Archive for the ‘iPhone SDK’ Tag

OpenGL ES: Batch Rendering on the iPhone

This one took me a while, simply because there was a LOT of research to do on my part. This is not going to be a tutorial post, per-se… but more so a “This is what I’ve found” and a request that someone take a look through it and see what I could have done better, and then let me know ! :)

Simply put, I was getting a few FPS problems with the development of my game, and thought I would come up with a way to batch all of my drawing into as few OpenGL calls as I could. I came across a few interesting tidbits, including a Stanford ‘iTunes U’ course (look that up in iTunes, its WELL worth viewing) Especially the one on OpenGL from Tim Omernick (Slide can be found HERE).

A copy of the code can be found at the google code repository, direct link to the TextureController is HERE. Well then, lets have a look at it!

The first thing that I attempted to do, was make a struct with the vertices, color information, and uv information. This is a result from Tim’s lecture and heavily influenced by his code. The hiccup was that I wanted to be able to batch based on the GLuint being drawn so I would only have to bind a texture once and then draw all vertices associated with that texture. I came up with the following solution:

struct Vertex
{
 short v[2];
 unsigned color;
 float uv[2];
};

struct VertexInfo
{
 Vertex vertex[MAX_VERTICES];
 int _vertexCount;
};

What will happen here, is VertexInfo will be stored in a map, while the Vertex struct houses all of the information that will be thrown at OpenGL to draw. MAX_VERTICES is defined at the top of the header file, and I really have not played around with it much so I am not sure how slow or fast it will be with a full game running. Currently its set for 100,000 but that was just a number I pulled out of nowhere :D I imagine it should be reduced.

The Map containing the vertex information looks like this;

typedef std::map<GLuint, VertexInfo> VertexMap;
VertexMap vertices;

You’ll see how to use this in a minute. My idea for this class was to sort of clone the way the SpriteBatch works from the XNA framework. This is another of my nods to how well this framework is put together, and how much I enjoy working with XNA. I wanted to be able to call a begin function to let the TextureController know if I plan to use blending (or any other parameter I may add, such as sorting), and then throw a bunch of stuff to draw using the Textures->draw functions provided. Each call to the Textures->draw function will take the texture to be drawn and any information needed (such as the location, source rectangle, color, etc) and pack that information into the VertexMap waiting to be thrown to OpenGL. Once all of my draw commands have been executed, a Textures->end() will initiate all drawing for the batch.

Keep in mind, is this the best way to put something like this together? Probably not.. although its my first time doing such an interesting task.. :) Lets see how it works!

NOTE: I will input breaks to make some comments… so if you want the full file, be sure to visit the code repository at code.google.com

void TextureController::draw( const Texture2D& texture, const Rectangle& destination,
 const Rectangle& source, const Color& color, const GLfloat depth )
{	

As you can see, we’re plugging in a few informational tidbits, but this is only one of the drawing commands that i’ve implemented. The simplest draw command, you only have to provide a texture and a destination rectangle… and “default” values will be put to fill in the blanks when calling this function.

 GLuint glid = texture.getId();

 //	if we don't have any vertices with the texture being drawn, create a
 //	vertex map for it.
 VertexMap::iterator it = vertices.find(glid);
 if (it == vertices.end())
 vertices[glid]._vertexCount = 0;		

 //	find all of the vertices we'll need for this sprite
 float topLeftX = destination.x;
 float topLeftY = destination.y;
 float topRightX = destination.x + destination.width;
 float topRightY = destination.y;
 float bottomLeftX = destination.x;
 float bottomLeftY = destination.y + destination.height;
 float bottomRightX = destination.x + destination.width;
 float bottomRightY = destination.y + destination.height;

The above section is interesting in that it will first find out if we’ve already batched a sprite using the texture. If we have, we’ll just add the vertices into that batch. Otherwise, we’ll create a new batch of vertices and start that new batch. Next, we find all of the vertices! This is done through the destination rectangle passed in. The destination rectangle is going to be the spritebox that the texture is drawn to. In other words, its your canvas and your texture is the paint.

 // Texture atlas
 float minUV[2];
 float maxUV[2];

 //	if the source rectangle of ZERO was passed in, it means the client want to just
 //	draw the texture as is.. otherwise, the client wishes to draw a portion of
 //	the rectangle
 if (source == Rectangle::ZERO())
 {
 float maxS = texture.getMaxS();
 float maxT = texture.getMaxT();
 float minS = 0;
 float minT = 0;

 minUV[0] = minS;
 minUV[1] = minT;
 maxUV[0] = maxS;
 maxUV[1] = maxT;
 }
 else
 {
 float minS = source.x / texture.getWidth();
 float minT = source.y / texture.getHeight();
 float maxS = source.width / texture.getWidth();
 float maxT = source.height / texture.getHeight();

 minUV[0] = minS;
 minUV[1] = minT;
 maxUV[0] = maxS;
 maxUV[1] = maxT;
 }

This section took me the longest to really figure out, because I had not done any research how Texture Atlas’s work. As I said, this was heavily influenced by Tim’s code and I really wanted to understand this section before I moved on. What we’re doing here, is if a blank rectangle is passed into the function (meaning the client didn’t specify a rectangle and therefore wishes to just use the texture ‘as is’) we’ll use the maxS and maxT coordinates for the TextureCoordinates. The way we find out what maxS and maxT are, is after the image goes through its modification to become a power of two texture (see my last article), maxS will become imageWidth / newTextureWidth. In other words
if the texture is passed into your game at 30 pixels by 30 pixels, it was re-sized by the Texture2D class to become 32 by 32. maxS will be 30 / 32, or 0.9375f. This value indicates that when using the default values, 93% of the image is drawn, while the remaining 7% of the image contains nothing more than padding in order to ensure it was a power of two texture.

