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* Lazy Font Loader - Only generates glyphs on demand
* This module provides a memory-efficient font loading system that generates
* character glyphs only when they are first needed, rather than pre-generating
* all 65,536 possible combinations (16 foregrounds × 16 backgrounds × 256 characters).
*/
import { createCanvas } from './ui.js';
import magicNumbers from './magicNumbers.js';
/**
* Creates a lazy font loader that generates glyphs on demand
* @param {Object} fontData - Font data with width, height, and bitmap data
* @param {Object} palette - Palette object with getRGBAColor method
* @param {boolean} letterSpacing - Whether to use letter spacing
* @param {number} scaleFactor - Scale factor for zoom (0.5x - 4x, default 1)
* @returns {Object} Lazy font object with methods for drawing and glyph access
*/
export const createLazyFont = (
fontData,
palette,
letterSpacing = false,
scaleFactor = 1,
) => {
// Cache for generated glyphs
const glyphCache = new Map();
const alphaGlyphCache = new Map();
const letterSpacingCache = new Map();
// Pre-generate bitmap data once
const bits = new Uint8Array(fontData.width * fontData.height * 256);
for (
let i = 0, k = 0;
i < (fontData.width * fontData.height * 256) / 8;
i += 1
) {
for (let j = 7; j >= 0; j -= 1, k += 1) {
bits[k] = (fontData.data[i] >> j) & 1;
}
}
// Calculate scaled dimensions
const scaledWidth = Math.floor(fontData.width * scaleFactor);
const scaledHeight = Math.floor(fontData.height * scaleFactor);
// Canvas for glyph generation at ORIGINAL size
const canvas = createCanvas(fontData.width, fontData.height);
const ctx = canvas.getContext('2d');
/**
* Generate a single glyph on demand with scaling
* @param {number} charCode - Character code (0-255)
* @param {number} foreground - Foreground color (0-15)
* @param {number} background - Background color (0-15)
* @returns {ImageData} Generated glyph image data at scaled size
*/
const getGlyph = (charCode, foreground, background) => {
// Include scaleFactor in cache key
const key = `${charCode}-${foreground}-${background}-${scaleFactor}`;
if (!glyphCache.has(key)) {
if (scaleFactor === 1) {
// No scaling - create directly at original size
const imageData = ctx.createImageData(fontData.width, fontData.height);
for (
let i = 0, j = charCode * fontData.width * fontData.height;
i < fontData.width * fontData.height;
i += 1, j += 1
) {
const color = palette.getRGBAColor(
bits[j] === 1 ? foreground : background,
);
imageData.data.set(color, i * 4);
}
glyphCache.set(key, imageData);
} else {
// Scaling needed - generate at original size, then scale
const tempCanvas = createCanvas(fontData.width, fontData.height);
const tempCtx = tempCanvas.getContext('2d');
const imageData = tempCtx.createImageData(
fontData.width,
fontData.height,
);
for (
let i = 0, j = charCode * fontData.width * fontData.height;
i < fontData.width * fontData.height;
i += 1, j += 1
) {
const color = palette.getRGBAColor(
bits[j] === 1 ? foreground : background,
);
imageData.data.set(color, i * 4);
}
tempCtx.putImageData(imageData, 0, 0);
// Scale using nearest-neighbor
const scaledCanvas = createCanvas(scaledWidth, scaledHeight);
const scaledCtx = scaledCanvas.getContext('2d');
scaledCtx.imageSmoothingEnabled = false;
scaledCtx.drawImage(
tempCanvas,
0,
0,
fontData.width,
fontData.height,
0,
0,
scaledWidth,
scaledHeight,
);
const scaledImageData = scaledCtx.getImageData(
0,
0,
scaledWidth,
scaledHeight,
);
glyphCache.set(key, scaledImageData);
}
}
return glyphCache.get(key);
};
/**
* Generate an alpha glyph (transparent background) with scaling
* @param {number} charCode - Character code
* @param {number} foreground - Foreground color (0-15)
* @returns {HTMLCanvasElement} Canvas with alpha glyph at scaled size
*/
const getAlphaGlyph = (charCode, foreground) => {
const key = `${charCode}-${foreground}-${scaleFactor}`;
if (!alphaGlyphCache.has(key)) {
// Only generate alpha glyphs for specific characters
Eif (
charCode === magicNumbers.LOWER_HALFBLOCK ||
charCode === magicNumbers.UPPER_HALFBLOCK ||
charCode === magicNumbers.CHAR_SLASH ||
charCode === magicNumbers.CHAR_PIPE ||
charCode === magicNumbers.CHAR_CAPITAL_X
) {
const imageData = ctx.createImageData(fontData.width, fontData.height);
for (
let i = 0, j = charCode * fontData.width * fontData.height;
i < fontData.width * fontData.height;
i += 1, j += 1
) {
if (bits[j] === 1) {
imageData.data.set(palette.getRGBAColor(foreground), i * 4);
}
}
