Ability to select multiple cels and edit them all at once

A rather significant change, so, while I have tested it, it might still be buggy. Implements a part of #306.

src/Classes/ImageEffect.gd

@@ -43,42 +43,51 @@ func _about_to_show() -> void:
 
 
 func _confirmed() -> void:
+	var project := Global.current_project
 	if affect == CEL:
-		if !Global.current_project.layers[Global.current_project.current_layer].can_layer_get_drawn(): # No changes if the layer is locked or invisible
+		if !project.layers[project.current_layer].can_layer_get_drawn(): # No changes if the layer is locked or invisible
 			return
+		if project.selected_cels.size() == 1:
 			Global.canvas.handle_undo("Draw")
 			commit_action(current_cel)
 			Global.canvas.handle_redo("Draw")
+		else:
+			Global.canvas.handle_undo("Draw", project, -1, -1)
+			for cel_index in project.selected_cels:
+				var cel : Cel = project.frames[cel_index[0]].cels[cel_index[1]]
+				var cel_image : Image = cel.image
+				commit_action(cel_image)
+			Global.canvas.handle_redo("Draw", project, -1, -1)
 	elif affect == FRAME:
-		Global.canvas.handle_undo("Draw", Global.current_project, -1)
+		Global.canvas.handle_undo("Draw", project, -1)
 		var i := 0
-		for cel in Global.current_project.frames[Global.current_project.current_frame].cels:
+		for cel in project.frames[project.current_frame].cels:
-			if Global.current_project.layers[i].can_layer_get_drawn():
+			if project.layers[i].can_layer_get_drawn():
 				commit_action(cel.image)
 			i += 1
-		Global.canvas.handle_redo("Draw", Global.current_project, -1)
+		Global.canvas.handle_redo("Draw", project, -1)
 
 	elif affect == ALL_FRAMES:
-		Global.canvas.handle_undo("Draw", Global.current_project, -1, -1)
-		for frame in Global.current_project.frames:
-			var i := 0
-			for cel in frame.cels:
-				if Global.current_project.layers[i].can_layer_get_drawn():
-					commit_action(cel.image)
-				i += 1
-		Global.canvas.handle_redo("Draw", Global.current_project, -1, -1)
-
-	elif affect == ALL_PROJECTS:
-		for project in Global.projects:
 		Global.canvas.handle_undo("Draw", project, -1, -1)
 		for frame in project.frames:
 			var i := 0
 			for cel in frame.cels:
 				if project.layers[i].can_layer_get_drawn():
-						commit_action(cel.image, project)
+					commit_action(cel.image)
 				i += 1
 		Global.canvas.handle_redo("Draw", project, -1, -1)
 
+	elif affect == ALL_PROJECTS:
+		for _project in Global.projects:
+			Global.canvas.handle_undo("Draw", _project, -1, -1)
+			for frame in _project.frames:
+				var i := 0
+				for cel in frame.cels:
+					if _project.layers[i].can_layer_get_drawn():
+						commit_action(cel.image, _project)
+					i += 1
+			Global.canvas.handle_redo("Draw", _project, -1, -1)
+
 
 func commit_action(_cel : Image, _project : Project = Global.current_project) -> void:
 	pass

src/Classes/Project.gd

@@ -12,6 +12,8 @@ var frames := [] setget frames_changed # Array of Frames (that contain Cels)
 var layers := [] setget layers_changed # Array of Layers
 var current_frame := 0 setget frame_changed
 var current_layer := 0 setget layer_changed
+var selected_cels := [[0, 0]] # Array of Arrays of 2 integers (frame & layer)
+
 var animation_tags := [] setget animation_tags_changed # Array of AnimationTags
 var guides := [] # Array of Guides
 var brushes := [] # Array of Images
@@ -386,6 +388,7 @@ func size_changed(value : Vector2) -> void:
 
 func frames_changed(value : Array) -> void:
 	frames = value
+	selected_cels.clear()
 	remove_cel_buttons()
 
 	for frame_id in Global.frame_ids.get_children():
@@ -419,6 +422,8 @@ func layers_changed(value : Array) -> void:
 		Global.layers_changed_skip = false
 		return
 