What if we wanted to use a sub image, only draw a portion? This would be useful if we had several images on one texture. Lets say you have a texture with 2 frames of animation, both frames are 24 by 24. This means your texture is 48 pixels wide, by 24 pixels tall. If you only want to draw the last half of the texture (your “2nd” frame of animation) your source rectangle would be:

x=24, y=0, width=24, height=24
Meaning you’re starting 24 pixels into the picture, at the top pixel of the picture, and you’re going 24 pixels wide and 24 pixels high. This is going to be the sub-image you’re drawing.

In order to change these numbers into texture coordinates, we need to divide by the image width or height. For example, 24 / 48 is .5, so your texture coordinate for x is .5, then 0, then .5, and .5.

 //	Convert the colors into bytes
 unsigned char red = color.red * 255.0f;
 unsigned char green = color.green * 255.0f;
 unsigned char blue = color.blue * 255.0f;
 unsigned char shortAlpha = color.alpha * 255.0f;

 //	pack all of the color data bytes into an unsigned int
 unsigned _color = (shortAlpha << 24) | (blue << 16) | (green << 8) | (red << 0);

 // Triangle #1
 addVertex(glid, topLeftX, topLeftY, minUV&#91;0&#93;, minUV&#91;1&#93;, _color);
 addVertex(glid, topRightX, topRightY, maxUV&#91;0&#93;, minUV&#91;1&#93;, _color);
 addVertex(glid, bottomLeftX, bottomLeftY, minUV&#91;0&#93;, maxUV&#91;1&#93;, _color);

 // Triangle #2
 addVertex(glid, topRightX, topRightY, maxUV&#91;0&#93;, minUV&#91;1&#93;, _color);
 addVertex(glid, bottomLeftX, bottomLeftY, minUV&#91;0&#93;, maxUV&#91;1&#93;, _color);
 addVertex(glid, bottomRightX, bottomRightY, maxUV&#91;0&#93;, maxUV&#91;1&#93;, _color);
}
&#91;/sourcecode&#93;

Aah, bit packing... how do I love thee, let me count the ways! When I first learned how to manipulate bits of data, I asked myself "Why would this ever be useful?" ... guess I learned the hard way, that its a very necessary skill to have. I don't fully understand it as much as I would like to, but I do a little research on it every day.

What we're doing in the above code is taking the red / green / blue / alpha color value (which is passed in as a 'between 0 and 1' value), multiplying that by 255, and packing the bits into a single value called _color. Apparently, its a lot faster for OpenGL to use this data in this way, so hi ho, hi ho.. its off to pack we go!

&#91;sourcecode="cpp"&#93;
void TextureController::addVertex(GLuint glid, float x, float y, float uvx, float uvy, unsigned color)
{
 VertexInfo *vertexInfo = &vertices&#91;glid&#93;;
 Vertex *vert = &vertexInfo->vertex[vertexInfo->_vertexCount];
 vert->v[0] = x;
 vert->v[1] = y;
 vert->uv[0] = uvx;
 vert->uv[1] = uvy;
 vert->color = color;
 vertexInfo->_vertexCount++;
}

And packing we do! This is where the batch work is done. What we’re doing is passing in a single Vertex data (the x location, y location, texture coordinates, color, and the texture used) and packing it into the struct I showed you above. Once we do that, we increase the _vertexCount, so we’re keeping tabs on how many vertices we’re batching.

So.. thats how we batch, how do we render? Simple!

NOTE: Keep in mind, this is only a portion of the code. This function is called from the “end()” function I talked about eariler. end() will ensure that beginning was called, and then pass the buck to the render function.

void TextureController::renderToScreen()
{
 glPushMatrix();
 glMatrixMode(GL_MODELVIEW);

 //	Texture Blending fuctions
 if ( blendAdditive )
 {
 glEnable(GL_BLEND);
 glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 }

 //	needed to draw textures using Texture2D
 glEnable(GL_TEXTURE_2D);		

 //	enables alpha for transparent textures
 //	I forget where I got these commands, iDevGames.net I think
 glAlphaFunc(GL_GREATER, 0.1f);
 glEnable(GL_ALPHA_TEST);

 //	Enable the various arrays used to draw texture to screen
 glEnableClientState(GL_VERTEX_ARRAY);
 glEnableClientState(GL_NORMAL_ARRAY);
 glEnableClientState(GL_TEXTURE_COORD_ARRAY);
 glEnableClientState(GL_COLOR_ARRAY);

 glLoadIdentity();

The above is just standard stuff to get ready for rendering. In fact, I think this was just cut / pasted from my Texture2D class. The real interesting part happens next!

