add brightness and contrast (#396)

* Imlib2 supports modifying gamma, brightness and contrast directly
  while sxiv only supports gamma. Makes sense to extend it to brightness
  and contrast as well.

* Since color corrections need to be aware of each other, they have been
  refactored into one centralized function.

* This also makes the code more hackable as it makes it easier to add
  more color correction functions without them interfering with each
  other.

Co-authored-by: 0ion9 <finticemo@gmail.com>
Co-authored-by: NRK <nrk@disroot.org>
Reviewed-on: https://codeberg.org/nsxiv/nsxiv/pulls/396
Reviewed-by: NRK <nrk@disroot.org>
Reviewed-by: TAAPArthur <taaparthur@noreply.codeberg.org>
Co-authored-by: Berke Kocaoğlu <kberke@metu.edu.tr>
Co-committed-by: Berke Kocaoğlu <kberke@metu.edu.tr>

commands.c

@@ -222,15 +222,28 @@ bool cg_navigate_marked(arg_t n)
 	return navigate_to(new);
 }
 
-bool cg_change_gamma(arg_t d)
+static bool change_color_modifier(arg_t d, int *target)
 {
-	if (img_change_gamma(&img, d * (prefix > 0 ? prefix : 1))) {
+	if (!img_change_color_modifier(&img, d * (prefix > 0 ? prefix : 1), target))
+		return false;
 	if (mode == MODE_THUMB)
 		tns.dirty = true;
 	return true;
-	} else {
-		return false;
 }
+
+bool cg_change_gamma(arg_t d)
+{
+	return change_color_modifier(d, &img.gamma);
+}
+
+bool cg_change_brightness(arg_t d)
+{
+	return change_color_modifier(d, &img.brightness);
+}
+
+bool cg_change_contrast(arg_t d)
+{
+	return change_color_modifier(d, &img.contrast);
 }
 
 bool ci_navigate(arg_t n)

commands.h

@@ -4,6 +4,8 @@
 
 /* global */
 bool cg_change_gamma(arg_t);
+bool cg_change_brightness(arg_t);
+bool cg_change_contrast(arg_t);
 bool cg_first(arg_t);
 bool cg_mark_range(arg_t);
 bool cg_n_or_last(arg_t);
@@ -47,6 +49,8 @@ bool ct_select(arg_t);
 #ifdef INCLUDE_MAPPINGS_CONFIG
 /* global */
 #define g_change_gamma { cg_change_gamma, MODE_ALL }
+#define g_change_brightness { cg_change_brightness, MODE_ALL }
+#define g_change_contrast { cg_change_contrast, MODE_ALL }
 #define g_first { cg_first, MODE_ALL }
 #define g_mark_range { cg_mark_range, MODE_ALL }
 #define g_n_or_last { cg_n_or_last, MODE_ALL }

config.def.h

@@ -33,11 +33,14 @@ static const float zoom_levels[] = {
 /* default slideshow delay (in sec, overwritten via -S option): */
 static const int SLIDESHOW_DELAY = 5;
 
-/* gamma correction: the user-visible ranges [-GAMMA_RANGE, 0] and
- * (0, GAMMA_RANGE] are mapped to the ranges [0, 1], and (1, GAMMA_MAX].
+/* color correction: the user-visible ranges [-CC_STEPS, 0] and
+ * (0, CC_STEPS] are mapped to the ranges [0, 1], and (1, *_MAX].
+ * Higher step count will have higher granulairy.
  */
+static const int    CC_STEPS        = 32;
 static const double GAMMA_MAX       = 10.0;
-static const int    GAMMA_RANGE = 32;
+static const double BRIGHTNESS_MAX  = 2.0;
+static const double CONTRAST_MAX    = 4.0;
 
 /* command i_scroll pans image 1/PAN_FRACTION of screen width/height */
 static const int PAN_FRACTION = 5;
@@ -118,6 +121,10 @@ static const keymap_t keys[] = {
 	{ 0,            XK_braceleft,     g_change_gamma,       -1 },
 	{ 0,            XK_braceright,    g_change_gamma,       +1 },
 	{ ControlMask,  XK_g,             g_change_gamma,        0 },
+	{ ControlMask,  XK_bracketright,  g_change_brightness,  +1 },
+	{ ControlMask,  XK_bracketleft,   g_change_brightness,  -1 },
+	{ 0,            XK_parenleft,     g_change_contrast,    -1 },
+	{ 0,            XK_parenright,    g_change_contrast,    +1 },
 