+	selected_cels.clear()
+
 	for container in Global.layers_container.get_children():
 		container.queue_free()
 
@@ -471,11 +476,16 @@ func frame_changed(value : int) -> void:
 			if i < layer.frame_container.get_child_count():
 				layer.frame_container.get_child(i).pressed = false
 
+	if selected_cels.empty():
+		selected_cels.append([current_frame, current_layer])
 	# Select the new frame
-	if current_frame < Global.frame_ids.get_child_count():
+	for cel in selected_cels:
-		Global.frame_ids.get_child(current_frame).add_color_override("font_color", Global.control.theme.get_color("Selected Color", "Label"))
+		var _current_frame : int = cel[0]
-	if layers and current_frame < layers[current_layer].frame_container.get_child_count():
+		var _current_layer : int = cel[1]
-		layers[current_layer].frame_container.get_child(current_frame).pressed = true
+		if _current_frame < Global.frame_ids.get_child_count():
+			Global.frame_ids.get_child(_current_frame).add_color_override("font_color", Global.control.theme.get_color("Selected Color", "Label"))
+		if _current_frame < layers[_current_layer].frame_container.get_child_count():
+			layers[_current_layer].frame_container.get_child(_current_frame).pressed = true
 
 	Global.disable_button(Global.remove_frame_button, frames.size() == 1)
 	Global.disable_button(Global.move_left_frame_button, frames.size() == 1 or current_frame == 0)
@@ -493,17 +503,18 @@ func layer_changed(value : int) -> void:
 	Global.canvas.selection.transform_content_confirm()
 	current_layer = value
 
-	for container in Global.layers_container.get_children():
-		container.pressed = false
-
-	if current_layer < Global.layers_container.get_child_count():
-		var layer_button = Global.layers_container.get_child(Global.layers_container.get_child_count() - 1 - current_layer)
-		layer_button.pressed = true
-
 	toggle_layer_buttons_current_layer()
 
 	yield(Global.get_tree().create_timer(0.01), "timeout")
 	self.current_frame = current_frame # Call frame_changed to update UI
+	for layer_button in Global.layers_container.get_children():
+		layer_button.pressed = false
+
+	for cel in selected_cels:
+		var _current_layer : int = cel[1]
+		if _current_layer < Global.layers_container.get_child_count():
+			var layer_button = Global.layers_container.get_child(Global.layers_container.get_child_count() - 1 - _current_layer)
+			layer_button.pressed = true
 
 
 func toggle_layer_buttons_layers() -> void:

src/Tools/BaseTool.gd

@@ -94,6 +94,15 @@ func _get_draw_image() -> Image:
 	return project.frames[project.current_frame].cels[project.current_layer].image
 
 
+func _get_selected_draw_images() -> Array: # Array of Images
+	var images := []
+	var project : Project = Global.current_project
+	for cel_index in project.selected_cels:
+		var cel : Cel = project.frames[cel_index[0]].cels[cel_index[1]]
+		images.append(cel.image)
+	return images
+
+
 func _flip_rect(rect : Rect2, size : Vector2, horizontal : bool, vertical : bool) -> Rect2:
 	var result := rect
 	if horizontal:

src/Tools/Bucket.gd

@@ -117,8 +117,9 @@ func draw_end(_position : Vector2) -> void:
 
 func fill_in_color(position : Vector2) -> void:
 	var project : Project = Global.current_project
-	var image := _get_draw_image()
+	var color : Color = _get_draw_image().get_pixelv(position)
-	var color := image.get_pixelv(position)
+	var images := _get_selected_draw_images()
+	for image in images:
 		if _fill_with == 0 or _pattern == null:
 			if tool_slot.color.is_equal_approx(color):
 				return
@@ -157,8 +158,9 @@ func fill_in_area(position : Vector2) -> void:
 