 //	loop through all of the elements of the map and draw the vertices
 VertexMap::iterator it = vertices.begin();
 for (/* none */; it != vertices.end(); it++)
 {
 //	easy access to our data
 VertexInfo *vertexInfo = &it->second;
 Vertex *vert = vertexInfo->vertex;

 //	bind the texture for the following vertices
 bindTexture( (*it).first );

 //	throw everything to OpenGL
 glVertexPointer(2, GL_SHORT, sizeof(Vertex), &vert->v);
 glTexCoordPointer(2, GL_FLOAT, sizeof(Vertex), &vert->uv);
 glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(Vertex), &vert->color);
 glDrawArrays(GL_TRIANGLES, 0, vertexInfo->_vertexCount);

 //	reset this batches vertex count
 vertexInfo->_vertexCount = 0;
 }

What we’re doing here is looping through every key (which is the GLuit of the texture, if you recall) binding that texture so that OpenGL knows which texture to draw with, and then throws all of the vertices and texture coordinates and all other info needed to render the batch. A few notes that some people might not know (I didn’t when I was researching this)

glVertexPointer(2, GL_SHORT, sizeof(Vertex), &vert->v);
the 2 means that there will be 2 vertices, and x and a y. This number could be a 3, if you’re also storing a z value. We will be using GL_SHORT (remember in the struct, all vertices are declared as short), and the interesting portion of this is the sizeof(Vertex). This is called a STRIDE, and basically tells OpenGL the distance between the data in memory. (I hope I explained that correctly!) The last value is the array of vertices!

glTexCoordPointer(2, GL_FLOAT, sizeof(Vertex), &vert->uv);
This is very similar to the above.. except we’re using different values. The 2 is referring to the fact that we have 2 points per vertex for the texture coordinates (an x and a y) but if you’re going to be using a z value, this number will be changed to 3. Remember, we are using floats for this (check the struct), and the STRIDE value stays the same. Then just pass it in the array of information.

glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(Vertex), &vert->color);
Again, similar concept, except we did a few things differently with this. Remember our color scheme is 4 colors (red, green, blue, and alpha) but we packed all that information into a single value? We specify that via the GL_UNSIGNED_BYTE. otherwise, everything else remains similar.

glDrawArrays(GL_TRIANGLES, 0, vertexInfo->_vertexCount);
This is the reason we’re keeping track of how many vertices we have! What we’re doing here is telling OpenGL to draw the arrays using triangles, the 0 is referring to the starting index (obviously we’re going to be starting at index 0, just as if we were looping through the index ourselves), and how many elements are in the arrays.

What this will do, is put together the information in a single stream of information.. something like:

XY RGBA USUV, XY RGBA USUV, XY RGBA USUV
This is much more efficient for OpenGL to render, and therefore it will chew through the data and at much greater speeds than if you render your data once per texture. (ala, my old method)

now all thats left to do is clean up by disabling any states we enabled

 //	disable all the stuff we enabled eariler
 glDisableClientState(GL_VERTEX_ARRAY);
 glDisableClientState(GL_TEXTURE_COORD_ARRAY);
 glDisableClientState(GL_COLOR_ARRAY);
 glDisable( GL_BLEND );
 glDisable( GL_TEXTURE_2D );
 glDisable( GL_ALPHA_TEST );

 glPopMatrix();
}

and voila!

Again, this is my first pass at writing such a system.. and I am still learning the form of graphics programming. I urge you to pick up the code from the svn repository (http://code.google.com/p/djinnengine) and play around with it. If you find anything that I could do better, or things that may help me understand this process a little better, feel free to post for everyone to learn from!

Happy Coding everyone!

D’Jinn Engine: Updates

Over the last few days I’ve been re-working a few of the OpenGL calls and a few classes in the D’Jinn Engine. The most notable change is removing the Texture2D class that apple provides, and instead loading up a Texture2D class of my own that uses the TextureController for memory management. In revamping the Textures from OpenGL, I was hopeful to figure out the problem I’ve been having with the Particle Emitter, and I have not been able to figure it out… but I’ll keep working!

The Emitters problem is documented in both the class file as well as issues on the SVN site.

Anyway, feel free to poke around and send me an email if you find anything that I could do better, or that could be re-structured better. I will start working on new extensions and making the “engine” an actual engine over the next few weeks.. especially now that the design for my game is starting to complete and I have a better idea of what I’ll need to add to the engine to make it work. After all, the D’Jinn Engine is a project of mine to help learn the in’s and out’s of C++ development, so send in that feedback!

Also of note, I obtained the 3.0 SDK and fixed the minor errors in the code that didn’t let you compile and run it under 3.0 OS. You should be able to now. Full list of changes can be found: HERE

Happy Coding everyone!
PS: D’Jinn Engine SVN: CLICK HERE

C++ on the iPhone: Djinn Engine

EDIT: I would like to point out that below, when mentioning “Mike” … I forgot to plug his website.. whoops! In any rate, he has a few great tutorials (in video form) located: http://www.71squared.co.uk/ … HIGHLY recommend you check them out if you’re using Obj-C on the iPhone.

Hello everyone! I have been reading through your emails and appreciate all the letters. One question I kept asking myself with this project was “Do I want to make the engine open source?” My decision came apparent when I realized that this engine, although it will be used for my iPhone games, was first and foremost a learning experience for me and a tool that I used in order to become a better programmer.

So here I am, with a working copy of the Djinn Engine, and I have decided to make the project ‘open source.’ Before I upload the source to a SVN however, I want to ask the communities opinion on what they want to see?

The engine works, but it is crude. Currently in the engine is the following:

TestGame – I’ve been using this as a static unit testing for the engine

Actor System – Handles any actors in the game. Started by using the Angel Engine as template

Animation System – Animation Manager used for stopping, starting, and updating various animation playlists.

