downscale_2x2(buf + 800 * 300 * 4, subbufs[2]);
downscale_2x2(buf + 800 * 300 * 4 + 400 * 4, subbufs[3]);
+ // make divider lines
+ unsigned char *ptr = buf + 300 * 800 * 4;
+ for (unsigned x = 0; x < 800; ++x) {
+ *ptr++ = 255;
+ *ptr++ = 255;
+ *ptr++ = 255;
+ *ptr++ = 0;
+ }
+
+ ptr = buf + 400 * 4;
+ for (unsigned y = 0; y < 600; ++y) {
+ ptr[0] = 255;
+ ptr[1] = 255;
+ ptr[2] = 255;
+ ptr[3] = 0;
+
+ ptr += 800 * 4;
+ }
+
valid = true;
}