ref: 3c953efcba01422102b00f4ee2c861f611a2e84d
dir: /tools/png_dimensions.c/
#include <stdio.h> #include <stdint.h> #include <stdlib.h> void usage(void) { fprintf(stderr, "Usage: png_dimensions infile outfile\n"); exit(1); } void output_dimensions(char* png_filename, char* out_filename) { FILE* f; int width, height; int i; uint8_t bytes[4]; uint8_t output; f = fopen(png_filename, "rb"); if (f == NULL) { fprintf(stderr, "failed to open file %s\n", png_filename); exit(1); } // width fseek(f, 16, SEEK_SET); int size = fread(bytes, 1, 4, f); fclose(f); if (size != 4) { fprintf(stderr, "failed to read at offset 0x10 in file %s\n", png_filename); exit(1); } width = 0; for (i = 0; i < 4; i++) { width |= bytes[i] << (8 * (3 - i)); } width >>= 3; height = width; output = width & 0xf; output |= (height & 0xf) << 4; f = fopen(out_filename, "wb"); if (f == NULL) { fprintf(stderr, "failed to open file %s\n", out_filename); exit(1); } fwrite(&output, 1, 1, f); fclose(f); } int main(int argc, char* argv[]) { if (argc < 3) { usage(); } output_dimensions(argv[1], argv[2]); return 0; }