 func _flood_fill(position : Vector2) -> void:
 	var project : Project = Global.current_project
-	var image := _get_draw_image()
+	var images := _get_selected_draw_images()
-	var color := image.get_pixelv(position)
+	for image in images:
+		var color : Color = image.get_pixelv(position)
 		if _fill_with == 0 or _pattern == null:
 			if tool_slot.color.is_equal_approx(color):
 				return
@@ -205,24 +207,30 @@ func _set_pixel(image : Image, x : int, y : int, color : Color) -> void:
 
 
 func commit_undo(action : String, undo_data : Dictionary) -> void:
-	var redo_data = _get_undo_data()
+	var redo_data := _get_undo_data()
 	var project : Project = Global.current_project
-	var image : Image = project.frames[project.current_frame].cels[project.current_layer].image
+	var frame := -1
+	var layer := -1
+	if Global.animation_timer.is_stopped() and project.selected_cels.size() == 1:
+		frame = project.current_frame
+		layer = project.current_layer
 
 	project.undos += 1
 	project.undo_redo.create_action(action)
-	project.undo_redo.add_do_property(image, "data", redo_data["image_data"])
+	for image in redo_data:
-	project.undo_redo.add_undo_property(image, "data", undo_data["image_data"])
+		project.undo_redo.add_do_property(image, "data", redo_data[image])
-	project.undo_redo.add_do_method(Global, "redo", project.current_frame, project.current_layer)
+	for image in undo_data:
-	project.undo_redo.add_undo_method(Global, "undo", project.current_frame, project.current_layer)
+		project.undo_redo.add_undo_property(image, "data", undo_data[image])
+	project.undo_redo.add_do_method(Global, "redo", frame, layer)
+	project.undo_redo.add_undo_method(Global, "undo", frame, layer)
 	project.undo_redo.commit_action()
 
 
 func _get_undo_data() -> Dictionary:
-	var data = {}
+	var data := {}
-	var project : Project = Global.current_project
+	var images := _get_selected_draw_images()
-	var image : Image = project.frames[project.current_frame].cels[project.current_layer].image
+	for image in images:
 		image.unlock()
-	data["image_data"] = image.data
+		data[image] = image.data
 		image.lock()
 	return data

src/Tools/Draw.gd

@@ -130,7 +130,7 @@ func update_mirror_brush() -> void:
 func update_mask(can_skip := true) -> void:
 	if can_skip and Global.pressure_sensitivity_mode == Global.PressureSensitivity.NONE:
 		return
-	var size := _get_draw_image().get_size()
+	var size : Vector2 = Global.current_project.size
 	# Faster than zeroing PoolByteArray directly. See: https://github.com/Orama-Interactive/Pixelorama/pull/439
 	var nulled_array := []
 	nulled_array.resize(size.x * size.y)
@@ -155,11 +155,11 @@ func prepare_undo() -> void:
 
 
 func commit_undo(action : String) -> void:
-	var redo_data = _get_undo_data()
+	var redo_data := _get_undo_data()
 	var project : Project = Global.current_project
 	var frame := -1
 	var layer := -1
-	if Global.animation_timer.is_stopped():
+	if Global.animation_timer.is_stopped() and project.selected_cels.size() == 1:
 		frame = project.current_frame
 		layer = project.current_layer
 
@@ -347,7 +347,8 @@ func _set_pixel(position : Vector2) -> void:
 	if !project.can_pixel_get_drawn(position):
 		return
 
