widget: re-layout Editor before processing events if layout is invalid

Editor's event processing assumes the cached layout is valid, but
it might not be if the program changed the Editor text between calling
Layout and Events.

Fixes #85 (I think)

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

widget/editor.go

@@ -35,6 +35,7 @@ type Editor struct {
 
 	eventKey     int
 	font         text.Font
+	shaper       text.Shaper
 	textSize     fixed.Int26_6
 	blinkStart   time.Time
 	focused      bool
@@ -97,10 +98,22 @@ func (e *Editor) Events(gtx *layout.Context) []EditorEvent {
 }
 
 func (e *Editor) processEvents(gtx *layout.Context) {
+	if e.shaper == nil {
+		// Can't process events without a shaper.
+		return
+	}
+	e.makeValid()
 	e.processPointer(gtx)
 	e.processKey(gtx)
 }
 
+func (e *Editor) makeValid() {
+	if !e.valid {
+		e.lines, e.dims = e.layoutText(e.shaper)
+		e.valid = true
+	}
+}
+
 func (e *Editor) processPointer(gtx *layout.Context) {
 	sbounds := e.scrollBounds()
 	var smin, smax int
@@ -223,14 +236,7 @@ func (e *Editor) Layout(gtx *layout.Context, sh text.Shaper, font text.Font, siz
 		e.font = font
 		e.textSize = textSize
 	}
-	e.processEvents(gtx)
+	maxWidth := gtx.Constraints.Width.Max
-	e.layout(gtx, sh)
-}
-
-func (e *Editor) layout(gtx *layout.Context, sh text.Shaper) {
-	cs := gtx.Constraints
-
-	maxWidth := cs.Width.Max
 	if e.SingleLine {
 		maxWidth = inf
 	}
@@ -238,13 +244,19 @@ func (e *Editor) layout(gtx *layout.Context, sh text.Shaper) {
 		e.maxWidth = maxWidth
 		e.invalidate()
 	}
-
+	if sh != e.shaper {
-	if !e.valid {
+		e.shaper = sh
-		e.lines, e.dims = e.layoutText(sh)
+		e.invalidate()
-		e.valid = true
 	}
 
-	e.viewSize = cs.Constrain(e.dims.Size)
+	e.processEvents(gtx)
+	e.layout(gtx)
+}
+
+func (e *Editor) layout(gtx *layout.Context) {
+	e.makeValid()
+
+	e.viewSize = gtx.Constraints.Constrain(e.dims.Size)
 	// Adjust scrolling for new viewport and layout.
 	e.scrollRel(0, 0)
 
@@ -272,7 +284,7 @@ func (e *Editor) layout(gtx *layout.Context, sh text.Shaper) {
 		if !ok {
 			break
 		}
-		path := sh.Shape(e.font, e.textSize, layout)
+		path := e.shaper.Shape(e.font, e.textSize, layout)
 		e.shapes = append(e.shapes, line{off, path})
 	}