/
DynamicCharAtlas.ts
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/
DynamicCharAtlas.ts
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/**
* Copyright (c) 2017 The xterm.js authors. All rights reserved.
* @license MIT
*/
import { DIM_OPACITY, IGlyphIdentifier, INVERTED_DEFAULT_COLOR } from './Types';
import { ICharAtlasConfig } from '../../shared/atlas/Types';
import { IColor } from '../../shared/Types';
import BaseCharAtlas from './BaseCharAtlas';
import { DEFAULT_ANSI_COLORS } from '../ColorManager';
import { clearColor } from '../../shared/atlas/CharAtlasGenerator';
import LRUMap from './LRUMap';
// In practice we're probably never going to exhaust a texture this large. For debugging purposes,
// however, it can be useful to set this to a really tiny value, to verify that LRU eviction works.
const TEXTURE_WIDTH = 1024;
const TEXTURE_HEIGHT = 1024;
const TRANSPARENT_COLOR = {
css: 'rgba(0, 0, 0, 0)',
rgba: 0
};
// Drawing to the cache is expensive: If we have to draw more than this number of glyphs to the
// cache in a single frame, give up on trying to cache anything else, and try to finish the current
// frame ASAP.
//
// This helps to limit the amount of damage a program can do when it would otherwise thrash the
// cache.
const FRAME_CACHE_DRAW_LIMIT = 100;
interface IGlyphCacheValue {
index: number;
isEmpty: boolean;
}
function getGlyphCacheKey(glyph: IGlyphIdentifier): string {
const styleFlags = (glyph.bold ? 0 : 4) + (glyph.dim ? 0 : 2) + (glyph.italic ? 0 : 1);
return `${glyph.bg}_${glyph.fg}_${styleFlags}${glyph.chars}`;
}
export default class DynamicCharAtlas extends BaseCharAtlas {
// An ordered map that we're using to keep track of where each glyph is in the atlas texture.
// It's ordered so that we can determine when to remove the old entries.
private _cacheMap: LRUMap<IGlyphCacheValue>;
// The texture that the atlas is drawn to
private _cacheCanvas: HTMLCanvasElement;
private _cacheCtx: CanvasRenderingContext2D;
// A temporary context that glyphs are drawn to before being transfered to the atlas.
private _tmpCtx: CanvasRenderingContext2D;
// The number of characters stored in the atlas by width/height
private _width: number;
private _height: number;
private _drawToCacheCount: number = 0;
constructor(document: Document, private _config: ICharAtlasConfig) {
super();
this._cacheCanvas = document.createElement('canvas');
this._cacheCanvas.width = TEXTURE_WIDTH;
this._cacheCanvas.height = TEXTURE_HEIGHT;
// The canvas needs alpha because we use clearColor to convert the background color to alpha.
// It might also contain some characters with transparent backgrounds if allowTransparency is
// set.
this._cacheCtx = this._cacheCanvas.getContext('2d', {alpha: true});
const tmpCanvas = document.createElement('canvas');
tmpCanvas.width = this._config.scaledCharWidth;
tmpCanvas.height = this._config.scaledCharHeight;
this._tmpCtx = tmpCanvas.getContext('2d', {alpha: this._config.allowTransparency});
this._width = Math.floor(TEXTURE_WIDTH / this._config.scaledCharWidth);
this._height = Math.floor(TEXTURE_HEIGHT / this._config.scaledCharHeight);
const capacity = this._width * this._height;
this._cacheMap = new LRUMap(capacity);
this._cacheMap.prealloc(capacity);
// This is useful for debugging
// document.body.appendChild(this._cacheCanvas);
}
public beginFrame(): void {
this._drawToCacheCount = 0;
}
public draw(
ctx: CanvasRenderingContext2D,
glyph: IGlyphIdentifier,
x: number,
y: number
): boolean {
const glyphKey = getGlyphCacheKey(glyph);
const cacheValue = this._cacheMap.get(glyphKey);
if (cacheValue !== null && cacheValue !== undefined) {
this._drawFromCache(ctx, cacheValue, x, y);
return true;
} else if (this._canCache(glyph) && this._drawToCacheCount < FRAME_CACHE_DRAW_LIMIT) {
let index;
if (this._cacheMap.size < this._cacheMap.capacity) {
index = this._cacheMap.size;
} else {
// we're out of space, so our call to set will delete this item
index = this._cacheMap.peek().index;
}
const cacheValue = this._drawToCache(glyph, index);
this._cacheMap.set(glyphKey, cacheValue);
this._drawFromCache(ctx, cacheValue, x, y);
return true;
}
return false;
}
private _canCache(glyph: IGlyphIdentifier): boolean {
// Only cache ascii and extended characters for now, to be safe. In the future, we could do
// something more complicated to determine the expected width of a character.
