Middle-click to Pan + Remember Scroll Position

In the editor, clicking and dragging with the middle mouse button
will scroll the view of the editor in place of the arrow keys.

When entering Play Mode, the original scroll position in the level
editor is remembered for when you come back - no more having to
scroll from 0,0 each time to get back to where you were working!

pkg/editor_scene.go

@@ -29,6 +29,7 @@ type EditorScene struct {
 	OpenFile               bool
 	Filename               string
 	DoodadSize             int
+	RememberScrollPosition render.Point // Play mode remembers it for us
 
 	UI *EditorUI
 	d  *Doodle
@@ -209,6 +210,11 @@ func (s *EditorScene) setupAsync(d *Doodle) error {
 	// Recompute the UI Palette window for the level's palette.
 	s.UI.FinishSetup(d)
 
+	// Scroll the level to the remembered position from when we went
+	// to Play Mode and back. If no remembered position, this is zero
+	// anyway.
+	s.UI.Canvas.ScrollTo(s.RememberScrollPosition)
+
 	d.Flash("Editor Mode.")
 	if s.DrawingType == enum.LevelDrawing {
 		d.Flash("Press 'P' to playtest this level.")
@@ -224,6 +230,7 @@ func (s *EditorScene) Playtest() {
 		Filename:               s.filename,
 		Level:                  s.Level,
 		CanEdit:                true,
+		RememberScrollPosition: s.UI.Canvas.Scroll,
 	})
 }
 

pkg/keybind/keybind.go

@@ -244,3 +244,8 @@ func Down(ev *event.State) bool {
 func Use(ev *event.State) bool {
 	return ev.Space || ev.KeyDown("q")
 }
+
+// MiddleClick of the mouse for panning the level.
+func MiddleClick(ev *event.State) bool {
+	return ev.Button2
+}

pkg/play_scene.go

@@ -27,6 +27,7 @@ type PlayScene struct {
 	Level                  *level.Level
 	CanEdit                bool         // i.e. you came from the Editor Mode
 	HasNext                bool         // has a next level to load next
+	RememberScrollPosition render.Point // for the Editor quality of life
 
 	// Private variables.
 	d            *Doodle
@@ -296,6 +297,7 @@ func (s *PlayScene) EditLevel() {
 	s.d.Goto(&EditorScene{
 		Filename:               s.Filename,
 		Level:                  s.Level,
+		RememberScrollPosition: s.RememberScrollPosition,
 	})
 }
 

pkg/uix/canvas.go

@@ -96,6 +96,9 @@ type Canvas struct {
 
 	// We inherit the ui.Widget which manages the width and height.
 	Scroll         render.Point // Scroll offset for which parts of canvas are visible.
+	scrollDragging bool         // Middle-click to pan scroll
+	scrollStartAt  render.Point // Cursor point at beginning of pan
+	scrollWasAt    render.Point // copy of Scroll at beginning of pan
 }
 
 // NewCanvas initializes a Canvas widget.

pkg/uix/canvas_scrolling.go

@@ -54,6 +54,24 @@ func (w *Canvas) loopEditorScroll(ev *event.State) error {
 		w.ScrollBy(scrollBy)
 	}
 
+	// Middle click of the mouse to pan the level.
+	// NOTE: returns are below!
+	if keybind.MiddleClick(ev) {
+		if !w.scrollDragging {
+			w.scrollDragging = true
+			w.scrollStartAt = shmem.Cursor
+			w.scrollWasAt = w.Scroll
+		} else {
+			delta := shmem.Cursor.Compare(w.scrollStartAt)
+			w.Scroll = w.scrollWasAt
+			w.Scroll.Subtract(delta)
+		}
+	} else {
+		if w.scrollDragging {
+			w.scrollDragging = false
+		}
+	}
+
 	return nil
 }