FruitMachine-Swift/FruitMachine/AppleI/Video/CharacterGenerator.swift

//
//  CharacterGenerator.swift
//  FruitMachine
//
//  Created by Christopher Rohl on 7/26/17.
//  Copyright © 2017 Christopher Rohl. All rights reserved.
//

import Cocoa

//The character generator ROM contains 64 8x5 glyphs.

class CharacterGenerator: NSObject {
    static let CHAR_WIDTH = 5
    static let CHAR_HEIGHT = 8
    
    var ROM: [UInt8]
    
    init(romPath: String) {
        ROM = [UInt8](repeating: 0xCC, count: 512)
        
        super.init()
        loadROM(path: romPath)
    }
    
    func loadROM(path: String) {
        do {
            let fileContent: NSData = try NSData(contentsOfFile: path)
            fileContent.getBytes(&ROM, range: NSRange(location: 0, length: 512))
        } catch {
            print(error)
        }
    }

    func getCharacterPixels(charIndex: UInt8) -> [UInt8] {
        var pixelArray = [UInt8](repeating: 0x00, count: CharacterGenerator.CHAR_HEIGHT)
        
        /* Instead of ignoring ASCII bit b6, we ignore bit b5. At the same time ASCII bit b6 must be inverted before it is fed to the character ROM. This way the entire character range from $40 to $7F will end up in the range $00 to $1F (twice of course). Now lower case characters are automatically translated into their corresponding upper case bit maps.
         */

        let convertedCharIndex = (charIndex & 0x1f) | (((charIndex ^ 0x40) & 0x40) >> 1)
        
        for scanlineIndex in 0..<CharacterGenerator.CHAR_HEIGHT {
            pixelArray[scanlineIndex] = ROM[scanlineIndex + (Int(convertedCharIndex) * CharacterGenerator.CHAR_HEIGHT)]
        }
        
        return pixelArray
    }
    
}