Add feature to adjust fade easing (without Elektra)

src/options.c

@@ -193,6 +193,10 @@ print_help(const char *program_name)
 		" color effect\n"
 		"  -x\t\tReset mode (remove adjustment from screen)\n"
 		"  -r\t\tDisable fading between color temperatures\n"
+		"  -e\t\tSet the fading mode to use during a fade between color temperatures.\n"
+		"  \t\tUse \"ease-in\", \"ease-out\" or \"ease-in-out\" to make fades pleasant for your eyes.\n"
+		"  \t\tOtherwise, use \"linear\".\n"
+		"  \t\tFor details about the supported easing functions, see https://easings.net/\n"
 		"  -t DAY:NIGHT\tColor temperature to set at daytime/night\n"),
 	      stdout);
 	fputs("\n", stdout);
@@ -320,6 +324,7 @@ options_init(options_t *options)
 	options->provider_args = NULL;
 
 	options->use_fade = -1;
+	options->fade_mode = FADE_MODE_NOT_SPECIFIED;
 	options->preserve_gamma = 1;
 	options->mode = PROGRAM_MODE_CONTINUAL;
 	options->verbose = 0;
@@ -456,10 +461,27 @@ parse_command_line_option(
 	case 'r':
 		options->use_fade = 0;
 		break;
+	case 'e':
+		if(strlen(value) == 0) {
+		  fprintf(stderr, _("No value was passed for option -e (fade mode).\nTry \"redshift -h\" for more information.\n"));
+		  return -1;
+		} else if (strcmp(value, "linear") == 0) {
+		  options->fade_mode = FADE_MODE_LINEAR;
+		} else if (strcmp(value, "ease-in") == 0) {
+		  options->fade_mode = FADE_MODE_EASE_IN;
+		} else if (strcmp(value, "ease-out") == 0) {
+		  options->fade_mode = FADE_MODE_EASE_OUT;
+		} else if (strcmp(value, "ease-in-out") == 0) {
+		  options->fade_mode = FADE_MODE_EASE_IN_OUT;
+		} else {
+		  fprintf(stderr, _("Value \"%s\" for option -e (fade mode) is not supported.\nTry \"redshift -h\" for more information."), value);
+		  return -1;
+		}
+		break;
 	case 't':
-		s = strchr(value, ':');
-		if (s == NULL) {
-			fputs(_("Malformed temperature argument.\n"), stderr);
+	  s = strchr(value, ':');
+	  if (s == NULL) {
+	    fputs(_("Malformed temperature argument.\n"), stderr);
 			fputs(_("Try `-h' for more information.\n"), stderr);
 			return -1;
 		}
@@ -495,7 +517,7 @@ options_parse_args(
 {
 	const char* program_name = argv[0];
 	int opt;
-	while ((opt = getopt(argc, argv, "b:c:g:hl:m:oO:pPrt:vVx")) != -1) {
+	while ((opt = getopt(argc, argv, "b:c:g:hl:m:oO:pPrt:e:vVx")) != -1) {
 		char option = opt;
 		int r = parse_command_line_option(
 			option, optarg, options, program_name, gamma_methods,
@@ -526,7 +548,26 @@ parse_config_file_option(
 		if (options->use_fade < 0) {
 			options->use_fade = !!atoi(value);
 		}
-	} else if (strcasecmp(key, "brightness") == 0) {
+	} else if (strcasecmp(key, "fade-mode") == 0) {
+		if (options->fade_mode == FADE_MODE_NOT_SPECIFIED) {
+		  if(strlen(value) == 0) {
+		    fprintf(stderr, _("fade-mode was set to an empty value in config file. Please execute \"redshift -h\" to see supported values.\n"));
+		    return -1;
+		  } else if (strcmp(value, "linear") == 0) {
+		    options->fade_mode = FADE_MODE_LINEAR;
+		  } else if (strcmp(value, "ease-in") == 0) {
+		    options->fade_mode = FADE_MODE_EASE_IN;
+		  } else if (strcmp(value, "ease-out") == 0) {
+		    options->fade_mode = FADE_MODE_EASE_OUT;
+		  } else if (strcmp(value, "ease-in-out") == 0) {
+		    options->fade_mode = FADE_MODE_EASE_IN_OUT;
+		  } else {
+		    fprintf(stderr, _("Fade mode \"%s\" set in config file is not supported.\n"), value);
+		    return -1;
+		  }
+		}
+	}
+	else if (strcasecmp(key, "brightness") == 0) {
 		if (isnan(options->scheme.day.brightness)) {
 			options->scheme.day.brightness = atof(value);
 		}
@@ -676,4 +717,6 @@ options_set_defaults(options_t *options)
 	}
 
