armorpaint/base/tools/iris.c/png.h

/*
 * PNG Decoder/Encoder - Single-header implementation
 *
 * A dependency-free C implementation for reading and writing PNG images.
 * Uses zlib-style deflate compression (store mode for writing, full inflate for reading).
 *
 * Usage:
 *   png_image *img = png_load("image.png");
 *   if (!img) { handle error }
 *
 *   // Access pixel data
 *   uint8_t *pixel = img->data + (y * img->width + x) * img->channels;
 *
 *   png_save(img, "output.png");
 *   png_free(img);
 *
 * To use as header-only, define PNG_IMPLEMENTATION before including:
 *   #define PNG_IMPLEMENTATION
 *   #include "png.h"
 */

#ifndef PNG_H
#define PNG_H

#include <stddef.h>
#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif

/* ========================================================================
 * Image Structure
 * ======================================================================== */

typedef struct {
	int      width;
	int      height;
	int      channels; /* 1=Grayscale, 2=Gray+Alpha, 3=RGB, 4=RGBA */
	uint8_t *data;     /* Row-major, channel-interleaved */
} png_image;

/* ========================================================================
 * Public API
 * ======================================================================== */

/*
 * Load PNG image from file.
 * Returns NULL on error.
 */
png_image *png_load(const char *path);

/*
 * Load PNG image from memory buffer.
 * Returns NULL on error.
 */
png_image *png_load_mem(const uint8_t *data, size_t len);

/*
 * Save PNG image to file.
 * Returns 0 on success, -1 on error.
 */
int png_save(const png_image *img, const char *path);

/*
 * Save PNG image with text metadata.
 * keyword: up to 79 characters, text: arbitrary length.
 * Returns 0 on success, -1 on error.
 */
int png_save_with_text(const png_image *img, const char *path, const char *keyword, const char *text);

/*
 * Create a new image with given dimensions.
 * Allocates zeroed pixel data.
 */
png_image *png_create(int width, int height, int channels);

/*
 * Free image and pixel data.
 */
void png_free(png_image *img);

/*
 * Clone an image (deep copy).
 */
png_image *png_clone(const png_image *img);

#ifdef __cplusplus
}
#endif

#endif /* PNG_H */

/* ========================================================================
 * Implementation
 * ======================================================================== */

#ifdef PNG_IMPLEMENTATION

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

/* ========================================================================
 * Image Creation and Management
 * ======================================================================== */

png_image *png_create(int width, int height, int channels) {
	png_image *img = (png_image *)malloc(sizeof(png_image));
	if (!img)
		return NULL;

	img->width    = width;
	img->height   = height;
	img->channels = channels;
	img->data     = (uint8_t *)calloc(width * height * channels, sizeof(uint8_t));

	if (!img->data) {
		free(img);
		return NULL;
	}

	return img;
}

void png_free(png_image *img) {
	if (img) {
		free(img->data);
		free(img);
	}
}

png_image *png_clone(const png_image *img) {
	if (!img)
		return NULL;

	png_image *clone = png_create(img->width, img->height, img->channels);
	if (!clone)
		return NULL;

	memcpy(clone->data, img->data, img->width * img->height * img->channels);
	return clone;
}

/* ========================================================================
 * CRC32 for PNG
 * ======================================================================== */

static uint32_t png_crc_table[256];
static int      png_crc_table_computed = 0;

static void png_make_crc_table(void) {
	for (int n = 0; n < 256; n++) {
		uint32_t c = (uint32_t)n;
		for (int k = 0; k < 8; k++) {
			if (c & 1)
				c = 0xedb88320u ^ (c >> 1);
			else
				c = c >> 1;
		}
		png_crc_table[n] = c;
	}
	png_crc_table_computed = 1;
}

static uint32_t png_update_crc(uint32_t crc, const uint8_t *buf, size_t len) {
	if (!png_crc_table_computed)
		png_make_crc_table();

	uint32_t c = crc;
	for (size_t n = 0; n < len; n++) {
		c = png_crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
	}
	return c;
}

static uint32_t png_crc(const uint8_t *buf, size_t len) {
	return png_update_crc(0xffffffffu, buf, len) ^ 0xffffffffu;
}

