1 files changed, 69 insertions, 0 deletions
diff --git a/gnu/build/svg.scm b/gnu/build/svg.scm
new file mode 100644
index 0000000000..d9b909cd73
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+++ b/gnu/build/svg.scm
@@ -0,0 +1,69 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2015 Andy Wingo <wingo@igalia.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix 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.
+;;;
+;;; GNU Guix 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 GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu build svg)
+  #:use-module (srfi srfi-11)
+  #:export (svg->png))
+
+;; We need Guile-RSVG and Guile-Cairo.  Load them lazily, at run time, to
+;; allow compilation to proceed.
+(module-use! (current-module) (resolve-interface '(rsvg)))
+(module-use! (current-module) (resolve-interface '(cairo)))
+
+(define* (downscaled-surface surface
+                             #:key
+                             source-width source-height
+                             width height)
+  "Return a new rendering context where SURFACE is scaled to WIDTH x HEIGHT."
+  (let ((cr (cairo-create (cairo-image-surface-create 'argb32
+                                                      width height))))
+    (cairo-scale cr (/ width source-width) (/ height source-height))
+    (cairo-set-source-surface cr surface 0 0)
+    (cairo-pattern-set-filter (cairo-get-source cr) 'best)
+    (cairo-rectangle cr 0 0 source-width source-height)
+    (cairo-fill cr)
+    cr))
+
+(define* (svg->png in-svg out-png
+                   #:key width height)
+  "Render the file at IN-SVG as a PNG file in OUT-PNG.  When WIDTH and HEIGHT
+are provided, use them as the dimensions of OUT-PNG; otherwise preserve the
+dimensions of IN-SVG."
+  (define svg
+    (rsvg-handle-new-from-file in-svg))
+
+  (let-values (((origin-width origin-height)
+                (rsvg-handle-get-dimensions svg)))
+    (let* ((surf (cairo-image-surface-create 'argb32
+                                             origin-width origin-height))
+           (cr   (cairo-create surf)))
+      (rsvg-handle-render-cairo svg cr)
+      (cairo-surface-flush surf)
+      (let ((cr (if (and width height
+                         (not (= width origin-width))
+                         (not (= height origin-height)))
+                    (downscaled-surface surf
+                                        #:source-width origin-width
+                                        #:source-height origin-height
+                                        #:width width
+                                        #:height height)
+                    cr)))
+        (cairo-surface-write-to-png (cairo-get-target cr) out-png)))))
+
+;;; svg.scm ends here