Event dispatching

Introduction

Let's take a simple scheme to explain how event are working :

This is a classical tree, that can be created with the code below :

Event are dispatched from the TOP to the BOTTOM of the graph : from window to leaf child. Many event are available by default :

• on_update - do some update in widget if necessary
• on_draw - draw the widget and his children
• on_touch_down - called when a touch is down
• on_touch_move - called when a touch is moved
• on_touch_up - called when a touch is up
• on_resize - the widget have been resized
• on_parent_resize - the parent widget have been resized

Update/Draw events

Every frame displayed on the screen, each widget in the tree will have 2 events called: on_update() and on_draw(). The on_draw() will call draw() function of widget, and dispatch on_draw() event in theses childrens.

If we try to represent it with a scheme, here is the call tree :

• window.on_update()
  • widA.on_update()
  • widB.on_update()
    • widC.on_update()
    • widD.on_update()

And, the drawing part :

• window.on_draw()
• window.draw()
  • widA.on_draw()
  • widA.draw()
  • widB.on_draw()
  • widB.draw()
    • widC.on_draw()
    • widC.draw()
    • widD.on_draw()
    • widD.draw()

Resize events

When a widget is resized, 2 events are fired :

• on_resize() on the widget itself
• on_parent_resize() on all the children

As soon as the size changed, event will be fired