Method readFramebufferRegion

src/webgl/p5.RendererGL.js:1778–1835

(framebuffer, x, y, w, h)

  }

  readFramebufferRegion(framebuffer, x, y, w, h) {
    const gl = this.GL;
    const colorFormat = this._getFramebufferColorFormat(framebuffer);

    const rawData = readPixelsWebGL(
      undefined,
      gl,
      framebuffer.framebuffer,
      x * framebuffer.density,
      y * framebuffer.density,
      w * framebuffer.density,
      h * framebuffer.density,
      colorFormat.format,
      colorFormat.type
    );

    // Framebuffer data might be either a Uint8Array or Float32Array
    // depending on its format, and it may or may not have an alpha channel.
    // To turn it into an image, we have to normalize the data into a
    // Uint8ClampedArray with alpha.
    const fullData = new Uint8ClampedArray(
      w * h * framebuffer.density * framebuffer.density * 4
    );
    // Default channels that aren't in the framebuffer (e.g. alpha, if the
    // framebuffer is in RGB mode instead of RGBA) to 255
    fullData.fill(255);

    const channels = colorFormat.format === gl.RGB ? 3 : 4;
    for (let yPos = 0; yPos < h * framebuffer.density; yPos++) {
      for (let xPos = 0; xPos < w * framebuffer.density; xPos++) {
        for (let channel = 0; channel < 4; channel++) {
          const idx = (yPos * w * framebuffer.density + xPos) * 4 + channel;
          if (channel < channels) {
            // Find the index of this pixel in `rawData`, which might have a
            // different number of channels
            const rawDataIdx = channels === 4
              ? idx
              : (yPos * w * framebuffer.density + xPos) * channels + channel;
            fullData[idx] = rawData[rawDataIdx];
          }
        }
      }
    }

    // Create image from data
    const region = new Image(w * framebuffer.density, h * framebuffer.density);
    region.imageData = region.canvas.getContext('2d').createImageData(
      region.width,
      region.height
    );
    region.imageData.data.set(fullData);
    region.pixels = region.imageData.data;
    region.updatePixels();
    if (framebuffer.density !== 1) {
      region.pixelDensity(framebuffer.density);
    }
    return region;
  }