Game Screen Management – A C++ version of the Screen Controller tutorial from below.

Serializable objects – All objects (Characters, particle effects, etc) will be serialized in .dat files for dynamic loading. This way they do not need to be hard coded into the engine.

Input management (single touch only) – A C++ version of the input manager tutorial below.

Particle System – Using Mike’s tutorial as a starting point, dynamic particle system that includes a controller, effect, and various emitters for every particle effect. The one i currently have been using is “fire”

OpenAL Sound Support (have not put in OGG support yet, plan to) – Also using Mike’s tutorials as a staging point, this is an OpenAL sound engine that currently only works with sound effects… I want to add OGG support in the future.

File Management – pass in the asset name of a file, and a pointer to the object you wish to unserialize, and the file manager will take care of the rest.

Random Number Generation – … does just what it says it will do :)

Modified version of Apples Texture2D for C++ (will need to revamp this)

Math Utilities class (IE: Clamp, Min / Max, Abs, Lerp, etc etc)

and a couple of other things. Keep in mind, this is a 2D engine! So… iPhone community… We have a few choices before this thing goes Open Source. I will continue working on it, adding things that will meet my needs (keeping in mind, this will be the engine I am using for my iPhone Game) and I figure if I need a feature, maybe the community could use it as well. Should I just release it “as is” right now and continue working on it while you all can get your hands on it and modify it depending on what you need? Should I clean it up a bit, so its easier to understand when you’re reading through the code? or should I wait til the engine is pretty much done and release it then?

Let me know either via comment or email what you wish, and we’ll make it happen. I’ll have to work on some documentation, especially for the crude object serialization haha.. but that shouldn’t be too hard to do. Let me know what you think, and for the few of us who actually enjoy C++ on the iPhone, lets make it happen!

iPhone Gaming Framework: Stage 1 Tutorial

Buckle in guys, this is going to be a rather large tutorial. The goal for this tutorial is to get a basic screen management system up and running, ready to start writing game code. I would like to start off by saying the following: This is not the only way to get a project up and running! There are many many many ways of solving problems in the programming world. Some people might prefer to use Cocos2D for the iPhone, while others might prefer to roll their own engine from scratch. I did this more as a learning process for myself, and now that I’ve learned what I could, i thought I should share the knowledge to everyone else who is struggling with the problems that I’ve solved.

Also, keep in mind that this screen management system is basically a port of the GameStateManagement demo from the XNA sample ( http://creators.xna.com/ ) from C# to Objective-C with some modifications. Anyone currently using XNA should have a fairly easy time porting this over, as a lot of the code should be recognizable to you.

So, now that I’ve got that out of the way, lets begin! Your first step is going to head over to Jeff’s blog iPhoneDevelopment and pick up the Updated OpenGL Xcode Project Template.

Next step, is to follow his directions and install it! Once you have it installed, load a new project using his template. You will find that a few things are different, and a whole lot is added. Open up the GLView.m in the classes subdirectory, and add the following four methods:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
	[controller touchesBegan:touches withEvent:event InView:self  WithTimer:animationTimer];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
	[controller touchesMoved:touches withEvent:event InView:self  WithTimer:animationTimer];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
	[controller touchesEnded:touches withEvent:event InView:self  WithTimer:animationTimer];
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
	[controller touchesCancelled:touches withEvent:event InView:self  WithTimer:animationTimer];
}

What this is going to do, is when your iPod touch or iPhone is touched, a message is sent to the GLView. We are going to capture that message, and send it to the GLViewController. Okay, got that done? GREAT! Now comes the fun stuff.

Open up your GLViewController.h file. You are going to be putting in quite a bit of code, and i’ll explain everything when we do the .m file, so for right now just adjust your .h file to look like the following. You’ll see the .m file is HEAVILY commented to show what everything is and what it does, and i’ll make some additional notes here as well… so here is the GLViewController.h file.

//
//	The View Controller is a service which mananges one or more GameScreen
//	instances. It maintains a stack of screens, calls their Update and Draw
//	methods at the appropriate times, and automatically routes the input to
//	the topmost active screen.
//
//	Created by XNA Development Team ( http://creators.xna.com/ ) as a 
//	ScreenManager.cs GameComponent.
//
//  Adapted for iPhone Game Development by Craig Giles on 1/1/09.
//

//
//	Import statements
//
#import <UIKit/UIKit.h>
#import <OpenGLES/EAGL.h>
#import <OpenGLES/ES1/gl.h>
#import <OpenGLES/ES1/glext.h>

#import "Texture2D.h"
#import "InputManager.h"
#import "GameScreen.h"
#import "TitleScreen.h"

@class GLView;
@interface GLViewController : UIViewController 
{	
	NSMutableArray *screens;
	NSMutableArray *screensToUpdate;
	InputManager *input;
	Texture2D *blankTexture;
	
	bool isInitialized;
	bool traceEnabled;	
	
	UIView *gameView;
	CGRect viewport;
}

//
//	Properties
//
@property (nonatomic, retain) NSMutableArray *screens;
@property (nonatomic, retain) NSMutableArray *screensToUpdate;
@property (nonatomic, retain) InputManager *input;
@property (nonatomic, retain) Texture2D *blankTexture;

@property (nonatomic, readwrite) bool isInitialized;
@property (nonatomic, readwrite) bool traceEnabled;

@property (nonatomic, retain) UIView *gameView;
@property (nonatomic, readwrite) CGRect viewport;

