In order to add some graphics capability I want to suggest two new commands just to start.
GRAPHICWIN width, height and PSET x, y, color$
These will enable us to open a window to draw in, and also to draw pixels of a specific color at a given x, y position. This will be a crude start, but it will be instructive because it will show the reader how to extend Tiny BASIC to do what is desired.
The first thing to do is figure out where in the code Tiny BASIC parses commands so we can add some more. The code below is the routine that does this. If you look carefully you will see a SELECT CASE statement and then a CASE statement for each Tiny BASIC command.
More later.
[NextStatement]
GOSUB [GetLabel]
IF E$<>"" THEN [Ready]
SELECT CASE D$
CASE "if"
GOSUB [GetExpression]
IF E$<>"" THEN [Ready]
IF N<1 font="" then="">
B$=A$(L) : C=LEN(B$)+1
GOTO [FinishStatement]
END IF
GOSUB [GetLabel]
IF E$<>"" THEN [Ready]
IF D$<>"then" THEN
E$="'THEN' expected"
GOTO [Ready]
END IF
GOTO [NextStatement]
CASE "rem"
B$=A$(L) : C=LEN(B$)+1
GOTO [FinishStatement]
CASE "input"
GOSUB [GetVar]
IF E$<>"" THEN [Ready]
INPUT N : A(V)=N
GOTO [FinishStatement]
CASE "print"
[Print]
GOSUB [SkipSpace]
GOSUB [GetChar]
IF C$=G$ THEN
B$=""
[NextChar]
C = C + 1 : C$=MID$(A$,C,1)
IF C$="" THEN
E$="Unterminated string"
GOTO [Ready]
ELSE
IF C$<>G$ THEN
B$=B$+C$
GOTO [NextChar]
END IF
END IF
C = C + 1 : C$=MID$(A$,C,1)
IF C$=G$ THEN
B$=B$+C$
GOTO [NextChar]
END IF
PRINT B$;
ELSE
GOSUB [GetExpression]
IF E$<>"" THEN [Ready]
B=N1
IF B=N THEN
PRINT N;"*";
ELSE
PRINT N;
END IF
END IF
GOSUB [SkipSpace]
GOSUB [GetChar]
IF C$="," THEN C = C + 1 : GOTO [Print]
GOSUB [SkipSpace]
GOSUB [GetChar]
IF C$<>";" THEN
ELSE
C = C + 1
END IF
GOTO [FinishStatement]
CASE "clear"
FOR I=27 TO 52 : A(I)=0 : NEXT I
GOTO [FinishStatement]
CASE "run"
FOR I=27 TO 52 : A(I)=0 : NEXT I
L=27 : C=1
GOTO [FinishStatement2]
CASE "goto"
GOSUB [GetExpression]
IF E$<>"" THEN [Ready]
IF E>=N THEN L=27
C=1 : T=N
[NextGoto]
IF L=126 THEN
E$="Line not found"
GOTO [Ready]
END IF
GOSUB [GetNumber]
IF N=T THEN E=N : GOTO [NextStatement]
L = L + 1 : C=1
GOTO [NextGoto]
CASE "new"
FOR I=27 TO 125 : A$(I)="" : NEXT I
FOR I=27 TO 52 : A(I)=0 : NEXT I
IF E=0 THEN [FinishStatement]
GOTO [Ready]
CASE "cls"
CLS : GOTO [FinishStatement]
CASE "help"
FOR I=9 TO 18
B$=A$(I) : PRINT B$
NEXT I
GOTO [FinishStatement]
CASE "mem"
B=126
FOR I=27 TO 125
diffI = 152 - I 'Cheating here
B$=A$(diffI) : IF B$="" THEN B=diffI
NEXT I
B=126-B : PRINT B;"*";
PRINT " lines free"
GOTO [FinishStatement]
CASE "end"
GOTO [Ready]
CASE "bye"
GOTO [ExitTinyBAS]
CASE "list"
GOSUB [GetNumber] : T=N : A=L : I=C
IF T=0 THEN
GOSUB [GetLabel]
IF E$="" AND D$="pause" THEN I=C
E$=""
END IF
FOR L=27 TO 125
C=1 : GOSUB [GetNumber]
B=(T=0) OR (N=T)
IF B=TRUE THEN
IF A$<>"" THEN
PRINT A$
IF D$="pause" THEN
B = (L-26) mod 10
IF B=0 THEN PRINT "Pause..."; : INPUT AAA$
END IF
END IF
END IF
NEXT L
L=A : C=I
GOTO [FinishStatement]
CASE "save"
PRINT "SAVE, TBD"
CASE "load"
PRINT "LOAD, TBD"
CASE "let"
GOSUB [GetLabel]
IF E$<>"" THEN [Ready]
END SELECT
