Use alpha compositing to add ivy-current-match face

* ivy.el (ivy--exhibit): Use `colir-blend-face-background'. In case it
  fails, try `font-lock-append-text-property', which was used before.

* colir.el (colir-join): New defun.
(colir-blend): New defun.
(colir-blend-face-background): New defun.

diff --git a/colir.el b/colir.el
new file mode 100644 (file)
index 0000000..734f902
--- /dev/null
+++ b/colir.el
@@ -0,0 +1,79 @@
+;;; colir.el --- Color blending library -*- lexical-binding: t -*-
+
+;; Copyright (C) 2015  Free Software Foundation, Inc.
+
+;; Author: Oleh Krehel <ohwoeowho@gmail.com>
+
+;; This file is part of GNU Emacs.
+
+;; This file is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 3, or (at your option)
+;; any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; For a full copy of the GNU General Public License
+;; see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+;; This package solves the problem of adding a face with a background
+;; to text which may already have a background.  In all conflicting
+;; areas, instead of choosing either the original or the new
+;; background face, their alpha blended sum is used.
+
+;;; Code:
+
+(defun colir-join (r g b)
+  "Build a color from R G B.
+Inverse of `color-values'."
+  (format "#%02x%02x%02x"
+          (ash r -8)
+          (ash g -8)
+          (ash b -8)))
+
+(defun colir-blend (c1 c2 &optional alpha)
+  "Blend the two colors C1 and C2 with ALPHA.
+C1 and C2 are in the format of `color-values'.
+ALPHA is a number between 0.0 and 1.0 which corresponds to the
+influence of C1 on the result."
+  (setq alpha (or alpha 0.5))
+  (apply #'colir-join
+         (cl-mapcar
+          (lambda (x y)
+            (round (+ (* x alpha) (* y (- 1 alpha)))))
+          c1 c2)))
+
+(defun colir-blend-face-background (start end face &optional object)
+  "Append to the face property of the text from START to END the face FACE.
+When the text already has a face with a non-plain background,
+blend it with the background of FACE.
+Optional argument OBJECT is the string or buffer containing the text.
+See also `font-lock-append-text-property'."
+  (let (next prev)
+    (while (/= start end)
+      (setq next (next-single-property-change start 'face object end)
+            prev (get-text-property start 'face object))
+      (if prev
+          (let ((background-prev (face-background prev)))
+            (progn
+              (put-text-property
+               start next 'face
+               (if background-prev
+                   (cons `(background-color
+                           . ,(colir-blend
+                               (color-values background-prev)
+                               (color-values (face-background face nil t))))
+                         prev)
+                 (list face prev))
+               object)))
+        (put-text-property start next 'face face object))
+      (setq start next))))
+
+(provide 'colir)
+
+;;; colir.el ends here

diff --git a/ivy.el b/ivy.el
index a58df5694290f964251d54a937e4acb30f2ef7ff..a1c088f8137d449a6c3bcc072c889beaaa76c913 100644 (file)
--- a/ivy.el
+++ b/ivy.el
@@ -788,8 +788,12 @@ Should be run via minibuffer `post-command-hook'."
   "Propertize STR with FACE.
 `font-lock-append-text-property' is used, since it's better than
 `propertize' or `add-face-text-property' in this case."
-  (ignore-errors
-    (font-lock-append-text-property 0 (length str) 'face face str))
+  (require 'colir)
+  (condition-case nil
+      (colir-blend-face-background 0 (length str) face str)
+    (error
+     (ignore-errors
+       (font-lock-append-text-property 0 (length str) 'face face str))))
   str)
 
 (defun ivy--filter (name candidates)