DOC: Add make rule and bash script to run doxygen

The output directory is not defined by the DOXYGEN_OUTPUT_DIRECTORY
environment variable instead of being hardcoded to `html`. Both the
make rule and the bash script set that variable to `html` by default,
but in the case of the bash script we can override it by defining
the variable in the environement before running the script.

Makefile.common

@@ -35,7 +35,8 @@ MODULES += \
 	graphics \
 	audio \
 	common \
-	po
+	po \
+	doc
 
 ifdef USE_MT32EMU
 MODULES += audio/softsynth/mt32

doc/doxygen/run_doxygen.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+DOX_DIR="$(cd $(dirname ${BASH_SOURCE[0]}) && pwd)"
+if [ -z "$DOXYGEN_OUTPUT_DIRECTORY" ] ; then
+	export DOXYGEN_OUTPUT_DIRECTORY=${DOX_DIR}/html
+fi
+echo "Generating reference documentation in ${DOXYGEN_OUTPUT_DIRECTORY}..."
+cd ${DOX_DIR}
+doxygen scummvm.doxyfile

doc/doxygen/scummvm.doxyfile

@@ -58,7 +58,7 @@ PROJECT_LOGO           = buildfiles/scummvm_logo.png
 # entered, it will be relative to the location where doxygen was started. If
 # left blank the current directory will be used.
 
-OUTPUT_DIRECTORY       = html/
+OUTPUT_DIRECTORY       = $(DOXYGEN_OUTPUT_DIRECTORY)
 
 # If the CREATE_SUBDIRS tag is set to YES then doxygen will create 4096 sub-
 # directories (in 2 levels) under the output directory of each output format and
@@ -781,7 +781,7 @@ WARN_FORMAT            = "$file:$line: $text"
 # messages should be written. If left blank the output is written to standard
 # error (stderr).
 
-WARN_LOGFILE           = html/doxygen_warnings.txt
+WARN_LOGFILE           = doxygen_warnings.txt
 
 #---------------------------------------------------------------------------
 # Configuration options related to the input files
@@ -2481,4 +2481,4 @@ GENERATE_LEGEND        = YES
 DOT_CLEANUP            = YES
 
 
-@INCLUDE = links.doxyfile
+@INCLUDE = links.doxyfile

doc/module.mk

@@ -0,0 +1,14 @@
+DOXYGEN_OUTPUT_DIRECTORY := html
+export DOXYGEN_OUTPUT_DIRECTORY
+
+doxygen:
+	@echo "Generating reference documentation in $(srcdir)/doc/doxygen/${DOXYGEN_OUTPUT_DIRECTORY}..."
+	@cd $(srcdir)/doc/doxygen ; doxygen scummvm.doxyfile
+
+clean-doxygen:
+	rm -rf $(srcdir)/doc/doxygen/html
+	rm -f $(srcdir)/doc/doxygen/doxygen_warnings.txt
+
+doc: doxygen
+
+clean-doc: clean-doxygen