#include <math.h>

#include "pixman.h"

#include "gtk-utils.h"

static uint32_t

linear_argb_to_premult_argb (float a,

			     float r,

			     float g,

			     float b)

{

    r *= a;

    g *= a;

    b *= a;

    return (uint32_t) (a * 255.0f + 0.5f) << 24

	 | (uint32_t) (r * 255.0f + 0.5f) << 16

	 | (uint32_t) (g * 255.0f + 0.5f) <<  8

	 | (uint32_t) (b * 255.0f + 0.5f) <<  0;

}

static float

lin2srgb (float linear)

{

    if (linear < 0.0031308f)

	return linear * 12.92f;

    else

	return 1.055f * powf (linear, 1.0f/2.4f) - 0.055f;

}

static uint32_t

linear_argb_to_premult_srgb_argb (float a,

				  float r,

				  float g,

				  float b)

{

    r = lin2srgb (r * a);

    g = lin2srgb (g * a);

    b = lin2srgb (b * a);

    return (uint32_t) (a * 255.0f + 0.5f) << 24

	 | (uint32_t) (r * 255.0f + 0.5f) << 16

	 | (uint32_t) (g * 255.0f + 0.5f) <<  8

	 | (uint32_t) (b * 255.0f + 0.5f) <<  0;

}

int

main (int argc, char **argv)

{

#define WIDTH 400

#define HEIGHT 200

    int y, x, p;

    float alpha;

    uint32_t *dest = malloc (WIDTH * HEIGHT * 4);

    uint32_t *src1 = malloc (WIDTH * HEIGHT * 4);

    pixman_image_t *dest_img, *src1_img;

    dest_img = pixman_image_create_bits (PIXMAN_a8r8g8b8_sRGB,

					 WIDTH, HEIGHT,

					 dest,

					 WIDTH * 4);

    src1_img = pixman_image_create_bits (PIXMAN_a8r8g8b8,

					 WIDTH, HEIGHT,

					 src1,

					 WIDTH * 4);

    for (y = 0; y < HEIGHT; y ++)

    {

	p = WIDTH * y;

	for (x = 0; x < WIDTH; x ++)

	{

	     alpha = (float) x / WIDTH;

	     src1[p + x] = linear_argb_to_premult_argb (alpha, 1, 0, 1);

	     dest[p + x] = linear_argb_to_premult_srgb_argb (1-alpha, 0, 1, 0);

	}

    }

    pixman_image_composite (PIXMAN_OP_ADD, src1_img, NULL, dest_img,

			    0, 0, 0, 0, 0, 0, WIDTH, HEIGHT);

    pixman_image_unref (src1_img);

    free (src1);

    show_image (dest_img);

    pixman_image_unref (dest_img);

    free (dest);

    return 0;

}