shared/image-loader.c - weston-imx - Git at Google

 /*
  * Copyright © 2008-2012 Kristian Høgsberg
  * Copyright © 2012 Intel Corporation
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
  * "Software"), to deal in the Software without restriction, including
  * without limitation the rights to use, copy, modify, merge, publish,
  * distribute, sublicense, and/or sell copies of the Software, and to
  * permit persons to whom the Software is furnished to do so, subject to
  * the following conditions:
  *
  * The above copyright notice and this permission notice (including the
  * next paragraph) shall be included in all copies or substantial
  * portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  */

 #include "config.h"

 #include <errno.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 #include <png.h>
 #include <pixman.h>

 #include "shared/helpers.h"
 #include "image-loader.h"

 #ifdef HAVE_JPEG
 #include <jpeglib.h>
 #endif

 #ifdef HAVE_WEBP
 #include <webp/decode.h>
 #endif

 static int
 stride_for_width(int width)
 {
 	return width * 4;
 }

 static void
 pixman_image_destroy_func(pixman_image_t *image, void *data)
 {
 	free(data);
 }

 #ifdef HAVE_JPEG

 static void
 swizzle_row(JSAMPLE *row, JDIMENSION width)
 {
 	JSAMPLE *s;
 	uint32_t *d;

 	s = row + (width - 1) * 3;
 	d = (uint32_t *) (row + (width - 1) * 4);
 	while (s >= row) {
 		*d = 0xff000000 | (s[0] << 16) | (s[1] << 8) | (s[2] << 0);
 		s -= 3;
 		d--;
 	}
 }

 static void
 error_exit(j_common_ptr cinfo)
 {
 	longjmp(cinfo->client_data, 1);
 }

 static pixman_image_t *
 load_jpeg(FILE *fp)
 {
 	struct jpeg_decompress_struct cinfo;
 	struct jpeg_error_mgr jerr;
 	pixman_image_t *pixman_image = NULL;
 	unsigned int i;
 	int stride, first;
 	JSAMPLE *data, *rows[4];
 	jmp_buf env;

 	cinfo.err = jpeg_std_error(&jerr);
 	jerr.error_exit = error_exit;
 	cinfo.client_data = env;
 	if (setjmp(env))
 		return NULL;

 	jpeg_create_decompress(&cinfo);

 	jpeg_stdio_src(&cinfo, fp);

 	jpeg_read_header(&cinfo, TRUE);

 	cinfo.out_color_space = JCS_RGB;
 	jpeg_start_decompress(&cinfo);

 	stride = cinfo.output_width * 4;
 	data = malloc(stride * cinfo.output_height);
 	if (data == NULL) {
 		fprintf(stderr, "couldn't allocate image data\n");
 		return NULL;
 	}

 	while (cinfo.output_scanline < cinfo.output_height) {
 		first = cinfo.output_scanline;
 		for (i = 0; i < ARRAY_LENGTH(rows); i++)
 			rows[i] = data + (first + i) * stride;

 		jpeg_read_scanlines(&cinfo, rows, ARRAY_LENGTH(rows));
 		for (i = 0; first + i < cinfo.output_scanline; i++)
 			swizzle_row(rows[i], cinfo.output_width);
 	}

 	jpeg_finish_decompress(&cinfo);

 	jpeg_destroy_decompress(&cinfo);

 	pixman_image = pixman_image_create_bits(PIXMAN_a8r8g8b8,
 					cinfo.output_width,
 					cinfo.output_height,
 					(uint32_t *) data, stride);

 	pixman_image_set_destroy_function(pixman_image,
 				pixman_image_destroy_func, data);

 	return pixman_image;
 }

 #else

 static pixman_image_t *
 load_jpeg(FILE *fp)
 {
 	fprintf(stderr, "JPEG support disabled at compile-time\n");
 	return NULL;
 }

