author Holmes Futrell <>
Fri, 15 Aug 2008 23:48:49 +0000
changeset 2441 ed6a41cc2bce
child 2459 c330dcd78e3a
permissions -rw-r--r--
Elaborated on features and limitations of SDL for iPhone. renamed and moved readme with all the other readmes.

Building the Simple DirectMedia Layer for iPhone OS 2.0

Requirements: Mac OS X v10.5 or later and the iPhone SDK.

To build SDL for iPhone, simply open the XCode Project (XCodeiPhoneOS/SDL/SDLiPhoneOS.xcodeproj), select the target you wish to build, and hit 'build'.  You can also build in a CLI environment using the xcodebuild command line tool, if you wish. 

There are three build targets:
- StaticLibiPhoneOS:
	Build SDL as a statically linked (armv6) library for iPhone OS 2.0.
- StaticLibSimulator:
	Build SDL as a statically linked (x86) library for the iPhone Simulator
- Template:
	Package a project template together with the SDL for iPhone static libraries and copies of the SDL headers.  The template includes proper references to the SDL library, skeleton code for a basic SDL program, and placeholder graphics for the application icon and startup screen.

Be advised that you'll most likely need to build both StaticLibiPhoneOS.a and StaticLibSimulator.a before you compile any projects that use SDL for iPhone.

Using the Simple DirectMedia Layer for iPhone OS 2.0

Here's probably the easiest method:
1.  Build the SDL libraries (libSDLiPhoneOS.a and libSDLSimulator.a) and the iPhone SDL Application template.
1.  Install the iPhone SDL Application template (recommended directory is /Developer/Platforms/iPhoneOS.platform/Developer/Library/XCode/Project Templates/SDL Application/)
2.  Start a new project using the template (SDL will be automatically included in your project)

Here's a more manual method:
1.  Create a new iPhone project
2.  Build the SDL libraries (libSDLiPhoneOS.a and libSDLSimulator.a) and include them in your project.  XCode will ignore the library that is not currently of the correct architecture, hence your app will work both on iPhone and in the iPhone Simulator.
3.  include the SDL header files in your project.
4.  Remove main.m and replace it with a new main.m (or main.c) which is coded like a normal SDL program.  To replace main.m with a main.c, you must tell XCode not to use the project prefix file, which includes references to Cocoa Touch.

Notes -- Touch Input

Touch input in SDL for iPhone OS is presently exposed through SDL's mouse input API.  Multi-touch input is reported as multiple mice, with each touch associated with a specific mouse.  This association stays coherent from the time the touch starts to the time a touch ends.

By default, multi-touch is turned ON.  This requires some care, because if you simply respond to mouse events without checking which mouse caused the event, you may end up fetching data from the wrong mouse, ie, an incorrect or invalid touch.  To turn multi-touch OFF, you can recompile SDL for iPhone with the macro SDL_IPHONE_MULTIPLE_MICE (found in SDL_config_iphoneos.h) set to 0.

Notes -- Accelerometer as Joystick

SDL for iPhone supports polling the built in accelerometer as a joystick device.  For an example on how to do this, see the accelerometer.c in the demos directory.

The main thing to note when using the accelerometer with SDL is that while the iPhone natively reports accelerometer as floating point values in units of g-force, SDL_JoystickGetAxis reports joystick values as signed integers.  Hence, in order to convert between the two, some clamping and scaling is necessary on the part of the iPhone SDL joystick driver.  To convert SDL_JoystickGetAxis reported values BACK to units of g-force, simply multiply the values by SDL_IPHONE_MAX_GFORCE / 0x7FFF.

Notes -- OpenGL ES

Your SDL application for iPhone uses OpenGL ES by default.

OpenGL ES for iPhone supports two display pixel formats, RGBA8 and RGB565.  By default, the implementation uses RGB565, but you may use RGBA8 by setting each color component to 8 bits in SDL_GL_SetAttribute.

If your application doesn't use the depth buffer, you may also find significant performance improvement by setting SDL_GL_DEPTH_SIZE to 0.

Finally, if your application completely redraws the screen each from, you may find significant performance improvement by setting the attribute SDL_GL_RETAINED_BACKING to 1.

Notes -- Keyboard

SDL for iPhone contains several additional functions related to keyboard functionality.  These functions are not part of the SDL standard API, but are necessary for revealing and hiding the iPhone's virtual onscreen keyboard.  You can use them in your own applications by including a copy of the SDL_uikitkeyboard.h header in your project.

int SDL_iPhoneKeyboardShow(SDL_WindowID windowID) 
	-- reveals the onscreen keyboard.  Returns 0 on success and -1 on error.
int SDL_iPhoneKeyboardHide(SDL_WindowID windowID) 
	-- hides the onscreen keyboard.  Returns 0 on success and -1 on error.
SDL_bool SDL_iPhoneKeyboardIsShown(SDL_WindowID windowID) 
	-- returns whether or not the onscreen keyboard is currently visible.
int SDL_iPhoneKeyboardToggle(SDL_WindowID windowID) 	
	-- toggles the visibility of the onscreen keyboard.  Returns 0 on success and -1 on error.

Notes -- Reading and Writing files

Each application installed on iPhone resides in a sandbox which includes its own Application Home directory.  For each installed application, the system generates a unique name for the application home director, which appears as a long, incomprehensible string of numbers.

Once your application is installed, the directory tree looks like:

MySDLApp Home/

When your SDL based iPhone application starts up, it sets the working directory to the main bundle (MySDLApp Home/, where your application resources are stored.  You cannot write to this directory, however -- instead, I advise you to write document files to "../Documents/" and preferences to "../Library/Preferences".  

More information on this subject is available here:

Notes -- iPhone SDL limitations

	Full-size, single window applications only.  You cannot create multi-window SDL applications for iPhone OS.  The application window will fill the display, though you have the option of turning on or off the menu-bar (pass SDL_CreateWindow the flag SDL_WINDOW_BORDERLESS).  Presently, landscape mode is not supported.

	For real time frame-rates, you are advised to use strictly SDL 1.3 video calls.  Using compatibility video calls uploads an OpenGL texture for each frame drawn, and this operation is excruciatingly slow.

	SDL for iPhone Textures supports only SDL_PIXELFORMAT_ABGR8888 and SDL_PIXELFORMAT_RGB24 pixel formats.  This is because texture support in SDL for iPhone is done through OpenGL ES, which supports fewer pixel formats than OpenGL, will not re-order pixel data for you, and has no support for color-paletted formats (without extensions).

	SDL for iPhone does not yet support audio input.

Loading Shared Objects:
	This is disabled by default since it seems to break the terms of the iPhone SDK agreement.  It can be re-enabled in SDL_config_iphoneos.h.