Emacs: rainbow-identifiers

From Amit’s Thoughts

After reading Evan Brook's post about using text editor colors for identifiers instead of keywords, I decided to try the Emacs rainbow-identifiers and color-identifiers-mode. I find rainbow-identifiers easier to configure (it's language agnostic), and the color choices are stable while editing. I find color-identifiers to generate better output when reading code. It highlights only the local identifiers instead of all words, so the colors are more meaningful. Try both and see which works best for you.

Before, using colors for keywords:

var edges = this.graph.edges_from(this.curr);
for (var i = 0; i < edges.length; i++) {
    var next = edges[i];
    var edge_weight = this.graph.edge_weight(this.curr, next);
    if (edge_weight != Infinity) {
        this.neighbors.push(next);
        mark_changed(next);
        if (!this.visited[next]) {
            this.g[next] = this.g[this.curr] + edge_weight;
            this.open.push(next);
            this.parent[next] = this.curr;
            this.visited[next] = true;
        }
    }
}

After, using rainbow-colors mode:

var edges = this.graph.edges_from(this.curr);
for (var i = 0; i < edges.length; i++) {
    var next = edges[i];
    var edge_weight = this.graph.edge_weight(this.curr, next);
    if (edge_weight != Infinity) {
        this.neighbors.push(next);
        mark_changed(next);
        if (!this.visited[next]) {
            this.g[next] = this.g[this.curr] + edge_weight;
            this.open.push(next);
            this.parent[next] = this.curr;
            this.visited[next] = true;
        }
    }
}

After, using color-identifiers mode (notice how it uses colors for fewer identifiers, so they stand out better):

var edges = this.graph.edges_from(this.curr);
for (var i = 0; i < edges.length; i++) {
    var next = edges[i];
    var edge_weight = this.graph.edge_weight(this.curr, next);
    if (edge_weight != Infinity) {
        this.neighbors.push(next);
        mark_changed(next);
        if (!this.visited[next]) {
            this.g[next] = this.g[this.curr] + edge_weight;
            this.open.push(next);
            this.parent[next] = this.curr;
            this.visited[next] = true;
        }
    }
}

Here's how — I first turned off font-lock colors:

(set-face-attribute 'font-lock-comment-face nil :foreground nil :slant 'italic)
(set-face-attribute 'font-lock-comment-delimiter-face nil :slant 'italic)
(set-face-attribute 'font-lock-constant-face nil :foreground nil :underline t)
(set-face-attribute 'font-lock-type-face nil :foreground nil)
(set-face-attribute 'font-lock-function-name-face nil :foreground nil :weight 'bold)
(set-face-attribute 'font-lock-variable-name-face nil :foreground nil)
(set-face-attribute 'font-lock-keyword-face nil :foreground nil :slant 'italic)
(set-face-attribute 'font-lock-string-face nil :background "#e0e0e0")
(set-face-attribute 'font-lock-builtin-face nil :foreground nil :slant 'italic)

Second, I want colors chosen from L*a*b* color space because it makes the perceived brightness consistent across colors. It turns out color-identifiers mode already uses L*a*b* colors. In rainbow-identifiers mode, I configured it like this:

(loop for i from 1 to 15 do
      (let* ((lightness 45)
             (saturation 40)
             (angle (* 2 pi (/ i 15.0)))
             (a (* saturation (cos angle)))
             (b (* saturation (sin angle))))
        (set-face-attribute 
             (intern (format "rainbow-identifiers-identifier-%s" i))
             nil
             :foreground (apply 'color-rgb-to-hex
                             (color-lab-to-srgb lightness a b)))))

This generates these colors:

rainbow-identifiers-identifier-1
rainbow-identifiers-identifier-2
rainbow-identifiers-identifier-3
rainbow-identifiers-identifier-4
rainbow-identifiers-identifier-5
rainbow-identifiers-identifier-6
rainbow-identifiers-identifier-7
rainbow-identifiers-identifier-8
rainbow-identifiers-identifier-9
rainbow-identifiers-identifier-10
rainbow-identifiers-identifier-11
rainbow-identifiers-identifier-12
rainbow-identifiers-identifier-13
rainbow-identifiers-identifier-14
rainbow-identifiers-identifier-15

Pretty! You can change the color selection by changing the lightness and saturation constants. I'll try this for a while. Update: [2014-05-15] rainbow-identifiers 0.1.3 now has an option for using L*a*b* colors without needing the above code. Use (setq rainbow-identifiers-choose-face-function 'rainbow-identifiers-cie-l*a*b*-choose-face)

Edit: [2014-05-18] The original post was about rainbow-identifiers mode; I updated it to also show color-identifiers mode.

Labels: emacs