Each bit or a group of bits in the Window ID Planes will represent a pixel attribute. For instance, the first 3 bits could represent the Pixel Type which describes the depth of the pixel as well as if the RAMDAC needs to use a colormap to display the pixel. The next 3 bits could represent which colormap the RAMDAC will use to display the pixel. The next bit could be used to tell the RAMDAC that Gamma correction is enabled or disabled. F...