public void clearCircle(int cx, int cy, int radius) {
		int ci = getI(cx);
		int cj = getJ(cy);
		int iradius = getI(radius);

		for (int i = ci - iradius; i < ci + iradius; i++) {
			for (int j = cj - iradius; j < cj + iradius; j++) {
				if (i < 0 || j < 0 || i >= voxels.length
						|| j >= voxels[0].length)
					continue;
				double di = i - ci;
				double dj = j - cj;
				double idist = Math.sqrt(di * di + dj * dj);

				if (idist < iradius) {
					voxels[i][j] = 0;
					double x = getX(i);
					double y = getY(j);
					for (ResourceClump clump : clumps) {
						double dx = clump.cx - x;
						double dy = clump.cy - y;
						if (dx * dx + dy * dy <= clump.radius * clump.radius) {
							clump.num_voxels--;
						}
					}
				}
			}
		}
	}