/* ========================================================================
 * Adler-32 for zlib
 * ======================================================================== */

static uint32_t png_adler32(const uint8_t *data, size_t len) {
	uint32_t a = 1, b = 0;
	for (size_t i = 0; i < len; i++) {
		a = (a + data[i]) % 65521;
		b = (b + a) % 65521;
	}
	return (b << 16) | a;
}

/* ========================================================================
 * Deflate Store Mode (for writing)
 * ======================================================================== */

static uint8_t *png_deflate_store(const uint8_t *data, size_t len, size_t *out_len) {
	/* Zlib header (2 bytes) + deflate blocks + adler32 (4 bytes) */
	size_t max_block  = 65535;
	size_t num_blocks = (len + max_block - 1) / max_block;
	size_t total      = 2 + num_blocks * 5 + len + 4;

	uint8_t *out = (uint8_t *)malloc(total);
	if (!out)
		return NULL;

	size_t pos = 0;

	/* Zlib header: CMF=0x78 (deflate, 32K window), FLG=0x01 (no dict, level 0) */
	out[pos++] = 0x78;
	out[pos++] = 0x01;

	/* Deflate stored blocks */
	size_t         remaining = len;
	const uint8_t *src       = data;
	while (remaining > 0) {
		size_t block_len = (remaining > max_block) ? max_block : remaining;
		int    is_final  = (remaining <= max_block) ? 1 : 0;

		/* Block header: BFINAL (1 bit) + BTYPE=00 (2 bits) = stored */
		out[pos++] = is_final;

		/* LEN and NLEN (little-endian) */
		out[pos++] = block_len & 0xff;
		out[pos++] = (block_len >> 8) & 0xff;
		out[pos++] = (~block_len) & 0xff;
		out[pos++] = ((~block_len) >> 8) & 0xff;

		memcpy(out + pos, src, block_len);
		pos += block_len;

		src += block_len;
		remaining -= block_len;
	}

	/* Adler-32 checksum (big-endian) */
	uint32_t checksum = png_adler32(data, len);
	out[pos++]        = (checksum >> 24) & 0xff;
	out[pos++]        = (checksum >> 16) & 0xff;
	out[pos++]        = (checksum >> 8) & 0xff;
	out[pos++]        = checksum & 0xff;

	*out_len = pos;
	return out;
}

/* ========================================================================
 * Chunk Writing
 * ======================================================================== */

static void png_write_chunk(FILE *f, const char *type, const uint8_t *data, size_t len) {
	/* Length (big-endian) */
	uint8_t len_bytes[4] = {(len >> 24) & 0xff, (len >> 16) & 0xff, (len >> 8) & 0xff, len & 0xff};
	fwrite(len_bytes, 1, 4, f);

	/* Type */
	fwrite(type, 1, 4, f);

	/* Data */
	if (len > 0 && data) {
		fwrite(data, 1, len, f);
	}

	/* CRC (over type + data) */
	uint8_t *crc_data = (uint8_t *)malloc(4 + len);
	memcpy(crc_data, type, 4);
	if (len > 0 && data) {
		memcpy(crc_data + 4, data, len);
	}
	uint32_t crc = png_crc(crc_data, 4 + len);
	free(crc_data);

	uint8_t crc_bytes[4] = {(crc >> 24) & 0xff, (crc >> 16) & 0xff, (crc >> 8) & 0xff, crc & 0xff};
	fwrite(crc_bytes, 1, 4, f);
}

static void png_write_text_chunk(FILE *f, const char *keyword, const char *text) {
	size_t key_len  = strlen(keyword);
	size_t text_len = strlen(text);
	size_t data_len = key_len + 1 + text_len; /* keyword + null + text */

	uint8_t *data = (uint8_t *)malloc(data_len);
	if (!data)
		return;

	memcpy(data, keyword, key_len);
	data[key_len] = 0; /* Null separator */
	memcpy(data + key_len + 1, text, text_len);

	png_write_chunk(f, "tEXt", data, data_len);
	free(data);
}

/* ========================================================================
 * PNG Writing
 * ======================================================================== */

static int png_save_internal(const png_image *img, FILE *f, const char *keyword, const char *text) {
	/* PNG signature */
	const uint8_t signature[8] = {0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a};
	fwrite(signature, 1, 8, f);

