new example: interactivity

In the process I made a few bugfixes:
* To improve the debug experience for myself I clear the canvas when
  recovering from any errors. (This should probably get ported
  upstream..)
* The `car` handlers for each pane are now siloed from each other. When
  you navigate away they go away, when you navigate back they're still
  active. Very nice.

0059-previous_pane_button

@@ -5,8 +5,10 @@ previous_pane_button = function()
 			love.graphics.polygon('fill', Menu_left+5, App.screen.height/2, Menu_left+25, App.screen.height/2-10, Menu_left+25, App.screen.height/2+10)
 		end,
 		onpress1 = function()
+			Current_pane.car = car
 			Current_pane_index = Current_pane_index-1
 			Current_pane = Panes[Current_pane_index]
+			car = Current_pane.car or {}
 		end,
 	})
 end

0060-next_pane_button

@@ -5,8 +5,10 @@ next_pane_button = function(r)
 			love.graphics.polygon('fill', r-25, App.screen.height/2-10, r-25, App.screen.height/2+10,  r-5, App.screen.height/2)
 		end,
 		onpress1 = function()
+			Current_pane.car = car
 			Current_pane_index = Current_pane_index+1
 			Current_pane = Panes[Current_pane_index]
+			car = Current_pane.car or {}
 		end,
 	})
 end

0078-Example_panes

@@ -40,10 +40,10 @@ Example_panes = {
 		'end',
 	},
 	{
-		'-- For animations and interactivity, you can define various functions that will get called for you.',
+		'-- For animations, you can define various functions that will get called for you.',
 		'-- LÖVE supports functions of the form love.*,',
-		'-- for example, love.draw, love.update, love.keypressed, etc.',
-		"-- You can't define those directly because Carousel Shell needs to define them, but you can define your own under car.*,",
+		'-- for example, love.draw, love.update, etc.',
+		"-- You can't define those directly because Carousel Shell needs to define them for its UI, but you can define your own under car.*,",
 		'-- for example, car.draw, car.update, etc.',
 		'Radius, dRadius = 100, 10',
 		'function car.draw()',
@@ -56,6 +56,38 @@ Example_panes = {
 		'  if Radius < 30 then dRadius = -dRadius end',
 		'end',
 	},
+	{
+		'-- For interactivity, LÖVE provides functions like love.keypressed, love.mousepressed, etc.',
+		'-- As before, define the corresponding car.keypressed, car.mousepressed, etc.',
+		"-- A pane's interactive events only activate when the editor is hidden using the 'hide' button above.",
+		"-- Try running this example and then pressing and holding the mouse and pressing and releasing keys.",
+		'-- Then try hiding the editor and again pressing and holding the mouse and pressing and releasing keys',
+		'X, Y, dX = 100, 0, 10',
+		"Log = ''",
+		'',
+		'function car.draw()',
+		'	love.graphics.line(X,Y, X,Y+300)',
+		'	love.graphics.print(Log, 50,50)',
+		'end',
+		'',
+		'function car.update(dt)',
+		'	if X > 500 then dX = -dX end',
+		'	if X < 100 then dX = -dX end',
+		'	X = X+dX',
+		'end',
+		'',
+		'function car.mousepressed(x,y, button)',
+		'	Y = y',
+		'end',
+		'',
+		'function car.mousereleased(x,y, button)',
+		'	Y = 0',
+		'end',
+		'',
+		'function car.keypressed(key)',
+		'	Log = Log..key',
+		'end',
+	},
 	{
 		'-- Some abbreviations to reduce typing.',
 		'g = love.graphics',

live.lua

@@ -382,6 +382,7 @@ end
 
 -- return nil to continue the event loop, non-nil to quit
 function live.handle_error(err)
+  love.graphics.setCanvas()  -- undo any canvas we happened to be within, otherwise LÖVE seizes up
   Mode = 'error'
   local callstack = debug.traceback('', --[[stack frame]]2)
   local cleaned_up_error = 'Error: ' .. cleaned_up_frame(tostring(err))..'\n'..cleaned_up_callstack(callstack)