/*
 * gl_cmap_gen.c
 *
 * OpenGL color map generators
 *
 * Copyright (C) 2013-2021 Sylvain Munaut
 * SPDX-License-Identifier: GPL-3.0-or-later
 */

/*! \addtogroup gl/cmap
 *  @{
 */

/*! \file gl_cmap_gen.c
 *  \brief OpenGL color map generators
 */

#include <stdint.h>
#include <math.h>

#include "gl_cmap_gen.h"


static void
_hsv2rgb(float *rgb, float *hsv)
{
	int i;
	float h, s, v;
	float r, g, b;
	float f, p, q, t;

	/* Unpack input */
	h = hsv[0];
	s = hsv[1];
	v = hsv[2];

	if( s <= 0.0f ) {
		/* achromatic (grey) */
		r = g = b = v;
		goto done;
	}

	h *= 5.0f;			/* sector 0 to 5 */
	i = floor(h);
	f = h - i;			/* fractional part of h */
	p = v * ( 1 - s );
	q = v * ( 1 - s * f );
	t = v * ( 1 - s * ( 1 - f ) );

	switch (i % 6) {
		case 0:
			r = v;
			g = t;
			b = p;
			break;
		case 1:
			r = q;
			g = v;
			b = p;
			break;
		case 2:
			r = p;
			g = v;
			b = t;
			break;
		case 3:
			r = p;
			g = q;
			b = v;
			break;
		case 4:
			r = t;
			g = p;
			b = v;
			break;
		case 5:
		default:
			r = v;
			g = p;
			b = q;
			break;
	}

done:
	/* Pack results */
	rgb[0] = r;
	rgb[1] = g;
	rgb[2] = b;
}

static void
_set_rgba_from_rgb(uint32_t *rgba, float r, float g, float b)
{
	unsigned char rc,gc,bc,ac;

	rc = (unsigned char) roundf(r * 255.0f);
	gc = (unsigned char) roundf(g * 255.0f);
	bc = (unsigned char) roundf(b * 255.0f);
	ac = 255;

	*rgba = (ac << 24) | (bc << 16) | (gc << 8) | rc;
}

static void
_set_rgba_from_hsv(uint32_t *rgba, float h, float s, float v)
{
	float hsv[3], rgb[3];

	hsv[0] = h;
	hsv[1] = s;
	hsv[2] = v;

	_hsv2rgb(rgb, hsv);

	_set_rgba_from_rgb(rgba, rgb[0], rgb[1], rgb[2]);
}


int
fosphor_gl_cmap_histogram(uint32_t *rgba, int N, void *arg)
{
	int i;
	int m = N >> 4;

	for (i=0; i<m; i++)
	{
		float p = (1.0f * i) / (N - 1);

		_set_rgba_from_hsv(&rgba[i],
			0.90f,				/* H */
			0.50f,				/* S */
			0.15f + 4.0f * p		/* V */
		);
	}

	for (i=m; i<N; i++)
	{
		float p = (1.0f * i) / (N - 1);

		_set_rgba_from_hsv(&rgba[i],
			0.80f -   p * 0.80f,
			1.00f - ((p < 0.85f) ? 0.0f : ((p - 0.85f) * 3.0f)),
			0.60f + ((p < 0.40f) ? p : 0.40f)
		);
	}

	return 0;
}


int
fosphor_gl_cmap_waterfall(uint32_t *rgba, int N, void *arg)
{
	int i;

	for (i=0; i<N; i++)
	{
		float p = (1.0f * i) / (N - 1);

		_set_rgba_from_hsv(&rgba[i],
			0.75f - (p * 0.75f),	/* H */
			1.0f,			/* S */
			((p * 0.95f) + 0.05f)	/* V */
		);
	}

	return 0;
}

/*! @} */