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Inter-Office Memorandum
To Mesa Users Date October 24, 1977
From R. 10hnsson Location Palo Alto
Subject Simple Display Package Organization SDD/SD
XEROX SDD ARCHIVES
XEROX I have read and understood
Pages _________To _________
Reviewer _________ Date _______
Filed on: [MAXC1 ]SimpleDisplay.bravo
:# of Pages ____ Ref .. 11~1,)1>
This memo describes a simplified display package which may be of interest to some Mesa
users. The package uses the DeB-per-line mode of operation in order to increase scroll
speed and maximize the amount of text that can be displayed for a given amount of
memory. There is no provision for other than Teletype style useage, i.e., there is no support
for pointing. selecting. etc. This package can be used to replace the Display. Menus,
Rectangles. and Windows modules in the standard Mesa system for applications which do
not require the generality of those interfaces.
The modules described here may be used separately or may be used in the configuration
SimpJeDisplay which includes a standard control module.
Fonts
FontDefs defines the interface to Font objects.
FontDefs: DEFINITIONS =
BEGIN
BitmapState: TYPE = RECORD [
origin: POINTER.
wordsPerLine, x, y: CARDINAL];
FontObject: TYPE = RECORD [
paintChar: PROCEDURE [FontHandle, CHARACTER, POINTER TO BitmapState],
clearChar: PROCEDURE [FontHandle, CHARACTER, POINTER TO BitmapState],
charWidth: PROCEDURE [FontHandle, CHARACTER] RETURNS [CARDINAL],
charHeight: PROCEDURE [FontHandle, CHARACTER] RETURNS [CARDINAL],
close: PROCEDURE [FontHandle],
destroy: PROCEDURE [FontHandle],
lock: PROCEDURE [FontHandle] RETURNS [POINTER],
unlock: PROCEDURE [FontHandle]];
FontHandle: TYPE = POINTER TO FontObject;
CharWidth: PROCEDURE [font: FontHandle, char: CHARACTER] RETURNS [CARDINAl.];
CharHeight: PROCEDURE [font: FontHandle, char: CHARACTER] RETURNS [CARDINAL];
CreateFont: PROCEDURE [SegmentDefs.FileSegmentHandle] RETURNS
[FontHandle];
Simple Display Package 2
END.
A FontObject contains the following operations:
paintChar: copies the specified character from the font to the bitmap position
specified in the BitmapState; x is updated to point to the next character position.
clearChar: erases the rectangle containing the character (i.e. it does not just clear the
bits of the character). The input state points just beyond the character and is
modified to point to where the character used to be. paintChar[f, c, s] followed by
clearChar[f, c, s] leaves s unchanged.
charWidth, charHeight: return the width and height of a character in bits and scan
lines respectively.
close: swaps the font out of memory if it is not otherwise in use. The font will
always be swapped in when needed, but may be swapped out at any time. It is not
generally locked.
destroy: destroys the FontObject.
lock: locks the font in memory and returns a POINTER to the first word. This can be
used to implement other operations on the bits in the font. Note that nothing in the
FontObject dictates what font format is used.
unlock: undoes lock.
The module AIFont implements FontObjects for Al format fonts. Other modules for other
font formats could be substituted easily. At this time no other modules have been written.
Display
The module SystemDisplay implements the following PROCEDURES from Stream Defs:
GetDefaultDisplayStream
ClearCurrentLine
ClearDisplayChar
DisplayDefs defines some additional interface procedures:
DisplayDefs: DEFINITIONS =
BEGIN
Background: TYPE = {white, black};
SetSystemDisplaySize: PROCEDURE [nTextLines, nPages: CARDINAL];
SetDummyDisplaySize: PROCEDURE [nScanLines: CARDINAL];
InitDisplay: PROCEDURE [dummySize, textLines, nPages: CARDINAL, f: FontDefs.FontHandle];
DisplayOff: PROCEDURE [color: Background];
DisplayOn: PROCEDURE;
Simple Display Package 3
END.
The display consists of a dummy DCB for spacing followed by the display area itself.
InitDisplay specifies the size of the dummy in scan lines (72 per inch), the size of the text
area in text lines, and the number of pages of memory to allocate for bitmap space. A small
display of 4-6 text lines works well with about 6 pages of bitmap space; a full screen of
about 50 lines of program text (lots of white space) can be handled with about 40 pages of
bitmap.
Once the display is initialized the size of either the dummy or the text area can be changed
(changing the size to zero works correctly). DisplayOff and DisplayOn provide a simple
means of reclaiming all of the display space. In addition DisplayOff calls font.close[font]
to swap out the font if possible.
System Display also contains the following PUBLIC items which are not in the DisplayDefs
interface (due to an oversight at the time the interface was frozen):
SetTypescript: PROCEDURE [StreamDefs.DiskHandle];
Set Font: PROCEDURE [FontDefs.FontHandle];
Call SetTypescript with a DiskHandle to enable the typescript facility; pass NIL to turn the
typescript off. Call SetFont with a new FontHandle to change the font (use this procedure
only when the display is off, i.e. size = 0).
Control Module
A standard control module, DisplayControl, is also provided. It will take care of initializing
the display, font and typescript using the same algorithm as the standard Mesa system (use
MesaFont.al or SysFont.al and Mesa.Typescript). It will also reestablish the font and
typescript correctly after a Makelmage and flush the typescript buffer during OutLd-Inld;
i.e. it does the things the standard Mesa system does. The configuration to make a stand
alone display package is:
SimpleDisplay: CONFIGURATION
IMPORTS DirectoryDefs, ImageDefs, SegmentDefs, StreamDefs, StringDefs, SystemDefs
EXPORTS DisplayDefs, FontDefs
CONTROL DisplayControl =
BEGIN
AIFont;
SystemDisplay;
DisplayControl;
END.
The source and object files for FontDefs, AIFont, DisplayDefs, SystemDisplay and
SimpleDisplay are on the (MESA) directory.
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