 #endif

 static inline int
 multiply_alpha(int alpha, int color)
 {
     int temp = (alpha * color) + 0x80;

     return ((temp + (temp >> 8)) >> 8);
 }

 static void
 premultiply_data(png_structp   png,
 		 png_row_infop row_info,
 		 png_bytep     data)
 {
     unsigned int i;
     png_bytep p;

     for (i = 0, p = data; i < row_info->rowbytes; i += 4, p += 4) {
 	png_byte  alpha = p[3];
 	uint32_t w;

 	if (alpha == 0) {
 		w = 0;
 	} else {
 		png_byte red   = p[0];
 		png_byte green = p[1];
 		png_byte blue  = p[2];

 		if (alpha != 0xff) {
 			red   = multiply_alpha(alpha, red);
 			green = multiply_alpha(alpha, green);
 			blue  = multiply_alpha(alpha, blue);
 		}
 		w = (alpha << 24) | (red << 16) | (green << 8) | (blue << 0);
 	}

 	* (uint32_t *) p = w;
     }
 }

 static void
 read_func(png_structp png, png_bytep data, png_size_t size)
 {
 	FILE *fp = png_get_io_ptr(png);

 	if (fread(data, 1, size, fp) != size)
 		png_error(png, NULL);
 }

 static void
 png_error_callback(png_structp png, png_const_charp error_msg)
 {
     longjmp (png_jmpbuf (png), 1);
 }

 static pixman_image_t *
 load_png(FILE *fp)
 {
 	png_struct *png;
 	png_info *info;
 	png_byte *data = NULL;
 	png_byte **row_pointers = NULL;
 	png_uint_32 width, height;
 	int depth, color_type, interlace, stride;
 	unsigned int i;
 	pixman_image_t *pixman_image = NULL;

 	png = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL,
 				     png_error_callback, NULL);
 	if (!png)
 		return NULL;

 	info = png_create_info_struct(png);
 	if (!info) {
 		png_destroy_read_struct(&png, &info, NULL);
 		return NULL;
 	}

 	if (setjmp(png_jmpbuf(png))) {
 		if (data)
 			free(data);
 		if (row_pointers)
 			free(row_pointers);
 		png_destroy_read_struct(&png, &info, NULL);
 		return NULL;
 	}

 	png_set_read_fn(png, fp, read_func);
 	png_read_info(png, info);
 	png_get_IHDR(png, info,
 		     &width, &height, &depth,
 		     &color_type, &interlace, NULL, NULL);

 	if (color_type == PNG_COLOR_TYPE_PALETTE)
 		png_set_palette_to_rgb(png);

 	if (color_type == PNG_COLOR_TYPE_GRAY)
 		png_set_expand_gray_1_2_4_to_8(png);

 	if (png_get_valid(png, info, PNG_INFO_tRNS))
 		png_set_tRNS_to_alpha(png);

 	if (depth == 16)
 		png_set_strip_16(png);

 	if (depth < 8)
 		png_set_packing(png);

 	if (color_type == PNG_COLOR_TYPE_GRAY ||
 	    color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
 		png_set_gray_to_rgb(png);

 	if (interlace != PNG_INTERLACE_NONE)
 		png_set_interlace_handling(png);

 	png_set_filler(png, 0xff, PNG_FILLER_AFTER);
 	png_set_read_user_transform_fn(png, premultiply_data);
 	png_read_update_info(png, info);
 	png_get_IHDR(png, info,
 		     &width, &height, &depth,
 		     &color_type, &interlace, NULL, NULL);


 	stride = stride_for_width(width);
 	data = malloc(stride * height);
 	if (!data) {
 		png_destroy_read_struct(&png, &info, NULL);
 		return NULL;
 	}

 	row_pointers = malloc(height * sizeof row_pointers[0]);
 	if (row_pointers == NULL) {
 		free(data);
 		png_destroy_read_struct(&png, &info, NULL);
 		return NULL;
 	}

 	for (i = 0; i < height; i++)
 		row_pointers[i] = &data[i * stride];

 	png_read_image(png, row_pointers);
 	png_read_end(png, info);

 	free(row_pointers);
 	png_destroy_read_struct(&png, &info, NULL);

 	pixman_image = pixman_image_create_bits(PIXMAN_a8r8g8b8,
 				width, height, (uint32_t *) data, stride);

 	pixman_image_set_destroy_function(pixman_image,
 				pixman_image_destroy_func, data);

 	return pixman_image;
 }

 #ifdef HAVE_WEBP

 static pixman_image_t *
 load_webp(FILE *fp)
 {
 	WebPDecoderConfig config;
 	uint8_t buffer[16 * 1024];
 	int len;
 	VP8StatusCode status;
 	WebPIDecoder *idec;

 	if (!WebPInitDecoderConfig(&config)) {
 		fprintf(stderr, "Library version mismatch!\n");
 		return NULL;
 	}