const tempCanvas = createCanvas(fontData.width, fontData.height);
tempCanvas.getContext('2d').putImageData(imageData, 0, 0);
// Scale if needed
if (scaleFactor === 1) {
alphaGlyphCache.set(key, tempCanvas);
} else {
const scaledCanvas = createCanvas(scaledWidth, scaledHeight);
const scaledCtx = scaledCanvas.getContext('2d');
scaledCtx.imageSmoothingEnabled = false;
scaledCtx.drawImage(
tempCanvas,
0,
0,
fontData.width,
fontData.height,
0,
0,
scaledWidth,
scaledHeight,
);
alphaGlyphCache.set(key, scaledCanvas);
}
}
}
return alphaGlyphCache.get(key);
};
/**
* Get letter spacing image data for a specific color with scaling
* @param {number} colorIndex - Color index (0-15)
* @returns {ImageData} Letter spacing image data at scaled size
*/
const getLetterSpacingData = colorIndex => {
const key = `${colorIndex}-${scaleFactor}`;
if (!letterSpacingCache.has(key)) {
const spacingCanvas = createCanvas(1, scaledHeight);
const spacingCtx = spacingCanvas.getContext('2d');
const imageData = spacingCtx.getImageData(0, 0, 1, scaledHeight);
const color = palette.getRGBAColor(colorIndex);
for (let j = 0; j < scaledHeight; j++) {
imageData.data.set(color, j * 4);
}
letterSpacingCache.set(key, imageData);
}
return letterSpacingCache.get(key);
};
/**
* Pre-generate commonly used glyphs for instant access
* Common characters: space (32) and block characters (176, 177, 178, 219)
*/
const preGenerateCommonGlyphs = () => {
const commonChars = [
32, // Space
176, // Light block ░
177, // Medium block ▒
178, // Dark block ▓
219, // Full block █
];
for (let fg = 0; fg < 16; fg++) {
for (let bg = 0; bg < 16; bg++) {
commonChars.forEach(charCode => {
getGlyph(charCode, fg, bg);
});
}
}
// Also pre-generate alpha glyphs for special drawing characters
const alphaChars = [
magicNumbers.LOWER_HALFBLOCK,
magicNumbers.UPPER_HALFBLOCK,
magicNumbers.CHAR_SLASH,
magicNumbers.CHAR_PIPE,
magicNumbers.CHAR_CAPITAL_X,
];
for (let fg = 0; fg < 16; fg++) {
alphaChars.forEach(charCode => {
getAlphaGlyph(charCode, fg);
});
}
// Pre-generate all letter spacing data
if (letterSpacing) {
for (let i = 0; i < 16; i++) {
getLetterSpacingData(i);
}
}
};
// Pre-generate common glyphs on initialization
preGenerateCommonGlyphs();
return {
getData: () => fontData,
// Return scaled dimensions
getWidth: () =>
letterSpacing ? scaledWidth + Math.floor(1 * scaleFactor) : scaledWidth,
getHeight: () => scaledHeight,
getScaleFactor: () => scaleFactor,
getGlyph: getGlyph,
getAlphaGlyph: getAlphaGlyph,
getLetterSpacingData: getLetterSpacingData,
getCacheSize: () => glyphCache.size,
getAlphaCacheSize: () => alphaGlyphCache.size,
/**
* Draw a character at specified position (scaling handled internally)
* @param {number} charCode - Character code
* @param {number} foreground - Foreground color
* @param {number} background - Background color
* @param {CanvasRenderingContext2D} drawCtx - Canvas context to draw on
* @param {number} x - X coordinate in character grid
* @param {number} y - Y coordinate in character grid
*/
draw: (charCode, foreground, background, drawCtx, x, y) => {
const glyph = getGlyph(charCode, foreground, background);
if (letterSpacing) {
drawCtx.putImageData(
glyph,
x * (scaledWidth + Math.floor(1 * scaleFactor)),
y * scaledHeight,
);
} else {
drawCtx.putImageData(glyph, x * scaledWidth, y * scaledHeight);
}
},
/**
* Draw a character with alpha transparency (scaling handled internally)
* @param {number} charCode - Character code
* @param {number} foreground - Foreground color
* @param {CanvasRenderingContext2D} drawCtx - Canvas context to draw on
* @param {number} x - X coordinate in character grid
* @param {number} y - Y coordinate in character grid
*/
drawWithAlpha: (charCode, foreground, drawCtx, x, y) => {
// Use fallback character (X) if requested character has no alpha glyph
const effectiveCharCode = getAlphaGlyph(charCode, foreground)
? charCode
: magicNumbers.CHAR_CAPITAL_X;
const canvasToUse = getAlphaGlyph(effectiveCharCode, foreground);
if (letterSpacing) {
const effectiveWidth = scaledWidth + Math.floor(1 * scaleFactor);
drawCtx.drawImage(canvasToUse, x * effectiveWidth, y * scaledHeight);
// Handle special line drawing characters
Eif (effectiveCharCode >= 192 && effectiveCharCode <= 223) {
drawCtx.drawImage(
canvasToUse,
scaledWidth - 1,
0,
1,
scaledHeight,
x * effectiveWidth + scaledWidth,
y * scaledHeight,
1,
scaledHeight,
);
}
} else {
drawCtx.drawImage(canvasToUse, x * scaledWidth, y * scaledHeight);
}
},
};
};
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