tethr/lib/CanvasMediaStream.js

Controlls USB-connected cameras, webcam, and smartphone camera from browser

export class CanvasMediaStream {
    #ctx = null;
    #stream = null;
    async begin(initialDraw, frameRequestRate = 60, size) {
        if (!this.#ctx) {
            const canvas = document.createElement('canvas');
            if (size) {
                canvas.width = size[0];
                canvas.height = size[1];
            }
            this.#ctx = canvas.getContext('2d');
        }
        await initialDraw();
        this.#stream = this.#ctx.canvas.captureStream(frameRequestRate);
        return this.#stream;
    }
    updateWithImage(image) {
        if (!this.#ctx) {
            throw new Error('CanvasMediaStream.begin() must be called first');
        }
        const sizeChanged = this.#ctx.canvas.width !== image.width ||
            this.#ctx.canvas.height !== image.height;
        if (sizeChanged) {
            this.#ctx.canvas.width = image.width;
            this.#ctx.canvas.height = image.height;
        }
        this.#ctx.drawImage(image, 0, 0);
    }
    end() {
        this.#stream?.getTracks().forEach(track => track.stop());
    }
}
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