	/* IHDR chunk */
	uint8_t ihdr[13];
	ihdr[0]  = (img->width >> 24) & 0xff;
	ihdr[1]  = (img->width >> 16) & 0xff;
	ihdr[2]  = (img->width >> 8) & 0xff;
	ihdr[3]  = img->width & 0xff;
	ihdr[4]  = (img->height >> 24) & 0xff;
	ihdr[5]  = (img->height >> 16) & 0xff;
	ihdr[6]  = (img->height >> 8) & 0xff;
	ihdr[7]  = img->height & 0xff;
	ihdr[8]  = 8;                                                                                  /* Bit depth */
	ihdr[9]  = (img->channels == 4) ? 6 : (img->channels == 3) ? 2 : (img->channels == 2) ? 4 : 0; /* Color type */
	ihdr[10] = 0;                                                                                  /* Compression */
	ihdr[11] = 0;                                                                                  /* Filter */
	ihdr[12] = 0;                                                                                  /* Interlace */

	png_write_chunk(f, "IHDR", ihdr, 13);

	/* Write metadata if provided */
	if (keyword && text) {
		png_write_text_chunk(f, keyword, text);
	}

	/* Prepare raw image data with filter bytes */
	int      channels  = img->channels;
	size_t   row_bytes = 1 + img->width * channels; /* +1 for filter byte */
	size_t   raw_len   = img->height * row_bytes;
	uint8_t *raw       = (uint8_t *)malloc(raw_len);

	for (int y = 0; y < img->height; y++) {
		raw[y * row_bytes] = 0; /* Filter: None */
		memcpy(raw + y * row_bytes + 1, img->data + y * img->width * channels, img->width * channels);
	}

	/* Compress with zlib (store mode) */
	size_t   compressed_len;
	uint8_t *compressed = png_deflate_store(raw, raw_len, &compressed_len);
	free(raw);

	if (!compressed)
		return -1;

	/* IDAT chunk */
	png_write_chunk(f, "IDAT", compressed, compressed_len);
	free(compressed);

	/* IEND chunk */
	png_write_chunk(f, "IEND", NULL, 0);

	return 0;
}

int png_save(const png_image *img, const char *path) {
	if (!img || !path)
		return -1;

	FILE *f = fopen(path, "wb");
	if (!f)
		return -1;

	int result = png_save_internal(img, f, NULL, NULL);
	fclose(f);
	return result;
}

int png_save_with_text(const png_image *img, const char *path, const char *keyword, const char *text) {
	if (!img || !path)
		return -1;

	FILE *f = fopen(path, "wb");
	if (!f)
		return -1;

	int result = png_save_internal(img, f, keyword, text);
	fclose(f);
	return result;
}

/* ========================================================================
 * Inflate (Decompression)
 * ======================================================================== */

#define PNG_MAXBITS 15

typedef struct {
	const uint8_t *data;
	size_t         len;
	size_t         bytepos;
	uint32_t       bitbuf;
	int            bitcount;
} png_bitstream;

static int png_bitstream_fill(png_bitstream *bs, int n) {
	while (bs->bitcount < n && bs->bytepos < bs->len) {
		bs->bitbuf |= (uint32_t)bs->data[bs->bytepos++] << bs->bitcount;
		bs->bitcount += 8;
	}
	return bs->bitcount >= n;
}

