lazy-widgets/dist/helpers/TextImageBitmap.js

Typescript retained mode GUI for the HTML canvas API

import { Msg } from '../core/Strings.js';
import { AsyncImageBitmap } from './AsyncImageBitmap.js';
import { measureTextDims } from './measureTextDims.js';
/**
 * Renders text as an ImageBitmap, which can then be used in widgets that
 * consume a {@link BackingMediaSource}, like {@link Icon}. Useful for using
 * font icons instead of images.
 *
 * Height is retreived by measuring the fontBoundingBoxAscent and
 * fontBoundingBoxDescent (falling back to actualBoundingBoxAscent and
 * actualBoundingBoxDescent), as well as the hangingBaseline (falling back to
 * the actualBoundingBoxAscent of the `M` character). Width is measured from the
 * text being rendered, however, it's set to be the same as the height if it's
 * smaller than the height to avoid issues with thin font icons (such as
 * vertical ellipsis). The font is assumed to already be loaded by the time this
 * class is instantiated.
 *
 * Throws if a scratch canvas can't be created.
 */
export class TextImageBitmap extends AsyncImageBitmap {
    constructor(text, font, fillStyle, options) {
        var _a, _b, _c, _d;
        super();
        this.text = text;
        this.font = font;
        this.fillStyle = fillStyle;
        this._bitmap = null;
        this._presentationHash = -1;
        const metrics = measureTextDims(text, font);
        const ascent = (_a = metrics.fontBoundingBoxAscent) !== null && _a !== void 0 ? _a : metrics.actualBoundingBoxAscent;
        const descent = (_b = metrics.fontBoundingBoxDescent) !== null && _b !== void 0 ? _b : metrics.actualBoundingBoxDescent;
        const hangingBaseline = (_c = metrics.hangingBaseline) !== null && _c !== void 0 ? _c : measureTextDims('M', font).actualBoundingBoxAscent;
        const pad = Math.max(ascent - hangingBaseline, descent);
        this.height = hangingBaseline + pad * 2;
        this.width = Math.max(metrics.width, this.height);
        this.resolution = (_d = options === null || options === void 0 ? void 0 : options.resolution) !== null && _d !== void 0 ? _d : 1;
        const canvas = document.createElement('canvas');
        canvas.width = this.width;
        canvas.height = this.height;
        const context = canvas.getContext('2d');
        if (!context) {
            throw new Error(Msg.CANVAS_CONTEXT);
        }
        context.textAlign = 'center';
        context.font = font;
        context.fillStyle = fillStyle;
        context.fillText(text, this.width * 0.5, this.height - pad);
        createImageBitmap(canvas).then((bitmap) => {
            this._presentationHash++;
            this._bitmap = bitmap;
        });
    }
    get bitmap() {
        return this._bitmap;
    }
    get presentationHash() {
        return this._presentationHash;
    }
}
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