docs/README-ios.md
author Ryan C. Gordon
Sun, 27 Aug 2017 22:15:57 -0400
changeset 11365 a9bd2625fa01
parent 10167 d3db276c1fa6
child 11400 9eefdf672499
permissions -rw-r--r--
vulkan: Initial Vulkan support!

This work was done by Jacob Lifshay and Mark Callow; I'm just merging it
into revision control.
     1 iOS
     2 ======
     3 
     4 ==============================================================================
     5 Building the Simple DirectMedia Layer for iOS 5.1+
     6 ==============================================================================
     7 
     8 Requirements: Mac OS X 10.8 or later and the iOS 7+ SDK.
     9 
    10 Instructions:
    11 
    12 1.  Either download [Molten](https://moltengl.com/free-trial/) and unzip it or download the Vulkan headers from Khronos's [Vulkan-Docs](https://github.com/KhronosGroup/Vulkan-Docs/tree/1.0/src/vulkan) repo and put them in a directory hierarchy `include/vulkan`.
    13 2.  Open SDL.xcodeproj (located in Xcode-iOS/SDL) in Xcode.
    14 3.  Set a `VULKAN_SDK` custom path in the Xcode preferences. Select *Custom Paths* on the *Locations* tab. The value should be either the `MoltenVK` directory within the unzipped Molten package or the parent of the `include/vulkan` hierarchy.
    15 4.  Select your desired target, and hit build.
    16 
    17 There are three build targets:
    18 - libSDL.a:
    19 	Build SDL as a statically linked library
    20 - testsdl:
    21 	Build a test program (there are known test failures which are fine)
    22 - Template:
    23 	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 and headers, skeleton code for a basic SDL program, and placeholder graphics for the application icon and startup screen.
    24 
    25 
    26 ==============================================================================
    27 Build SDL for iOS from the command line
    28 ==============================================================================
    29 
    30 1. Follow step 1 above.
    31 2. Either create and export a `VULKAN_SDK` environment variable with the value described in step 3 above or open Xcode, set the custom path described in step 3 above and close Xcode.
    32 3. cd (PATH WHERE THE SDL CODE IS)/build-scripts
    33 2. ./iosbuild.sh
    34 
    35 If everything goes fine, you should see a build/ios directory, inside there's
    36 two directories "lib" and "include". 
    37 "include" contains a copy of the SDL headers that you'll need for your project,
    38 make sure to configure XCode to look for headers there.
    39 "lib" contains find two files, libSDL2.a and libSDL2main.a, you have to add both 
    40 to your XCode project. These libraries contain three architectures in them,
    41 armv6 for legacy devices, armv7, and i386 (for the simulator).
    42 By default, iosbuild.sh will autodetect the SDK version you have installed using 
    43 xcodebuild -showsdks, and build for iOS >= 3.0, you can override this behaviour 
    44 by setting the MIN_OS_VERSION variable, ie:
    45 
    46 MIN_OS_VERSION=4.2 ./iosbuild.sh
    47 
    48 ==============================================================================
    49 Using the Simple DirectMedia Layer for iOS
    50 ==============================================================================
    51 
    52 FIXME: This needs to be updated for the latest methods
    53 
    54 Here is the easiest method:
    55 1.  Build the SDL library (libSDL2.a) and the iPhone SDL Application template.
    56 2.  Install the iPhone SDL Application template by copying it to one of Xcode's template directories.  I recommend creating a directory called "SDL" in "/Developer/Platforms/iOS.platform/Developer/Library/Xcode/Project Templates/" and placing it there.
    57 3.  Start a new project using the template.  The project should be immediately ready for use with SDL.
    58 
    59 Here is a more manual method:
    60 1.  Create a new iOS view based application.
    61 2.  Build the SDL static library (libSDL2.a) for iOS 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 iOS and in the iOS Simulator.
    62 3.  Include the SDL header files in your project.
    63 4.  Remove the ApplicationDelegate.h and ApplicationDelegate.m files -- SDL for iOS provides its own UIApplicationDelegate.  Remove MainWindow.xib -- SDL for iOS produces its user interface programmatically.
    64 5.  Delete the contents of main.m and program your app as a regular SDL program instead.  You may replace main.m with your own main.c, but you must tell Xcode not to use the project prefix file, as it includes Objective-C code.