//
//	Methods
//	
- (void) setupView:(GLView*)view;
- (void) loadContent;
- (void) addScreen:(GameScreen *)screen;
- (void) removeScreen:(GameScreen *)screen;
- (void) releaseScreen:(GameScreen *)screen;
- (void) updateView:(GLView *)view WithTime:(float)deltaTime;
- (void) drawView:(GLView *)view WithTime:(float)deltaTime;
- (void) traceScreens;
- (void) fadeBackBufferToBlack:(double)alpha;

//
//	Touches events
//
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event InView:(UIView *)touchView WithTimer:(NSTimer *)timer;
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event InView:(UIView *)touchView WithTimer:(NSTimer *)timer;
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event InView:(UIView *)touchView WithTimer:(NSTimer *)timer;
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event InView:(UIView *)touchView WithTimer:(NSTimer *)timer;

@end

Its a good idea to look through the .h file to see what you can do with the screen manager. Obviously you can do the touch events (remember we connected those from the GLView?) but also, looking at the methods you will be able to add and remove screens from the screen manager, update and draw, fade back buffer to black, and a few other things. Lets see how it all works!

//
//	The View Controller is a service which mananges one or more GameScreen
//	instances. It maintains a stack of screens, calls their Update and Draw
//	methods at the appropriate times, and automatically routes the input to
//	the topmost active screen.
//
//	Created by XNA Development Team ( http://creators.xna.com/ ) as a 
//	ScreenManager.cs GameComponent.
//
//  Adapted for iPhone Game Development by Craig Giles on 1/1/09.
//

//
//	Import commands from Jeff's template
//
#import "GLViewController.h"
#import "GLView.h"
#import "OpenGLCommon.h"
#import "ConstantsAndMacros.h"

//
//	This indicates weather or not the game will be played in 
//	landscape or portrait mode. While in landscape mode, the
//	screen will be rotated, but also the input will be off.
//	Touch coordinates for the screen will have to be converted
//	before it reaches the input manager class.
//
const bool LANDSCAPE_MODE = NO;

//
//	The time it takes for a game screen to transition
//	These can be over written in the game screen init.
//	If there is no values in the game screen itself, these
//	will be used as the default values.
//
const float TRANSITION_ON_TIME = .70f;
const float TRANSITION_OFF_TIME = .20f;

//
//	Implementation of the Screen Manager class
//
@implementation GLViewController

//
//	Getters / Setters
//
@synthesize screens;
@synthesize screensToUpdate;
@synthesize input;
@synthesize blankTexture;

@synthesize isInitialized;
@synthesize traceEnabled;

@synthesize gameView;
@synthesize viewport;

//
//	Setup View handles setting up OpenGL's Projection Matrix and 
//	enables all states needed for rendering the game to screen.
//
-(void)setupView:(GLView*)view
{	
	//	Set the view to the gameView
	gameView = view;
	
	//	Modify the Projection matrix
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	
	//
	//	Orthof projection is used for 2d games. This sets the coordinates to
	//	(0, 0) at the top left corner of the screen, and as you move downward
	//	your y value will increase. As you move to the right, your x value will
	//	increase.
	//	(left, right, bottom, top, near, far)
	//
	//	If the game is going to be played in landscape mode, enable
	//	it via the bool switch at the top of the GLViewController.m file.
	if ( LANDSCAPE_MODE )
	{
		viewport = CGRectMake(0, 0, 480, 320);
		glViewport(0, 0, viewport.size.height, viewport.size.width);
		glRotatef(-90, 0, 0, 1);
        glOrthof(0, viewport.size.width, viewport.size.height, 0, -10.0, 10.0);  
		
	}
	else	//	Game is to be played in portrait
	{
		viewport = CGRectMake(0, 0, 320, 480);
		glViewport(0, 0, viewport.size.width, viewport.size.height);
		glOrthof(0.0, viewport.size.width, viewport.size.height, 0.0, -1.0, 1.0);	
			
	}
	
	//
	//	Setup Model view matrix
	//	Load graphics settings
	//
	glMatrixMode(GL_MODELVIEW);
	
	glDisable(GL_DEPTH_TEST);
	glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
	glEnable(GL_BLEND);	
	
	//	needed to draw textures using Texture2D
	glEnable(GL_TEXTURE_2D);	
	glEnableClientState(GL_TEXTURE_COORD_ARRAY);
	glEnableClientState(GL_VERTEX_ARRAY);
	
	
	//	enables alpha for transparent textures
	//	I forget where I got these commands, iDevGames.net I think
	glAlphaFunc(GL_GREATER, 0.1f);
	glEnable(GL_ALPHA_TEST);
	
	//
	//	Setup clear color (cornflower blue'ish)
	//	Call me crazy, but I got so used to this color developing
	//	for XNA. This is a little nod to the Microsoft Development
	//	Team :)
	//
	glLoadIdentity(); 
	glClearColor(.39f, 0.58f, 0.920f, 1.0f); 

	
	//
	//	Call the view controllers loadContent method
	//	
	[self loadContent];
	
}

//
//	Loads all content needed to run the screen manager. This is seperated 
//	from the setupView method in order to seperate what is needed from OpenGL 
//	to setup the screen, and what is needed from the screen manager to set 
//	up the game structure. 
//
- (void)loadContent
{
	//
	//	Allocate memory for your arrays to hold the Screens "stacks." 
	//	All game screens will be housed in this array for easy manipulation. 
	//
	screens = [[NSMutableArray alloc] init];
	screensToUpdate = [[NSMutableArray alloc] init];
	