//
// If we switch the renderer over to webgl at some point, we may be able to use blending modes
// to draw overlapping glyphs from the atlas:
// https://github.com/servo/webrender/issues/464#issuecomment-255632875
// https://webglfundamentals.org/webgl/lessons/webgl-text-texture.html
return glyph.code < 256;
}
private _toCoordinates(index: number): [number, number] {
return [
(index % this._width) * this._config.scaledCharWidth,
Math.floor(index / this._width) * this._config.scaledCharHeight
];
}
private _drawFromCache(
ctx: CanvasRenderingContext2D,
cacheValue: IGlyphCacheValue,
x: number,
y: number
): void {
// We don't actually need to do anything if this is whitespace.
if (cacheValue.isEmpty) {
return;
}
const [cacheX, cacheY] = this._toCoordinates(cacheValue.index);
ctx.drawImage(
this._cacheCanvas,
cacheX,
cacheY,
this._config.scaledCharWidth,
this._config.scaledCharHeight,
x,
y,
this._config.scaledCharWidth,
this._config.scaledCharHeight
);
}
private _getColorFromAnsiIndex(idx: number): IColor {
if (idx < this._config.colors.ansi.length) {
return this._config.colors.ansi[idx];
}
return DEFAULT_ANSI_COLORS[idx];
}
private _getBackgroundColor(glyph: IGlyphIdentifier): IColor {
if (this._config.allowTransparency) {
// The background color might have some transparency, so we need to render it as fully
// transparent in the atlas. Otherwise we'd end up drawing the transparent background twice
// around the anti-aliased edges of the glyph, and it would look too dark.
return TRANSPARENT_COLOR;
} else if (glyph.bg === INVERTED_DEFAULT_COLOR) {
return this._config.colors.foreground;
} else if (glyph.bg < 256) {
return this._getColorFromAnsiIndex(glyph.bg);
}
return this._config.colors.background;
}
private _getForegroundColor(glyph: IGlyphIdentifier): IColor {
if (glyph.fg === INVERTED_DEFAULT_COLOR) {
return this._config.colors.background;
} else if (glyph.fg < 256) {
// 256 color support
return this._getColorFromAnsiIndex(glyph.fg);
}
return this._config.colors.foreground;
}
// TODO: We do this (or something similar) in multiple places. We should split this off
// into a shared function.
private _drawToCache(glyph: IGlyphIdentifier, index: number): IGlyphCacheValue {
this._drawToCacheCount++;
this._tmpCtx.save();
// draw the background
const backgroundColor = this._getBackgroundColor(glyph);
// Use a 'copy' composite operation to clear any existing glyph out of _tmpCtxWithAlpha, regardless of
// transparency in backgroundColor
this._tmpCtx.globalCompositeOperation = 'copy';
this._tmpCtx.fillStyle = backgroundColor.css;
this._tmpCtx.fillRect(0, 0, this._config.scaledCharWidth, this._config.scaledCharHeight);
this._tmpCtx.globalCompositeOperation = 'source-over';
// draw the foreground/glyph
const fontWeight = glyph.bold ? this._config.fontWeightBold : this._config.fontWeight;
const fontStyle = glyph.italic ? 'italic' : '';
this._tmpCtx.font =
`${fontStyle} ${fontWeight} ${this._config.fontSize * this._config.devicePixelRatio}px ${this._config.fontFamily}`;
this._tmpCtx.textBaseline = 'top';
this._tmpCtx.fillStyle = this._getForegroundColor(glyph).css;
// Apply alpha to dim the character
if (glyph.dim) {
this._tmpCtx.globalAlpha = DIM_OPACITY;
}
// Draw the character
this._tmpCtx.fillText(glyph.chars, 0, 0);
this._tmpCtx.restore();
// clear the background from the character to avoid issues with drawing over the previous
// character if it extends past it's bounds
const imageData = this._tmpCtx.getImageData(
0, 0, this._config.scaledCharWidth, this._config.scaledCharHeight
);
let isEmpty = false;
if (!this._config.allowTransparency) {
isEmpty = clearColor(imageData, backgroundColor);
}
// copy the data from imageData to _cacheCanvas
const [x, y] = this._toCoordinates(index);
// putImageData doesn't do any blending, so it will overwrite any existing cache entry for us
this._cacheCtx.putImageData(imageData, x, y);
return {
index,
isEmpty
};
}
}