 	if (options->use_fade < 0) options->use_fade = 1;
+
+	if (options->fade_mode == FADE_MODE_NOT_SPECIFIED) options->fade_mode = FADE_MODE_LINEAR;
 }

src/options.h

@@ -34,6 +34,8 @@ typedef struct {
 	int temp_set;
 	/* Whether to fade between large skips in color temperature. */
 	int use_fade;
+        /* The fading function to use when transitioning between color temperatures. */ 
+        fade_mode_t fade_mode;
 	/* Whether to preserve gamma ramps if supported by gamma method. */
 	int preserve_gamma;
 

src/redshift.c

@@ -586,15 +586,23 @@ provider_get_location(
 	return 1;
 }
 
-/* Easing function for fade.
-   See https://github.com/mietek/ease-tween */
+/* Easing function for fade.*/
 static double
-ease_fade(double t)
+ease_fade(double t, fade_mode_t fade_mode)
 {
+	// Mathematical functions for easing were adapted from https://github.com/d3/d3-ease/blob/a0919680efc6f8e667275ba1d6330bf6a4cc9301/src/sin.js
 	if (t <= 0) return 0;
 	if (t >= 1) return 1;
-	return 1.0042954579734844 * exp(
-		-6.4041738958415664 * exp(-7.2908241330981340 * t));
+	switch (fade_mode) {
+	  case FADE_MODE_LINEAR:
+	    return t;
+	  case FADE_MODE_EASE_IN:
+	    return 1 - cos(t * M_PI_2);
+	  case FADE_MODE_EASE_OUT:
+	    return sin(t * M_PI_2);
+	  case FADE_MODE_EASE_IN_OUT:
+	    return (1 - cos (M_PI * t)) / 2;
+	}
 }
 
 
@@ -608,7 +616,8 @@ run_continual_mode(const location_provider_t *provider,
 		   const transition_scheme_t *scheme,
 		   const gamma_method_t *method,
 		   gamma_state_t *method_state,
-		   int use_fade, int preserve_gamma, int verbose)
+		   int use_fade, fade_mode_t fade_mode,
+		   int preserve_gamma, int verbose)
 {
 	int r;
 
@@ -771,7 +780,7 @@ run_continual_mode(const location_provider_t *provider,
 		if (fade_length != 0) {
 			fade_time += 1;
 			double frac = fade_time / (double)fade_length;
-			double alpha = CLAMP(0.0, ease_fade(frac), 1.0);
+			double alpha = CLAMP(0.0, ease_fade(frac, fade_mode), 1.0);
 
 			interpolate_color_settings(
 				&fade_start_interp, &target_interp, alpha,
@@ -1307,7 +1316,8 @@ main(int argc, char *argv[])
 		r = run_continual_mode(
 			options.provider, location_state, scheme,
 			options.method, method_state,
-			options.use_fade, options.preserve_gamma,
+			options.use_fade, options.fade_mode,
+			options.preserve_gamma,
 			options.verbose);
 		if (r < 0) exit(EXIT_FAILURE);
 	}

src/redshift.h

@@ -57,6 +57,16 @@ typedef enum {
 	PROGRAM_MODE_MANUAL
 } program_mode_t;
 
+/* Fade modes. */
+typedef enum {
+        FADE_MODE_NOT_SPECIFIED,
+        FADE_MODE_LINEAR,
+        FADE_MODE_EASE_IN,
+        FADE_MODE_EASE_OUT,
+        FADE_MODE_EASE_IN_OUT,
+} fade_mode_t;
+
+
 /* Time range.
    Fields are offsets from midnight in seconds. */
 typedef struct {