	//
	//	Allocate memory for the input manager and the blankTexture used
	//	to fade the screen in / out.
	//
	input = [[InputManager alloc] init];
	input.isLandscape = LANDSCAPE_MODE;
	blankTexture = [[Texture2D alloc] initWithImage:[UIImage imageNamed:@"blankTexture.png"]];
	
	for (GameScreen *screen in screens)
		[screen loadContent];
	
	//
	//	Once we are initialized, set the bool values to appropriate values. 
	//
	isInitialized = YES;
	traceEnabled = NO;
	
	//
	//	Adds a title screen to the game stack. This will be taken out 
	//	later, and right now is only used for debugging purposes. It
	//	will be replaced with your splash screen or game introduction
	//	screen.
	//
	TitleScreen *newScreen = [[TitleScreen alloc] init];
	[self addScreen:newScreen];
	[newScreen release];
}

//
//	When the view controller exits, we will need to clean up any memory used.
//
- (void)dealloc 
{
	//
	//	setup a delete screens array and add all of the current game screens
	//	to this array. We will then cycle through all game screens, unloading
	//	their content, and releasing them from the view controller. After all
	//	is said and done, we will then remove the deleteScreens array, and 
	//	continue on releasing any other memory allocated for the view controller.
	//
	NSMutableArray *deleteScreens = [[NSMutableArray alloc] initWithArray:screens];
	
	for (GameScreen *screen in deleteScreens)
	{
		[self removeScreen:screen];
		[self releaseScreen:screen];
	}
	
	[deleteScreens release];
	[screens release];
	[screensToUpdate release];
	[input release];
	[blankTexture release];
	
    [super dealloc];
}

//
//	If the game is going over memory, this method will be called by the device
//	warning that we are running low on memory and should release any un needed
//	items.
//
- (void)didReceiveMemoryWarning 
{
	//	<<TODO: Unload any un-needed game content here>>
    [super didReceiveMemoryWarning]; 
}

//
//	Add a screen to the view controller
//
- (void) addScreen:(GameScreen *)screen
{
	//
	//	When adding a screen to the view controller, we will be
	//	setting some default values for the screen, and then call
	//	the screens "loadContent" method. Once everything is loaded,
	//	the view controller will retain the screen and add it to the
	//	screens array.
	//
	screen.controller = self;
	screen.viewport = self.viewport;
	screen.transitionOnTime = TRANSITION_ON_TIME;
	screen.transitionOffTime = TRANSITION_OFF_TIME;
	screen.currentScreenState = TransitionOn;
	screen.transitionPosition = 1;
	[screen loadContent];
	
	[screen retain];
	[screens addObject:screen];
}

//
//	Unload all game content from the screen. This in turn
//	sets a flag within the screen itself, that the content has
//	been unloaded, and in the controllers Update method, all game
//	screens that have been unloaded will be released from memory.
//
- (void) removeScreen:(GameScreen *)screen
{
	//unload any content it has stored
	[screen unloadContent];
}

//
//	Release all game screens from memory, that have had their content
//	unloaded. This will release all screens themselves, as well as remove
//	them from the screens arrays.
//
- (void) releaseScreen:(GameScreen *)screen
{	
	//	remove the screen from all screen arrays
	[screens removeObject:screen];
	[screensToUpdate removeObject:screen];
	
	//	deallocate any memory used for the screen
	[screen release];
}


//
//	Update every screen in the screens stack, keeping track
//	of which screens are covered and which are fully active.
//	if a screen is fully active and "on top" of the stack, it
//	should receive any input.
//
- (void) updateView:(GLView *)view WithTime:(float)deltaTime
{
	//	Read the touch input
	[input update:deltaTime];
	
	//	make a copy of hte master screen list, to avoid confusion if
	//	the process of updating one screens adds or removes others.
	[screensToUpdate removeAllObjects];
	
	for(GameScreen *screen in screens)
		[screensToUpdate addObject:screen];
	
	bool otherScreenHasFocus = NO;
	bool coveredByOtherScreen = NO;
	
	//	loop as long as there are screens waiting to be updated
	while ([screensToUpdate count] > 0) 
	{
		//	pop the topmost screen off the waiting list
		GameScreen *screen = [screensToUpdate objectAtIndex:([screensToUpdate count] - 1)];
		
		[screensToUpdate removeObjectAtIndex:[screensToUpdate count] - 1];
		
		//	update the screen
		[screen update:deltaTime OtherScreenHasFocus:otherScreenHasFocus 
								CoveredByOtherScreen:coveredByOtherScreen];
		
		
		if ([screen currentScreenState] == TransitionOn ||
			[screen currentScreenState] == Active)
		{
			//	if this is the first active screen we came across,
			//	give it a chance to handle input.
			if (!otherScreenHasFocus)
			{
				[screen handleInput:input];
				otherScreenHasFocus = YES;
			}
			
			//	if this is an active non-popup, inform any subsequent
			//	screens that they are covered by it
			if (![screen isPopup])
				coveredByOtherScreen = YES;
			
		}
	}
	
	//	do we need to print the debug trace?
	if (traceEnabled)
		[self traceScreens];
	