static int png_bitstream_get(png_bitstream *bs, int n, uint32_t *out) {
	if (n == 0) {
		*out = 0;
		return 1;
	}
	if (!png_bitstream_fill(bs, n))
		return 0;
	*out = bs->bitbuf & ((1u << n) - 1u);
	bs->bitbuf >>= n;
	bs->bitcount -= n;
	return 1;
}

static int png_bitstream_align(png_bitstream *bs) {
	uint32_t discard;
	int      skip = bs->bitcount & 7;
	if (skip == 0)
		return 1;
	return png_bitstream_get(bs, skip, &discard);
}

static int png_bitstream_read_bytes(png_bitstream *bs, uint8_t *out, size_t len) {
	if (bs->bitcount == 0) {
		if (bs->bytepos + len > bs->len)
			return 0;
		memcpy(out, bs->data + bs->bytepos, len);
		bs->bytepos += len;
		return 1;
	}
	for (size_t i = 0; i < len; i++) {
		uint32_t v;
		if (!png_bitstream_get(bs, 8, &v))
			return 0;
		out[i] = (uint8_t)v;
	}
	return 1;
}

typedef struct {
	uint16_t count[PNG_MAXBITS + 1];
	uint16_t symbol[288];
} png_huffman;

static int png_huffman_build(png_huffman *h, const uint8_t *lengths, int n) {
	uint16_t offs[PNG_MAXBITS + 1];
	int      left = 1;

	memset(h->count, 0, sizeof(h->count));
	for (int i = 0; i < n; i++) {
		if (lengths[i] > PNG_MAXBITS)
			return 0;
		h->count[lengths[i]]++;
	}

	for (int len = 1; len <= PNG_MAXBITS; len++) {
		left <<= 1;
		left -= h->count[len];
		if (left < 0)
			return 0;
	}

	offs[1] = 0;
	for (int len = 1; len < PNG_MAXBITS; len++) {
		offs[len + 1] = offs[len] + h->count[len];
	}

	for (int i = 0; i < n; i++) {
		int len = lengths[i];
		if (len) {
			h->symbol[offs[len]++] = (uint16_t)i;
		}
	}

	return 1;
}

static int png_huffman_decode(png_bitstream *bs, const png_huffman *h, int *symbol) {
	uint32_t code  = 0;
	uint32_t first = 0;
	uint32_t index = 0;

	for (int len = 1; len <= PNG_MAXBITS; len++) {
		uint32_t bit;
		if (!png_bitstream_get(bs, 1, &bit))
			return 0;
		code |= bit;
		uint32_t count = h->count[len];
		if (code < first + count) {
			*symbol = h->symbol[index + (code - first)];
			return 1;
		}
		index += count;
		first += count;
		first <<= 1;
		code <<= 1;
	}
	return 0;
}

static int png_build_fixed_huffman(png_huffman *litlen, png_huffman *dist) {
	uint8_t litlen_lengths[288];
	uint8_t dist_lengths[32];

	for (int i = 0; i <= 143; i++)
		litlen_lengths[i] = 8;
	for (int i = 144; i <= 255; i++)
		litlen_lengths[i] = 9;
	for (int i = 256; i <= 279; i++)
		litlen_lengths[i] = 7;
	for (int i = 280; i <= 287; i++)
		litlen_lengths[i] = 8;
	for (int i = 0; i < 32; i++)
		dist_lengths[i] = 5;

	if (!png_huffman_build(litlen, litlen_lengths, 288))
		return 0;
	if (!png_huffman_build(dist, dist_lengths, 32))
		return 0;
	return 1;
}

static int png_build_dynamic_huffman(png_bitstream *bs, png_huffman *litlen, png_huffman *dist) {
	static const uint8_t order[19] = {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
	uint32_t             hlit, hdist, hclen;
	uint8_t              code_lengths[19] = {0};
	png_huffman          code_huff;

	if (!png_bitstream_get(bs, 5, &hlit))
		return 0;
	if (!png_bitstream_get(bs, 5, &hdist))
		return 0;
	if (!png_bitstream_get(bs, 4, &hclen))
		return 0;
	int nlen  = (int)hlit + 257;
	int ndist = (int)hdist + 1;
	int ncode = (int)hclen + 4;

