opengl update model position while camera position not updated in time causes blinking (model fly out of view)

问题

I rendered a scene having earth and a satellite. The position of the satellite is collected and updated by a thread. The position data is provided by an background calculation program.

// main.cpp
void CollectCraft(void)
{
    SetupChannel();
    int iFlag = 1;
    while(iFlag > 0)
    {
        iFlag = CollectData();
        Sleep(10);
    }
    CloseChannel();
}

int main(void)
{
    CreateThread(NULL, NULL, (LPTHREAD_START_ROUTINE)CollectCraft, 0, NULL, NULL); // in collect.cpp
    RenderMainWindow(); // in render.cpp
    return 1;
}

The CollectCraft function receives data from a background program. Once it receives any data, it stores in a double

// collect.cpp
double Craft_R[3] = {0.0};
...
int CollectData(void)
{
    char chrMessage[255] = {0};
    int iFlag = CollectSocket(&sListen, &sServer, chrMessage);
    if (iFlag <= 0) return iFlag;
    else
    {
        unsigned char i = 0, j = 0;
        unsigned short usLength = 0;
        for ( i = 0; i < dimCraft; i++)
        {
            for (j=0; j<3; j++)
            {
                memcpy(&Craft_R[j], &chrMessage[usLength], 8);
                usLength += 8;
            }
        }
    }
    return iFlag;
}

I fixed my camera on one of the satellite (following it and staring at it). It updates its position and the view matrix according to the position of the satellite.

The satellite updated it's position according to the latest received data (I simply get it through a extern double Craft_R).

// render.cpp
extern double Craft_R[3]; // directly get latest satellite position data
...
RenderMainWindow()
{
    ...
    while (!glfwWindowShouldClose(MainWindow))
    {
        glm::dmat4 view = camera.GetViewMatrix();
        ...
        Sate1Pos = glm::dvec3(Craft_R[0], Craft_R[1], Craft_R[2]); // update satellite position
        glm::dmat4 model_sate1(1.0);
        model_sate1 = glm::translate(model_sate1, Sate1Pos);
        ...
        switch (CameraPosID)
        {
        case 0:
            camera.Focus(EarthPos);
            break;
        case 1:
            camera.Focus(Sate1Pos); // update camera position
        }
        glfwSwapBuffers(MainWindow);
        glfwPollEvents();
    }
}

The problem is, the collection of the latest satellite position data always happens BETWEEN the update of the camera position and the update of the satellite position. It means my satellite flies to the latest position but my camera still stays at the last position. After glfwSwapBuffers(), the next while (!glfwWindowShouldClose(MainWindow)) will render the satellite far away out of the field of view of the camera. And it will last until the next while for the camera to update its position and get the satellite back to its field of view.

If the background program keeps sending the satellite position, the scene will render as if the satellite is blinking. And if the background program stops sending the satellite position, everything is ok and stable. If I control the background program to send the satellite position once, the satellite in the scene will blink one time and then remains stable.

My question is if there is a way to simultaneously update position of the camera and the satellite? Many thanks and sorry for my poor English since it is not my mother tongue.

来源：https://stackoverflow.com/questions/62087825/opengl-update-model-position-while-camera-position-not-updated-in-time-causes-bl

标签

opengl

model

position

refresh

blink