-	var image := _get_draw_image()
+	var images := _get_selected_draw_images()
+	for image in images:
 		var i := int(position.x + position.y * image.get_size().x)
 		if _mask.size() >= i + 1:
 			if _mask[i] < Tools.pen_pressure:
@@ -515,13 +516,18 @@ func _line_angle_constraint(start : Vector2, end : Vector2) -> Dictionary:
 
 
 func _get_undo_data() -> Dictionary:
-	var data = {}
+	var data := {}
 	var project : Project = Global.current_project
-	var frames := project.frames
+	var cels := [] # Array of Cels
 	if Global.animation_timer.is_stopped():
-		frames = [project.frames[project.current_frame]]
+		for cel_index in project.selected_cels:
-	for frame in frames:
+			cels.append(project.frames[cel_index[0]].cels[cel_index[1]])
-		var image : Image = frame.cels[project.current_layer].image
+	else:
+		for frame in project.frames:
+			var cel : Cel = frame.cels[project.current_layer]
+			cels.append(cel)
+	for cel in cels:
+		var image : Image = cel.image
 		image.unlock()
 		data[image] = image.data
 		image.lock()

src/Tools/Eraser.gd

@@ -73,4 +73,7 @@ func _draw_brush_image(_image : Image, src_rect: Rect2, dst: Vector2) -> void:
 	var size := _image.get_size()
 	if _clear_image.get_size() != size:
 		_clear_image.resize(size.x, size.y, Image.INTERPOLATE_NEAREST)
-	_get_draw_image().blit_rect_mask(_clear_image, _image, src_rect, dst)
+
+	var images := _get_selected_draw_images()
+	for draw_image in images:
+		draw_image.blit_rect_mask(_clear_image, _image, src_rect, dst)

src/Tools/Move.gd

@@ -1,6 +1,7 @@
 extends BaseTool
 
 
+var _undo_data := {}
 var _start_pos : Vector2
 var _offset : Vector2
 
@@ -29,6 +30,7 @@ func _input(event : InputEvent) -> void:
 func draw_start(position : Vector2) -> void:
 	_start_pos = position
 	_offset = position
+	_undo_data = _get_undo_data()
 	if Global.current_project.has_selection:
 		selection_node.transform_content_start()
 	_content_transformation_check = selection_node.is_moving_content
@@ -72,19 +74,60 @@ func draw_end(position : Vector2) -> void:
 
 		var pixel_diff : Vector2 = position - _start_pos
 		var project : Project = Global.current_project
-		var image : Image = _get_draw_image()
 
 		if project.has_selection:
 			selection_node.move_borders_end()
 		else:
 			Global.canvas.move_preview_location = Vector2.ZERO
+			var images := _get_selected_draw_images()
+			for image in images:
 				var image_copy := Image.new()
 				image_copy.copy_from(image)
-			Global.canvas.handle_undo("Draw")
 				image.fill(Color(0, 0, 0, 0))
 				image.blit_rect(image_copy, Rect2(Vector2.ZERO, project.size), pixel_diff)
 
-			Global.canvas.handle_redo("Draw")
+			commit_undo("Draw")
 
 	_start_pos = Vector2.INF
 	_snap_to_grid = false
+
+
+func commit_undo(action : String) -> void:
+	var redo_data := _get_undo_data()
+	var project : Project = Global.current_project
+	var frame := -1
+	var layer := -1
+	if Global.animation_timer.is_stopped() and project.selected_cels.size() == 1:
+		frame = project.current_frame
+		layer = project.current_layer
+
+	project.undos += 1
+	project.undo_redo.create_action(action)
+	for image in redo_data:
+		project.undo_redo.add_do_property(image, "data", redo_data[image])
+	for image in _undo_data:
+		project.undo_redo.add_undo_property(image, "data", _undo_data[image])
+	project.undo_redo.add_do_method(Global, "redo", frame, layer)
+	project.undo_redo.add_undo_method(Global, "undo", frame, layer)
+	project.undo_redo.commit_action()
+
+	_undo_data.clear()
+
+
+func _get_undo_data() -> Dictionary:
+	var data := {}
+	var project : Project = Global.current_project
+	var cels := [] # Array of Cels
+	if Global.animation_timer.is_stopped():
+		for cel_index in project.selected_cels:
+			cels.append(project.frames[cel_index[0]].cels[cel_index[1]])
+	else:
+		for frame in project.frames:
+			var cel : Cel = frame.cels[project.current_layer]
+			cels.append(cel)
+	for cel in cels:
+		var image : Image = cel.image
+		image.unlock()
+		data[image] = image.data
+		image.lock()
+	return data