    65 
    66 ==============================================================================
    67 Notes -- Retina / High-DPI and window sizes
    68 ==============================================================================
    69 
    70 Window and display mode sizes in SDL are in "screen coordinates" (or "points",
    71 in Apple's terminology) rather than in pixels. On iOS this means that a window
    72 created on an iPhone 6 will have a size in screen coordinates of 375 x 667,
    73 rather than a size in pixels of 750 x 1334. All iOS apps are expected to
    74 size their content based on screen coordinates / points rather than pixels,
    75 as this allows different iOS devices to have different pixel densities
    76 (Retina versus non-Retina screens, etc.) without apps caring too much.
    77 
    78 By default SDL will not use the full pixel density of the screen on
    79 Retina/high-dpi capable devices. Use the SDL_WINDOW_ALLOW_HIGHDPI flag when
    80 creating your window to enable high-dpi support.
    81 
    82 When high-dpi support is enabled, SDL_GetWindowSize() and display mode sizes
    83 will still be in "screen coordinates" rather than pixels, but the window will
    84 have a much greater pixel density when the device supports it, and the
    85 SDL_GL_GetDrawableSize() or SDL_GetRendererOutputSize() functions (depending on
    86 whether raw OpenGL or the SDL_Render API is used) can be queried to determine
    87 the size in pixels of the drawable screen framebuffer.
    88 
    89 Some OpenGL ES functions such as glViewport expect sizes in pixels rather than
    90 sizes in screen coordinates. When doing 2D rendering with OpenGL ES, an
    91 orthographic projection matrix using the size in screen coordinates
    92 (SDL_GetWindowSize()) can be used in order to display content at the same scale
    93 no matter whether a Retina device is used or not.
    94 
    95 ==============================================================================
    96 Notes -- Application events
    97 ==============================================================================
    98 
    99 On iOS the application goes through a fixed life cycle and you will get
   100 notifications of state changes via application events. When these events
   101 are delivered you must handle them in an event callback because the OS may
   102 not give you any processing time after the events are delivered.
   103 
   104 e.g.
   105 
   106     int HandleAppEvents(void *userdata, SDL_Event *event)
   107     {
   108         switch (event->type)
   109         {
   110         case SDL_APP_TERMINATING:
   111             /* Terminate the app.
   112                Shut everything down before returning from this function.
   113             */
   114             return 0;
   115         case SDL_APP_LOWMEMORY:
   116             /* You will get this when your app is paused and iOS wants more memory.
   117                Release as much memory as possible.
   118             */
   119             return 0;
   120         case SDL_APP_WILLENTERBACKGROUND:
   121             /* Prepare your app to go into the background.  Stop loops, etc.
   122                This gets called when the user hits the home button, or gets a call.
   123             */
   124             return 0;
   125         case SDL_APP_DIDENTERBACKGROUND:
   126             /* This will get called if the user accepted whatever sent your app to the background.
   127                If the user got a phone call and canceled it, you'll instead get an SDL_APP_DIDENTERFOREGROUND event and restart your loops.
   128                When you get this, you have 5 seconds to save all your state or the app will be terminated.
   129                Your app is NOT active at this point.
   130             */
   131             return 0;
   132         case SDL_APP_WILLENTERFOREGROUND:
   133             /* This call happens when your app is coming back to the foreground.
   134                Restore all your state here.
   135             */
   136             return 0;
   137         case SDL_APP_DIDENTERFOREGROUND:
   138             /* Restart your loops here.
   139                Your app is interactive and getting CPU again.
   140             */
   141             return 0;
   142         default:
   143             /* No special processing, add it to the event queue */
   144             return 1;
   145         }
   146     }
   147     
   148     int main(int argc, char *argv[])
   149     {
   150         SDL_SetEventFilter(HandleAppEvents, NULL);
   151     
   152         ... run your main loop
   153     
   154         return 0;
   155     }
   156 
   157     
   158 ==============================================================================
   159 Notes -- Accelerometer as Joystick
   160 ==============================================================================
   161 
   162 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.
   163 
   164 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.
   165 
   166 ==============================================================================
   167 Notes -- OpenGL ES
   168 ==============================================================================
   169 
   170 Your SDL application for iOS uses OpenGL ES for video by default.
   171 
   172 OpenGL ES for iOS supports several display pixel formats, such as RGBA8 and RGB565, which provide a 32 bit and 16 bit color buffer respectively. By default, the implementation uses RGB565, but you may use RGBA8 by setting each color component to 8 bits in SDL_GL_SetAttribute().
   173 
   174 If your application doesn't use OpenGL's depth buffer, you may find significant performance improvement by setting SDL_GL_DEPTH_SIZE to 0.
