Apple-2-SW/apple2_hgr_font_tutorial
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Add more missing .ORG

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michaelangel007 2016-01-10 19:57:34 -08:00
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README.md
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@ -1,6 +1,6 @@
#Apple ]\[ HGR Font Tutorial
Revision: 17, Jan 10, 2016.
Revision: 18, Jan 10, 2016.
# Table of Contents
@ -614,15 +614,15 @@ Before we can start a simple `DrawChar(char c)` function, we also first need to
Here's the disassembly of our (hard-coded) DrawChar() program:
```assembly
; FUNC: DrawChar() = $0300
; FUNC: DrawChar()
; NOTES: A, X, Y is destroyed
.ORG $300
.ORG $0300
300: JSR ScreenPtrToTempPtr
303: LDA #00 ; glyph 'c' to draw (not used yet)
305: LDY #00 ; Y = column to draw at (hard-coded)
307: JMP _DrawChar
.ORG $352
.ORG $0352
352: _DrawChar
352: LDX #0
354: .1 LDA $6200,X ; A = font[ offset + i ]
@ -705,10 +705,11 @@ After drawing a character with `DrawChar()` it is handy if we can advance both:
* the pointer to the screen where the next glyph will be drawn
```assembly
; FUNC: IncCursorCol() = $0370
; FUNC: IncCursorCol()
; OUTPUT: Y-Register (column) is incremented
; Increment the cursor column and move the destination screen pointer back
; up 8 scan lines previously to what it was when DrawChar() was called.
.ORG $0370
370:C8 INY
371:18 CLC
372:A5 F6 LDA $F6
@ -829,10 +830,11 @@ 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:
```assembly
; FUNC: DrawCharCol( c, col ) = $033B
; FUNC: DrawCharCol( c, col )
; PARAM: A = glyph to draw
; PARAM: Y = column to draw at; $0 .. $27 (Columns 0 .. 39) (not modified)
; NOTES: X is destroyed
.ORG $033B
33B:48 PHA ; push c = %PQRSTUVW to draw
33C:29 1F AND #1F ; = %000STUVW R=0, Optimization: implicit CLC
33E:0A ASL ; c * 2 %00STUVW0
@ -850,7 +852,7 @@ Our prefix code to setup the source address becomes:
34F:8D 56 03 STA $356 ; AddressHi = FontHi + (c/32)
```
Recall we'll re-use our existing font drawing code at $0352:
Recall we'll re-use our existing font drawing code `_DrawChar` at $0352:
```assembly
352:A2 00 LDX #0
@ -1235,11 +1237,12 @@ And change the low byte to add `X` instead:
This is a little clunky but it is progress. Let's write the new SetCursorColRow() version with the CursorRow() inlined so we don't have to use a JSR.
```assembly
; FUNC: SetCursorColRow( col, row ) = $0379
; FUNC: SetCursorColRow( col, row )
; PARAM: X = column to draw at; $0 .. $27 (Columns 0 .. 39) (not modified)
; PARAM: Y = row to draw at; $0 .. $17 (Rows 0 .. 23) (not modified)
; NOTES: Version 3! X and Y is swapped from earlier version!
; [$F5] = HgrLo[ Y ] + ScreenLo + X
.ORG $0379
379:86 F5 STX $F5
37B:B9 00 64 LDA HgrLo,Y ; HgrLo[ row ]
37E:18 CLC
@ -1268,6 +1271,7 @@ Now that we have the basic print char working lets extend it to print a C-style
; FUNC: DrawString( *text ) = $038E
; PARAM: X = High byte of string address
; PARAM: Y = Low byte of string address
.ORG $038E
38E:84 F0 STY $F0
390:86 F1 STX $F1
392:A0 00 LDY #0