From 2bc167f8ee4d02e3fe35ac476558472b648ba867 Mon Sep 17 00:00:00 2001
From: Mike Gerwitz <mtg@gnu.org>
Date: Mon, 25 Mar 2019 14:00:27 -0400
Subject: [PATCH] XCF->PNG build

In the end it would have been easier just to use Imagemagick for this.  What
a mess.  Another example where a GUI seemed simple at first but then turned
out to be a poor tool for the job.
---
 Makefile              | 10 +++++++---
 build-aux/xcf2png.scm | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 3 deletions(-)
 create mode 100644 build-aux/xcf2png.scm

diff --git a/Makefile b/Makefile
index c1232d9..fba5f65 100644
--- a/Makefile
+++ b/Makefile
@@ -18,12 +18,16 @@
 
 default: slides.pdf
 
+xcfs = $(wildcard images/*.xcf)
+pngs = $(xcfs:.xcf=.png)
+
+.PRECIOUS: $(pngs)
+
 # TODO: No local init.el!  Isolate required options so that this is actually
 # portable!
-%.pdf: %.org %-preamble.tex
+%.pdf: %.org %-preamble.tex $(pngs)
 	emacs --batch -l ~/.emacs.d/init.el $< -f org-beamer-export-to-pdf
 
 # TODO: Either script with GIMP or just use ImageMagick and get rid of xcfs
 %.png: %.xcf
-	@echo 'Not yet implemented!' >&2
-	@false
+	GIMP_INPUT="$<" GIMP_OUTPUT="$@" gimp -ni -b - < build-aux/xcf2png.scm
diff --git a/build-aux/xcf2png.scm b/build-aux/xcf2png.scm
new file mode 100644
index 0000000..8633fd1
--- /dev/null
+++ b/build-aux/xcf2png.scm
@@ -0,0 +1,35 @@
+;;; Convert XCF files to PNG
+;;;
+;;;  Copyright (C) 2019 Mike Gerwitz
+;;;
+;;;  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/>.
+
+(let* ((input-filename  (getenv "GIMP_INPUT"))
+       (output-filename (getenv "GIMP_OUTPUT"))
+       (image           (car (gimp-file-load RUN-NONINTERACTIVE
+                                             input-filename
+                                             input-filename)))
+       (layer           (car (gimp-image-merge-visible-layers
+                              image
+                              CLIP-TO-IMAGE))))
+
+    (gimp-file-save RUN-NONINTERACTIVE
+                    image
+                    layer
+                    output-filename
+                    output-filename)
+
+    (gimp-image-delete image)
+    (gimp-quit 0))
+