ui: rename TransformOp.Mul to Multiply and split InvTransform

Multiply is a bit longer but more clear. InvTransform was really
two operations: Invert and Transform.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/app/internal/gpu/gpu.go

@@ -650,7 +650,7 @@ loop:
 		case ops.TypeTransform:
 			var op ui.TransformOp
 			op.Decode(encOp.Data)
-			state.t = state.t.Mul(op)
+			state.t = state.t.Multiply(op)
 		case ops.TypeAux:
 			aux = encOp.Data[ops.TypeAuxLen:]
 			auxKey = encOp.Key

ui/app/internal/input/pointer.go

@@ -88,7 +88,7 @@ func (q *pointerQueue) collectHandlers(r *ui.OpsReader, events *handlerEvents, t
 		case ops.TypeTransform:
 			var op ui.TransformOp
 			op.Decode(encOp.Data)
-			t = t.Mul(op)
+			t = t.Multiply(op)
 		case ops.TypePointerHandler:
 			var op pointer.HandlerOp
 			op.Decode(encOp.Data, encOp.Refs)
@@ -150,7 +150,7 @@ func (q *pointerQueue) hit(areaIdx int, p f32.Point) bool {
 }
 
 func (a *areaNode) hit(p f32.Point) bool {
-	p = a.trans.InvTransform(p)
+	p = a.trans.Invert().Transform(p)
 	return a.area.Hit(p)
 }
 
@@ -246,7 +246,7 @@ func (q *pointerQueue) Push(e pointer.Event, events *handlerEvents) {
 			e.Priority = pointer.Foremost
 		}
 		e.Hit = q.hit(h.area, e.Position)
-		e.Position = h.transform.InvTransform(e.Position)
+		e.Position = h.transform.Invert().Transform(e.Position)
 		events.Add(k, e)
 		if e.Type == pointer.Release {
 			// Release grab when the number of grabs reaches zero.

ui/ui.go

@@ -56,19 +56,23 @@ func (r *InvalidateOp) Decode(d []byte) {
 	}
 }
 
+// Offset the transformation.
 func (t TransformOp) Offset(o f32.Point) TransformOp {
-	return t.Mul(TransformOp{o})
+	return t.Multiply(TransformOp{o})
 }
 
-func (t TransformOp) InvTransform(p f32.Point) f32.Point {
-	return p.Sub(t.offset)
+// Invert the transformation.
+func (t TransformOp) Invert() TransformOp {
+	return TransformOp{offset: t.offset.Mul(-1)}
 }
 
+// Transform a point.
 func (t TransformOp) Transform(p f32.Point) f32.Point {
 	return p.Add(t.offset)
 }
 
-func (t TransformOp) Mul(t2 TransformOp) TransformOp {
+// Multiply by a transformation.
+func (t TransformOp) Multiply(t2 TransformOp) TransformOp {
 	return TransformOp{
 		offset: t.offset.Add(t2.offset),
 	}