diff --git a/src/step.wgsl b/src/step.wgsl
index a84b2ca..13f6288 100644
--- a/src/step.wgsl
+++ b/src/step.wgsl
@@ -16,20 +16,25 @@ fn on_vertex(@builtin(vertex_index) vi: u32) -> Varying {
 
 @fragment
 fn on_fragment(in: Varying) -> @location(0) u32 {
-	let a = textureGather(0, field, smp, in.uv, vec2(0, 0));
-	let b = textureGather(0, field, smp, in.uv, vec2(0, 1));
-	let c = textureGather(0, field, smp, in.uv, vec2(1, 0));
-	let d = textureGather(0, field, smp, in.uv, vec2(1, 1));
+	let aa = textureGather(0, field, smp, in.uv, vec2(0, 0));
+	let ab = textureGather(0, field, smp, in.uv, vec2(0, 1));
+	let ba = textureGather(0, field, smp, in.uv, vec2(1, 0));
+	let bb = textureGather(0, field, smp, in.uv, vec2(1, 1));
+	let s = aa.y;
+	let a = vec4(aa.xzw, bb.y);
+	let b = vec4(ab.xy, ba.yz);
 	var ret = 0u;
 	for (var layer = 0u; layer < 8u; layer++) {
-		ret |= calc(a >> vec4(layer) & vec4(1u), b >> vec4(layer) & vec4(1u), c >> vec4(layer) & vec4(1u), d >> vec4(layer) & vec4(1u)) << layer;
+		let s = s >> layer & 1u;
+		let a = a >> vec4(layer) & vec4(1u);
+		let b = b >> vec4(layer) & vec4(1u);
+		ret |= calc(s, a, b) << layer;
 	}
 	return ret;
 }
 
-fn calc(a: vec4u, b: vec4u, c: vec4u, d: vec4u) -> u32 {
-	let state = a.y;
-	let n = a.x + a.z + a.w + b.x + b.y + c.y + c.z + d.y;
+fn calc(state: u32, a: vec4u, b: vec4u) -> u32 {
+	let n = dot(a, vec4(1u)) + dot(b, vec4(1u));
 	switch (n) {
 	case 2u: { return state; }
 	case 3u: { return 1u; }