This document discusses programming for the iPhone using OpenGL ES. It provides an overview of Objective-C and the OpenGL ES pipeline, describes a block game project to gain experience with the OpenGL ES API, and discusses some of the challenges encountered with object selection, game structure, and using Foundation collections.

1. Adventures in OpenGL ES Or: What Not To Expect From OpenGL ESPresented by: David Kolb, Undergrad, Columbus State University

2. Why iPhone/iPod Touch? Copyright Apple, 2009. Source: http://www.apple.com/ipodtouch/

3. Requirements Requirements: An Intel Mac An iPod Touch Development License iPhone Developer University Program Free for degree-granting institutions Allows for a development team of up to 200 student developers.

4. Programming for iPhone OS Objective-C The OpenGL ES Pipeline

5. Objective-C

6. Obj-C Crashcourse Creating a new object: Rectangle *rect = [[Rectangle alloc] init]; id rect = [Rectangle alloc]; Sending a message: [rectinitWithWidth: 30 andHeight: 45 int area = [rect area]; Accessing a field rect.width = 10;

7. Obj-C Crashcourse Defining a class: @interface Rectangle : NSObject {int width;int height;}@property (nonatomic) int width, height;-(id) init;-(id) initWithHeight: (int) handWidth: (int) w;-(int) area;@end

8. Obj-C Crashcourse Implementing a class @implementation Rectangle@synthesize width, height;-(id) init{ self = [super init]; if (self) {self.width = 0;self.height = 0; } return self;}@end

9. Obj-C Crashcourse SelectorsSEL draw = @selector(“draw”);SEL init = @selector(“initWithHeight:andWidth:”);if([rectrespondsToSelector:draw]) {...} Can freely mix in C-style arrays, pointers, calls to malloc() and free(). Obj-C class pointers managed through retain, release, autorelease messages[rect release];

10. OpenGL ES Source: iPhone Game Development Technologies, Part 1 http://developer.apple.com/adconitunes

11. OpenGL ES Continued Geometry glVertexPointer, glNormalPointer, glTexCoordPointer Points, Lines, Triangles, Triangle Fans, Triangle Strips glDrawArrays, glDrawElement Textures 8888, 4444, and more. PVRTC 2D only iPhone hardware optimized for floats, not double’s or fixed.

12. The Game A clone of other “block” exploding games. Select an orb of a particular color, if it neighbors at least one orb of the same color, all orbs of the same color connected to that orb will be removed from the game. The remaining orbs fall into the space remaining. Simple enough concept to give experience in the OpenGL ES API and interacting with touches.

13. The Experience Wrapping a C API in a set of Objective-C classes Lack of glu functions Object selection when receiving a touch event. Writing a framework from scratch

14. Program Structure Vector3D Required for nearly any work in a 3D space. Supports add and copy operations. Sphere Contains the geometry for the Bubble class. Vertices are computed ahead of time, at application load.

15. Program Structure Bubble Main “game piece” Maintains a reference to a Sphere Provides bounding boxes and drawing functions Receives an update message for future animation Scene3D Manages, updates, draws objects Manages lights and camera, which have their own objects.

16. Program Structure BubblesGame Root of game logic and drawing. Receives regular update calls via EAGLView’sdrawView message Receives “taps” via EAGLView’stouchesEnd:Event: message Contains the “game board” and game logic.

17. Selection No rendering in selection mode. Most commonly suggested solution: Generate and bind an entirely new set of buffers (color, depth, etc.) Disable lighting, fog, and any other features that may change the color of a pixel. Render the entire scene into the buffers, making each object a slightly different color. Read the pixel located under the touch and match the color to one of the objects.

18. Another Solution Produce the projection and model/view matrices. Multiply the matrices together. Invert the resulting matrix. Multiply the screen coordinates by the inverted matrix, generating a line. Compute the intersection of the line with an object.

20. Use an orthographic projection that aligns 0,0 with one corner of the screen and matches a distance of 1.0 with the length of a pixel.

21. Simply use screen coordinates as 2D world coordinates with simple adjustments as needed.

23. Foundation Collections NSArray/NSMutableArray Does not accept nil object references. A deletion at n adjusts all elements at valid indices greater than n down by one. The game board needs to accept empty slots. Solution is to use a dictionary with NSNumber objects as keys and the actual Bubble objects as values.

24. Conclusions Even for very active and animated 2D games, Quartz should be seriously considered and fully discounted before selecting OpenGL ES. Consider using one of the available iPhone game frameworks. Cocos2D Sio2Engine Oolong Engine

25. Next Steps Complete logic and animations Control the direction of falling/compacting with accelerometer Scoring Endless mode

26. Demo

27. Questions

28. The End