Huge input delay although framerate is stable - possibly related to the DirectX Tool Kit?

Question

I'm in the process of learning how to use the DirectX 11 API and came upon the following problem:
Although my rendering function executes quite fast at around 150 fps (as one expects considering how little geometry is rendered), the mouse and keyboard input is massivly delayed. Sometimes the "game" reacts several seconds too late or doesn't react at all; looking around is a pain.
When I increase the framerate even further to, let's say, 400 (by reducing the rendering resolution/rendering less objects), the effect vanishes and the every keystroke is detected precisely.

My update() function (see code below) is called by the StepTimer class of the DirectX Tool Kit from the main message handling loop. I tried both fixed and variable timestep mode.

Main loop calling update() and render()

while (msg.message != WM_QUIT)
{
    if (PeekMessage(&msg, 0, 0, 0, PM_REMOVE))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    static DX::StepTimer stepTimer;
    stepTimer.Tick([&]() { update(stepTimer); });
    render();
}

The update() function:

void update(DX::StepTimer const &timer)
{
    static Keyboard::KeyboardStateTracker keyboardTracker;
    static Mouse::ButtonStateTracker mouseTracker;
    Keyboard::State keyboardState = keyboard->GetState();
    Mouse::State mouseState = mouse->GetState();
    keyboardTracker.Update(keyboardState);
    mouseTracker.Update(mouseState);
    fps = timer.GetFramesPerSecond();

    if (keyboardState.Escape) PostQuitMessage(0);


    static float pitch = 0.0f;
    static float yaw = 0.0f;

    if (mouseState.positionMode == Mouse::MODE_RELATIVE)
    {
        pitch = std::max(std::min(pitch - float(mouseState.y) * 0.001f, XM_PI / 2.0f - 0.01f), -XM_PI / 2.0f + 0.01f);
        yaw -= float(mouseState.x) * 0.001f;
        if (yaw < -XM_PI) yaw += XM_PI * 2.0f;
        if (yaw > XM_PI) yaw -= XM_PI * 2.0f;
    }
    if(mouseTracker.leftButton == Mouse::ButtonStateTracker::RELEASED) mouse->SetMode(mouseState.positionMode == Mouse::MODE_ABSOLUTE ? Mouse::MODE_RELATIVE : Mouse::MODE_ABSOLUTE);

    Vector3 cameraDir(-sin(yaw) * cos(pitch), sin(pitch), cos(yaw) * cos(pitch));


    Vector3 motionVec = { 0.0f, 0.0f, 0.0f };
    float speed = 4.2f;
    if (keyboardState.W || keyboardState.Up)
    {
        motionVec.x += cameraDir.x;
        motionVec.z += cameraDir.z;
    }
    if (keyboardState.S || keyboardState.Down)
    {
        motionVec.x -= cameraDir.x;
        motionVec.z -= cameraDir.z;
    }
    if (keyboardState.A || keyboardState.Left)
    {
        motionVec.x -= cameraDir.z;
        motionVec.z += cameraDir.x;
    }
    if (keyboardState.D || keyboardState.Right)
    {
        motionVec.x += cameraDir.z;
        motionVec.z -= cameraDir.x;
    }
    if (keyboardState.Space || keyboardState.PageUp)
    {
        motionVec.y += 1.0f;
    }
    if (keyboardState.LeftShift || keyboardState.PageDown)
    {
        motionVec.y -= 1.0f;
    }
    motionVec *= speed;

    static Vector3 cameraPos = { 0.0f, 2.0f, 0.0f };
    if (keyboardState.R)
    {
        cameraPos = { 0.0f, 2.0f, 0.0f };
        pitch = 0.0f;
        yaw = 0.0f;
    }
    cameraPos += motionVec * float(timer.GetElapsedSeconds());
    matrixCamera = XMMatrixLookToLH(cameraPos.XMVECTOR(), cameraDir.XMVECTOR(), { 0.0f, 1.0f, 0.0f });
}

Is there any hint you can give me? Or might this even by a bug in the StepTimer class?

Answer 1

Your main Win32 message pump is only ever processing a single Win32 message per frame. You need to empty the message queue between each render frame since there are usually dozens or more messages queued up in a single frame time.

Here's a common pattern. Notice that here I'm only doing the tick/update/render cycle if there is no Win32 message to process:

while (WM_QUIT != msg.message)
{
    if (PeekMessage(&msg, nullptr, 0, 0, PM_REMOVE))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    else // <---- This is the key part you are missing.
    {
        stepTimer.Tick([&]() { update(stepTimer); });
        render();
    }
}

See GitHub for complete basic Direct3D render loops for various Microsoft platforms.

Note that StepTimer is not my invention or strictly a part of the DirectX Tool Kit. It was created by Shawn Hargreaves (MSFT) for the Visual Studio DirectX templates for Windows Store 8.1 to replace the somewhat less robust BasicTimer class that was shipped in the Visual Studio DirectX templates for Windows Store 8.0. As Shawn was one of the original engineers on XNA Game Studio, that team really deserves the credit as the creators of the StepTimer design as talked about on his blog.

I have made sure that StepTimer has gotten more adoption and use in various other templates, samples, etc. and I use it for the DirectX Tool Kit tutorials extensively per my blog post.