The function call ShowDemoWindow of ImGui make FPS low

[onon1101]

Problem

As you can see, the FPS low when open the demo-window of ImGui

2024-04-08.224030.mp4

Ps: the Problem occur commit between 823926c and 22ef5ca

Steps to reproduce

git clone https://github.com/ntut-open-source-club/practical-tools-for-simple-design
cd practical-tools-for-simple-design
git checkout 823926c

cmake -Bbuild -G "Ninja" -DCMAKE_BUILD_TYPE=Debug
cmake --build build -j 32
./build/Sample

Expected behavior

It will keep 60fps in window.

PTSD version

commit 823926c

Operating system/version

Unix Window 11 24H2

CMake version

3.27.6

CMakeCache.txt

OpenGL Info

[info] OpenGL Info
 [info]   Vendor: NVIDIA Corporation
 [info]   Renderer: NVIDIA GeForce RTX 3060/PCIe/SSE2
 [info]   Version: 4.1.0 NVIDIA 537.13
 [info]   GLSL Version: 4.10 NVIDIA via Cg compiler

[onon1101]

and comment out this code can also make fps normal,

glDebugMessageCallback(Core::OpenGLDebugMessageCallback, nullptr);

[HeavenManySugar]

This is because PR #162 would result in a large amount of OpenGL Severity NOTIFICATION. Besides commenting out, you can also try this method.

The reason why commenting out this code can solve the problem can be referred to in this.

glDebugMessageCallback(Core::OpenGLDebugMessageCallback, nullptr);

[HeavenManySugar]

It work but not elegant
NTUT-FUCK-PTSD@c463129

Original code
SDL_Delay(static_cast<Uint32>(frameTime - Util::Time::GetDeltaTime())); is incorrect , milliseconds-seconds

[onon1101]

This problem seems not to occurs in macOS.

result.mov

[Dragonfly911117]

It work but not elegant NTUT-FUCK-PTSD@c463129

Original code SDL_Delay(static_cast<Uint32>(frameTime - Util::Time::GetDeltaTime())); is incorrect , milliseconds-seconds

We are working on that. Should have the PR open this week.

[Dragonfly911117]

It work but not elegant NTUT-FUCK-PTSD@c463129
Original code SDL_Delay(static_cast<Uint32>(frameTime - Util::Time::GetDeltaTime())); is incorrect , milliseconds-seconds

We are working on that. Should have the PR open this week.

Shoot, thought this was #167.

[HeavenManySugar]

It work but not elegant NTUT-FUCK-PTSD@c463129
Original code SDL_Delay(static_cast<Uint32>(frameTime - Util::Time::GetDeltaTime())); is incorrect , milliseconds-seconds

We are working on that. Should have the PR open this week.

Shoot, thought this was #167.

其實不僅僅是相減會有問題而已，他們兩個數字的單位就不同了，frameTime(單位:毫秒)而Util::Time::GetDeltaTime(單位:秒)，兩個不同單位的值做相減，我想結果應該不會是正確的結果，但儘管我把他更改為正確單位，他仍然有錯誤，會發生下面這件事情
測試程式碼:

constexpr double frameTime =
    FPS_CAP != 0 ? 1000 / static_cast<double>(FPS_CAP) : 0;
m_FPS_DeltaTime = Util::Time::GetDeltaTime()*1000;
if (m_FPS_DeltaTime < frameTime) {
    SDL_Delay(static_cast<Uint32>(frameTime - m_FPS_DeltaTime));
}
m_FPS_Timer = Util::Time::GetElapsedTimeMs();
LOG_INFO("GetDeltaTime: {}", Util::Time::GetDeltaTime());

可以看到他的DeltaTime一上一下，這是因為GetDeltaTime()他並不會記錄上次Delay了多久，因此他會將那部分再下次也計算進入上次的Delay時間，這導致了GetDeltaTime()的值上下波動，顯然這樣的幀生成時間是不正確的

而我的那份commit其實他大致上的行為和目前差不多，唯一的區別就是他會將Delay的時間排除掉，我修改過後的

但這一切都成立於我沒有理解錯誤當前PTSD的程式碼，如果理解錯誤那可能是我造了一台鴿子直升機