Enable smooth transitions for Create Deck.

Add the basic framework for being able to set smooth un/highlight
visual transitions for the `Create Deck` widget canvas.

data/objects/library_new_deck.cfg

@@ -9,15 +9,32 @@
 
 		area: "{width: py(260), height: py(72)}",
 
-		highlighted: { type: "bool", default: false, set: "if(_data != value, [set(_data, value); render()])" },
+		highlighted: {
+			type: "bool",
+			default: false,
+			set: "
+				if (
+					_data != value,
+						[
+							set(_data, value)
+							;
+							render(false)
+						],
+					// else
+						debug(['library_new_deck#highlighted#set: this code should never run'])
+				)
+			"
+		},
 
 		_show_plus: { default: true },
 		_text: { default: "Create Deck" },
 
 		_font: { type: "string", init: "lib.font.regular_font" },
 
-		render: "def() ->commands
+		render: "def (bool creating) -> commands
 		[
+		map(range(transition_steps),
+		schedule(step + delay,
 		set(animation, {
 			id: 'fbo',
 			image: 'fbo',
@@ -29,8 +46,19 @@
 				c.fill(),
 
 				if(highlighted,
-						c.set_source_rgba(1.0, 1.0, 1.0, 1.0),
-						c.set_source_rgba(0.29, 0.33, 0.36, 1.0)),
+						c.set_source_rgba(
+							if (creating, 1.0, clamp(mix(.29, 1.0, (step + 1) / transition_steps_dec), .29, 1.0)),
+							if (creating, 1.0, clamp(mix(.33, 1.0, (step + 1) / transition_steps_dec), .33, 1.0)),
+							if (creating, 1.0, clamp(mix(.36, 1.0, (step + 1) / transition_steps_dec), .36, 1.0)),
+							1.0
+						),
+						c.set_source_rgba(
+							if (creating, .29, clamp(mix(1.0, .29, (step + 1) / transition_steps_dec), .29, 1.0)),
+							if (creating, .33, clamp(mix(1.0, .33, (step + 1) / transition_steps_dec), .33, 1.0)),
+							if (creating, .36, clamp(mix(1.0, .36, (step + 1) / transition_steps_dec), .36, 1.0)),
+							1.0
+						)
+				),
 				c.rectangle(0, area.height*0.1, area.width, area.height*0.8),
 				c.set_line_width(py(20)/10.0),
 				c.stroke(),
@@ -58,7 +86,16 @@
 			]),
 		}
 		  where c = canvas()
-		),
+		)  //   set(animation, ...)
+		)  //   schedule(int, set(animation, ...))
+		//   A little bit of syntactic sugar.
+		where step = value
+		)  //   map(range(...), schedule(int, set(animation, ...)))
+		//   Casted to `decimal` for convenience.
+		where transition_steps_dec = transition_steps * 1.0
+		where transition_steps = 1
+		where delay = 0
+		,
 		set(x2, x2),
 		set(y, y)
 		]",
@@ -75,6 +112,6 @@
 	on_mouse_enter: "set(highlighted, true)",
 	on_mouse_leave: "set(highlighted, false)",
 
-	on_create: "render()",
-	on_type_updated: "render()",
+	on_create: "render(true)",
+	on_type_updated: "render(true)",
 }