Allow greater flexibility with the trim feature about free-tex-packer

[odrick]

This is a very rare feature. And yes, right now ftp trimms by alpha only. I can suggest you to fork the project and implement the required functionality. Look at utils/Trimmer.js, https://github.com/odrick/free-tex-packer-core/blob/master/utils/Trimmer.js . Something like:

static getAlpha(data, width, x, y) {
    let pos = ((y * (width * 4)) + (x * 4));

    let r = data[pos];
    let g = data[pos + 1];
    let b = data[pos + 2];
    let a = data[pos + 3];

    if(r === 0 && g === 0 && b === 0) {
        return a;
    }
   
    return 1; 
}

[JannikGM]

This is a very rare feature.

My use-case is, but in general this should be an extremely common use-case, because it allows for additive blending if textures are stored in pre-multiplied alpha: https://github.com/dtrebilco/PreMulAlpha#the-three-in-one-blend-mode

So alpha = 0, but color in RGB, is often seen with particle systems (which is exactly when you'll want to use an atlas, so you can have many different particles in the same texture).