添加双打时的奇怪行为

Question

我正在做一个 Direct3D 项目，在我的代码中有一个函数将双精度作为参数，这个双精度代表自上一帧以来的时间，我的想法是将这个时间与另一个双精度相加，它代表立方体的旋转角度，然后将新值存储为新角度，但在调试后我注意到角度（在代码中称为 rot）从第一帧的零跳到 ~79800 之类的值，每次都略有不同，但总是79作为第一个数字，我真的不明白问题是什么。

这里是运行每一帧：

double rot = 0.0f;
double seconds = 0.0;
unsigned int frames = 0;

// this is the function used to render a single frame
void RenderFrame(double time)
{
    // clear the back buffer to a deep blue
    devcon->ClearRenderTargetView(renderTarget, D3DXCOLOR(0.0f, 0.2f, 0.4f, 1.0f));
    devcon->ClearDepthStencilView(stencilView, D3D11_CLEAR_DEPTH, 1.0f, 0);

    //PROBLEM HERE
    //////
    rot += time;
    //////


    VSCBdata.transformation = XMMatrixTranspose(XMMatrixRotationX(rot) * XMMatrixRotationZ(rot) * XMMatrixTranslation(0.0f, 0.0f, 4.0f) * XMMatrixPerspectiveLH(1.0f, 1.0f, 0.5f, 10.0f));

    devcon->UpdateSubresource(VSConstantBuffer, 0, NULL, &VSCBdata, 0, 0);

    // draw the vertex buffer to the back buffer
    devcon->DrawIndexed(ARRAYSIZE(indices), 0, 0);

    VSCBdata.transformation = XMMatrixTranspose(XMMatrixRotationY(rot) * XMMatrixRotationZ(rot) * XMMatrixTranslation(0.0f, 2.0f, 6.0f) * XMMatrixPerspectiveLH(1.0f, 1.0f, 0.5f, 10.0f));

    devcon->UpdateSubresource(VSConstantBuffer, 0, NULL, &VSCBdata, 0, 0);

    // draw the vertex buffer to the back buffer
    devcon->DrawIndexed(ARRAYSIZE(indices), 0, 0);

    // do 3D rendering on the back buffer here

    // switch the back buffer and the front buffer
    swapchain->Present(0, 0);
}

这里是计算时间的代码：

double frequency = 0.0;
__int64 start = 0;
__int64 lastFrame = 0;

void StartTimer()
{
    LARGE_INTEGER shish;
    QueryPerformanceFrequency(&shish);
    frequency = double(shish.QuadPart);
    QueryPerformanceCounter(&shish);
    start = shish.QuadPart;
}

double GetTime()
{
    LARGE_INTEGER time;
    QueryPerformanceCounter(&time);
    return (time.QuadPart - start) / frequency;
}

double GetFrameTime()
{
    LARGE_INTEGER time;
    QueryPerformanceCounter(&time);
    __int64 result = time.QuadPart - lastFrame;
    lastFrame = time.QuadPart;
    if (result < 0.0) result = 0.0;
    return double(result)/frequency;
}

Answer 1

由于 lastFrame 被初始化为 0，第一次调用 GetFrameTime 将 return QueryPerformanceCounter 的值（以秒为单位）。

您应该在程序开始时调用 GetFrameTime 一次并丢弃该值或在 StartTimer.

中初始化 lastFrame

添加双打时的奇怪行为

Strange behaviour when adding doubles

c++

double

visual-studio