   175 
   176 Finally, if your application completely redraws the screen each frame, you may find significant performance improvement by setting the attribute SDL_GL_RETAINED_BACKING to 0.
   177 
   178 OpenGL ES on iOS doesn't use the traditional system-framebuffer setup provided in other operating systems. Special care must be taken because of this:
   179 
   180 - The drawable Renderbuffer must be bound to the GL_RENDERBUFFER binding point when SDL_GL_SwapWindow() is called.
   181 - The drawable Framebuffer Object must be bound while rendering to the screen and when SDL_GL_SwapWindow() is called.
   182 - If multisample antialiasing (MSAA) is used and glReadPixels is used on the screen, the drawable framebuffer must be resolved to the MSAA resolve framebuffer (via glBlitFramebuffer or glResolveMultisampleFramebufferAPPLE), and the MSAA resolve framebuffer must be bound to the GL_READ_FRAMEBUFFER binding point, before glReadPixels is called.
   183 
   184 The above objects can be obtained via SDL_GetWindowWMInfo() (in SDL_syswm.h).
   185 
   186 ==============================================================================
   187 Notes -- Keyboard
   188 ==============================================================================
   189 
   190 The SDL keyboard API has been extended to support on-screen keyboards:
   191 
   192 void SDL_StartTextInput()
   193 	-- enables text events and reveals the onscreen keyboard.
   194 
   195 void SDL_StopTextInput()
   196 	-- disables text events and hides the onscreen keyboard.
   197 
   198 SDL_bool SDL_IsTextInputActive()
   199 	-- returns whether or not text events are enabled (and the onscreen keyboard is visible)
   200 
   201 
   202 ==============================================================================
   203 Notes -- Reading and Writing files
   204 ==============================================================================
   205 
   206 Each application installed on iPhone resides in a sandbox which includes its own Application Home directory.  Your application may not access files outside this directory.
   207 
   208 Once your application is installed its directory tree looks like:
   209 
   210     MySDLApp Home/
   211         MySDLApp.app
   212         Documents/
   213         Library/
   214             Preferences/
   215         tmp/
   216 
   217 When your SDL based iPhone application starts up, it sets the working directory to the main bundle (MySDLApp Home/MySDLApp.app), where your application resources are stored.  You cannot write to this directory.  Instead, I advise you to write document files to "../Documents/" and preferences to "../Library/Preferences".  
   218 
   219 More information on this subject is available here:
   220 http://developer.apple.com/library/ios/#documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/Introduction/Introduction.html
   221 
   222 ==============================================================================
   223 Notes -- iPhone SDL limitations
   224 ==============================================================================
   225 
   226 Windows:
   227 	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).
   228 
   229 Textures:
   230 	The optimal texture formats on iOS are SDL_PIXELFORMAT_ABGR8888, SDL_PIXELFORMAT_ABGR8888, SDL_PIXELFORMAT_BGR888, and SDL_PIXELFORMAT_RGB24 pixel formats.
   231 
   232 Loading Shared Objects:
   233 	This is disabled by default since it seems to break the terms of the iOS SDK agreement for iOS versions prior to iOS 8. It can be re-enabled in SDL_config_iphoneos.h.
   234 
   235 ==============================================================================
   236 Game Center 
   237 ==============================================================================
   238 
   239 Game Center integration might require that you break up your main loop in order to yield control back to the system. In other words, instead of running an endless main loop, you run each frame in a callback function, using:
   240 
   241     int SDL_iPhoneSetAnimationCallback(SDL_Window * window, int interval, void (*callback)(void*), void *callbackParam);
   242 
   243 This will set up the given function to be called back on the animation callback, and then you have to return from main() to let the Cocoa event loop run.
   244 
   245 e.g.
   246 
   247     extern "C"
   248     void ShowFrame(void*)
   249     {
   250         ... do event handling, frame logic and rendering ...
   251     }
   252     
   253     int main(int argc, char *argv[])
   254     {
   255         ... initialize game ...
   256     
   257     #if __IPHONEOS__
   258         // Initialize the Game Center for scoring and matchmaking
   259         InitGameCenter();
   260     
   261         // Set up the game to run in the window animation callback on iOS
   262         // so that Game Center and so forth works correctly.
   263         SDL_iPhoneSetAnimationCallback(window, 1, ShowFrame, NULL);
   264     #else
   265         while ( running ) {
   266             ShowFrame(0);
   267             DelayFrame();
   268         }
   269     #endif
   270         return 0;
   271     }