Date: Wed, 1 Mar 1995 09:55:05 -0700
From: ron@apple.com (Ron Hochsprung)
Subject: Item #238: Open Firmware - Graphics Extension

P1275 Open Firmware Working Group Proposal -- Proposal #238 Ver <Auth-Vers#>

Title:          Graphics extension

Author:         Ron Hochsprung

Date:           March 1, 1995

Ed/Tech:        Technical

Synopsis:       graphics capabilites for "display" devices

Doc & Version:  IEEE Std 1275-1994

Problem:        new client programs desire graphical support

Proposal:

Title:      Graphics support methods for "display" devices

Author:     Ron Hochsprung

Date:       March 1, 1995

Revision:   3

Scope/Documents Affected: Core standard (next revision)

Motivation:  Client Programs require a mechanism to implement "bit-mapped"
graphics via client interface calls.

References: [1] IEEE Std 1275-1994, [2] ISO 6429-1983, [3] PowerPC Binding

Goals:  extended capability for "display" devices.

Proposal:

Section:  Introduction

A set of "bit-mapped" graphics methods (DRAW-RECTANGLE, FILL-RECTANGLE,
READ-RECTANGLE) is defined by this extension that are available to
Client Programs (via CALL-METHOD client callback) to display and read
rectangular areas of the display buffer.

The display buffer model is an extension of the standard fb8 package.  I.e.,
the display buffer is considered to consist of 8-bits per pixel, allowing up
to 256 colors for each pixel.  The data format of Client Program pixel-maps
follows this 1 byte per pixel model.  If the display buffer is not in 8-bit
per pixel mode (e.g., 24-bit), the display driver must map the bit map
accordingly.

The pixel-maps consist of rectangular regions of the display.  Their location
is determined by specifying an x,y location, where the pixel corresponding to
the top,left-most screen location is considered 0,0;  x increases to the
right, y increases down the screen.  The size of the rectangle is specified
by w,h values that represent the width and height, respectively.

The memory area containing the source (target) of data for DRAW-RECTANGLE
(READ-RECTANGLE) consist of w*h consecutive bytes, with the first byte
representing the top,left-most pixel, the second byte representing the pixel
to the right of the first, etc.  Each byte is the color index of the desired
pixel.

Note:  a Client Program can detect whether the display package implements
this extension by using the TEST client callback.


Section:  Requirements

A display package (i.e., a package of device-type "display") that implements
this extension shall provide all of the following methods.

    draw-rectangle    ( adr x y w h -- )

        Displays a rectangular image at pixel location 'x','y' of size
        'w','h' from the data defined by 'adr'.  'x','y' are display coordinates
        where 0,0 corresponds to the top,left displayed pixels;  'w','h' are
        the width and height of the image.

    fill-rectangle    ( index x y w h -- )

        This method fills a rectangular display area, defined by 'x','y','w','h'
        with the color corresponding to 'index'.

    read-rectangle    ( adr x y w h -- )

        This method copies the 8-bit index values corresponding to the display
        pixels , defined by 'x','y','w','h' into the buffer specified by 'adr'.

Note: for displays that are not in 8-bit per pixel mode, the read-rectangle
method is admittedly difficult.  For this reason, it is recommended that
displays provide an 8-bit mode and that this mode is used during Open
Firmware execution.




[ P1275 Item #238 -- Received: Wed Mar  1 09:57:53 PST 1995 ]