	//
	//	For every screen that had their content unloaded.. release
	//	the memory used for that screen here. We do this up front
	//	to ensure that any released screen doesn't get their update
	//	or draw methods called, when there is nothing to update or draw.
	//
	for (GameScreen *screen in screens)
	{
		if (screen.hasBeenUnloaded)
		{
			[self releaseScreen:screen];
		}
	}
}

//
//	Draw the game screens from "Bottom to Top." This is done 
//	in order to ensure that any pop'up screens are drawn on top
//	of the full screen below it. 
//
- (void) drawView:(GLView *)view WithTime:(float)deltaTime
{
	//	Clear the screen to preset color before drawing
	glClear(GL_COLOR_BUFFER_BIT);
	
	//	Draw every screen in the screens array
	for (GameScreen *screen in screens)
	{
		//if the screens content has been unloaded, don't draw
		if (screen.hasBeenUnloaded)
			continue;
		
		[screen draw:deltaTime];
	}
}

//
//	Helper method designed to draw the screen names currently
//	in the game stack in order to see if they are being added
//	and removed correctly. 
//
- (void) traceScreens
{
	//	<<TODO: Input code to draw the screen names>>
}

//
//	Helper method to draw a translecent black fullscreen sprite, used
//	for fading screens in and out, and for darkening the background
//	behind pop up screens.
//
- (void) fadeBackBufferToBlack:(double)alpha 
{
	glColor4f(alpha,alpha,alpha,alpha);
	[blankTexture drawInRect:self.viewport];
	glColor4f(1, 1, 1, 1);
}


//
//	When the screen is touched by the user, the GLView will pass along a message
//	to the view controller that the screen has been touched. The view controller
//	will take the message, and pass it along to the input manager where the
//	necessary information will be stored and filtered to the game screen that
//	will handle the user input.
//
//	In order for this to work, in your GLView, you need to write the following
//	4 methods:
//	- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
//	- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
//	- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
//	- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
//
//	Those methods will call the methods below.
//
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event InView:(UIView *)touchView WithTimer:(NSTimer *)timer
{
	[input touchesBegan:touches withEvent:event InView:touchView  WithTimer:timer];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event InView:(UIView *)touchView WithTimer:(NSTimer *)timer
{
	[input touchesMoved:touches withEvent:event InView:touchView  WithTimer:timer];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event InView:(UIView *)touchView WithTimer:(NSTimer *)timer
{
	[input touchesEnded:touches withEvent:event InView:touchView  WithTimer:timer];
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event InView:(UIView *)touchView WithTimer:(NSTimer *)timer
{
	[input touchesCancelled:touches withEvent:event InView:touchView  WithTimer:timer];
}

@end

As you can see, this is a pretty good sized class. What makes it bigger is I have a nasty habit of commenting everything to hell! I always believe it is best to comment heavily, because if you come back a year later and want to adjust your game, comments make it very helpful for remembering what does what.

The comments in the GLViewController (screen manager) class explains what everything does, but if you have any questions feel free to post them here.

So… now we need a game screen or two!! Remember, the following code should never be used to make a game screen directly. What I mean is, use this as a super class and inherit from it with your screens. For example, your TitleScreen should inherit from GameScreen. Make sense?

here is the GameScreen.h file

//	
//	A screen is a single layer that has update and draw logic, and which
//	can be combined with other layers to build up a complex screen system
//	or menu system, or even dialog system.
//
//	Developed by XNA Development Studio ( http://creators.xna.com/ ) 
//	Modified for the iPhone Gameing Framework by Craig Giles on 1/1/09.
//

#import <Foundation/Foundation.h>

#import <OpenGLES/EAGL.h>
#import <OpenGLES/ES1/gl.h>
#import <OpenGLES/ES1/glext.h>

#import "InputManager.h"
#import "Texture2D.h"

//
//	Enum to describe the screens transition state
//
enum ScreenState {
	TransitionOn = 0,
	Active,
	TransitionOff,
	Hidden
};

//
//	Forward Declarations
//
@class GLViewController;

@interface GameScreen : NSObject 
{	
@private
	GLViewController *controller;
	CGRect viewport;
	
	bool hasBeenUnloaded;
	bool isPopup;
	
	float transitionOnTime;
	float transitionOffTime;
	float transitionPosition;
	float transitionAlpha;
	enum ScreenState currentScreenState;
	
	bool isExiting;
	bool isActive;
	bool otherScreenHasFocus;	
}

@property (nonatomic, retain) GLViewController *controller;
@property (readwrite) CGRect viewport;

@property (readwrite) bool hasBeenUnloaded;
@property (readwrite) bool isPopup;

@property (readwrite) float transitionOnTime;
@property (readwrite) float transitionOffTime;
@property (readwrite) float transitionPosition;
@property (readwrite) float transitionAlpha;

@property (readwrite) enum ScreenState currentScreenState;

@property (readwrite) bool isExiting;
@property (readwrite) bool isActive;
@property (readwrite) bool otherScreenHasFocus;


- (void) loadContent;
- (void) unloadContent;

- (void) handleInput:(InputManager *)input;
- (void) update:(float)deltaTime	OtherScreenHasFocus:(bool)otherFocus	CoveredByOtherScreen:(bool)coveredByOtherScreen;
- (bool) updateTransition:(float)deltaTime	TransitionTime:(float)transition	Direction:(int)direction;
- (void) draw:(float)deltaTime;

- (void) exitScreen;