 	/* webp decoding api doesn't seem to specify a min size that's
 	   usable for GetFeatures, but 256 works... */
 	len = fread(buffer, 1, 256, fp);
 	status = WebPGetFeatures(buffer, len, &config.input);
 	if (status != VP8_STATUS_OK) {
 		fprintf(stderr, "failed to parse webp header\n");
 		WebPFreeDecBuffer(&config.output);
 		return NULL;
 	}

 	config.output.colorspace = MODE_BGRA;
 	config.output.u.RGBA.stride = stride_for_width(config.input.width);
 	config.output.u.RGBA.size =
 		config.output.u.RGBA.stride * config.input.height;
 	config.output.u.RGBA.rgba =
 		malloc(config.output.u.RGBA.stride * config.input.height);
 	config.output.is_external_memory = 1;
 	if (!config.output.u.RGBA.rgba) {
 		WebPFreeDecBuffer(&config.output);
 		return NULL;
 	}

 	rewind(fp);
 	idec = WebPINewDecoder(&config.output);
 	if (!idec) {
 		WebPFreeDecBuffer(&config.output);
 		return NULL;
 	}

 	while (!feof(fp)) {
 		len = fread(buffer, 1, sizeof buffer, fp);
 		status = WebPIAppend(idec, buffer, len);
 		if (status != VP8_STATUS_OK) {
 			fprintf(stderr, "webp decode status %d\n", status);
 			WebPIDelete(idec);
 			WebPFreeDecBuffer(&config.output);
 			return NULL;
 		}
 	}

 	WebPIDelete(idec);
 	WebPFreeDecBuffer(&config.output);

 	return pixman_image_create_bits(PIXMAN_a8r8g8b8,
 					config.input.width,
 					config.input.height,
 					(uint32_t *) config.output.u.RGBA.rgba,
 					config.output.u.RGBA.stride);
 }

 #else

 static pixman_image_t *
 load_webp(FILE *fp)
 {
 	fprintf(stderr, "WebP support disabled at compile-time\n");
 	return NULL;
 }

 #endif


 struct image_loader {
 	unsigned char header[4];
 	int header_size;
 	pixman_image_t *(*load)(FILE *fp);
 };

 static const struct image_loader loaders[] = {
 	{ { 0x89, 'P', 'N', 'G' }, 4, load_png },
 	{ { 0xff, 0xd8 }, 2, load_jpeg },
 	{ { 'R', 'I', 'F', 'F' }, 4, load_webp }
 };

 pixman_image_t *
 load_image(const char *filename)
 {
 	pixman_image_t *image = NULL;
 	unsigned char header[4];
 	FILE *fp;
 	unsigned int i;

 	if (!filename || !*filename)
 		return NULL;

 	fp = fopen(filename, "rb");
 	if (!fp) {
 		fprintf(stderr, "%s: %s\n", filename, strerror(errno));
 		return NULL;
 	}

 	if (fread(header, sizeof header, 1, fp) != 1) {
 		fclose(fp);
 		fprintf(stderr, "%s: unable to read file header\n", filename);
 		return NULL;
 	}

 	rewind(fp);
 	for (i = 0; i < ARRAY_LENGTH(loaders); i++) {
 		if (memcmp(header, loaders[i].header,
 			   loaders[i].header_size) == 0) {
 			image = loaders[i].load(fp);
 			break;
 		}
 	}

 	fclose(fp);

 	if (i == ARRAY_LENGTH(loaders)) {
 		fprintf(stderr, "%s: unrecognized file header "
 			"0x%02x 0x%02x 0x%02x 0x%02x\n",
 			filename, header[0], header[1], header[2], header[3]);
 	} else if (!image) {
 		/* load probably printed something, but just in case */
 		fprintf(stderr, "%s: error reading image\n", filename);
 	}

