Add C build tools.

tools/png_dimensions.c

@@ -0,0 +1,53 @@
+#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);
+	fread(bytes, 1, 4, f);
+	fclose(f);
+
+	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;
+}