/*
 * Copyright (C) 2013  Patrick "P. J." McDermott
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program.  If not, see
 * <http://www.gnu.org/licenses/>.
 */

#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;
}