src/Tools/Pencil.gd

@@ -103,17 +103,14 @@ func draw_end(_position : Vector2) -> void:
 		if _fill_inside:
 			_draw_points.append(_position)
 			if _draw_points.size() > 3:
-				var image = _get_draw_image()
 				var v = Vector2()
-				var image_size = image.get_size()
+				var image_size = Global.current_project.size
 				for x in image_size.x:
 					v.x = x
 					for y in image_size.y:
 						v.y = y
 						if Geometry.is_point_in_polygon(v, _draw_points):
-							image.lock()
 							draw_tool(v)
-							image.unlock()
 	if _changed or _drawer.color_op.changed:
 		commit_undo("Draw")
 	cursor_text = ""
@@ -122,9 +119,10 @@ func draw_end(_position : Vector2) -> void:
 
 func _draw_brush_image(image : Image, src_rect: Rect2, dst: Vector2) -> void:
 	_changed = true
+	var images := _get_selected_draw_images()
 	if _overwrite:
-		_get_draw_image().blit_rect(image, src_rect, dst)
+		for draw_image in images:
+			draw_image.blit_rect(image, src_rect, dst)
 	else:
-		_get_draw_image().blend_rect(image, src_rect, dst)
+		for draw_image in images:
-
+			draw_image.blend_rect(image, src_rect, dst)
-

src/UI/Canvas/Canvas.gd

@@ -78,8 +78,6 @@ func _input(event : InputEvent) -> void:
 
 	sprite_changed_this_frame = false
 
-	var current_project : Project = Global.current_project
-
 	if Global.has_focus:
 		if !cursor_image_has_changed:
 			cursor_image_has_changed = true
@@ -96,7 +94,7 @@ func _input(event : InputEvent) -> void:
 	Tools.handle_draw(current_pixel.floor(), event)
 
 	if sprite_changed_this_frame:
-		update_texture(current_project.current_layer)
+		update_selected_cels_textures()
 
 
 func camera_zoom() -> void:
@@ -231,6 +229,20 @@ func update_texture(layer_index : int, frame_index := -1, project : Project = Gl
 			frame_texture_rect.texture = current_cel.image_texture
 
 
+func update_selected_cels_textures(project : Project = Global.current_project) -> void:
+	for cel_index in project.selected_cels:
+		var frame_index : int = cel_index[0]
+		var layer_index : int = cel_index[1]
+		if frame_index < project.frames.size() and layer_index < project.layers.size():
+			var current_cel : Cel = project.frames[frame_index].cels[layer_index]
+			current_cel.image_texture.create_from_image(current_cel.image, 0)
+
+			if project == Global.current_project:
+				var frame_texture_rect : TextureRect
+				frame_texture_rect = Global.find_node_by_name(project.layers[layer_index].frame_container.get_child(frame_index), "CelTexture")
+				frame_texture_rect.texture = current_cel.image_texture
+
+
 func onion_skinning() -> void:
 	# Past
 	if Global.onion_skinning_past_rate > 0:

src/UI/Timeline/AnimationTimeline.gd

@@ -193,10 +193,6 @@ func _on_CopyFrame_pressed(frame := -1) -> void:
 	Global.current_project.undo_redo.add_do_property(Global.current_project, "frames", new_frames)
 	Global.current_project.undo_redo.add_do_property(Global.current_project, "current_frame", frame + 1)
 	Global.current_project.undo_redo.add_do_property(Global.current_project, "animation_tags", new_animation_tags)
-	for i in range(Global.current_project.layers.size()):
-		for child in Global.current_project.layers[i].frame_container.get_children():
-			Global.current_project.undo_redo.add_do_property(child, "pressed", false)
-			Global.current_project.undo_redo.add_undo_property(child, "pressed", child.pressed)
 
