1. Game and animation control flow
CSE 3541/5541
Matt Boggus

2. Overview Pseudocode for a game/animation loop Undo/redo example
Tradeoff in saving cause vs. effect
Unity transform and hierarchy computations as saving the effect

3. Game/Animation loop
main(){ Initialize(); while(true){ DrawScene(); HandleEvents(); Update(); }

4. Draw() and HandleEvents()
Draw() handled by Unity
Types of events
I/O
Timers
Scripted events
Network message

5. Initialize() frame time Scene/Hierarchy objects
Initially 0, increases by 1 every time the scene is drawn
time
Initially 0, increases by dt (a.k.a. timestep, Δt) every update
Units might be seconds, minutes, or days, etc.
Unity Time and Framerate Management
Scene/Hierarchy objects
Geometric objects
Lights
Camera
Note the ese of your own dt value for controlling the speed of the animation vs. the Unity Time.deltatime which controls frame-rate for different hardware or run-time conditions

6. Update() P’(time+dt) = P(time) + Displacement(dt)
Displacement(dt) is the change in position over the amount of time, dt, passing
Can have similar equation for change in orientation
How is Displacement(dt) calculated?
Real-time user input
Physics
Behavior
Key-frame data / Interpolation
(Motion capture – save positions at each frame instead of computing displacement)

7. Time control or frame selection
Braid (2008)
Autodesk MotionBuilder
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8. Two approaches P(time-dt) = P’(time) - Displacement(dt)
Save the cause (of the position change):
Displacement(dt)
Save the effect or result (of the position change)
P’(time)

9. Timeline control – undo/redo of drawing shapes
Ex: see MSPaint
Removes the last drawn shape
Replace removed shapes, unless a new one is drawn

10. Undo/Redo – two options
Save the cause (the data to draw each shape)
Which shape?
Starting mouse (x, y)
Ending mouse (x, y)
Save the effect (the image after drawing the new shape)
Image width * image height pixels
Each pixel has a red, green, and blue value

11. Undo/Redo – two options
Save the cause (of each drawn shape)
Algorithm: to undo, clear the background and redraw shapes
Storage cost: 5 ints per shape
Save the effect (image after each shape is drawn)
Algorithm: to undo, revert to previous image
Storage cost: x * y * 3 ints per shape

12. Tie-in with hierarchical scenes in Unity
Storing the result of a series of geometric transformations in an object’s transform is comparable to “saving the effect”
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13. Additional slides

14. draw_scene() Input: 3D scene + camera Output: 2D image When to redraw?
Camera change [1]
Object in view moves [1]
Every frame [2]
Every xth frame [3]
[1] if(flag_set){ draw(); flag_set = false; } [2] [3] counter = (counter + 1)%draw_rate; if(counter == 0)

15. Graphics pipeline