A ReShade macro allowing smooth variation of presets based on Guild Wars 2 in-game time.

GW2DayNight.h

/*
 * The GW2DayNight(,) macro
 *
 * The following defines a macro (think function) that allows parameters of a
 * reshade preset to fade smoothly with no stutter or sudden changes between one
 * value at daytime (in the Guild Wars 2 game world), and another at nighttime.
 *
 * The macro is used as follows: Instead of a plain number in your preset, say
 * '1.02', you put 'GW2DayNight(1.02,1.06)'. Now, that number will be 1.02 at
 * daytime, 1.06 at nighttime, and something inbetween (changing every second)
 * during dusk and dawn.
 *
 * The macro needs to know your time-zone to work. It can either be provided by
 * the GW2ReshadeMap tool (https://github.com/margnus1/gw2-reshade-map), or
 * manually with a line as follows (UTC+4 as example):
 *  '#define TimeZone (4*60*60)'
 * In either case, the line above *or* the '#include "gw2map.h"' line needs to
 * be put before here.
 */

#define GW2DayOrigin (25 * 60)
#define GW2DayDuration (120 * 60)

uniform float4 Date < source = "date"; >;

#if TimeZone % GW2DayDuration
#  define SecsOfDay ((Date.w - TimeZone + 24 * 60 * 60) % (24 * 60 * 60))
#else
#  define SecsOfDay Date.w
#endif

#define TimeOfDay (((SecsOfDay - GW2DayOrigin + GW2DayDuration) \
		    / GW2DayDuration) % 1.0)

#define GW2Dawn  0
#define GW2Day   (5  / 120.0)
#define GW2Dusk  (75 / 120.0)
#define GW2Night (80 / 120.0)

/*
 * Defines a value that is 1 at daytime, 0 at nighttime, and
 * decreases/increases linearly during dusk and dawn.
 *
 * GW2DaySaw
 * ^      ______________
 * | ____/              \____
 * |     ^ Dawn         ^ Dusk
 * +---------------------------> In-game time
 */
#define GW2DayMidpoint ((GW2Day + GW2Dusk) / 2)
#define GW2SawMult (1 / (GW2Day - GW2Dawn))

#define UnclampedGW2DaySaw						\
  ((((GW2DayMidpoint - GW2Day) + (1 / GW2SawMult))			\
    - abs(GW2DayMidpoint - TimeOfDay))					\
   * GW2SawMult)
#define GW2DaySaw (clamp(UnclampedGW2DaySaw, 0.0, 1.0))

/*
 * Is Day at daytime, Night at nighttime, and fades between them at dusk and
 * dawn.
 */
#define GW2DayNight(Day, Night) \
  lerp(Night, Day, smoothstep(0.0, 1.0, UnclampedGW2DaySaw))
  
/*
 * Fades from Day to Twilight for the first 2.5 minutes of dusk, and from
 * Twilight to Night for the last 2.5 minutes. It does the reverse during dawn.
 */
#define GW2DayTwilightNight(Day, Twilight, Night)               \
  lerp(Night,                                                   \
       lerp(Twilight, Day,                                      \
            smoothstep(0.0, 1.0, 2.0*UnclampedGW2DaySaw-1.0)),  \
       smoothstep(0.0, 1.0, 2.0*UnclampedGW2DaySaw))

/*
 * Fades from Day to Dusk for the first 2.5 minutes of dusk, and from
 * Dusk to Night for the last 2.5 minutes.
 * Fades from Night to Dawn for the first 2.5 minutes of dawn, and from Dawn to
 * Day for the last 2.5 minutes.
 */
#define GW2DayDuskNightDawn(Day, Dusk, Night, Dawn) \
  GW2DayTwilightNight(Day,                          \
                      TimeOfDay > GW2DayMidpoint    \
                      ? (Dusk) : (Dawn),            \
                      Night)