apt: Add aptLaunchSystemApplet (#557)

Needed for launching system applets like the Miiverse posting applet
"solv3". The screen transfer is expected to be done after launching the
applet.

libctru/include/3ds/services/apt.h

@@ -227,6 +227,15 @@ void aptSetMessageCallback(aptMessageCb callback, void* user);
  */
 void aptLaunchLibraryApplet(NS_APPID appId, void* buf, size_t bufsize, Handle handle);
 
+/**
+ * @brief Launches a system applet.
+ * @param appId ID of the applet to launch.
+ * @param buf Input/output buffer that contains launch parameters on entry and result data on exit.
+ * @param bufsize Size of the buffer.
+ * @param handle Handle to pass to the system applet.
+ */
+void aptLaunchSystemApplet(NS_APPID appId, void* buf, size_t bufsize, Handle handle);
+
 /// Clears the chainloader state.
 void aptClearChainloader(void);
 

libctru/source/services/apt.c

@@ -909,6 +909,31 @@ void aptLaunchLibraryApplet(NS_APPID appId, void* buf, size_t bufsize, Handle ha
 	aptSetSleepAllowed(sleep);
 }
 
+void aptLaunchSystemApplet(NS_APPID appId, void* buf, size_t bufsize, Handle handle)
+{
+	bool sleep = aptIsSleepAllowed();
+
+	aptSetSleepAllowed(false);
+	aptFlags &= ~FLAG_SPURIOUS; // If we haven't received a spurious wakeup by now, we probably never will (see aptInit)
+	APT_PrepareToStartSystemApplet(appId);
+	aptSetSleepAllowed(sleep);
+
+	aptCallHook(APTHOOK_ONSUSPEND);
+
+	GSPGPU_SaveVramSysArea();
+	GSPGPU_ReleaseRight();
+
+	aptSetSleepAllowed(false);
+	APT_StartSystemApplet(appId, buf, bufsize, handle);
+	aptFlags &= ~FLAG_ACTIVE;
+
+	aptScreenTransfer(appId, true);
+
+	aptWaitForWakeUp(TR_SYSAPPLET);
+	memcpy(buf, aptParameters, bufsize);
+	aptSetSleepAllowed(sleep);
+}
+
 Result APT_GetLockHandle(u16 flags, Handle* lockHandle)
 {
 	u32 cmdbuf[16];