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

@@ -25,10 +25,11 @@ import (
 // EditorScene manages the "Edit Level" game mode.
 type EditorScene struct {
 	// Configuration for the scene initializer.
-	DrawingType enum.DrawingType
-	OpenFile    bool
-	Filename    string
-	DoodadSize  int
+	DrawingType            enum.DrawingType
+	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.")
@@ -221,9 +227,10 @@ func (s *EditorScene) setupAsync(d *Doodle) error {
 func (s *EditorScene) Playtest() {
 	log.Info("Play Mode, Go!")
 	s.d.Goto(&PlayScene{
-		Filename: s.filename,
-		Level:    s.Level,
-		CanEdit:  true,
+		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

@@ -23,10 +23,11 @@ import (
 // PlayScene manages the "Edit Level" game mode.
 type PlayScene struct {
 	// Configuration attributes.
-	Filename string
-	Level    *level.Level
-	CanEdit  bool // i.e. you came from the Editor Mode
-	HasNext  bool // has a next level to load next
+	Filename               string
+	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
@@ -294,8 +295,9 @@ func (s *PlayScene) setupPlayer() {
 func (s *PlayScene) EditLevel() {
 	log.Info("Edit Mode, Go!")
 	s.d.Goto(&EditorScene{
-		Filename: s.Filename,
-		Level:    s.Level,
+		Filename:               s.Filename,
+		Level:                  s.Level,
+		RememberScrollPosition: s.RememberScrollPosition,
 	})
 }
 

pkg/uix/canvas.go

@@ -95,7 +95,10 @@ type Canvas struct {
 	lastPixel     *level.Pixel
 
 	// We inherit the ui.Widget which manages the width and height.
-	Scroll render.Point // Scroll offset for which parts of canvas are visible.
+	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
 }