 	{ 0,            XK_h,             t_move_sel,           DIR_LEFT },
 	{ 0,            XK_Left,          t_move_sel,           DIR_LEFT },

etc/nsxiv.1

@@ -209,6 +209,26 @@ steps.
 .TP
 .B Ctrl-g
 Reset gamma correction.
+.TP
+.B [
+Decrease brightness correction by
+.I count
+steps.
+.TP
+.B ]
+Increase brightness correction by
+.I count
+steps.
+.TP
+.B (
+Decrease contrast by
+.I count
+steps.
+.TP
+.B )
+Increase contrast by
+.I count
+steps.
 .SS Thumbnail mode
 The following keyboard commands are only available in thumbnail mode:
 .TP

image.c

@@ -90,7 +90,9 @@ void img_init(img_t *img, win_t *win)
 
 	img->cmod = imlib_create_color_modifier();
 	imlib_context_set_color_modifier(img->cmod);
-	img_change_gamma(img, options->gamma);
+	img->brightness = 0;
+	img->contrast = 0;
+	img_change_color_modifier(img, options->gamma, &img->gamma);
 
 	img->ss.on = options->slideshow > 0;
 	img->ss.delay = options->slideshow > 0 ? options->slideshow : SLIDESHOW_DELAY * 10u;
@@ -840,32 +842,36 @@ void img_toggle_antialias(img_t *img)
 	img->dirty = true;
 }
 
-bool img_change_gamma(img_t *img, int d)
+static double steps_to_range(int d, double max, double offset)
 {
-	/* d < 0: decrease gamma
-	 * d = 0: reset gamma
-	 * d > 0: increase gamma
-	 */
-	int gamma;
-	double range;
+	return offset + d * ((d <= 0 ? 1.0 : (max - 1.0)) / CC_STEPS);
+}
 
-	if (d == 0)
-		gamma = 0;
-	else
-		gamma = MIN(MAX(img->gamma + d, -GAMMA_RANGE), GAMMA_RANGE);
-
-	if (img->gamma != gamma) {
+void img_update_color_modifiers(img_t *img)
+{
+	assert(imlib_context_get_color_modifier() == img->cmod);
 	imlib_reset_color_modifier();
-		if (gamma) {
-			range = gamma <= 0 ? 1.0 : GAMMA_MAX - 1.0;
-			imlib_modify_color_modifier_gamma(1.0 + gamma * (range / GAMMA_RANGE));
-		}
-		img->gamma = gamma;
+
+	if (img->gamma != 0)
+		imlib_modify_color_modifier_gamma(steps_to_range(img->gamma, GAMMA_MAX, 1.0));
+	if (img->brightness != 0)
+		imlib_modify_color_modifier_brightness(steps_to_range(img->brightness, BRIGHTNESS_MAX, 0.0));
+	if (img->contrast != 0)
+		imlib_modify_color_modifier_contrast(steps_to_range(img->contrast, CONTRAST_MAX, 1.0));
+
 	img->dirty = true;
-		return true;
-	} else {
-		return false;
 }
+
+bool img_change_color_modifier(img_t *img, int d, int *target)
+{
+	int value = d == 0 ? 0 : MIN(MAX(*target + d, -CC_STEPS), CC_STEPS);
+
+	if (*target == value)
+		return false;
+
+	*target = value;
+	img_update_color_modifiers(img);
+	return true;
 }
 
 static bool img_frame_goto(img_t *img, int n)

main.c

@@ -444,6 +444,10 @@ static void update_info(void)
 		}
 		if (img.gamma)
 			bar_put(r, "G%+d" BAR_SEP, img.gamma);
+		if (img.brightness)
+			bar_put(r, "B%+d" BAR_SEP, img.brightness);
+		if (img.contrast)
+			bar_put(r, "C%+d" BAR_SEP, img.contrast);
 		bar_put(r, "%3d%%" BAR_SEP, (int) (img.zoom * 100.0));
 		if (img.multi.cnt > 0) {
 			for (fn = 0, i = img.multi.cnt; i > 0; fn++, i /= 10);

nsxiv.h

@@ -181,6 +181,8 @@ struct img {
 
 	Imlib_Color_Modifier cmod;
 	int gamma;
+	int brightness;
+	int contrast;
 
 	scalemode_t scalemode;
 	float zoom;
@@ -212,7 +214,8 @@ bool img_pan_edge(img_t*, direction_t);
 void img_rotate(img_t*, degree_t);
 void img_flip(img_t*, flipdir_t);
 void img_toggle_antialias(img_t*);
-bool img_change_gamma(img_t*, int);
+void img_update_color_modifiers(img_t*);
+bool img_change_color_modifier(img_t*, int, int*);
 bool img_frame_navigate(img_t*, int);
 bool img_frame_animate(img_t*);
 Imlib_Image img_open(const fileinfo_t*);