	if (nlen > 288 || ndist > 32)
		return 0;

	for (int i = 0; i < ncode; i++) {
		uint32_t v;
		if (!png_bitstream_get(bs, 3, &v))
			return 0;
		code_lengths[order[i]] = (uint8_t)v;
	}

	if (!png_huffman_build(&code_huff, code_lengths, 19))
		return 0;

	uint8_t lengths[320];
	int     total = nlen + ndist;
	int     i     = 0;
	int     prev  = 0;

	while (i < total) {
		int sym;
		if (!png_huffman_decode(bs, &code_huff, &sym))
			return 0;
		if (sym <= 15) {
			lengths[i++] = (uint8_t)sym;
			prev         = sym;
		}
		else if (sym == 16) {
			uint32_t repeat;
			if (i == 0)
				return 0;
			if (!png_bitstream_get(bs, 2, &repeat))
				return 0;
			repeat += 3;
			if (i + (int)repeat > total)
				return 0;
			for (uint32_t r = 0; r < repeat; r++)
				lengths[i++] = (uint8_t)prev;
		}
		else if (sym == 17) {
			uint32_t repeat;
			if (!png_bitstream_get(bs, 3, &repeat))
				return 0;
			repeat += 3;
			if (i + (int)repeat > total)
				return 0;
			for (uint32_t r = 0; r < repeat; r++)
				lengths[i++] = 0;
			prev = 0;
		}
		else if (sym == 18) {
			uint32_t repeat;
			if (!png_bitstream_get(bs, 7, &repeat))
				return 0;
			repeat += 11;
			if (i + (int)repeat > total)
				return 0;
			for (uint32_t r = 0; r < repeat; r++)
				lengths[i++] = 0;
			prev = 0;
		}
		else {
			return 0;
		}
	}

	if (!png_huffman_build(litlen, lengths, nlen))
		return 0;
	if (!png_huffman_build(dist, lengths + nlen, ndist))
		return 0;

	return 1;
}

/* Zlib inflate (stored, fixed, and dynamic blocks) */
static uint8_t *png_inflate_zlib(const uint8_t *data, size_t len, size_t expected_len) {
	if (len < 6)
		return NULL;

	uint8_t cmf = data[0];
	uint8_t flg = data[1];
	if ((cmf & 0x0f) != 8)
		return NULL;
	if (((cmf << 8) + flg) % 31 != 0)
		return NULL;

	size_t pos = 2;
	if (flg & 0x20) {
		if (len < 10)
			return NULL;
		pos += 4;
	}
	if (len < pos + 4)
		return NULL;

	size_t        deflate_len = len - pos - 4;
	png_bitstream bs          = {data + pos, deflate_len, 0, 0, 0};

	uint8_t *out = (uint8_t *)malloc(expected_len);
	if (!out)
		return NULL;
	size_t out_pos = 0;

	static const int len_base[29]   = {3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258};
	static const int len_extra[29]  = {0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0};
	static const int dist_base[30]  = {1,   2,   3,   4,   5,   7,    9,    13,   17,   25,   33,   49,   65,    97,    129,
	                                   193, 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 8193, 12289, 16385, 24577};
	static const int dist_extra[30] = {0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13};

	int final = 0;
	while (!final) {
		uint32_t bfinal, btype;
		if (!png_bitstream_get(&bs, 1, &bfinal))
			goto fail;
		if (!png_bitstream_get(&bs, 2, &btype))
			goto fail;
		final = (int)bfinal;