 	Global.current_project.undo_redo.add_undo_property(Global.current_project, "frames", Global.current_project.frames)
 	Global.current_project.undo_redo.add_undo_property(Global.current_project, "current_frame", frame)
@@ -279,6 +275,7 @@ func _on_AnimationTimer_timeout() -> void:
 	var fps = Global.current_project.fps
 	if animation_forward:
 		if Global.current_project.current_frame < last_frame:
+			Global.current_project.selected_cels.clear()
 			Global.current_project.current_frame += 1
 			Global.animation_timer.wait_time = Global.current_project.frames[Global.current_project.current_frame].duration * (1/fps)
 			Global.animation_timer.start() # Change the frame, change the wait time and start a cycle, this is the best way to do it
@@ -289,6 +286,7 @@ func _on_AnimationTimer_timeout() -> void:
 					Global.play_backwards.pressed = false
 					Global.animation_timer.stop()
 				1: # Cycle loop
+					Global.current_project.selected_cels.clear()
 					Global.current_project.current_frame = first_frame
 					Global.animation_timer.wait_time = Global.current_project.frames[Global.current_project.current_frame].duration * (1/fps)
 					Global.animation_timer.start()
@@ -298,6 +296,7 @@ func _on_AnimationTimer_timeout() -> void:
 
 	else:
 		if Global.current_project.current_frame > first_frame:
+			Global.current_project.selected_cels.clear()
 			Global.current_project.current_frame -= 1
 			Global.animation_timer.wait_time = Global.current_project.frames[Global.current_project.current_frame].duration * (1/fps)
 			Global.animation_timer.start()
@@ -308,6 +307,7 @@ func _on_AnimationTimer_timeout() -> void:
 					Global.play_forward.pressed = false
 					Global.animation_timer.stop()
 				1: # Cycle loop
+					Global.current_project.selected_cels.clear()
 					Global.current_project.current_frame = last_frame
 					Global.animation_timer.wait_time = Global.current_project.frames[Global.current_project.current_frame].duration * (1/fps)
 					Global.animation_timer.start()
@@ -355,20 +355,24 @@ func play_animation(play : bool, forward_dir : bool) -> void:
 
 
 func _on_NextFrame_pressed() -> void:
+	Global.current_project.selected_cels.clear()
 	if Global.current_project.current_frame < Global.current_project.frames.size() - 1:
 		Global.current_project.current_frame += 1
 
 
 func _on_PreviousFrame_pressed() -> void:
+	Global.current_project.selected_cels.clear()
 	if Global.current_project.current_frame > 0:
 		Global.current_project.current_frame -= 1
 
 
 func _on_LastFrame_pressed() -> void:
+	Global.current_project.selected_cels.clear()
 	Global.current_project.current_frame = Global.current_project.frames.size() - 1
 
 
 func _on_FirstFrame_pressed() -> void:
+	Global.current_project.selected_cels.clear()
 	Global.current_project.current_frame = 0
 
 

src/UI/Timeline/CelButton.gd

@@ -43,13 +43,50 @@ func _on_CelButton_resized() -> void:
 
