Fix issue where nothing would be drawn in the canvas if the first cel is a GroupCel

src/Classes/Project.gd

@@ -158,6 +158,7 @@ func new_empty_frame() -> Frame:
 	return frame
 
 
+## Returns the currently selected [BaseCel].
 func get_current_cel() -> BaseCel:
 	return frames[current_frame].cels[current_layer]
 
@@ -644,6 +645,22 @@ func can_pixel_get_drawn(
 		return true
 
 
+## Loops through all of the cels until it finds a drawable (non-[GroupCel]) [BaseCel]
+## in the specified [param frame] and returns it. If no drawable cel is found,
+## meaning that all of the cels are [GroupCel]s, the method returns null.
+## If no [param frame] is specified, the method will use the current frame.
+func find_first_drawable_cel(frame := frames[current_frame]) -> BaseCel:
+	var result: BaseCel
+	var cel := frame.cels[0]
+	var i := 0
+	while cel is GroupCel and i < layers.size():
+		cel = frame.cels[i]
+		i += 1
+	if not cel is GroupCel:
+		result = cel
+	return result
+
+
 # Timeline modifications
 # Modifying layers or frames Arrays on the current project should generally only be done
 # through these methods.

src/UI/Canvas/Canvas.gd

@@ -39,12 +39,13 @@ func _draw() -> void:
 	if Global.mirror_view:
 		position_tmp.x = position_tmp.x + Global.current_project.size.x
 		scale_tmp.x = -1
+	# If we just use the first cel and it happens to be a GroupCel
+	# nothing will get drawn
+	var cel_to_draw := Global.current_project.find_first_drawable_cel()
 	draw_set_transform(position_tmp, rotation, scale_tmp)
 	# Placeholder so we can have a material here
-	draw_texture(
+	if is_instance_valid(cel_to_draw):
-		Global.current_project.frames[Global.current_project.current_frame].cels[0].image_texture,
+		draw_texture(cel_to_draw.image_texture, Vector2.ZERO)
-		Vector2.ZERO
-	)
 	draw_layers()
 	if Global.onion_skinning:
 		refresh_onion()

src/UI/Canvas/CanvasPreview.gd

@@ -40,8 +40,12 @@ func _draw() -> void:
 				frame_index = project.current_frame
 			var frame := project.frames[frame_index]
 			animation_timer.wait_time = frame.duration * (1.0 / project.fps)
-			var texture := frame.cels[0].image_texture
+			# If we just use the first cel and it happens to be a GroupCel
-			draw_texture(texture, Vector2.ZERO)  # Placeholder so we can have a material here
+			# nothing will get drawn
+			var cel_to_draw := Global.current_project.find_first_drawable_cel(frame)
+			# Placeholder so we can have a material here
+			if is_instance_valid(cel_to_draw):
+				draw_texture(cel_to_draw.image_texture, Vector2.ZERO)
 			if material == animation_material:
 				# Only use a unique material if the animation of the canvas preview is playing
 				# Otherwise showing a different frame than the main canvas is impossible
@@ -58,9 +62,12 @@ func _draw() -> void:
 				frame_index = start_sprite_sheet_frame - 1
 			var src_rect := slices[frame_index]
 			var rect := Rect2(Vector2.ZERO, src_rect.size)
-			var texture := project.frames[project.current_frame].cels[0].image_texture
+			# If we just use the first cel and it happens to be a GroupCel
+			# nothing will get drawn
+			var cel_to_draw := Global.current_project.find_first_drawable_cel()
 			# Placeholder so we can have a material here
-			draw_texture_rect_region(texture, rect, src_rect)
+			if is_instance_valid(cel_to_draw):
+				draw_texture_rect_region(cel_to_draw.image_texture, rect, src_rect)
 			transparent_checker.fit_rect(rect)