		if (btype == 0) {
			if (!png_bitstream_align(&bs))
				goto fail;
			uint32_t stored_len, stored_nlen;
			if (!png_bitstream_get(&bs, 16, &stored_len))
				goto fail;
			if (!png_bitstream_get(&bs, 16, &stored_nlen))
				goto fail;
			if ((stored_len ^ 0xffffu) != stored_nlen)
				goto fail;
			if (out_pos + stored_len > expected_len)
				goto fail;
			if (!png_bitstream_read_bytes(&bs, out + out_pos, stored_len))
				goto fail;
			out_pos += stored_len;
		}
		else if (btype == 1 || btype == 2) {
			png_huffman litlen, dist;
			if (btype == 1) {
				if (!png_build_fixed_huffman(&litlen, &dist))
					goto fail;
			}
			else {
				if (!png_build_dynamic_huffman(&bs, &litlen, &dist))
					goto fail;
			}

			for (;;) {
				int sym;
				if (!png_huffman_decode(&bs, &litlen, &sym))
					goto fail;
				if (sym < 256) {
					if (out_pos >= expected_len)
						goto fail;
					out[out_pos++] = (uint8_t)sym;
				}
				else if (sym == 256) {
					break;
				}
				else if (sym <= 285) {
					int      len_sym = sym - 257;
					uint32_t extra, dist_extra_bits;
					int      dist_sym;
					int      length = len_base[len_sym];
					if (len_extra[len_sym]) {
						if (!png_bitstream_get(&bs, len_extra[len_sym], &extra))
							goto fail;
						length += (int)extra;
					}
					if (!png_huffman_decode(&bs, &dist, &dist_sym))
						goto fail;
					if (dist_sym >= 30)
						goto fail;
					int distance = dist_base[dist_sym];
					if (dist_extra[dist_sym]) {
						if (!png_bitstream_get(&bs, dist_extra[dist_sym], &dist_extra_bits))
							goto fail;
						distance += (int)dist_extra_bits;
					}
					if (distance <= 0 || (size_t)distance > out_pos)
						goto fail;
					if (out_pos + length > expected_len)
						goto fail;
					for (int i = 0; i < length; i++) {
						out[out_pos] = out[out_pos - distance];
						out_pos++;
					}
				}
				else {
					goto fail;
				}
			}
		}
		else {
			goto fail;
		}
	}

	if (out_pos != expected_len)
		goto fail;

	uint32_t expected_adler = ((uint32_t)data[len - 4] << 24) | ((uint32_t)data[len - 3] << 16) | ((uint32_t)data[len - 2] << 8) | (uint32_t)data[len - 1];
	if (png_adler32(out, expected_len) != expected_adler)
		goto fail;

	return out;

fail:
	free(out);
	return NULL;
}

/* ========================================================================
 * PNG Filtering
 * ======================================================================== */

static int png_abs(int x) {
	return x < 0 ? -x : x;
}

static void png_unfilter_row(uint8_t *row, const uint8_t *prev_row, int filter, int width, int channels) {
	int bpp = channels;

	switch (filter) {
	case 0: /* None */
		break;
	case 1: /* Sub */
		for (int i = bpp; i < width * channels; i++) {
			row[i] = row[i] + row[i - bpp];
		}
		break;
	case 2: /* Up */
		if (prev_row) {
			for (int i = 0; i < width * channels; i++) {
				row[i] = row[i] + prev_row[i];
			}
		}
		break;
	case 3: /* Average */
		for (int i = 0; i < width * channels; i++) {
			int a  = (i >= bpp) ? row[i - bpp] : 0;
			int b  = prev_row ? prev_row[i] : 0;
			row[i] = row[i] + (a + b) / 2;
		}
		break;
	case 4: /* Paeth */
		for (int i = 0; i < width * channels; i++) {
			int a  = (i >= bpp) ? row[i - bpp] : 0;
			int b  = prev_row ? prev_row[i] : 0;
			int c  = (prev_row && i >= bpp) ? prev_row[i - bpp] : 0;
			int p  = a + b - c;
			int pa = png_abs(p - a);
			int pb = png_abs(p - b);
			int pc = png_abs(p - c);
			int pr = (pa <= pb && pa <= pc) ? a : (pb <= pc) ? b : c;
			row[i] = row[i] + pr;
		}
		break;
	}
}

/* ========================================================================
 * PNG Reading
 * ======================================================================== */