 
 func _on_CelButton_pressed() -> void:
+	var project := Global.current_project
 	if Input.is_action_just_released("left_mouse"):
-		Global.current_project.current_frame = frame
+		var change_cel := true
-		Global.current_project.current_layer = layer
+		var prev_curr_frame : int = project.current_frame
+		var prev_curr_layer : int = project.current_layer
+
+		if Input.is_action_pressed("shift"):
+			var frame_diff_sign = sign(frame - prev_curr_frame)
+			if frame_diff_sign == 0:
+				frame_diff_sign = 1
+			var layer_diff_sign = sign(layer - prev_curr_layer)
+			if layer_diff_sign == 0:
+				layer_diff_sign = 1
+			for i in range(prev_curr_frame, frame + frame_diff_sign, frame_diff_sign):
+				for j in range(prev_curr_layer, layer + layer_diff_sign, layer_diff_sign):
+					var frame_layer := [i, j]
+					if !project.selected_cels.has(frame_layer):
+						project.selected_cels.append(frame_layer)
+		elif Input.is_action_pressed("ctrl"):
+			var frame_layer := [frame, layer]
+			if project.selected_cels.has(frame_layer):
+				if project.selected_cels.size() > 1:
+					project.selected_cels.erase(frame_layer)
+					change_cel = false
+			else:
+				project.selected_cels.append(frame_layer)
+		else: # If the button is pressed without Shift or Control
+			project.selected_cels.clear()
+			var frame_layer := [frame, layer]
+			if !project.selected_cels.has(frame_layer):
+				project.selected_cels.append(frame_layer)
+
+		if change_cel:
+			project.current_frame = frame
+			project.current_layer = layer
+		else:
+			project.current_frame = project.selected_cels[0][0]
+			project.current_layer = project.selected_cels[0][1]
+			release_focus()
+
 	elif Input.is_action_just_released("right_mouse"):
 		popup_menu.popup(Rect2(get_global_mouse_position(), Vector2.ONE))
 		pressed = !pressed
-	elif Input.is_action_just_released("middle_mouse"): # Middle mouse click
+	elif Input.is_action_just_released("middle_mouse"):
 		pressed = !pressed
 		delete_cel_contents()
 	else: # An example of this would be Space
@@ -147,6 +184,8 @@ func can_drop_data(_pos, data) -> bool:
 func drop_data(_pos, data) -> void:
 	var new_frame = data[1]
 	var new_layer = data[2]
+	if new_frame == frame and new_layer == layer:
+		return
 
 	var this_frame_new_cels = Global.current_project.frames[frame].cels.duplicate()
 	var new_frame_new_cels
@@ -161,6 +200,9 @@ func drop_data(_pos, data) -> void:
 	Global.current_project.undo_redo.create_action("Move Cels")
 	Global.current_project.undo_redo.add_do_property(Global.current_project.frames[frame], "cels", this_frame_new_cels)
 
+	Global.current_project.undo_redo.add_do_property(Global.current_project, "current_layer", layer)
+	Global.current_project.undo_redo.add_undo_property(Global.current_project, "current_layer", Global.current_project.current_layer)
+
 	if frame != new_frame: # If the cel moved to a different frame
 		Global.current_project.undo_redo.add_do_property(Global.current_project.frames[new_frame], "cels", new_frame_new_cels)
 

src/UI/Timeline/FrameButton.gd

@@ -12,7 +12,29 @@ func _ready() -> void:
 
 func _button_pressed() -> void:
 	if Input.is_action_just_released("left_mouse"):
+		var prev_curr_frame : int = Global.current_project.current_frame
+		if Input.is_action_pressed("shift"):
+			var frame_diff_sign = sign(frame - prev_curr_frame)
+			if frame_diff_sign == 0:
+				frame_diff_sign = 1
+			for i in range(prev_curr_frame, frame + frame_diff_sign, frame_diff_sign):
+				for j in range(0, Global.current_project.layers.size()):
+					var frame_layer := [i, j]
+					if !Global.current_project.selected_cels.has(frame_layer):
+						Global.current_project.selected_cels.append(frame_layer)
+		elif Input.is_action_pressed("ctrl"):
+			for j in range(0, Global.current_project.layers.size()):
+				var frame_layer := [frame, j]
+				if !Global.current_project.selected_cels.has(frame_layer):
+					Global.current_project.selected_cels.append(frame_layer)
+		else: # If the button is pressed without Shift or Control
+			Global.current_project.selected_cels.clear()
+			var frame_layer := [frame, Global.current_project.current_layer]
+			if !Global.current_project.selected_cels.has(frame_layer):
+				Global.current_project.selected_cels.append(frame_layer)
+
 		Global.current_project.current_frame = frame
+
 	elif Input.is_action_just_released("right_mouse"):
 		if Global.current_project.frames.size() == 1:
 			popup_menu.set_item_disabled(0, true)
@@ -26,7 +48,7 @@ func _button_pressed() -> void:
 				popup_menu.set_item_disabled(3, false)
 		popup_menu.popup(Rect2(get_global_mouse_position(), Vector2.ONE))
 		pressed = !pressed
-	elif Input.is_action_just_released("middle_mouse"): # Middle mouse click
+	elif Input.is_action_just_released("middle_mouse"):
 		pressed = !pressed
 		Global.animation_timeline._on_DeleteFrame_pressed(frame)
 	else: # An example of this would be Space
@@ -59,12 +81,14 @@ func change_frame_order(rate : int) -> void:
 
