IOMobileFramebuffer

IOMobileFramebuffer is a kernel extension for managing the screen framebuffer. It is controlled by the user-land framework IOMobileFramework.

Methods

Selector	Action	Input	Output
3	getDefaultSurface	-	IOSurfaceID surfaceID
4	swapBegin	-	IOMobileFramebufferSwapID swapID
5	swapEnd	struct IOMobileFramebufferSwapArg	-
6	swapWait	IOMobileFramebufferSwapID swapID, uint32_t waitOptions, (iOS 4.2+ only) uint64_t timeout_millis	-
7	getId	-	IOSwapNotificationID framebufferID
8	getDisplaySize	-	struct IOMobileFramebufferDisplaySize
9	setVSyncNotifications	size_t functionAddress (if 0, notification is disabled), size_t userData	-
12	requestPowerChange	uint32_t value	-
15	setDebugFlags	uint32_t ???[2]	uint32_t ???
17	setGammaTable	struct IOMobileFramebufferGammaTables	-
18	isMainDisplay	-	uint32_t result
19	setWhiteOnBlackMode	uint32_t value	-
22	setDisplayDevice	uint32_t value	-
27	getGammaTable	-	struct IOMobileFramebufferGammaTables
33(*)	setVideoPowerSaving	uint32_t value	-
50(**)	setBrightnessCorrection	uint32_t value	-

(*) - was 32 before 4.0

(**) - was 49 before 8.0

where

// This can be the first argument to a layer swap notification.
// In that case, the other two arguments are interpreted as
//   IOMobileFramebufferSwapID ''swapID'', uint32_t ''
// Swap notifications can be sent, for example, via -[EAGLContext sendNotification: forTransaction: onLayer:]
typedef uint32_t IOSwapNotificationID;

struct UInt32Rect {
  uint32_t x, y, width, height;
};

struct UInt8Bgra {
  uint8_t b, g, r, a;
};

// bits 0.. 3 - bit per layer
// bit 31 - bit for bg color
typedef uint32_t IOMobileFramebufferSwapFlags;

#if IOS_VERSION >= 7.0
const int NUM_LAYERS = 4;
#else
const int NUM_LAYERS = 3;
#endif

struct IOMobileFramebufferSwapArg {

#if IOS_VERSION >= 7.0
  int64_t timeStamps[3];
#endif

#if IOS_VERSION >= 8.0
  uint64_t imageSources[16]; // ?
  uint32_t numImageSources; // 0..16
  uint32_t ???; // padding?
#endif

  IOMobileFramebufferSwapID swapID;
  IOSurfaceID surfaceID[NUM_LAYERS];

  UInt32Rect bounds[NUM_LAYERS]; // surface source bounds

#if IOS_VERSION >= 4.3
  UInt32Rect uiSubRegion[NUM_LAYERS]; // ?
  uint32_t edgeMode[NUM_LAYERS]; // ?
  float32_t edgeCoverage[NUM_LAYERS]; // ?
#endif

  UInt32Rect frames[NUM_LAYERS]; // framebuffer target frame

  IOMobileFramebufferSwapFlags providedFlags; // which layers are provided for swap (in this structure)
  IOMobileFramebufferSwapFlags readyFlags; // which layers are ready to be swapped
                                           // (layers that aren't ready must be notified as ready later via layer swap notifications)
  
  UInt8Bgra bgColor;
  uint32_t gammaTable; // 0..2, index to gamma table to use
  
  uint32_t rotation[NUM_LAYERS]; // 0 - none, 1 - 90 left, 2 - 180, 3 - 90 right

#if IOS_VERSION >= 4.3
  uint32_t destEdgeAlpha; // ?
#endif
#if IOS_VERSION >= 7.0
  uint32_t ???[2];
#endif
};

struct IOMobileFramebufferDisplaySize {
  uint32_t width;
  uint32_t height;
};

struct IOMobileFramebufferGammaTables {
  struct GammaTable {

    // Each value has 2 bitfields: [0..9] and [10..19]. Meanings unknown.
#if IOS_VERSION >= 7.0
    uint32_t value[0x101];
#else
    uint32_t value[0x100];
#endif

  } gammaTable[3];
};

Sync Notification

The notification can be registered for a IOMobileFramebuffer connection by setting the mach port via IOConnectSetNotificationPort and then setting the function and userdata via method setVSyncNotifications.

The message is parsed by IODispatchCalloutFromCFMessage, and is most likely an IO Async Completion notification. The function and user data are in elements 1 & 2 of the OSAsyncReference64 array. This async completion notification most likely has the following data as arguments:

struct IOMobileFramebufferTimingData {
  int64wtf frameNumber; // frame number
  int64wtf frameTime; // frame time, mach absolute time
  int64wtf frameDuration; // duration of last frame, mach absolute time
};

// where int64wtf is:

#if <is 32bit process>
typedef int64_t int64wtf;
#else
typedef struct {
  int64_t low32; // low 32 bits of 64 bit value. (upper bits are wasted)
  int64_t high32; // high 32 bits of 64 bit value. (upper bits are wasted)
} int64wtf;
#endif