Native VSync Development

When to Use

The NativeVSync module is used to obtain virtual synchronization (VSync) signals from the system. It provides APIs for creating and destroying an OH_NativeVSync instance and setting the VSync callback function, which is triggered when a VSync signal arrives.

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.
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 will be 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 to CMakeLists.txt:

libnative_vsync.so

Including Header Files

#include <native_vsync/native_vsync.h>

  1. Implement a VSync callback function.

    #include <iostream>

static bool flag = false;
static void OnVSync(long long timestamp, void* data)
{
    flag = true;
    std::cout << "OnVSync: " << timestamp << std::endl;
}
OH_NativeVSync_FrameCallback callback = OnVSync; // The callback function must be of the OH_NativeVSync_FrameCallback type.

  2. Create an OH_NativeVSync instance.

    char name[] = "hello_vsync";
OH_NativeVSync* nativeVSync = OH_NativeVSync_Create(name, strlen(name));

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

    #include <unistd.h>
#include <iostream>

OH_NativeVSync_RequestFrame(nativeVSync, callback, nullptr);
while (!flag) { // Check the flag value. The while loop exits only after the VSync callback function is executed, indicating that a VSync signal is received.
    std::cout << "wait for vsync!\n";
    sleep(1);
}
std::cout << "vsync come, end this thread\n";

  4. Destroy the OH_NativeVSync instance.

    OH_NativeVSync_Destroy(nativeVSync); // Destroy the OH_NativeVSync instance when the application does not need to receive VSync signals.