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README.md
135
README.md
@ -565,7 +565,7 @@ If you were wondering how this data was generated, you see the great thing about
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<body onload="OnLoad()">
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<img id="Apple2eFont7x8" src="Apple2eFont7x8.png">
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<hr>
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<pre id="hexdump"></pre>
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<pre id="hexdump"></pre>IncCursorCol
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</body>
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</html>
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```
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@ -609,37 +609,47 @@ Before we can start a simple `DrawChar(char c)` function, we also first need to
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$F5 Low byte (16-bit address) Working pointer to screen byte
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$F6 High byte (16-bit address) Working pointer to screen byte
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```assembly
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HgrLo EQU $E5
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HgrHi EQU $E6
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TmpLo EQU $F5
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TmpHi EQU $F6
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```
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Here's the disassembly of our (hard-coded) DrawChar() program:
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```assembly
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; FUNC: DrawChar()
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; NOTES: A, X, Y is destroyed
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ORG $0300
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300: JSR ScreenPtrToTempPtr
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303: LDA #00 ; glyph 'c' to draw (not used yet)
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305: LDY #00 ; Y = column to draw at (hard-coded)
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307: JMP _DrawChar
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300:20 66 03 DrawChar JSR HgrToTmpPtr
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303:A9 00 LDA #00 ; glyph 'c' to draw (not used yet)
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305:A0 00 LDY #00 ; Y = column to draw at (hard-coded)
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307:4C 52 03 JMP _DrawChar
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ORG $0352
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352: _DrawChar
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352: LDX #0
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354: .1 LDA $6200,X ; A = font[ offset + i ]
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357: STA ($F5),Y ; screen[col] = A
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359: CLC
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35A: LDA $F6
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35C: ADC #4
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35E: STA $F6
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360: INX
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361: CPX #8
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363: BNE .1
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365: RTS
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352:A2 00 LDX #0 ; next instruction is Self-Modifying!
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354:BD 00 00 LoadFont LDA $0000,X ; A = font[ offset + i ]
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357:91 F5 STA (TmpLo),Y ; screen[col] = A
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359:18 CLC
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35A:A5 F6 LDA TmpHi
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35C:69 04 ADC #4 ; screen += 0x400
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35E:85 F6 STA TmpHi
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360:E8 INX
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361:E0 08 CPX #8
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363:D0 EF BNE LoadFont
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365:60 RTS
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; FUNC: ScreenPtrToTempPtr() = $0366
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366: LDA $E5 ; Copy initial screen
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368: STA $F5 ; destination pointer
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36A: LDA $E6 ; to working pointer
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36C: STA $F6
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36D: RTS
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; FUNC: HgrToTmpPtr()
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ORG $0366
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366: HgrToTmpPtr
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366:A5 E5 LDA HgrLo ; Copy initial screen
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368:85 F5 STA TmpLo ; destination pointer
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36A:A5 E6 LDA HgrHi ; to working pointer
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36C:85 F6 STA TmpHi
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36D:60 RTS
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```
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Enter in:
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@ -708,7 +718,7 @@ After drawing a character with `DrawChar()` it is handy if we can advance both:
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; Increment the cursor column and move the destination screen pointer back
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; up 8 scan lines previously to what it was when DrawChar() was called.
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ORG $0370
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370:C8 INY
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370:C8 IncCursorCol INY
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371:18 CLC
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372:A5 F6 LDA $F6
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374:E9 1F SBC #$1F
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@ -853,16 +863,18 @@ Our prefix code to setup the source address becomes:
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Recall we'll re-use our existing font drawing code `_DrawChar` at $0352:
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```assembly
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352:A2 00 LDX #0
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354:BD 00 00 LDA $0000,X ; A = font[ offset + i ]
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357:91 F5 STA ($F5),Y ; screen[col] = A
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ORG $0352
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352: _DrawChar
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352:A2 00 LDX #0 ; next instruction is Self-Modifying!