/* Read 4-byte big-endian integer from buffer */
static uint32_t png_read_be32_mem(const uint8_t *p) {
	return ((uint32_t)p[0] << 24) | ((uint32_t)p[1] << 16) | ((uint32_t)p[2] << 8) | p[3];
}

png_image *png_load_mem(const uint8_t *data, size_t len) {
	if (len < 8)
		return NULL;

	/* Verify signature */
	const uint8_t expected[8] = {0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a};
	if (memcmp(data, expected, 8) != 0)
		return NULL;

	int      width = 0, height = 0, color_type = 0;
	uint8_t *idat_data = NULL;
	size_t   idat_len  = 0;

	size_t pos = 8;

	/* Read chunks */
	while (pos + 8 <= len) {
		uint32_t       chunk_len  = png_read_be32_mem(data + pos);
		const uint8_t *chunk_type = data + pos + 4;
		pos += 8;

		if (pos + chunk_len + 4 > len)
			break;

		if (memcmp(chunk_type, "IHDR", 4) == 0) {
			if (chunk_len < 13)
				break;
			width  = png_read_be32_mem(data + pos);
			height = png_read_be32_mem(data + pos + 4);
			/* Skip bit_depth */
			color_type = data[pos + 9];
			pos += chunk_len + 4; /* Skip data and CRC */
		}
		else if (memcmp(chunk_type, "IDAT", 4) == 0) {
			/* Accumulate IDAT chunks */
			idat_data = (uint8_t *)realloc(idat_data, idat_len + chunk_len);
			memcpy(idat_data + idat_len, data + pos, chunk_len);
			idat_len += chunk_len;
			pos += chunk_len + 4;
		}
		else if (memcmp(chunk_type, "IEND", 4) == 0) {
			break;
		}
		else {
			/* Skip unknown chunk */
			pos += chunk_len + 4;
		}
	}

	if (width == 0 || height == 0 || !idat_data) {
		free(idat_data);
		return NULL;
	}

	/* Determine channels from color type */
	int channels;
	switch (color_type) {
	case 0:
		channels = 1;
		break; /* Grayscale */
	case 2:
		channels = 3;
		break; /* RGB */
	case 4:
		channels = 2;
		break; /* Grayscale + Alpha */
	case 6:
		channels = 4;
		break; /* RGBA */
	default:
		free(idat_data);
		return NULL;
	}

	/* Decompress */
	size_t   raw_len = height * (1 + width * channels);
	uint8_t *raw     = png_inflate_zlib(idat_data, idat_len, raw_len);
	free(idat_data);

	if (!raw)
		return NULL;

	/* Create image and apply filters */
	png_image *img = png_create(width, height, channels);
	if (!img) {
		free(raw);
		return NULL;
	}

	int      row_bytes = 1 + width * channels;
	uint8_t *prev_row  = NULL;

	for (int y = 0; y < height; y++) {
		uint8_t *row_data = raw + y * row_bytes;
		int      filter   = row_data[0];
		uint8_t *row      = row_data + 1;

		png_unfilter_row(row, prev_row, filter, width, channels);

		memcpy(img->data + y * width * channels, row, width * channels);
		prev_row = row;
	}

	free(raw);
	return img;
}

png_image *png_load(const char *path) {
	FILE *f = fopen(path, "rb");
	if (!f)
		return NULL;

	fseek(f, 0, SEEK_END);
	size_t file_size = ftell(f);
	fseek(f, 0, SEEK_SET);

	uint8_t *file_data = (uint8_t *)malloc(file_size);
	if (!file_data) {
		fclose(f);
		return NULL;
	}

	if (fread(file_data, 1, file_size, f) != file_size) {
		free(file_data);
		fclose(f);
		return NULL;
	}
	fclose(f);

	png_image *img = png_load_mem(file_data, file_size);
	free(file_data);
	return img;
}

/* Clean up internal macros */
#undef PNG_MAXBITS

#endif /* PNG_IMPLEMENTATION */