Add DoubleSizePrint library page

Author: boriel

docs/library/doublesizeprint.bas.md

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+#DoubleSizePrint.bas
+
+This routine will print out Strings at double size. It will stop if it reaches the end of the screen, however
+- so you have to deal with new rows on your own! (143 bytes long for main routine)
+
+The core subroutine is capable of printing one character on screen at specified location, in double size.
+Of course, this is the basis for the second subroutine, that takes a string and prints it all.
+
+Both routines are capable of printing from the User Definable Graphics locations.
+
+Usage:
+
+```
+REM Requires ascii code of character to print.
+doubleSizePrintChar(y, x, code("a"))
+```
+```
+REM This version calls the first one, and will print a whole string.
+doubleSizePrint(y, x, thingToPrint$)
+```
+
+Code:
+
+```
+SUB doubleSizePrintChar(y as uByte, x as uByte, thingToPrint as uByte)
+' Prints a single character double sized.
+' Takes X and Y values as character positions, like print.
+' takes an ascii code value for a character.
+' By Britlion, 2012.
+
+ASM
+LD A,(IX+5) 	;' Y value
+CP 22
+JP NC, doubleSizePrintCharEnd
+
+;' A=y value
+LD E,A
+AND 24			 ; calculate
+OR 64			 ; screen
+LD H,A			 ; address
+LD A,E			 ; for 
+AND 7			 ; row
+OR a			 ; Y
+RRA
+RRA
+RRA
+RRA
+LD E,A
+
+LD A,(IX+7) 	;' X Value
+CP 30
+JP NC, doubleSizePrintCharEnd
+
+ADD A,E			;' correct address for column value. (add it in)
+LD L,A
+EX DE,HL		;' Save it in DE
+
+LD A,(IX+9) 	;'Character
+
+CP 164 		;' > UDG "U" ?
+JP NC, doubleSizePrintCharEnd
+
+CP 32  		;' < space+1?
+JP C, doubleSizePrintCharEnd
+
+CP 144 		;' >144?
+JP NC, doubleSizePrintCharUDGAddress
+
+LD L,A
+LD H,0
+
+ADD HL,HL
+ADD HL,HL
+ADD HL,HL	;' multiply by 8.
+LD BC,(23606)	;' Chars
+ADD HL,BC 	;' Hl -> Character data.
+EX DE,HL	;' DE -> character data, HL-> screen address.
+JP doubleSizePrintCharRotateLoopCharStart
+
+doubleSizePrintCharUDGAddress:
+LD HL,(23675)    ;'UDG address
+SUB 144
+ADD A,A         ;multiply by 8.
+ADD A,A
+ADD A,A
+ADD A,L
+LD L,A
+
+JR NC, doubleSizePrintCharUDGAddressNoCarry 
+INC H
+doubleSizePrintCharUDGAddressNoCarry:
+
+;' At this point HL -> Character data in UDG block.
+EX DE,HL ;' DE -> character data, HL-> screen address.
+
+doubleSizePrintCharRotateLoopCharStart:
+LD C,2 ;' 2 character rows.
+doubleSizePrintCharRotateLoopCharRowLoopOuter:
+LD b,4 ;' 4 source bytes to count through per character row.
+doubleSizePrintCharRotateLoopCharRowLoopInner:
+   PUSH BC
+
+   LD A,(DE) ;' Grab a bitmap.
+   PUSH DE
+
+   LD B,4
+   LD C,A ; Copy byte so we can put two into the big version.
+   doubleSizePrintCharRotateLoop1:
+      RRA  ; one bit into carry
+      RR E ; one bit into result
+      RR C ; same bit into carry again
+      RR E ; duplicated bit into result
+   DJNZ doubleSizePrintCharRotateLoop1 
+
+   LD B,4
+   doubleSizePrintCharRotateLoop2:
+       RRA
+       RR D ; Other register for other half of big 16 bit line. 
+       RR C
+       RR D
+   DJNZ doubleSizePrintCharRotateLoop2 
+
+   LD (HL),D	;' Output first byte
+   INC HL	;' Move right
+   LD (HL),E	;' Second half.
+   DEC HL	;' Move left
+   INC H	;' Move down
+   LD (HL),D	;' Output second row (copy of first), first byte.
+   INC HL	;' Move right
+   LD (HL),E	; Output second row, second byte
+   DEC HL	; Move left
+   INC H	; Move down.
+   POP DE
+   INC DE 
+   POP BC
+
+DJNZ doubleSizePrintCharRotateLoopCharRowLoopInner
+; CALL __DECY+2 	;'Jump into the DRAW next_line_down routine, at a convenient point (accounting for the INC H above)
+; Can't seem to call to this at the moment! Here in longhand form:
+
+ld a, h
+and 7
+jr nz, doubleSizePrintCharRotateNextCharRow
+ld a, l
+add a, 32
+ld l, a
+jr c, doubleSizePrintCharRotateNextCharRow
+ld a, h
+sub 8
+ld h, a
+
+doubleSizePrintCharRotateNextCharRow:
+
+DEC C
+JR NZ, doubleSizePrintCharRotateLoopCharRowLoopOuter 
+
+doubleSizePrintCharEnd:
+END ASM
+END SUB
+```
+```
+SUB doubleSizePrint(y as uByte, x as uByte, thingToPrint$ as String)
+'Uses doubleSizePrintChar subroutine to print a string.
+'By Britlion, 2012
+
+   DIM n as uByte
+   for n=0 to LEN thingToPrint - 1
+      doubleSizePrintChar(y,x,CODE thingToPrint$(n) )
+      x=x+2
+   next n
+
+END SUB
+```
+
+Example:
+
+```
+cls
+doubleSizePrintChar(0,0,145)
+doubleSizePrint(10,0,"Hello World")
+```