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354:BD 00 00 _Draw LDA $0000,X ; A = font[ offset + i ]
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357:91 F5 STA (TmpLo),Y ; screen[col] = A
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359:18 CLC
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35A:A5 F6 LDA $F6
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35A:A5 F6 LDA TmpHi
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35C:69 04 ADC #4 ; screen += 0x400
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35E:85 F6 STA $F6
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35E:85 F6 STA TmpHi
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360:E8 INX
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361:E0 08 CPX #8
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363:D0 EF BNE $304
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363:D0 EF BNE _Draw
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365:60 RTS
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```
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@ -974,7 +986,7 @@ Let's fix it up to print the hex value of the current character we are inspectin
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; PARAM: A = nibble to print as hex char
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1048:29 0F AND #F ; base 16
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104A:AA TAX ;
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104B:20 66 03 JSR ScreenPtrToTempPtr
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104B:20 66 03 JSR HgrToTmpPtr
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104E:BD 58 10 LDA NIB2HEX,X ; nibble to ASCII
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1051:C8 INY ; IncCursorCol()
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1052:20 3B 03 JSR $033B ; DrawCharCol()
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@ -1008,12 +1020,14 @@ And now we have our own DrawHexByte() function.
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Let's use IncCursorCol() to automatically advance the cusor. We'll also add a space after the character but before the hex value to improve readability of the output.
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```assembly
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; FUNC: PrintChar() = $0310
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; FUNC: PrintChar()
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; PARAM: A = glyph to draw
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; PARAM: Y = column to draw at; $0 .. $27 (Columns 0 .. 39) (not modified)
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; INPUT : $F5,$F6 pointer to the destination screen scanline
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; Must start at every 8 scanlines.
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; OUTPUT: The Y-Register (cursor column) is automatically incremented.
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ORG $0310
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310 PrintChar
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310:20 3B 03 JSR DrawCharCol
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313:4C 70 03 JMP IncCursorCol
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```
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@ -1113,13 +1127,13 @@ This is our mini HGR Y Address look-up table. "Funny" that it has 24 entries --
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Enter these bytes (or save [hgrtable.bin](hgrtable.bin) and `bload hgrtable.bin,6400`):
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Our `HgrLo` table:
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Our `HgrLoY` table:
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6400:00 80 00 80 00 80 00 80
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6408:28 A8 28 A8 28 A8 28 A8
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6410:50 D0 50 D0 50 D0 50 D0
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Our `HgrHi` table:
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Our `HgrHiY` table:
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6418:00 00 01 01 02 02 03 03
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6420:00 00 01 01 02 02 03 03
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@ -1130,14 +1144,16 @@ To save this AppleWin press `F7`, at the debugger console `bsave "hgrtable.bin",
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To select which row to draw at we'll pass that in the X register to our DrawCharColRow() routine:
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```assembly
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; FUNC: DrawCharColRow() = $0320
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; FUNC: DrawCharColRow()
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; PARAM: A = glyph to draw
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; PARAM: Y = column to draw at; $0 .. $27 (Columns 0 .. 39) (not modified)
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; PARAM: X = row to draw at; $0 .. $17 (Rows 0 .. 23) (destroyed)
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ORG $0320
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320: DrawCharColRow
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320:48 PHA
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321:20 28 03 JSR SetCursorRow
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324:68 PLA
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325:4C 3B 03 JMP DrawCharCol()
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325:4C 3B 03 JMP DrawCharCol
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; FUNC: SetCursorRow( row )
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; PARAM: X = row to draw at; $0 .. $17 (Rows 0 .. 23) (not modified)
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@ -1145,14 +1161,14 @@ To select which row to draw at we'll pass that in the X register to our DrawChar
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; Note: Must start at every 8 scanlines.
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; OUTPUT: $F5,$F5 working pointer to the destination screen scanline
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ORG $0328
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328:BD 00 64 LDA $6400,X ; HgrLo[ row ]
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328:BD 00 64 LDA HgrLoY,X ; HgrLoY[ row ]
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32B:18 CLC
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32C:65 E5 ADC $E5
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32E:85 F5 STA $F5
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330:BD 18 64 LDA $6418,X ; HgrHi[ row ]
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32C:65 E5 ADC HgrLo
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32E:85 F5 STA TmpLo
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330:BD 18 64 LDA HgrHiY,X ; HgrHiY[ row ]
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333:18 CLC
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334:65 E6 ADC $E6
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336:85 F6 STA $F6
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334:65 E6 ADC HgrHi
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336:85 F6 STA TmpHi
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338:60 RTS
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```
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@ -1166,10 +1182,11 @@ Enter in:
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Now we can print a char at any location:
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```assembly
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1100:A9 41 ; A-register = char
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1102:A0 01 ; Y-register = col 1 (2nd column)
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1104:A2 02 ; X-register = row 2 (3rd row)
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1106:4C 20 03 ; DrawCharColRow( c, col )
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ORG $1100
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1100:A9 41 LDA #41 ; A-register = char
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1102:A0 01 LDY #1 ; Y-register = col 1 (2nd column)
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1104:A2 02 LDX #2 ; X-register = row 2 (3rd row)
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1106:4C 20 03 JSR DrawCharColRow
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```
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Enter in:
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@ -1241,15 +1258,15 @@ This is a little clunky but it is progress. Let's write the new SetCursorColRow(
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; PARAM: X = column to draw at; $0 .. $27 (Columns 0 .. 39) (not modified)
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; PARAM: Y = row to draw at; $0 .. $17 (Rows 0 .. 23) (not modified)
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; NOTES: Version 3! X and Y is swapped from earlier version!