@end

and the GameScreen.m file

//
// A screen is a single layer that has update and draw logic, and which
// can be combined with other layers to build up a complex screen system
// or menu system, or even dialog system.
//
// Developed by XNA Development Studio ( http://creators.xna.com/ )
// Modified for the iPhone Gameing Framework by Craig Giles on 1/1/09.
//

#import “GameScreen.h”

@implementation GameScreen

//
// Properties
//
@synthesize controller;
@synthesize viewport;

@synthesize hasBeenUnloaded;
@synthesize isPopup;

@synthesize transitionOnTime;
@synthesize transitionOffTime;
@synthesize transitionPosition;
@synthesize transitionAlpha;

@synthesize currentScreenState;

@synthesize isExiting;
@synthesize otherScreenHasFocus;

@dynamic isActive;
– (bool) isActive
{
return !otherScreenHasFocus &&
(currentScreenState == TransitionOn ||
currentScreenState == Active);
}

//
// Constructor(s) / destructors
//
– (id) init
{
self = [super init];
if (self != nil)
{
//initializations go here
isExiting = NO;
}
return self;
}

– (void) dealloc
{
//Deallocations go here
[super dealloc];
}

//
// Loads all content associated with the current screen
//
– (void) loadContent
{

}

//
// Unloads all content associated with the current screen
//
– (void) unloadContent
{
// Release the screen manager
[controller release];

// inidicate that the screens content has been unloaded
hasBeenUnloaded = YES;
}

//
// Allows the screen to perform its update logic.
//
– (void) handleInput:(InputManager *)input
{
}

//
// Updates the base screen. Since any game screen
// wil be inheriting from this class, the game screen will
// call this update method. This update just helps with the
// transition between two screens, and if a screen is
// transitioning on and off.
//
– (void) update:(float)deltaTime OtherScreenHasFocus:(bool)otherFocus CoveredByOtherScreen:(bool)coveredByOtherScreen
{
otherScreenHasFocus = otherFocus;

if (isExiting)
{
//if the screen is going to die, it should transition off
currentScreenState = TransitionOff;

if (![self updateTransition:deltaTime TransitionTime:transitionOffTime Direction: 1])
{
//when transition finishes, remove the screen
[controller removeScreen:self];
}
}
else if (coveredByOtherScreen)
{
//if the screen is covered by another, it should transition off
if ([self updateTransition:deltaTime TransitionTime:transitionOffTime Direction: 1])
{
//scren is still transitioning
currentScreenState = TransitionOff;
}
else
{
//transition has finished
currentScreenState = Hidden;
}
}
else
{
if ([self updateTransition:deltaTime TransitionTime:transitionOnTime Direction: -1])
{
//still busy transitioning
currentScreenState = TransitionOn;
}
else
{
//transition finished
currentScreenState = Active;
}
}
}

//
// Helper method for updating the screen transition position
// (how much the screen has faded in / out)
//
– (bool) updateTransition:(float)deltaTime TransitionTime:(float)time Direction:(int)direction
{
// how much should we move by?
float transitionDelta;

if (time <= 0) transitionDelta = 1; else transitionDelta = deltaTime / time; //update the transition position transitionPosition += transitionDelta * direction; //did we reach the end of the transition? if (direction < 0 && transitionPosition <= 0 || direction > 0 && transitionPosition >= 1)
{
//clamp transition position to 0, 1, or value;
if (transitionPosition >= 1)
transitionPosition = 1;
else if (transitionPosition <= 0) transitionPosition = 0; return NO; }//end "end of transition" //otherwise, we are still busy transitioning return YES; } // // Each screen will have their own draw method. EVERY SCREEN // should call [super draw:deltaTime] in order to draw // the fade correctly when the screen manager wishes to fade // the screen in or out. // - (void) draw:(float)deltaTime { [self.controller fadeBackBufferToBlack:self.transitionPosition]; } // // Tells the screen to go away. Unlike [controller removeScreen] which // instantly kills the screen, this method respects the transition timings // and will give the scren a chance to gradually transition off. // - (void) exitScreen { if (transitionOffTime == 0) { //if the screen has zero transition time, kill it [controller removeScreen:self]; } else { //otherwise flag that it should transition off and exit isExiting = YES; } } @end [/sourcecode] Well that does it for the screen manager and the game screen classes.. But keep in mind.. this will NOT build until the InputManager is built. Why don't you try to fiddle with that for a while, see what you can come up with? I'll post Part 2 of this tutorial detailing how I did my input manager and two screens (TitleScreen and PausedScreen) in my next update. Two thing before I go: I would really like to find a way to turn this into a template for anyone wishing to use it, but I simply do not know how. If you know how to do so, please send me an email at: CraigGiles9@yahoo.com Secondly, if you have any questions, comments, sly remarks, please post them. I am very good at reading everyones comments, and getting back to you if needed. You can either post a comment or send me an email and I'll get back to you. EDIT: I just wanted to let everyone know that there have been a few changes to this article since first posting. I just modified the code within the GLViewController in several places. The following changes were made: - Added [self releaseScreen:screen]; in the dealloc method inside the for loop. - added const bool LANDSCAPE_MODE = NO; at the top of the view controller, and an if / else statement in the setup view method to help with setting up a landscape view rather than a portrait view. (The first screen manager was written for only portrait view) - added input.isLandscape = LANDSCAPE_MODE; to the loadContent method. Again, there are too many people to thank for helping me to get to where I am with my current knowledge. I hope this was informational to a few of you! Happy coding everyone!