Apple-2-SW/apple2_hgr_font_tutorial
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Claried "C:/Program Files (x86)/Git/bin/sh.exe"400, and added note about non-standard assembly

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michaelangel007 2016-01-10 14:44:25 -08:00
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@ -559,7 +559,7 @@ Assuming we want to draw the `A` glyph at the top-left of the screen we would ne
For simplicity, we're going to "quantize" our destination Y so that we render font glyphs only on the start of every 8 rows and every 7 pixel columns. If we then had the starting address we simply could move to the next scan line by successively adding $0400 to our destination screen pointer. For simplicity, we're going to "quantize" our destination Y so that we render font glyphs only on the start of every 8 rows and every 7 pixel columns. If we then had the starting address we simply could move to the next scan line by successively adding $0400 to our destination screen pointer.
How did I know $0400? One quirk of the HGR screen is that every 8 successive scan lines start this many bytes away. How did I know to use $0400 when going to the next line? One quirk of the HGR screen is that every 8 successive scan lines start this many bytes away. Refer back to the `HGR Memory-mapped IO` table listed above.
## DrawChar() version 1 ## DrawChar() version 1
@ -1449,6 +1449,8 @@ Michael "AppleWin Debug Dev"
Figure it out ! You have all the tools and knowledge. Figure it out ! You have all the tools and knowledge.
## Solution 2: ScrollHgrUpPixel() ## Solution 2: ScrollHgrUpPixel()
There are many different ways to solve this depending if we want to prioritize space or speed. There are many different ways to solve this depending if we want to prioritize space or speed.
@ -1675,11 +1677,11 @@ And let's try it out:
Sweet ! Sweet !
Here's the assembly to scroll the HGR screen up one pixel: Here's the (non-standard) assembly to scroll the HGR screen up one pixel: (I'm using the non-conventional `:` as an assembler end-of-statement sepearator to logically group the byte copies together.)
```assembly ```assembly
; FUNC: ScrollHgrUpPixel() = $1400 ; FUNC: ScrollHgrUpPixel() = $1400
1400: LDX #27 ; 39 columns 1400: LDX #27 ; 39 columns ; Src Y Dst Y
1402: .1 LDA $2400,X : STA $2000,X ; [ 1] -> [ 0] 1402: .1 LDA $2400,X : STA $2000,X ; [ 1] -> [ 0]
1408: LDA $2800,X : STA $2400,X ; [ 2] -> [ 1] 1408: LDA $2800,X : STA $2400,X ; [ 2] -> [ 1]
140E: LDA $2C00,X : STA $2800,X ; [ 3] -> [ 2] 140E: LDA $2C00,X : STA $2800,X ; [ 3] -> [ 2]