NativeVSync Development (C/C++)

Overview

The NativeVSync module is used to obtain the system VSync signal, create and destroy an OH_NativeVSync instance, and set the VSync callback function. When the VSync signal is triggered, the callback function is called.

Available APIs

API	Description
OH_NativeVSync_Create (const char *name, unsigned int length)	Creates an OH_NativeVSync instance. A new OH_NativeVSync instance is created each time this API is called. This function must be used in pair with OH_NativeVSync_Destroy. Otherwise, memory leak occurs.
OH_NativeVSync_Destroy (OH_NativeVSync *nativeVsync)	Destroys an OH_NativeVSync instance.
OH_NativeVSync_FrameCallback (long long timestamp, void *data)	Sets a callback function. timestamp indicates the timestamp, and data indicates a pointer to the input parameters of the callback function.
OH_NativeVSync_RequestFrame (OH_NativeVSync *nativeVsync, OH_NativeVSync_FrameCallback callback, void *data)	Requests the next VSync signal. When the signal arrives, a callback function is invoked.

For details about the APIs, see native_vsync.

How to Develop

The following steps describe how to use the native APIs provided by NativeVSync to create and destroy an OH_NativeVSync instance and set the VSync callback function.

Adding Dynamic Link Libraries

Add the following library file to the CMakeLists.txt file.

libnative_vsync.so

Including Header Files

#include <native_vsync/native_vsync.h>

1. Define a VSync callback function.

   void RenderEngine::OnVsync(long long timestamp, void *data)
   {
       OH_LOG_Print(LOG_APP, LOG_DEBUG, LOG_PRINT_DOMAIN, "RenderEngine", "OnVsync %{public}lld.", timestamp);
       auto renderEngine = reinterpret_cast<RenderEngine *>(data);
       if (renderEngine == nullptr) {
           return;
       }
   
       renderEngine->vSyncCnt_++;
       renderEngine->wakeUpCond_.notify_one();
   }
   

   render_engine.cpp

2. Create an OH_NativeVSync instance.

   const char* demoName = "NativeImageSample";
   nativeVsync_ = OH_NativeVSync_Create(demoName, strlen(demoName));
   

   render_engine.cpp

3. Set the VSync callback function through the OH_NativeVSync instance.

   wakeUpCond_.wait(lock, [this]() { return wakeUp_ || vSyncCnt_ > 0; });
   wakeUp_ = false;
   if (vSyncCnt_ > 0) {
       vSyncCnt_--;
       (void)OH_NativeVSync_RequestFrame(nativeVsync_, &RenderEngine::OnVsync, this);
       OH_NativeVSync_GetPeriod(nativeVsync_, &period);
   }
   

   render_engine.cpp

4. Destroy the OH_NativeVSync instance.

   OH_NativeVSync_Destroy(nativeVsync_);
   nativeVsync_ = nullptr;
   

   render_engine.cpp