Add powder material deposit logic for surface placement

src/shaders/antsCompute.frag

@@ -246,6 +246,21 @@ void main()	{
         }
     }
 
+    // deposit carried powder material when standing on air with solid ground below
+    if (isCarrying == 1. && int(cargoMaterialId) != MAT_FOOD) {
+        float cellMatId = texture(tWorld, roundUvToCellCenter(pos)).x;
+        if (int(cellMatId) == MAT_AIR) {
+            vec2 belowPos = pos - vec2(0., cellSize);
+            float belowMatId = texture(tWorld, roundUvToCellCenter(belowPos)).x;
+            if (int(belowMatId) != MAT_AIR || belowPos.y <= 0.) {
+                isCarrying = 0.;
+                // keep cargoMaterialId set so discretize can read it this frame
+                angle += PI;
+                storage = getMaxScentStorage(vUv);
+            }
+        }
+    }
+
     FragColor = vec4(
         pos.x,
         pos.y,