 	return image;
 }
	/*
	* Copyright © 2008-2012 Kristian Høgsberg
	* Copyright © 2012 Intel Corporation
	*
	* Permission is hereby granted, free of charge, to any person obtaining
	* a copy of this software and associated documentation files (the
	* "Software"), to deal in the Software without restriction, including
	* without limitation the rights to use, copy, modify, merge, publish,
	* distribute, sublicense, and/or sell copies of the Software, and to
	* permit persons to whom the Software is furnished to do so, subject to
	* the following conditions:
	*
	* The above copyright notice and this permission notice (including the
	* next paragraph) shall be included in all copies or substantial
	* portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
	* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
	* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
	* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
	* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
	* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	* SOFTWARE.
	*/

	#include "config.h"

	#include <errno.h>
	#include <stdlib.h>
	#include <stdint.h>
	#include <stdio.h>
	#include <string.h>
	#include <png.h>
	#include <pixman.h>

	#include "shared/helpers.h"
	#include "image-loader.h"

	#ifdef HAVE_JPEG
	#include <jpeglib.h>
	#endif

	#ifdef HAVE_WEBP
	#include <webp/decode.h>
	#endif

	static int
	stride_for_width(int width)
	{
	return width * 4;
	}

	static void
	pixman_image_destroy_func(pixman_image_t image, void data)
	{
	free(data);
	}

	#ifdef HAVE_JPEG

	static void
	swizzle_row(JSAMPLE *row, JDIMENSION width)
	{
	JSAMPLE *s;
	uint32_t *d;

	s = row + (width - 1) * 3;
	d = (uint32_t ) (row + (width - 1) 4);
	while (s >= row) {
	*d = 0xff000000 \| (s[0] << 16) \| (s[1] << 8) \| (s[2] << 0);
	s -= 3;
	d--;
	}
	}

	static void
	error_exit(j_common_ptr cinfo)
	{
	longjmp(cinfo->client_data, 1);
	}

	static pixman_image_t *
	load_jpeg(FILE *fp)
	{
	struct jpeg_decompress_struct cinfo;
	struct jpeg_error_mgr jerr;
	pixman_image_t *pixman_image = NULL;
	unsigned int i;
	int stride, first;
	JSAMPLE data, rows[4];
	jmp_buf env;

	cinfo.err = jpeg_std_error(&jerr);
	jerr.error_exit = error_exit;
	cinfo.client_data = env;
	if (setjmp(env))
	return NULL;

	jpeg_create_decompress(&cinfo);

	jpeg_stdio_src(&cinfo, fp);

	jpeg_read_header(&cinfo, TRUE);

	cinfo.out_color_space = JCS_RGB;
	jpeg_start_decompress(&cinfo);

	stride = cinfo.output_width * 4;
	data = malloc(stride * cinfo.output_height);
	if (data == NULL) {
	fprintf(stderr, "couldn't allocate image data\n");
	return NULL;
	}

	while (cinfo.output_scanline < cinfo.output_height) {
	first = cinfo.output_scanline;
	for (i = 0; i < ARRAY_LENGTH(rows); i++)
	rows[i] = data + (first + i) * stride;

	jpeg_read_scanlines(&cinfo, rows, ARRAY_LENGTH(rows));
	for (i = 0; first + i < cinfo.output_scanline; i++)
	swizzle_row(rows[i], cinfo.output_width);
	}

	jpeg_finish_decompress(&cinfo);

	jpeg_destroy_decompress(&cinfo);

	pixman_image = pixman_image_create_bits(PIXMAN_a8r8g8b8,
	cinfo.output_width,
	cinfo.output_height,
	(uint32_t *) data, stride);

	pixman_image_set_destroy_function(pixman_image,
	pixman_image_destroy_func, data);

	return pixman_image;
	}

	#else

	static pixman_image_t *
	load_jpeg(FILE *fp)
	{
	fprintf(stderr, "JPEG support disabled at compile-time\n");
	return NULL;
	}

