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Add PRINT64 library
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‎docs/library/print64.bas.md‎

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#Print64.bas
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The 64 column printing routine allows text to be 4 pixels wide instead of 8.
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It is NOT proportional printing, but this is still useful for lining things up in columns.
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This routine has been adopted as an included library - so you may include it with
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```
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#include <print64.bas>
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```
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##Usage
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```
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printat64(y,x)
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```
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Moves the print64 system's print cursor to row Y, column X. Note that `0 <= x <= 63` - that is the range of values
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for X can be up to 63. The range of values for Y is the normal 0-23.
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* Note that the print64 system's cursor position is independent from that of the ZX Basic Print routine,
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or any other, such as the print42 system.
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```
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printat64(STRING)
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```
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Prints the string to the screen at the current Print64 co-ordinates. It does so in the current permanent colours.
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NOTE: The ZX Spectrum's attribute system is encoded into the hardware as a 32 character grid. Print64 does its best,
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but changing the paper/bright/flash colour from the background is likely to look imperfect as the attribute
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blocks cannot line up well with the pixel blocks.
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##CODE
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* There is a version of this code included with the compiler
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(though the version listed here may or may not be more recent). Code converted to ZXBasic by Britlion,
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based on Andrew Owen's 64 Character code http://www.worldofspectrum.org/forums/showpost.php?p=167447&postcount=1
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```
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SUB printat64 (y as uByte, x as uByte)
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IF y<24 AND x<64 then
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POKE @p64coords,x
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POKE @p64coords+1,y
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ELSE
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asm
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rst 8 ; error "5 Out of screen"
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defb 4
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end asm
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END IF
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END SUB
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SUB print64 (characters$ as String)
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ASM
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; This frankencode created by Paul Fisher, Andrew Owen, Chris Born and Einar Saukas
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; TODO:
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; * Inverse
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; * Bold (which will use a Second font)
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LD L,(IX+4)
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LD H,(IX+5) ; Get String address of characters$ into HL.
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; Load BC with length of string, and move HL to point to first character.
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ld c, (hl) ; 60020 78
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inc hl ; 60021 35
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ld b, (hl) ; 60022 70
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inc hl ; 60023 35
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; Test string length. If Zero, exit.
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ld a, c ; 60024 121
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or b ; 60025 176
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jp z, p64_END ; 60026 200
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examineChar:
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ld a, (hl) ; Grab the character
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cp 128 ; too high to print?
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jr nc, nextChar ; then we go to next.
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newLine:
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cp 13 ; Is this a newline character? 60056 254 13
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jr nz, p64_isPrintable ; If not, hop to testing to see if we can print this 60058 32 13
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push hl
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push bc
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ld b,0
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ld hl, p64_coords ; Get coords 60060 237 91 68 235
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call BLp64_NEXT_ROW ; Go to next line. ; 60064 205 58 235
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pop bc
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pop hl
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ld (p64_coords), de ; 60067 237 83 68 235
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jr nextChar ; 60071 24 11
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p64_isPrintable:
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cp 31 ; Bigger than 31? 60073 254 31
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jr c, nextChar ; If not, get the next one. 60075 56 7
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push hl ; Save position 60077 229
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push bc ; Save Count 60078 197
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call p64_PrintChar ; Call Print SubRoutine
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pop bc ; Recover length count 60082 193
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pop hl ; Recover Position 60083 225
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nextChar:
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inc hl ; Point to next character 60084 35
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dec bc ; Count off this character 60085 11
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ld a, b ; Did we run out? 60086 120
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or c ; 60087 177
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jr nz, examineChar ; If not, examine the next one 60088 32 193
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jp p64_END ; Otherwise hop to END. 60090 201
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p64_PrintChar:
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; Arrives with A as a byte to print.
