Apple-2-SW/apple2_hgr_font_tutorial
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Fixup _DrawChar and bad DrawCharCol address comment

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michaelangel007 2016-01-10 19:34:04 -08:00
parent 2177111f62
commit c018dca939
1 changed files with 3 additions and 3 deletions
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@ -623,7 +623,7 @@ Here's the disassembly of our (hard-coded) DrawChar() program:
307: JMP _DrawChar 307: JMP _DrawChar
.ORG $352 .ORG $352
352: _DrawChar: 352: _DrawChar
352: LDX #0 352: LDX #0
354: .1 LDA $6200,X ; A = font[ offset + i ] 354: .1 LDA $6200,X ; A = font[ offset + i ]
357: STA ($F5),Y ; screen[col] = A 357: STA ($F5),Y ; screen[col] = A
@ -829,7 +829,7 @@ However we can save one instruction (and 2 cycles) if we optimize `c/32` to use
Our prefix code to setup the source address becomes: Our prefix code to setup the source address becomes:
```assembly ```assembly
; FUNC: DrawCharCol( c, col ) = $03BB ; FUNC: DrawCharCol( c, col ) = $033B
; PARAM: A = glyph to draw ; PARAM: A = glyph to draw
; PARAM: Y = column to draw at; $0 .. $27 (Columns 0 .. 39) (not modified) ; PARAM: Y = column to draw at; $0 .. $27 (Columns 0 .. 39) (not modified)
; NOTES: X is destroyed ; NOTES: X is destroyed
@ -974,7 +974,7 @@ Let's fix it up to print the hex value of the current character we are inspectin
; PARAM: A = nibble to print as hex char ; PARAM: A = nibble to print as hex char
1048:29 0F AND #F ; base 16 1048:29 0F AND #F ; base 16
104A:AA TAX ; 104A:AA TAX ;
104B:20 66 03 JSR $0366 ; update dest screen pointer 104B:20 66 03 JSR ScreenPtrToTempPtr
104E:BD 58 10 LDA $1058,X ; nibble to ASCII 104E:BD 58 10 LDA $1058,X ; nibble to ASCII
1051:C8 INY ; IncCursorCol() 1051:C8 INY ; IncCursorCol()
1052:20 3B 03 JSR $033B ; DrawCharCol() 1052:20 3B 03 JSR $033B ; DrawCharCol()