1. Lecture 8: Graphics
By: Eliav Menachi

2. Graphics Android custom 2D graphics library
OpenGL ES 1.0 for high performance 3D graphics

3. 2D graphics
When drawing 2D graphics, you'll typically do so in one of two ways
Draw your graphics or animations into a View object from your layout.
Draw directly to a Canvas

4. Drawing into a view Best choice when drawing simple graphics
Where is no need to change dynamically
Its not part of a performance-intensive game
The drawing and animation is handled by the system's normal View hierarchy drawing process
You simply define the graphics to go inside the View

5. Simple Graphics Inside a View
Android offers a custom 2D graphics library for drawing and animating shapes and images:
android.graphics.drawable
android.view.animation

6. Drawables
A Drawable is a general abstraction for "something that can be drawn"
There are three ways to define and instantiate a Drawable:
using an image saved in your project resouces
using an XML file that defines the Drawable properties
using the normal class constructors

7. ShapeDrawable
ShapeDrawable is used to dynamically draw some two-dimensional graphics
A ShapeDrawable is an extension of Drawable
ShapeDrawable has its own draw() method
you can create a subclass of View that draws the ShapeDrawable during the View.onDraw() method
See Simple Shape example

8. Drawing directly to a Canvas
When you're application needs to regularly re-draw itself (like games)
There's more than one way to do this:
In the same thread as your UI Activity, using a custom View in your layout, call invalidate() and then handle the onDraw() callback..
In a separate thread, by managing a SurfaceView and performing draws to the Canvas as fast as your thread is capable.

9. Draw with a Canvas
A Canvas works for you as a pretense, or interface, to the actual surface upon which your graphics will be drawn
The Canvas holds all of your "draw" calls
Via the Canvas, your drawing is actually performed upon an underlying Bitmap, which is placed into the window.
Using the canvas:
On a View
On a SurfaceView

10. On a View Create a custom View component
Override the onDraw() callback method
This method will be called by the Android framework to request that the View draw itself
Use the given Canvas for drawing
The View is drawn by Android only when invalidated
Use Invalidate() to invalidate the View
See SimpleShape Example

11. Programmatic Animation
Create an animated View
Create a Drawable to hold our animated image
Override the onDraw method which draw the view
Setting bounds defines the position and size of the image inside the View
Display the view in your activity and update the view periodically

12. On a SurfaceView
The SurfaceView is a special subclass of View that offers a dedicated drawing surface within the View hierarchy
The aim is to offer this drawing surface to an application's secondary thread
The application isn't required to wait until the system's View hierarchy is ready to draw
Secondary thread can draw to its own Canvas at its own pace using a reference to the SurfaceView

13. Using the Surface View 1 Create a new class that extends SurfaceView
The class should also implement SurfaceHolder.Callback
an interface that will notify you with information about the underlying Surface (created, changed, or destroyed)
Define your secondary Thread class
The thread will perform all the drawing procedures to your Canvas

14. Using the Surface View 2
When your SurfaceView is initialized, get the SurfaceHolder by calling getHolder()
Instead of handling the Surface object directly, you should handle it via a SurfaceHolder
Notify the SurfaceHolder that you'd like to receive SurfaceHolder callbacks by calling addCallback()
Override each of the SurfaceHolder.Callback methods inside your SurfaceView class.

15. The Drawing Thread Pass the SurfaceHandler to the thread
Retrieve the Canvas with lockCanvas()
Do the drawing
Call unlockCanvasAndPost(), passing it your Canvas object
The Surface will now draw the Canvas as you left it

16. Tween Animation
A tween animation can perform a series of simple transformations (position, size, rotation, and transparency) on the contents of a View object
A sequence of animation instructions defines the tween animation
The instructions are defined by either XML or Android code

17. Tween Animation The animation instructions defines:
The transformations
when the transformation will occur
How long they should take to apply
Transformations can be sequential or simultaneous

18. Frame Animation
Created a sequence of different images, played in order, like a roll of film
The XML file that lists the frames that compose the animation
The XML file consists of an <animation-list> element as the root node and a series of child <item> nodes that each define a frame
The frame is a drawable resource for the frame and the frame duration.
See simple animation example

19. OpenGL ES (Embedded Systems)
OpenGL defines a cross-platform and cross-language API for computer graphics
OpenGL ES is a limited version of OpenGL costumed for mobile phones, PDAs, video game consoles, and other embedded systems
OpenGL ES standard:

20. Use OpenGL ES Create a custom View subclass.
Get a handle to an OpenGLContext, which provides access to Android’s OpenGL ES functionality.
In the View’s onDraw() method, use the handle to the GL object and then use its methods to perform any GL functions.