Add dummy gamma adjustment method

This method does not do anything but print the temperature to the terminal.
An external program implementing a color temperature adjustment scheme that
is not supported by redshift can use this method to determine the desired
color temperature. It is also useful for testing other parts of redshift on
systems where neither RandR nor VidMode works.

src/Makefile.am

@@ -14,7 +14,8 @@ redshift_SOURCES = \
 	config-ini.c config-ini.h \
 	location-manual.c location-manual.h \
 	solar.c solar.h \
-	systemtime.c systemtime.h
+	systemtime.c systemtime.h \
+	gamma-dummy.c gamma-dummy.h
 
 EXTRA_redshift_SOURCES = \
 	gamma-randr.c gamma-randr.h \

src/gamma-dummy.c

@@ -0,0 +1,76 @@
+/* gamma-randr.c -- No-op gamma adjustment
+   This file is part of Redshift.
+
+   Redshift 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.
+
+   Redshift 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 Redshift.  If not, see <http://www.gnu.org/licenses/>.
+
+   Copyright (c) 2013  Jon Lund Steffensen <jonlst@gmail.com>
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#ifdef ENABLE_NLS
+# include <libintl.h>
+# define _(s) gettext(s)
+#else
+# define _(s) s
+#endif
+
+#include "gamma-randr.h"
+
+
+int
+gamma_dummy_init(void *state)
+{
+	return 0;
+}
+
+int
+gamma_dummy_start(void *state)
+{
+	fputs(_("WARNING: Using dummy gamma method! Display will not be affected by this gamma method.\n"), stderr);
+	return 0;
+}
+
+void
+gamma_dummy_restore(void *state)
+{
+}
+
+void
+gamma_dummy_free(void *state)
+{
+}
+
+void
+gamma_dummy_print_help(FILE *f)
+{
+	fputs(_("Does not affect the display but prints the color temperature to the terminal.\n"), f);
+	fputs("\n", f);
+}
+
+int
+gamma_dummy_set_option(void *state, const char *key, const char *value)
+{
+	fprintf(stderr, _("Unknown method parameter: `%s'.\n"), key);
+	return -1;
+}
+
+int
+gamma_dummy_set_temperature(void *state, int temp, float brightness,
+			    float gamma[3])
+{
+	printf(_("Temperature: %i\n"), temp);
+	return 0;
+}

src/gamma-dummy.h

@@ -0,0 +1,38 @@
+/* gamma-dummy.h -- No-op gamma adjustment header
+   This file is part of Redshift.
+
+   Redshift 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.
+
+   Redshift 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 Redshift.  If not, see <http://www.gnu.org/licenses/>.
+
+   Copyright (c) 2013  Jon Lund Steffensen <jonlst@gmail.com>
+*/
+
+#ifndef _REDSHIFT_GAMMA_DUMMY_H
+#define _REDSHIFT_GAMMA_DUMMY_H
+
+#include "redshift.h"
+
+
+int gamma_dummy_init(void *state);
+int gamma_dummy_start(void *state);
+void gamma_dummy_free(void *state);
+
+void gamma_dummy_print_help(FILE *f);
+int gamma_dummy_set_option(void *state, const char *key, const char *value);
+
+void gamma_dummy_restore(void *state);
+int gamma_dummy_set_temperature(void *state, int temp, float brightness,
+				float gamma[3]);
+
+
+#endif /* ! _REDSHIFT_GAMMA_DUMMY_H */

src/redshift.c

@@ -51,11 +51,7 @@
 #define MAX(x,y)  ((x) > (y) ? (x) : (y))
 
 
-#if !(defined(ENABLE_RANDR) ||			\
-      defined(ENABLE_VIDMODE) ||		\
-      defined(ENABLE_WINGDI))
-# error "At least one of RANDR, VidMode or WinGDI must be enabled."
-#endif
+#include "gamma-dummy.h"
 
 #ifdef ENABLE_RANDR
 # include "gamma-randr.h"
@@ -133,6 +129,16 @@ static const gamma_method_t gamma_methods[] = {
 		(gamma_method_set_temperature_func *)w32gdi_set_temperature
 	},
 #endif
+	{
+		"dummy",
+		(gamma_method_init_func *)gamma_dummy_init,
+		(gamma_method_start_func *)gamma_dummy_start,
+		(gamma_method_free_func *)gamma_dummy_free,
+		(gamma_method_print_help_func *)gamma_dummy_print_help,
+		(gamma_method_set_option_func *)gamma_dummy_set_option,
+		(gamma_method_restore_func *)gamma_dummy_restore,
+		(gamma_method_set_temperature_func *)gamma_dummy_set_temperature
+	},
 	{ NULL }
 };