关闭了VSync，但在DirectX 9应用程序中仍然获得60FPS

问题描述

我有一个DirectX9应用程序，它只能在屏幕上渲染一个三角形，但是无论是否启用了VSync，我的帧速率都为60 FPS.为什么会这样?

I have an DirectX9 application which only renders a triangle on the screen, but I am getting a frame rate of 60 FPS no matter if I've got VSync on or not. Why is this?

这是我用来计算FPS的代码，但我不知道这是否是问题所在.

Here is the code I've done to calculate the FPS, but I dont know if this is the problem to it.

GameTimer.h

#pragma once

#include "Windows.h"

class GameTimer {
public:
    GameTimer();
    ~GameTimer(){}

    void Update();

    float GetFrameTime();

    inline float GetFramePerSec(){return framesPerSec;}
    inline float GetMillSecPerFrame(){return millSecPerFrame;}

private:
    float secsPerCount;
    _int64 prevTimeStamp;

    float framesPerSec;
    float millSecPerFrame;
};

GameTimer.cpp

#include "GameTimer.h"

GameTimer::GameTimer()  {

    _int64 countsPerSec = 0;
    QueryPerformanceFrequency((LARGE_INTEGER*)&countsPerSec);
    secsPerCount = 1.0f / (float)countsPerSec;

    prevTimeStamp = 0;
    QueryPerformanceCounter((LARGE_INTEGER*)&prevTimeStamp);

    framesPerSec = 0.0f;
    millSecPerFrame = 0.0f;
}

void GameTimer::Update()
{
    static float numFrames = 0.0f;
    static float timeElapsed = 0.0f;

    numFrames += 1.0f;
    timeElapsed += GetFrameTime();

    if(timeElapsed >= 1.0f)
    {
        framesPerSec = numFrames;
        millSecPerFrame = 1000.0f / numFrames;

        numFrames = 0;
        timeElapsed = 0;
    }
}

float GameTimer::GetFrameTime() {
    _int64 currentTimeStamp = 0;
    QueryPerformanceCounter((LARGE_INTEGER*)&currentTimeStamp);
    float timeDiff = (currentTimeStamp - prevTimeStamp) * secsPerCount;
    prevTimeStamp = currentTimeStamp;

    return timeDiff;
}

知道它只是屏幕上的一个三角形(没有绘制任何复杂的东西)，如果我关闭了VSync，它应该每秒渲染1000帧以上吗?

Knowing that it's only a triangle on the screen (no complicated stuff being drawn), it should render over 1000 frames per second if I have VSync off shouldn't it?

推荐答案

在CreateDevice调用中，将D3DPRESENT_PARAMETERS参数的PresentationInterval设置为D3DPRESENT_INTERVAL_IMMEDIATE.

In the CreateDevice call, set the PresentationInterval of the D3DPRESENT_PARAMETERS parameter to D3DPRESENT_INTERVAL_IMMEDIATE.

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