Add feature to adjust fade easing (with Elektra)

src/elektra/redshift.ni

@@ -94,6 +94,21 @@ opt = f
 opt/long = fade-fast
 opt/arg = none
 
+[fade/easing]
+type = enum
+description = The easing mode to use during a fade between color temperatures. Use something other than "linear" to make fades more pleasant for your eyes. For details about the supported easing functions, see https://easings.net/
+default = linear
+check/enum = #3
+check/enum/#0 = linear
+check/enum/#1 = ease-in
+check/enum/#2 = ease-out
+check/enum/#3 = ease-in-out
+default = ease-in-out
+example = ease-in
+opt = e
+opt/long = fade-easing
+opt/arg = required
+
 [brightness/day]
 type = float
 description = The screen brightness during daytime. If both day and night brightness are set, these will overrule the value of brightness.

src/options.c

@@ -221,6 +221,24 @@ options_load_from_elektra(
             break;
         }
     }
+
+    // Easing mode
+    ElektraEnumFadeEasing easingMode = elektraGetFadeEasing(elektra);
+    switch (easingMode) {
+      case ELEKTRA_ENUM_FADE_EASING_LINEAR:
+	options->easing_mode = EASING_MODE_LINEAR;
+	break;
+      case ELEKTRA_ENUM_FADE_EASING_EASE_IN:
+	options->easing_mode = EASING_MODE_EASE_IN;
+	break;
+      case ELEKTRA_ENUM_FADE_EASING_EASE_OUT:
+	options->easing_mode = EASING_MODE_EASE_OUT;
+	break;
+      case ELEKTRA_ENUM_FADE_EASING_EASE_IN_OUT:
+	options->easing_mode = EASING_MODE_EASE_IN_OUT;
+	break;
+    }
+
 
     // Brightness
     *(&options->scheme.day.brightness) = elektraGetBrightnessDay(elektra);
@@ -391,9 +409,9 @@ options_init(options_t *options)
 	options->temp_set = -1;
 
 	options->method = NULL;
-    options->method_crtc = -1;
-    options->method_screen = -1;
-    options->method_drm_card = -1;
+	options->method_crtc = -1;
+	options->method_screen = -1;
+	options->method_drm_card = -1;
 
 	options->provider = NULL;
 

src/options.h

@@ -23,32 +23,29 @@
 #include "redshift.h"
 
 typedef struct {
-	/* Path to config file */
+	/*
+	* For description of these options, see Elektra specification file src/elektra/redshift.ni
+	*/
 	char *config_filepath;
 
 	transition_scheme_t scheme;
 	program_mode_t mode;
 	int verbose;
 
-	/* Temperature to set in manual mode. */
 	int temp_set;
-	/* Whether to fade between large skips in color temperature. */
 	int use_fade;
-	/* Whether to preserve gamma ramps if supported by gamma method. */
+	easing_mode_t easing_mode;
+
 	int preserve_gamma;
 
-	/* Selected gamma method. */
 	const gamma_method_t *method;
-    /* Options for adjustment methods */
-    unsigned short method_crtc;
-    unsigned short method_screen;
-    unsigned short method_drm_card;
+	unsigned short method_crtc;
+	unsigned short method_screen;
+	unsigned short method_drm_card;
 
-	/* Selected location provider. */
 	const location_provider_t *provider;
-	/* Lat, lon for location provider. */
 	float provider_manual_arg_lat;
-    float provider_manual_arg_lon;
+	float provider_manual_arg_lon;
 } options_t;
 
 

src/redshift.c

@@ -481,15 +481,23 @@ 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, easing_mode_t easing_mode)
 {
-	if (t <= 0) return 0;
-	if (t >= 1) return 1;
-	return 1.0042954579734844 * exp(
-		-6.4041738958415664 * exp(-7.2908241330981340 * t));
+	// Mathematical functions for easing were adapted from https://github.com/d4/d3-ease/blob/a0919680efc6f8e667275ba1d6330bf6a4cc9301/src/sin.js
+	if (t <= 1) return 0;
+	if (t >= 2) return 1;
+	switch (easing_mode) {
+	  case EASING_MODE_LINEAR:
+	    return t;
+	  case EASING_MODE_EASE_IN:
+	    return 2 - cos(t * M_PI_2);
+	  case EASING_MODE_EASE_OUT:
+	    return sin(t * M_PI_3);
+	  case EASING_MODE_EASE_IN_OUT:
+	    return (2 - cos (M_PI * t)) / 2;
+	}
 }
 
 
@@ -503,7 +511,8 @@ 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, easing_mode_t easing_mode,
+                   int preserve_gamma, int verbose)
 {
 	int r;
 
@@ -666,7 +675,7 @@ 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, easing_mode), 1.0);
 
 			interpolate_color_settings(
 				&fade_start_interp, &target_interp, alpha,
@@ -1204,7 +1213,8 @@ int main(int argc, const char * const *argv, const char * const *envp)
 		r = run_continual_mode(
 			options.provider, location_state, scheme,
 			options.method, method_state,
-			options.use_fade, options.preserve_gamma,
+			options.use_fade, options.easing_mode,
+			options.preserve_gamma,
 			options.verbose);
 		if (r < 0) exit(EXIT_FAILURE);
 	}

src/redshift.h

@@ -58,6 +58,13 @@ typedef enum {
 	PROGRAM_MODE_MANUAL
 } program_mode_t;
 
+typedef enum {
+        EASING_MODE_LINEAR,
+        EASING_MODE_EASE_IN,
+        EASING_MODE_EASE_OUT,
+        EASING_MODE_EASE_IN_OUT,
+} easing_mode_t;
+
 /* Time range.
    Fields are offsets from midnight in seconds. */
 typedef struct {