Apple-2-SW/apple2_hgr_font_tutorial
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Fix up TOC DrawChar()

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michaelangel007 2016-01-10 18:47:18 -08:00
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#Apple ]\[ HGR Font Tutorial
Revision: 14, Jan 10, 2016.
Revision: 15, Jan 10, 2016.
# Table of Contents
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* Font Data
* Raw Font Data
* Image to Font Data (Javascript)
* Font -> Screen Memory Trace
* DrawChar version 1
* DrawChar()
* Font -> Screen Memory Trace
* DrawChar() version 1
* X Cursor Position
* CursorCol()
* DrawChar() version 2
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* Misc. Utilities and Files
* TODO
## Introduction
# Introduction
A lot of people in comp.sys.apple2.programmer and other places on the internet have wondered how to "print" text onto the Apple's High Resolution Graphics (HGR) screen. Here's a tutorial on "6502 Font Blitting."
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There are other emulators written in Javascript but they are poor due to 2 reasons:
* Don't support paste -- you'll be forced to manually enter in the hex code. :-/
* Don't support paste -- you'll be forced to manually enter in the hex code. :-/ Yeah, right!
* Don't emulate the half-pixel shift of real hardware at all.
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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.
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. :-)
You can find a picture of the Apple ][ ROM text font on Page 8-9, diagram 8.4 of "Understanding the Apple ]\["
https://archive.org/stream/understanding_the_apple_ii#page/n203/mode/2up
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Another solution is to use a web browser that isn't "broken" such as Firefox, etc. when trying to read _local_ files.
# DrawChar()
## Font -> Screen Memory Trace
OK, so now that we have the font data, how do we draw a character "on screen" ?