I was wondering if WebGL is considered stable enough to be enabled by default. It makes some PDFs render much faster and it has been off by default for a while now, so we have had quite some time to test it.

If we decide to enable WebGL by default, we should not forget to update https://github.com/mozilla/pdf.js/blob/master/extensions/chromium/preferences_schema.json#L39 as well.

/cc @yurydelendik 
/cc @Snuffleupagus (because IIRC you were testing WebGL too)

imgData,
      scaleX,
      skewX = 0,
      skewY = 0,
      scaleY,
      positions
    ) {
      if (!this.contentVisible) {
        return;
      }
      const width = imgData.width;
      const height = imgData.height;
      const fillColor = this.current.fillColor;
      const isPatternFill = this.current.patternFill;
      const maskCanvas = this.cachedCanvases.getCanvas(
        "maskCanvas",
        width,
        height
      );
      const maskCtx = maskCanvas.context;
      maskCtx.save();
      putBinaryImageMask(maskCtx, imgData);
      maskCtx.globalCompositeOperation = "source-in";
      maskCtx.fillStyle = isPatternFill
        ? fillColor.getPattern(maskCtx, this)
        : fillColor;
      maskCtx.fillRect(0, 0, width, height);
      maskCtx.restore();
      const ctx = this.ctx;
      for (let i = 0, ii = positions.length; i < ii; i += 2) {