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ld hl,p64_coords
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push hl ; save COL address for later
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ld e, a ; store character value in E
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ld b,0
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ld c, (hl) ; store current column in BC
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; Check if character font must be rotated, self-modifying the code accordingly
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xor c ; compare BIT 0 from character value and column
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rra
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ld a, 256-(BLp64_END_LOOP-BLp64_SKIP_RLC) ; instruction DJNZ skipping rotation
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jr nc, BLp64_NOT_RLC ; decide based on BIT 0 comparison
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ld a, 256-(BLp64_END_LOOP-BLp64_INIT_RLC) ; instruction DJNZ using rotation
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BLp64_NOT_RLC:
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ld (BLp64_END_LOOP - 1), a ; modify DJNZ instruction directly
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; Check the half screen byte to be changed, self-modifying the code accordingly
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srl c ; check BIT 0 from current column
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ld a, %00001111 ; mask to change left half of the screen byte
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jr nc, BLp64_SCR_LEFT ; decide based on odd or even column
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cpl ; mask to change right half of the screen byte
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BLp64_SCR_LEFT:
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ld (BLp64_SCR_MASK + 1), a ; modify screen mask value directly
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cpl
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ld (BLp64_FONT_MASK + 1), a ; modify font mask value directly
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; Calculate location of the first byte to be changed on screen
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; The row value is a 5 bits value (0-23), here represented as %000RRrrr
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; The column value is a 6 bits value (0-63), here represented as %00CCCCCc
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; Formula: 0x4000 + ((row & 0x18) << 8) + ((row & 0x07) << 5) + (col >> 1)
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inc hl ; now HL references ROW address
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ld a, (hl) ; now A = %000RRrrr
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call 0e9eh ; now HL = %010RR000rrr00000
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add hl, bc ; now HL = %010RR000rrrCCCCC
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ex de, hl ; now DE = %010RR000rrrCCCCC
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; and e=char -> l=char
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; Calculate location of the character font data in p64_charset
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; Formula: p64_charset + 7 * INT ((char-32)/2) - 1
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ld h, b ; now HL = char (because b=0)
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srl l ; now HL = INT (char/2)
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ld c, l ; now BC = INT (char/2)
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add hl, hl ; now HL = 2 * INT (char/2)
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add hl, hl ; now HL = 4 * INT (char/2)
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add hl, hl ; now HL = 8 * INT (char/2)
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sbc hl, bc ; now HL = 7 * INT (char/2)
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ld bc, p64_charset - 71h
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add hl, bc ; now HL = p64_charset + 7 * INT (char/2) - 0x71
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; Main loop to copy 8 font bytes into screen (1 blank + 7 from font data)
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xor a ; first font byte is always blank
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ld b, 8 ; execute loop 8 times
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BLp64_INIT_RLC:
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rlca ; switch position between bits 0-3 and bits 4-7
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rlca
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rlca
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rlca
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BLp64_SKIP_RLC:
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; -----------------------------------------------------------------------------
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; STANDARD OR INVERSE
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;
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BLp64_INV_C: nop ; either 'NOP' or 'CPL' (modified)
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; -----------------------------------------------------------------------------
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BLp64_FONT_MASK:
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and %11110000 ; mask half of the font byte
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ld c, a ; store half of the font byte in C
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ld a, (de) ; get screen byte
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BLp64_SCR_MASK:
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and %00001111 ; mask half of the screen byte
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or c ; combine half screen and half font
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ld (de), a ; write result back to screen
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inc d ; next screen location
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inc hl ; next font data location
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ld a, (hl) ; store next font byte in A
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djnz BLp64_INIT_RLC ; repeat loop 8 times (this instruction gets modified)
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BLp64_END_LOOP:
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; attributes
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ld de,(p64_coords) ; grab coords
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and a ; clear carry
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rr e ; divide x by 2 to get bytes instead of nybbles
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ld a, d ; Get Y coord
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sra a ;
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sra a ;
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sra a ; Multiply by 8 60155 203 47
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add a, 88 ; Add to attrbute base address
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ld h, a ; Put high byte value for attribute into H.
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ld a, d ; get y value again
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and 7 ; set within third
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rrca ;
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rrca ;
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rrca ;
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add a, e ; add in x value
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ld l, a ; Put low byte for attribute into l
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ld a, (23693) ; Get permanent Colours from System Variable
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ld (hl), a ; Write new attribute
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pop hl ; restore AT_COL address
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inc (hl) ; next column
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bit 6, (hl) ; column lower than 64?