	#endif

	static inline int
	multiply_alpha(int alpha, int color)
	{
	int temp = (alpha * color) + 0x80;

	return ((temp + (temp >> 8)) >> 8);
	}

	static void
	premultiply_data(png_structp png,
	png_row_infop row_info,
	png_bytep data)
	{
	unsigned int i;
	png_bytep p;

	for (i = 0, p = data; i < row_info->rowbytes; i += 4, p += 4) {
	png_byte alpha = p[3];
	uint32_t w;

	if (alpha == 0) {
	w = 0;
	} else {
	png_byte red = p[0];
	png_byte green = p[1];
	png_byte blue = p[2];

	if (alpha != 0xff) {
	red = multiply_alpha(alpha, red);
	green = multiply_alpha(alpha, green);
	blue = multiply_alpha(alpha, blue);
	}
	w = (alpha << 24) \| (red << 16) \| (green << 8) \| (blue << 0);
	}

	* (uint32_t *) p = w;
	}
	}

	static void
	read_func(png_structp png, png_bytep data, png_size_t size)
	{
	FILE *fp = png_get_io_ptr(png);

	if (fread(data, 1, size, fp) != size)
	png_error(png, NULL);
	}

	static void
	png_error_callback(png_structp png, png_const_charp error_msg)
	{
	longjmp (png_jmpbuf (png), 1);
	}

	static pixman_image_t *
	load_png(FILE *fp)
	{
	png_struct *png;
	png_info *info;
	png_byte *data = NULL;
	png_byte **row_pointers = NULL;
	png_uint_32 width, height;
	int depth, color_type, interlace, stride;
	unsigned int i;
	pixman_image_t *pixman_image = NULL;

	png = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL,
	png_error_callback, NULL);
	if (!png)
	return NULL;

	info = png_create_info_struct(png);
	if (!info) {
	png_destroy_read_struct(&png, &info, NULL);
	return NULL;
	}

	if (setjmp(png_jmpbuf(png))) {
	if (data)
	free(data);
	if (row_pointers)
	free(row_pointers);
	png_destroy_read_struct(&png, &info, NULL);
	return NULL;
	}

	png_set_read_fn(png, fp, read_func);
	png_read_info(png, info);
	png_get_IHDR(png, info,
	&width, &height, &depth,
	&color_type, &interlace, NULL, NULL);

	if (color_type == PNG_COLOR_TYPE_PALETTE)
	png_set_palette_to_rgb(png);

	if (color_type == PNG_COLOR_TYPE_GRAY)
	png_set_expand_gray_1_2_4_to_8(png);

	if (png_get_valid(png, info, PNG_INFO_tRNS))
	png_set_tRNS_to_alpha(png);

	if (depth == 16)
	png_set_strip_16(png);

	if (depth < 8)
	png_set_packing(png);

	if (color_type == PNG_COLOR_TYPE_GRAY \|\|
	color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
	png_set_gray_to_rgb(png);

	if (interlace != PNG_INTERLACE_NONE)
	png_set_interlace_handling(png);

	png_set_filler(png, 0xff, PNG_FILLER_AFTER);
	png_set_read_user_transform_fn(png, premultiply_data);
	png_read_update_info(png, info);
	png_get_IHDR(png, info,
	&width, &height, &depth,
	&color_type, &interlace, NULL, NULL);


	stride = stride_for_width(width);
	data = malloc(stride * height);
	if (!data) {
	png_destroy_read_struct(&png, &info, NULL);
	return NULL;
	}

	row_pointers = malloc(height * sizeof row_pointers[0]);
	if (row_pointers == NULL) {
	free(data);
	png_destroy_read_struct(&png, &info, NULL);
	return NULL;
	}

	for (i = 0; i < height; i++)
	row_pointers[i] = &data[i * stride];

	png_read_image(png, row_pointers);
	png_read_end(png, info);

	free(row_pointers);
	png_destroy_read_struct(&png, &info, NULL);

	pixman_image = pixman_image_create_bits(PIXMAN_a8r8g8b8,
	width, height, (uint32_t *) data, stride);

	pixman_image_set_destroy_function(pixman_image,
	pixman_image_destroy_func, data);

	return pixman_image;
	}

	#ifdef HAVE_WEBP

	static pixman_image_t *
	load_webp(FILE *fp)
	{
	WebPDecoderConfig config;
	uint8_t buffer[16 * 1024];
	int len;
	VP8StatusCode status;
	WebPIDecoder *idec;

	if (!WebPInitDecoderConfig(&config)) {
	fprintf(stderr, "Library version mismatch!\n");
	return NULL;
	}

