/*
 * image.c -- PNG decoding for ez3d, wrapped around the vendored
 * stb_image.h (public domain, v2.30).
 *
 * We always ask stb for 4 channels (RGBA): it replicates gray into RGB
 * and fills alpha with 255 when the source has none, which gives us one
 * uniform code path regardless of the PNG's actual color type.
 * 16-bit PNGs are converted down to 8 bits by stb (documented limitation).
 */
#define STB_IMAGE_IMPLEMENTATION
#include "vendor/stb_image.h"

#include <stdlib.h>
#include <string.h>

#include "image.h"

void ez3d_free_image(ez3d_image_t *img)
{
    if (!img)
        return;
    free(img->gray);
    free(img->alpha);
    img->gray = img->alpha = NULL;
}

int ez3d_load_image(const char *path, ez3d_image_t *img)
{
    int w, h, n;
    unsigned char *rgba = stbi_load(path, &w, &h, &n, 4);

    if (!rgba) {
        fprintf(stderr, "ez3d: cannot load '%s': %s\n", path,
                stbi_failure_reason());
        return -1;
    }
    if (w < 1 || h < 1) {
        fprintf(stderr, "ez3d: '%s' has degenerate size %dx%d\n", path, w, h);
        stbi_image_free(rgba);
        return -1;
    }

    img->w = w;
    img->h = h;
    img->has_alpha = (n == 2 || n == 4); /* original had an alpha channel */
    img->gray = malloc((size_t)w * h);
    img->alpha = malloc((size_t)w * h);
    if (!img->gray || !img->alpha) {
        fprintf(stderr, "ez3d: out of memory for %dx%d image\n", w, h);
        stbi_image_free(rgba);
        ez3d_free_image(img);
        return -1;
    }

    for (size_t i = 0; i < (size_t)w * h; i++) {
        img->gray[i] = rgba[4 * i];
        img->alpha[i] = rgba[4 * i + 3];
    }

    stbi_image_free(rgba);
    return 0;
}