1 files changed, 41 insertions, 0 deletions
diff --git a/go/ui/hoverDetector.go b/go/ui/hoverDetector.go
new file mode 100644
index 00000000..49161f4f
--- /dev/null
+++ b/go/ui/hoverDetector.go
@@ -0,0 +1,41 @@
+package ui
+
+// A simple structure to detect if the cursor has not moved or started moving again.
+// hoverDetector.update must be called during each Update invocation to track the
+// frame and the current cursor position.
+type hoverDetector struct {
+	last_x, last_y int
+	ticks          int
+	hovering       Hoverable
+}
+
+func (h *hoverDetector) update(collection *Collection, x, y int, w Widget) {
+	if x == h.last_x && y == h.last_y {
+		h.hover(collection, x, y, w)
+	} else {
+		h.reset(x, y)
+		h.last_x, h.last_y = x, y
+	}
+}
+
+func (h *hoverDetector) hover(collection *Collection, x, y int, w Widget) {
+	h.ticks++
+
+	if w == nil || h.hovering != nil {
+		return
+	}
+
+	if hoverable, ok := w.(Hoverable); ok && hoverable.onHover(h.ticks, x, y, collection) {
+		h.hovering = hoverable
+	}
+}
+
+func (h *hoverDetector) reset(x, y int) {
+	if h.hovering != nil {
+		if !h.hovering.stopHover(h.ticks, x, y) {
+			return
+		}
+		h.hovering = nil
+	}
+	h.ticks = 0
+}