mirror of
https://github.com/thangisme/notes.git
synced 2024-06-11 19:01:00 +00:00
47 lines
1.5 KiB
JavaScript
47 lines
1.5 KiB
JavaScript
// Adapted from http://gimp.sourcearchive.com/documentation/2.6.6-1ubuntu1/color-to-alpha_8c-source.html
|
|
// toAlpha returns a color where the values of the argument have been converted to alpha
|
|
module.exports = function toAlpha(color) {
|
|
color.installMethod('toAlpha', function (color) {
|
|
var me = this.rgb(),
|
|
other = color(color).rgb(),
|
|
epsilon = 1e-10,
|
|
a = new color.RGB(0, 0, 0, me._alpha),
|
|
channels = ['_red', '_green', '_blue'];
|
|
|
|
channels.forEach(function (channel) {
|
|
if (me[channel] < epsilon) {
|
|
a[channel] = me[channel];
|
|
} else if (me[channel] > other[channel]) {
|
|
a[channel] = (me[channel] - other[channel]) / (1 - other[channel]);
|
|
} else if (me[channel] > other[channel]) {
|
|
a[channel] = (other[channel] - me[channel]) / other[channel];
|
|
} else {
|
|
a[channel] = 0;
|
|
}
|
|
});
|
|
|
|
if (a._red > a._green) {
|
|
if (a._red > a._blue) {
|
|
me._alpha = a._red;
|
|
} else {
|
|
me._alpha = a._blue;
|
|
}
|
|
} else if (a._green > a._blue) {
|
|
me._alpha = a._green;
|
|
} else {
|
|
me._alpha = a._blue;
|
|
}
|
|
|
|
if (me._alpha < epsilon) {
|
|
return me;
|
|
}
|
|
|
|
channels.forEach(function (channel) {
|
|
me[channel] = (me[channel] - other[channel]) / me._alpha + other[channel];
|
|
});
|
|
me._alpha *= a._alpha;
|
|
|
|
return me;
|
|
});
|
|
};
|