Fix up cmake stuff with help from franciscod and convert to PIL.

CMakeLists.txt

@@ -53,6 +53,7 @@ doxygen_configure(cpp/ py/)
 
 add_subdirectory(cpp/)
 add_subdirectory(py/)
+add_subdirectory(assets/)
 
 # process the included python sources, generate setup.py
 process_python_modules()

assets/CMakeLists.txt

@@ -1,9 +1,12 @@
-message("Cropping gaben.png to create placeholder icon...")
+message("Cropping gaben.png to create placeholder desktop icon...")
 
-execute_process(convert -crop 512x512+92+137 gaben.png "${CMAKE_BINARY_DIR}/assets/dist/openage.png")
+execute_process(COMMAND python3 -c "
+import PIL.Image;
+cropped=PIL.Image.open('${GLOBAL_ASSET_DIR}/gaben.png').crop((92,137,604,649));
+cropped.save('${CMAKE_BINARY_DIR}/dist/openage.png')")
 
 install(FILES ${GLOBAL_ASSET_DIR}/dist/openage.desktop
         DESTINATION ${CMAKE_INSTALL_PREFIX}/usr/share/applications)
 
-install(FILES ${CMAKE_BINARY_DIR}/assets/dist/openage.png
+install(FILES ${CMAKE_BINARY_DIR}/dist/openage.png
         DESTINATION ${CMAKE_INSTALL_PREFIX}/usr/share/pixmaps)