support multi-module (#4)

* add multimodule
* re-package modules

util/map.go

@@ -0,0 +1,81 @@
+package util
+
+import "math"
+
+func ShortDistance(w, h uint32, x1, y1, x2, y2 float64) float64 {
+	return math.Hypot(deltas(w, h, x1, y1, x2, y2))
+}
+
+func NextTravelCoord(w, h uint32, x1, y1, x2, y2, delta float64) (float64, float64, bool) {
+	deltaX, deltaY := deltas(w, h, x1, y1, x2, y2)
+	distance := math.Hypot(deltaX, deltaY)
+	if distance <= delta {
+		return x2, y2, true
+	}
+	// [ ] refactor - remove extra vars
+	xa := 0.
+	ya := 0.
+	xb := deltaX
+	yb := deltaY
+	d := distance
+	d2 := delta
+	xc := xa - (d2*(xa-xb))/d
+	yc := ya - (d2*(ya-yb))/d
+
+	// ---
+	var tx, ty float64
+
+	if math.Abs(x2-x1) > float64(w/2) {
+		// moving across X boundary
+		if x2 < x1 {
+			// moving across higher border
+			tx = math.Mod(x1+xc, float64(w))
+		} else {
+			// moving across lower border
+			tx = x1 - xc
+			if tx < 0 {
+				tx = float64(w) + tx
+			}
+		}
+	} else {
+		if x2 < x1 {
+			tx = x1 - xc
+		} else {
+			tx = x1 + xc
+		}
+	}
+
+	if math.Abs(y2-y1) > float64(h/2) {
+		// moving across Y boundary
+		if y2 < y1 {
+			// moving across higher border
+			ty = math.Mod(y1+yc, float64(h))
+		} else {
+			// moving across lower border
+			ty = y1 - yc
+			if ty < 0 {
+				ty = float64(h) + ty
+			}
+		}
+	} else {
+		if y2 < y1 {
+			ty = y1 - yc
+		} else {
+			ty = y1 + yc
+		}
+	}
+
+	return tx, ty, false
+}
+
+func deltas(w, h uint32, x1, y1, x2, y2 float64) (float64, float64) {
+	dx := math.Abs(x2 - x1)
+	dy := math.Abs(y2 - y1)
+	if dx > float64(w/2) {
+		dx = float64(h) - dx
+	}
+	if dy > float64(h/2) {
+		dy = float64(h) - dy
+	}
+	return dx, dy
+}