[elpa] 03/07: add xpm-m2z-circle.el

[Thien-Thi Nguyen]

ttn pushed a commit to branch ttn-xpm
in repository elpa.

commit fa7a06990f0d0c3159780b812e392b04d660a553
Author: Thien-Thi Nguyen <address@hidden>
Date:   Tue May 13 12:40:44 2014 +0200

    add xpm-m2z-circle.el
---
 packages/xpm/xpm-m2z-circle.el |   79 ++++++++++++++++++++++++++++++++++++++++
 1 files changed, 79 insertions(+), 0 deletions(-)

diff --git a/packages/xpm/xpm-m2z-circle.el b/packages/xpm/xpm-m2z-circle.el
new file mode 100644
index 0000000..8a744bc
--- /dev/null
+++ b/packages/xpm/xpm-m2z-circle.el
@@ -0,0 +1,79 @@
+;;; xpm-m2z-circle.el --- (% diameter 2) => 0    -*- lexical-binding: t -*-
+
+;; Copyright (C) 2014  Free Software Foundation, Inc.
+
+;; Author: Thien-Thi Nguyen <address@hidden>
+;; Version: -1
+
+;; This program 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 of the License, 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.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Although artist.el is wonderful, it doesn't (yet) do subpixel-centered
+;; circles (or ellipses).  This means that circles rendered by artist.el
+;; always have an "outer diameter" modulo 2 of 1, because the origin is
+;; *on* a pixel (i.e., coordinate, i.e., intersection of row and column).
+;; That's a bummer when you're trying to generate circles with outer
+;; diameter modulo 2 of 0 (hereby dubbed "m2z").
+;;
+;; This file adds provides func `xpm-m2z-circle' to locally rectify the
+;; current situation, with the hope that eventually a generalization can
+;; be worked back into artist.el, perhaps as a subpixel-center minor mode
+;; of some sort.
+
+;;; Code:
+
+(require 'artist)
+(require 'cl-lib)
+
+;;;###autoload
+(defun xpm-m2z-circle (cx cy radius)    ; => ((X . Y) ...)
+  "Return coords for a circle with center (CX,CY) and RADIUS.
+RADIUS must be integer and both CX and CY must be non-integer,
+preferably precisely half-way between integers, e.g., 13/2 => 6.5.
+The returned coordinates are unique but unordered."
+  (assert (not (integerp cx)))
+  (assert (not (integerp cy)))
+  (assert (integerp radius))
+  (when (< 0 radius)
+    (cl-flet*
+        ((offset (coord idx)
+                 (- (aref coord idx) 0.5))
+         (normal (coord)
+                 ;; flip axes: artist (ROW,COL) to xpm (X,Y)
+                 (cons
+                  (offset coord 1)      ; 1: COL -> car: X
+                  (offset coord 0)))    ; 0: ROW -> cdr: Y
+         (placed (origin scale n)
+                 (truncate (+ origin (* scale n))))
+         (orient (coords quadrant)
+                 (loop with (sx . sy) = quadrant
+                       for (x . y) in coords
+                       collect (cons (placed cx sx x)
+                                     (placed cy sy y)))))
+      (delete-dups
+       (loop with coords = (mapcar
+                            #'normal
+                            (artist-ellipse-generate-quadrant
+                             radius radius))
+             for quadrant               ; these are in order: I-IV
+             in '(( 1 .  1)             ; todo: "manually" remove single
+                  (-1 .  1)             ;       (border point) overlaps;
+                  (-1 . -1)             ;       zonk ‘delete-dups’
+                  ( 1 . -1))
+             append (orient coords quadrant))))))
+
+(provide 'xpm-m2z-circle)
+
+;;; xpm-m2z-circle.el ends here