Layout: review r2 fixes

internal/layout.go

@@ -0,0 +1,14 @@
+package internal
+
+import "github.com/egoist/mygo/ui"
+
+// Remeasure rebuilds the view when layout gives e another size than the w×h it was built for.
+func Remeasure(c *ui.Context, e *ui.Element, w, h float32) *ui.Element {
+	return e.DrawOver(func(_ *ui.Painter, r ui.Rect) {
+		if abs(r.W-w) > 0.5 || abs(r.H-h) > 0.5 {
+			c.Invalidate()
+		}
+	})
+}
+
+func abs(v float32) float32 { return max(v, -v) }