gaussian & transparency issue

[incanus]

I'm not sure if I'm using things correctly, but I think I might have a bug in the way that the gaussian (as well as blur) filter works on transparent images.

Here is a test image pre-masked with text and then having the filter applied to the whole image:

Left side is actually transparent and will show through GitHub page color.

Steps to create:

1. Make a new 200x100 image
2. Set every pixel transparent white
3. Paint the right half fully opaque green
4. Use a fully opaque mask (default for new image)
5. Apply filter

I would expect that both texts would be blurred, but only the one with opacity is.

Am I using things wrong or is it a bug?

Code:

#!/usr/bin/env node

const { Image } = require('image-js');

async function test() {
    var image = new Image(200, 100);

    // set the whole image transparent white
    for (var x = 0; x < image.width; x++) {
      for (var y = 0; y < image.height; y++) {
        image.setPixelXY(x, y, [255, 255, 255, 0]);
      }
    }

    // paint the right half opaque green
    image = image.paintPolygon([
      [image.width / 2, 0],
      [image.width - 1, 0],
      [image.width - 1, image.height - 1],
      [image.width / 2, image.height - 1]
      ], {
        color: [0, 255, 0, 255],
        filled: true
      });

    mask = new Image(200, 100);

    const i = 2;

    image = image.paintMasks([mask, mask], {
      labels: ['r = ' + i, 'r = ' + i],
      labelsPosition: [[42, 55], [140, 55]],
      labelColor: 'black',
      labelFont: '12px Helvetica'
    });

    image = image.gaussianFilter({ radius: i });

    image.save('output' + i + '.png');
}

test();