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ret z ; return if so
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BLp64_NEXT_ROW:
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ld (hl), b ; reset AT_COL
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inc hl ; store AT_ROW address in HL
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inc (hl) ; next row
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ld a, (hl)
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cp 24 ; row lower than 23?
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ret c ; return if so
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ld (hl), b ; reset AT_ROW
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ret ; done!
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end asm
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p64coords:
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asm
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p64_coords:
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defb 0; X Coordinate store
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defb 0; Y Coordinate Store
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p64_charset: ; 60230
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DEFB 2,2,2,2,0,2,0 ; Space !
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DEFB 80,82,7,2,7,2,0 ; " #
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DEFB 37,113,66,114,20,117,32 ; $ %
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DEFB 34,84,32,96,80,96,0 ; & '
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DEFB 36,66,66,66,66,36,0 ; ( )
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DEFB 0,82,34,119,34,82,0 ; * +
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DEFB 0,0,0,7,32,32,64 ; , -
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DEFB 1,1,2,2,100,100,0 ; . /
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DEFB 34,86,82,82,82,39,0 ; 0 1
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DEFB 34,85,18,33,69,114,0 ; 2 3
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DEFB 87,84,118,17,21,18,0 ; 4 5
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DEFB 55,65,97,82,84,36,0 ; 6 7
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DEFB 34,85,37,83,85,34,0 ; 8 9
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DEFB 0,2,32,0,34,2,4 ; : ;
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DEFB 0,16,39,64,39,16,0 ; < =
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DEFB 2,69,33,18,32,66,0 ; > ?
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DEFB 98,149,183,181,133,101,0 ; @ A
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DEFB 98,85,100,84,85,98,0 ; B C
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DEFB 103,84,86,84,84,103,0 ; D E
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DEFB 114,69,116,71,69,66,0 ; F G
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DEFB 87,82,114,82,82,87,0 ; H I
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DEFB 53,21,22,21,85,37,0 ; J K
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DEFB 69,71,71,69,69,117,0 ; L M
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DEFB 82,85,117,117,85,82,0 ; N O
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DEFB 98,85,85,103,71,67,0 ; P Q
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DEFB 98,85,82,97,85,82,0 ; R S
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DEFB 117,37,37,37,37,34,0 ; T U
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DEFB 85,85,85,87,39,37,0 ; V W
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DEFB 85,85,37,82,82,82,0 ; X Y
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DEFB 119,20,36,36,68,119,0 ; Z [
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DEFB 71,65,33,33,17,23,0 ; \ ]
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DEFB 32,112,32,32,32,47,0 ; ^ _
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DEFB 32,86,65,99,69,115,0 ; £ a
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DEFB 64,66,101,84,85,98,0 ; b c
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DEFB 16,18,53,86,84,35,0 ; d e
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DEFB 32,82,69,101,67,69,2 ; f g
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DEFB 66,64,102,82,82,87,0 ; h i
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DEFB 20,4,53,22,21,85,32 ; j k
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DEFB 64,69,71,71,85,37,0 ; l m
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DEFB 0,98,85,85,85,82,0 ; n o
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DEFB 0,99,85,85,99,65,65 ; p q
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DEFB 0,99,84,66,65,70,0 ; r s
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DEFB 64,117,69,69,85,34,0 ; t u
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DEFB 0,85,85,87,39,37,0 ; v w
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DEFB 0,85,85,35,81,85,2 ; x y
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DEFB 0,113,18,38,66,113,0 ; z {
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DEFB 32,36,34,35,34,36,0 ; | {
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DEFB 6,169,86,12,6,9,6 ; ~ (c)
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p64_END:
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End Asm
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End Sub
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```
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There's an example of usage here:
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```
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REM Example
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DIM n,x,y as uInteger
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CLS
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FOR n=1 to 1000
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y=rnd*23
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x=rnd*62
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ink rnd*8
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printat64(y, x)
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print64 ("ABCDEFGHIJKLMNOPQRSTUVWXYZ"(n MOD 26 TO n MOD 26))
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NEXT n
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END
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```

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