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; [$F5] = HgrLo[ Y ] + ScreenLo + X
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; [$F5] = HgrLoY[ Y ] + ScreenLo + X
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ORG $0379
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379:86 F5 STX $F5
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37B:B9 00 64 LDA HgrLo,Y ; HgrLo[ row ]
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37B:B9 00 64 LDA HgrLoY,Y ; HgrLoY[ row ]
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37E:18 CLC
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37F:65 E5 ADC $E5
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381:65 F5 ADC $F5 ; add column
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383:85 F5 STA $F5
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385:B9 18 64 LDA HgrHi,Y ; HgrHi[ row ]
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385:B9 18 64 LDA HgrHiY,Y ; HgrHiY[ row ]
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388:18 CLC
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389:65 E6 ADC $E6
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38B:85 F6 STA $F6
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@ -1417,7 +1434,7 @@ Technically, to convert the HGR high byte address to a Text high byte address, w
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Which we could do via:
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```assembly
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LDA HgrHi, Y ; Y is row
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LDA HgrHiY, Y ; Y is row
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AND #7 ; strip off top 6 bits
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OR #4 ; Set text page 1 = $0400
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````
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@ -1425,8 +1442,8 @@ Which we could do via:
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But we'll save a byte and use the normal subtraction instead:
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```assembly
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LDA HgrHi, Y ; Y is row
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CLC ; Convert HgrHi to TextHi byte
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LDA HgrHiY, Y ; Y is row
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CLC ; Convert HgrHiY to TextHiY byte
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SBC #$1B ; A -= 0x1C
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```
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@ -1439,11 +1456,11 @@ Here's the Pseudo-code to copy the text screen to the HGR Screen:
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```c
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for( row = 0; row < 24; row++ )
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{
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SrcTextLo = HgrLo[ row ];
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SrcTextHi = HgrHi[ row ] - 0x1C;
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SrcTextLo = HgrLoY[ row ];
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SrcTextHi = HgrHiY[ row ] - 0x1C;
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// SetCursorColRow( 0, row ) which does:
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DstHgrLo = HgrLo[ row ]
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DstHgrHi = HgrHi[ row ]
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DstHgrLo = HgrLoY[ row ]
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DstHgrHi = HgrHiY[ row ]
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for( col = 0; col < 40; col++ )
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{
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@ -1460,7 +1477,7 @@ And here is the assembly:
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; FUNC: CopyTextToHGR()
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; DATA:
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; $6000.$63FF Font 7x8 Data
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; $6400.$642F HgrLo, HgrHi table for every 8 scanlines
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; $6400.$642F HgrLoY, HgrHiY table for every 8 scanlines
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ORG $1300
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1300:A9 00 LDA #0
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1302:85 F3 STA row
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@ -1472,11 +1489,11 @@ And here is the assembly:
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130E:B0 20 BCS .3 ; Y >= 24
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1310:A2 00 LDX #0
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1312:86 F2 STX col ; X = col
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1314:20 79 03 JSR SetCursorColRow ; A = HgrHi[ row ]
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1317:18 CLC ; Convert HgrHi to TextHi byte
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1314:20 79 03 JSR SetCursorColRow ; A = HgrHiY[ row ]
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1317:18 CLC ; Convert HgrHiY to TextHiY byte
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1318:E9 1B SBC #$1B ; A -= 0x1C
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131A:85 F8 STA $F8
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131C:B9 00 64 LDA $6400, Y ; A = HgrLo[ row ]
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131C:B9 00 64 LDA $6400, Y ; A = HgrLoY[ row ]
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131F:85 F7 STA $F7
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1321:A4 F2 LDY col
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1323:B1 F7 .2 LDA ($F7),Y
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