Convert raw BGRA framebuffer to RGB png file

Framebuffer to PNG

This program can be used to convert raw BGRA 8888 framebuffer to standard PNG file.

data.c

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

typedef struct {
	uint8_t red;
	uint8_t green;
	uint8_t blue;
} pixel_t;

typedef struct {
	pixel_t *pixels;
	size_t width;
	size_t height;
} bitmap_t;

static pixel_t * pixel_at (bitmap_t *bitmap, int x, int y) {
	return bitmap->pixels + x + bitmap->width * y;
}

static int save_png_to_file (bitmap_t *bitmap, const char* path) {
	FILE *p_file;
	png_structp	p_png = NULL;
	png_infop p_info = NULL;
	size_t x, y;
	png_byte ** row_pointers = NULL;
	int status = -1;
	int pixel_size = 3;
	int depth = 8;

	p_file = fopen(path, "wb");
	if (!p_file) {
		goto fopen_failed;
	}
	p_png = png_create_write_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
	if (p_png == NULL) {
		goto png_create_write_struct_failed;
	}
	p_info = png_create_info_struct (p_png);
	if (p_info == NULL) {
		goto png_create_info_struct_failed;
	}
	if (setjmp (png_jmpbuf (p_png))) {
		goto png_failure;
	}

	png_set_IHDR (	p_png,
					p_info,
					bitmap->width,
					bitmap->height,
					depth,
					PNG_COLOR_TYPE_RGB,
					PNG_INTERLACE_NONE,
					PNG_COMPRESSION_TYPE_DEFAULT,
					PNG_FILTER_TYPE_DEFAULT);

	row_pointers = png_malloc (p_png, bitmap->height * sizeof (png_byte*));
	for (y = 0; y < bitmap->height; ++y) {
		png_byte *row = png_malloc (p_png, sizeof (uint8_t) * bitmap->width * pixel_size);
		row_pointers[y] = row;
		for (x = 0; x < bitmap->width; ++x) {
			pixel_t *pixel = pixel_at (bitmap, x, y);
			*row++ = pixel->red;
			*row++ = pixel->green;
			*row++ = pixel->blue;
		}
	}

	png_init_io (p_png, p_file);
	png_set_rows (p_png, p_info, row_pointers);
	png_write_png (p_png, p_info, PNG_TRANSFORM_IDENTITY, NULL);

	status = 0;
	for (y = 0; y < bitmap->height; y++) {
		png_free (p_png, row_pointers[y]);
	}
	png_free (p_png, row_pointers);

png_failure:
png_create_info_struct_failed:
	png_destroy_write_struct(&p_png, &p_info);
png_create_write_struct_failed:
	fclose(p_file);
fopen_failed:
	return status;
}

int main (int argc, char **argv) {
	size_t width, height, read = 0, length;
	int i, status = 0;
	char *input, *output;
	uint8_t *buffer = NULL;
	bitmap_t *bitmap = NULL;
	pixel_t *pixel_out;
	uint8_t *pixel_in;
	FILE * fp = NULL;

	if (argc != 5) {
		printf("Usage: %s <width> <height> <input> <output>\n", argv[0]);
		exit(1);
	}
	width  = (size_t) atoi (argv[1]);
	height = (size_t) atoi (argv[2]);
	input  = argv[3];
	output = argv[4];
	length = width * height * 4;
	
	buffer = malloc (length);
	bitmap = malloc (sizeof (pixel_t*) + sizeof (size_t) * 2);
	bitmap->pixels = malloc(sizeof (pixel_t) * width * height);
	bitmap->width  = width;
	bitmap->height = height;

	fp = fopen(input, "rb");
	if (!fp) {
		printf ("Error opening file (%d): %s.\n", errno, strerror (errno));
		status = 1;
		goto free_val;
	}

	do {
		read = fread (buffer + read, length - read, 1, fp);
	} while (read > 0);

	read = fclose (fp);
	if (read == EOF) {
		printf ("Error closing file (%d): %s.\n", errno, strerror (errno));
		status = 1;
		goto free_val;
	}

	pixel_in = buffer;
	pixel_out = bitmap->pixels;
	for (i = 0; i < width * height; i++) {
		pixel_out->blue  = *(pixel_in++);
		pixel_out->green = *(pixel_in++);
		pixel_out->red   = *(pixel_in++);
		pixel_in++; // ignore alpha
		pixel_out++; // to next pixel
	}
	pixel_in = NULL;
	pixel_out = NULL;

	int retval = save_png_to_file (bitmap, output);
	if (retval != 0) {
		printf ("Error saving PNG.\n");
		goto free_val;
	}

free_val:
	free(buffer);
	free(bitmap->pixels);
	free(bitmap);
	return status;
}

Yes, there's unnecessary copying to bitmap_t, but I've created this mainly for fun. PNG write function comes from www.lemoda.net/c/write-png/.

For this program to work correctly fbset must return rgba 8/16,8/8,8/0,0/0 and bit depth must be 32.

How to compile: enter this to terminal while you're in the directory with data.c

gcc data.c -O2 -lpng -o data

Usage:

• use framebuffer:
  ./data <fb width> <fb height> /dev/fb0 <out>.png (replace <...> with corresponding values)
• use framebuffer snapshot:

dd if=/dev/fb0 of=fb.raw
./data <fb width> <fb height> fb.raw <out>.png

Replace <...> with corresponding values.