- dx = (int)((heightmap[i] - heightmap[i + 1]) * offsetPower);
- dy = (int)((heightmap[i] - heightmap[i + fb_width]) * offsetPower);
+ dx = i < fb_size - 1 ? (int)((heightmap[i] - heightmap[i + 1]) * offsetPower) : 0;
+ dy = i < fb_size - fb_width ? (int)((heightmap[i] - heightmap[i + fb_width]) * offsetPower) : 0;