	/* webp decoding api doesn't seem to specify a min size that's
	usable for GetFeatures, but 256 works... */
	len = fread(buffer, 1, 256, fp);
	status = WebPGetFeatures(buffer, len, &config.input);
	if (status != VP8_STATUS_OK) {
	fprintf(stderr, "failed to parse webp header\n");
	WebPFreeDecBuffer(&config.output);
	return NULL;
	}

	config.output.colorspace = MODE_BGRA;
	config.output.u.RGBA.stride = stride_for_width(config.input.width);
	config.output.u.RGBA.size =
	config.output.u.RGBA.stride * config.input.height;
	config.output.u.RGBA.rgba =
	malloc(config.output.u.RGBA.stride * config.input.height);
	config.output.is_external_memory = 1;
	if (!config.output.u.RGBA.rgba) {
	WebPFreeDecBuffer(&config.output);
	return NULL;
	}

	rewind(fp);
	idec = WebPINewDecoder(&config.output);
	if (!idec) {
	WebPFreeDecBuffer(&config.output);
	return NULL;
	}

	while (!feof(fp)) {
	len = fread(buffer, 1, sizeof buffer, fp);
	status = WebPIAppend(idec, buffer, len);
	if (status != VP8_STATUS_OK) {
	fprintf(stderr, "webp decode status %d\n", status);
	WebPIDelete(idec);
	WebPFreeDecBuffer(&config.output);
	return NULL;
	}
	}

	WebPIDelete(idec);
	WebPFreeDecBuffer(&config.output);

	return pixman_image_create_bits(PIXMAN_a8r8g8b8,
	config.input.width,
	config.input.height,
	(uint32_t *) config.output.u.RGBA.rgba,
	config.output.u.RGBA.stride);
	}

	#else

	static pixman_image_t *
	load_webp(FILE *fp)
	{
	fprintf(stderr, "WebP support disabled at compile-time\n");
	return NULL;
	}

	#endif


	struct image_loader {
	unsigned char header[4];
	int header_size;
	pixman_image_t (load)(FILE *fp);
	};

	static const struct image_loader loaders[] = {
	{ { 0x89, 'P', 'N', 'G' }, 4, load_png },
	{ { 0xff, 0xd8 }, 2, load_jpeg },
	{ { 'R', 'I', 'F', 'F' }, 4, load_webp }
	};

	pixman_image_t *
	load_image(const char *filename)
	{
	pixman_image_t *image = NULL;
	unsigned char header[4];
	FILE *fp;
	unsigned int i;

	if (!filename \|\| !*filename)
	return NULL;

	fp = fopen(filename, "rb");
	if (!fp) {
	fprintf(stderr, "%s: %s\n", filename, strerror(errno));
	return NULL;
	}

	if (fread(header, sizeof header, 1, fp) != 1) {
	fclose(fp);
	fprintf(stderr, "%s: unable to read file header\n", filename);
	return NULL;
	}

	rewind(fp);
	for (i = 0; i < ARRAY_LENGTH(loaders); i++) {
	if (memcmp(header, loaders[i].header,
	loaders[i].header_size) == 0) {
	image = loaders[i].load(fp);
	break;
	}
	}

	fclose(fp);

	if (i == ARRAY_LENGTH(loaders)) {
	fprintf(stderr, "%s: unrecognized file header "
	"0x%02x 0x%02x 0x%02x 0x%02x\n",
	filename, header[0], header[1], header[2], header[3]);
	} else if (!image) {
	/* load probably printed something, but just in case */
	fprintf(stderr, "%s: error reading image\n", filename);
	}

	return image;
	}