Week 7: SceneNodes and SceneTrees

Link to source code (zipped)

• Example 1: Allowing arbitrary tree depth
• SceneNode:
• Now define a name, so we can identify them
• A ArmSegment that can be place anywhere (no rotation support)

• How to create/instantiate this to create something strange looking?
• Lesson:
• Draw out your object in a convenient coordinate space (Modeling Coordinate Space)
• Define user transformable parts (these are the SceneNode pxf)
• Construct the scene tree, and that is that!
  
  
• Talk about instancing, (e.g., pre-fab in Unity3D may be implemented this way
• How can we have multiple complex geometries and yet ensure not consume too much memory?
  
  
• Example 2: Simple animated objects
• Simplest way: update transform continuously
• ArmSegment:
• Define a update function: rotate the center square and pulsing the top rectangle
• Notice: how to “pulse”
• We must remember the original size of renderables
• Center blue circle: pulsing between 0.7 and 0.4
• ClassExample object, new update function
• Calls all of the update of ArmSegment (all three of them!)
• That’s why all three are updating J
• Hardcoded some other cheesy animations
• Lesson:
• Animation is nothing but calling the update() function during timer handler from the MainController!
• Each object in the world, if they want to animate, they should define an update function.
  
  
• Example 3: Object position
• Notice debugging (learn this trick for your MP5): Draw Control Points
• Check on/off to see: 4 squares (Gray, Redish, Blue-ish, and Green-ish)
• Gray: always follow the mouse
• Redish: top of TopChild, controls left arm pulsing and top spinning
• Blueish: mid of LeftChild, controls ArmSegment update
• Greenish: mid of Parent head, controls head spinning
• Notice:
• If you adjust the slider bars, the squares will be “out of place” (this is on purpose)
• If you move your mouse into the main view, the square “snap” to their proper locations
• Point: show that we can compute ALL of the positions in WC
• ClassExamxple:
• toggleHeadSpin, toggleArmRotate, toggleChildUpdate
• Define functions and allow toggling of these
• update() function: only animate with toggle is on
• ClassExample_MouseOver:
• withInBound() function check for position distance with kBoundTol (in WC)
• dectectMouseOver:
• HeadPos: is (0,0) after Head Translation
• Note: scale/rotate will not change this, so, simply compare!
• leftArm’s blue circle:
• center position sees two transforms:
• 1. leftArm xfrom
• 2. parent xform
• Note: the order of matrix multiplication (what happens if we switch this)?
• Try it!!
• topArm’s red rotated rect:
• center position sees three transforms:
• 1. topArm xform
• 2. leftArm xform
• 3. parent xform
• Again, note the order!
• Stop head spin: click on the center of head
• Stop all children: click on center of the blue circle on left arm
• Stop left arm rotation/pulsing: click on center of top arm red rotated rect
• Lesson:
• We need to know what are the transforms our shapes go through
• We need to know how to composite these transforms together