1 files changed, 109 insertions, 0 deletions
diff --git a/src/palettes.c b/src/palettes.c
new file mode 100644
index 0000000..19a41bf
--- /dev/null
+++ b/src/palettes.c
@@ -0,0 +1,109 @@
+#include <math.h>
+#include <SDL.h>
+#include "palettes.h"
+#include "logging.h"
+
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
+static inline Uint8 cycle_palettes_cosine_channel(Uint8, Uint8, double);
+static inline Uint8 cycle_palettes_linear_channel(Uint8, Uint8, double);
+
+SDL_Palette *
+cycle_palettes_cosine(Uint32 t, Uint32 t_max,
+		SDL_Palette *pal_start, SDL_Palette *pal_end,
+		SDL_Palette *pal_step)
+{
+	double x;
+	int col_i;
+
+	if (pal_start->ncolors != pal_end->ncolors) {
+		return NULL;
+	}
+	if (pal_start->ncolors != pal_step->ncolors) {
+		return NULL;
+	}
+
+	x = (double) (t % t_max) / (double) t_max * M_PI;
+
+	for (col_i = 0; col_i < pal_step->ncolors; ++col_i) {
+		pal_step->colors[col_i].r = cycle_palettes_cosine_channel(
+				pal_start->colors[col_i].r,
+				pal_end->colors[col_i].r,
+				x);
+		pal_step->colors[col_i].g = cycle_palettes_cosine_channel(
+				pal_start->colors[col_i].g,
+				pal_end->colors[col_i].g,
+				x);
+		pal_step->colors[col_i].b = cycle_palettes_cosine_channel(
+				pal_start->colors[col_i].b,
+				pal_end->colors[col_i].b,
+				x);
+	}
+
+	return pal_step;
+}
+
+SDL_Palette *
+cycle_palettes_linear(Uint32 t, Uint32 t_max,
+		SDL_Palette *pal_start, SDL_Palette *pal_end,
+		SDL_Palette *pal_step)
+{
+	double x;
+	int col_i;
+
+	if (pal_start->ncolors != pal_end->ncolors) {
+		return NULL;
+	}
+	if (pal_start->ncolors != pal_step->ncolors) {
+		return NULL;
+	}
+
+	x = (double) (t % t_max) / (double) t_max;
+
+	for (col_i = 0; col_i < pal_step->ncolors; ++col_i) {
+		pal_step->colors[col_i].r = cycle_palettes_linear_channel(
+				pal_start->colors[col_i].r,
+				pal_end->colors[col_i].r,
+				x);
+		pal_step->colors[col_i].g = cycle_palettes_linear_channel(
+				pal_start->colors[col_i].g,
+				pal_end->colors[col_i].g,
+				x);
+		pal_step->colors[col_i].b = cycle_palettes_linear_channel(
+				pal_start->colors[col_i].b,
+				pal_end->colors[col_i].b,
+				x);
+	}
+
+	return pal_step;
+}
+
+static inline Uint8
+cycle_palettes_cosine_channel(Uint8 y_start, Uint8 y_end, double x)
+{
+	double m;
+	Uint8 b;
+	Uint8 y;
+
+	m = y_end - y_start;
+	b = y_start;
+	y = m * ((cos(x) / -2.0) + 0.5) + b;
+
+	return y;
+}
+
+static inline Uint8
+cycle_palettes_linear_channel(Uint8 y_start, Uint8 y_end, double x)
+{
+	double m;
+	Uint8 b;
+	Uint8 y;
+
+	m = y_end - y_start;
+	b = y_start;
+	y = m * x + b;
+
+	return y;
+}