 	Global.current_project.undo_redo.create_action("Change Frame Order")
 	Global.current_project.undo_redo.add_do_property(Global.current_project, "frames", new_frames)
+	Global.current_project.undo_redo.add_undo_property(Global.current_project, "frames", Global.current_project.frames)
 
 	if Global.current_project.current_frame == frame:
 		Global.current_project.undo_redo.add_do_property(Global.current_project, "current_frame", change)
-		Global.current_project.undo_redo.add_undo_property(Global.current_project, "current_frame", Global.current_project.current_frame)
+	else:
+		Global.current_project.undo_redo.add_do_property(Global.current_project, "current_frame", Global.current_project.current_frame)
 
-	Global.current_project.undo_redo.add_undo_property(Global.current_project, "frames", Global.current_project.frames)
+	Global.current_project.undo_redo.add_undo_property(Global.current_project, "current_frame", Global.current_project.current_frame)
 
 	Global.current_project.undo_redo.add_undo_method(Global, "undo")
 	Global.current_project.undo_redo.add_do_method(Global, "redo")

src/UI/Timeline/LayerButton.gd

@@ -45,9 +45,33 @@ func _input(event : InputEvent) -> void:
 		save_layer_name(line_edit.text)
 
 
-func _on_LayerContainer_gui_input(event : InputEvent):
+func _on_LayerContainer_gui_input(event : InputEvent) -> void:
+	var project := Global.current_project
+
 	if event is InputEventMouseButton:
-		Global.current_project.current_layer = layer
+		var prev_curr_layer : int = project.current_layer
+		if Input.is_action_pressed("shift"):
+			var layer_diff_sign = sign(layer - prev_curr_layer)
+			if layer_diff_sign == 0:
+				layer_diff_sign = 1
+			for i in range(0, project.frames.size()):
+				for j in range(prev_curr_layer, layer + layer_diff_sign, layer_diff_sign):
+					var frame_layer := [i, j]
+					if !project.selected_cels.has(frame_layer):
+						project.selected_cels.append(frame_layer)
+		elif Input.is_action_pressed("ctrl"):
+			for i in range(0, project.frames.size()):
+				var frame_layer := [i, layer]
+				if !project.selected_cels.has(frame_layer):
+					project.selected_cels.append(frame_layer)
+		else: # If the button is pressed without Shift or Control
+			project.selected_cels.clear()
+			var frame_layer := [project.current_frame, layer]
+			if !project.selected_cels.has(frame_layer):
+				project.selected_cels.append(frame_layer)
+
+		project.current_layer = layer
+
 		if event.doubleclick:
 			label.visible = false
 			line_edit.visible = true

src/UI/Timeline/LayerButton.tscn

@@ -9,6 +9,7 @@
 margin_right = 210.0
 margin_bottom = 36.0
 rect_min_size = Vector2( 212, 36 )
+mouse_default_cursor_shape = 2
 size_flags_horizontal = 0
 toggle_mode = true
 action_mode = 0