Apple-2-SW/apple2_hgr_font_tutorial
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Fix spelling, and added 7x8 cell calc

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Michaelangel007 2016-01-11 14:21:16 -08:00
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1 changed files with 8 additions and 2 deletions
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README.md
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@ -238,7 +238,13 @@ Here's the [Javascript source code](list_hgr_table.html) to generate this table:
### No FONT data in ROM ### No FONT data in ROM
Second, each glyph in the Apple font is in a 7x8 cell -- the leading line on the bottom is usually blank but we'll store that too so that we have a true "underline" and bottom descender on 'j', 'y', etc. Second, each glyph in the Apple font is in a 7x8 cell -- the leading line on the bottom is usually blank but we'll store that too so that we have a true "underline" and bottom descender on 'j', 'y', etc. How do we know this?
The `TEXT` screen is 40x24 characters. The high resolution graphics `HGR` screen is 280x192.
Char Width (px/character) = Screen Width (px) / Columns (characters) = 280/40 = 7
Char Height (px/character) = Screen Height (px) / Rows (characters) = 192/24 = 8
Unfortunately, the data for the TEXT ROM 25123 hardware chip is **not** accessible from the 6502. :-/ This means you will need to manually enter in the 8 bytes/character. :-( The good news is that I've already done this so you can copy / paste. :-) Unfortunately, the data for the TEXT ROM 25123 hardware chip is **not** accessible from the 6502. :-/ This means you will need to manually enter in the 8 bytes/character. :-( The good news is that I've already done this so you can copy / paste. :-)
@ -328,7 +334,7 @@ Enter in:
![Screenshot 5](pics/hgrfont_05.png?raw=true) ![Screenshot 5](pics/hgrfont_05.png?raw=true)
We actually _also_ need to move the right-edge pixel of these 2 scanlins over left by 1 pixel so it appears in the correct location when shifted: We actually _also_ need to move the right-edge pixel of these 2 scanlines over left by 1 pixel so it appears in the correct location when shifted:
2304:22 2304:22
2704:92 ; 2704:92 ;