This Technical Note describes the Apple II Pascal SHORTGRAPHICS routine, which is available as part of the 48K Run-Time System.
Many applications, especially those designed to use the 48K Run-Time System, run out of memory quickly if they use the TURTLEGRAPHICS unit provided with the standard SYSTEM.LIBRARY.
This document describes a library unit called SHORTGRAPHICS which removes the relative polar coordinate features of TURTLEGRAPHICS to save memory.
If your application uses (or can be modified to use) only those TURTLEGRAPHICS procedures which refer to absolute screen coordinates, you can use the SHORTGRAPHICS unit. The SHORTGRAPHICS unit has the same segment numbers assigned to it, as does TURTLEGRAPHICS, thus you may not use both in the same program.
The following routines are not available in the SHORTGRAPHICS unit:
PROCEDURE TURN(ANGLE: INTEGER); PROCEDURE TURNTO(ANGLE: INTEGER); PROCEDURE MOVE(DIST: INTEGER); FUNCTION TURTLEANG: INTEGER;
The following definitions have been added to the INTERFACE section of SHORTGRAPHICS:
TYPE FONT=PACKED ARRAY[0..127,0..7] OF 0..255; VAR FONTPTR:^FONT;
The variable FONTPTR is a pointer to the memory area used by the WCHAR and WSTRING procedures to display text on the graphics screen.
Thus, if you have a character set named KATAKANA.FONT, you could load it into memory and use it as follows:
VAR SPECIALFONT:^FONT; (* where the new font goes *) SAVEFONT:^FONT; (* to save pointer to standard font area *) PROCEDURE LOADFONT; VAR F:FILE; NIO:INTEGER; BEGIN NEW(SPECIALFONT); RESET(F,'KATAKANA.FONT'); NIO:=BLOCKREAD(F,SPECIALFONT^,2,0); CLOSE(F) END; PROCEDURE USESPECIAL; BEGIN SAVEFONT:=FONTPTR; (* save standard font pointer *) FONTPTR:=SPECIALFONT; (* and point to special font *) END; PROCEDURE USENORMAL; BEGIN FONTPTR:=SAVEFONT (* restore pointer to normal font *) END;
When the system is booted, the heap pointer is normally below the start of high-resolution page one. The TURTLEGRAPHICS unit automatically sets the heap pointer above high-resolution page one. This protects the high-resolution page from being overwritten by your program, but it also prevents you from using the space between the original top of the heap and the start of high-resolution page one for your own variables.
SHORTGRAPHICS does not protect the high-resolution page, thus you may use this extra space for yourself. The following code will check to see if you have n bytes available between the top of the heap and high-resolution page one. If the room is not available, the heap pointer will be jumped to the top of the high-resolution page.
PROCEDURE MAKEROOM(N:INTEGER); CONST BOTTOM=8192; TOP=16384; VAR CHEAT:RECORD CASE BOOLEAN TRUE:(IPART:INTEGER); FALSE:(PPART:^INTEGER); END; BEGIN MARK(CHEAT.PPART); IF (CHEAT.IPART+N)>=BOTTOM THEN BEGIN CHEAT.IPART:=TOP; RELEASE(CHEAT.PPART) END END;
Thus, if you wanted to allocate a special font (which requires 1,024 bytes) below the high-resolution page, you could use this code:
If there are at least 1,024 bytes beneath the high-resolution page, the new font will be allocated there. If there is not enough space there, the new font will be allocated above the high-resolution page.
All of these heap allocations should be done as the very first actions of your program. When you finish allocating your variables, you should invoke the following procedure to make sure the heap pointer is above high-resolution page one (thus protecting it).
PROCEDURE PROTECT; CONST TOP=16384; VAR CHEAT:RECORD CASE BOOLEAN OF TRUE:(IPART:INTEGER); FALSE:(PPART:^INTEGER); END; BEGIN MARK(CHEAT.PPART); IF CHEAT.IPART<TOP THEN BEGIN CHEAT.IPART:=TOP; RELEASE(CHEAT.PPART); END; END;
Warning: Every program written using SHORTGRAPHICS is unprotected from a heap which grows large enough to go into the high-resolution page one area. Therefore, every program using SHORTGRAPHICS should protect page one by using PROCEDURE PROTECT. You should protect page one even if the program does not use the space below it.
When you look at TURTLEGRAPHICS with the LIBRARY program, the code segment has a length of 5,230 bytes and the data segment a length of 386 bytes. SHORTGRAPHICS has a code segment 3,140 bytes in length and a data segment of 18 bytes. Thus, in a test of a null program, you have 2,458 bytes more space available.
The following files are on the SHORT GRAPHICS disk:
The following is the interface section of the SHORTGRAPHICS unit:
UNIT SHORTGRAPHICS; INTRINSIC CODE 20 DATA 21; INTERFACE TYPE SCREENCOLOR=(none,white,black,reverse,radar, black1,green,violet,white1, black2,orange,blue,white2); FONT=PACKED ARRAY[0..127,0..7] OF 0..255; VAR FONTPTR:^FONT; PROCEDURE INITTURTLE; PROCEDURE MOVETO(X,Y: INTEGER); PROCEDURE PENCOLOR(PENMODE: SCREENCOLOR); PROCEDURE TEXTMODE; PROCEDURE GRAFMODE; PROCEDURE FILLSCREEN(FILLCOLOR: SCREENCOLOR); PROCEDURE VIEWPORT(LEFT,RIGHT,BOTTOM,TOP: INTEGER); FUNCTION TURTLEX: INTEGER; FUNCTION TURTLEY: INTEGER; FUNCTION SCREENBIT(X,Y: INTEGER): BOOLEAN; PROCEDURE DRAWBLOCK(VAR SOURCE; ROWSIZE,XSKIP,YSKIP,WIDTH, HEIGHT,XSCREEN,YSCREEN,MODE: INTEGER); PROCEDURE WCHAR(CH: CHAR); PROCEDURE WSTRING(S: STRING); PROCEDURE CHARTYPE(MODE: INTEGER);
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