Apple-2-SW/apple2_hgr_font_tutorial
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Start adding AppleWin symbols

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Michaelangel007 2016-01-11 14:42:51 -08:00
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README.md
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@ -618,19 +618,17 @@ How did I know to use $0400 when going to the next line? One quirk of the HGR s
Before we can start a simple `DrawChar(char c)` function, we also first need to assign some zero page memory locations for our static and temporary variables:
$E5 Low byte (16-bit address) Pointer to screen destination
$E6 High byte (16-bit Address) Pointer to screen destination
$F5 Low byte (16-bit address) Working pointer to screen byte
$F6 High byte (16-bit address) Working pointer to screen byte
```assembly
HgrLo EQU $E5
HgrHi EQU $E6
TmpLo EQU $F5
TmpHi EQU $F6
HgrLo EQU $E5 ; Low byte (16-bit address) Pointer to screen destination
HgrHi EQU $E6 ; High byte (16-bit Address) Pointer to screen destination
TmpLo EQU $F5 ; Low byte (16-bit address) Working pointer to screen byte
TmpHi EQU $F6 ; High byte (16-bit address) Working pointer to screen byte
Font EQU $6000
```
Since we also had our font data, we need a symbol for that.
Here's the disassembly of our (hard-coded) DrawChar() program:
```assembly
@ -665,6 +663,7 @@ Here's the disassembly of our (hard-coded) DrawChar() program:
036D:60 RTS
```
Enter in:
300:20 66 03 A9 00 A0 00 4C 52 03
@ -682,6 +681,22 @@ And with any luck you should see the at sign `@` in the top-left.
![Screenshot 8](pics/hgrfont_08.png?raw=true)
If you are using AppleWin, you can enter these symbols into the debugger to make the disassembly more readable. Press `F7`, then type in (paste with `Ctrl-V`):
sym HgrLo = E5
sym HgrHi = E6
sym TmpLo = F5
sym TmpHi = F6
sym DrawChar = 0300
sym _DrawChar = 0352
sym _LoadFont = 0354
sym HgrToTmpPtr = 0366
sym Font = 6000
352L
When you are done with the debugger, press `F7` to return to emulator.
## X Cursor Position
If we wanted to draw in columns 1 and 2 instead of column 0 then we need to set the Y register which controls which "column" we'll draw at.