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Simplify idling logic
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@pthom
pthom committed Jul 1, 2024
1 parent 772497e commit 7bec671
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Showing 2 changed files with 67 additions and 101 deletions.
165 changes: 67 additions & 98 deletions src/hello_imgui/internal/backend_impls/abstract_runner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1019,21 +1019,56 @@ void AbstractRunner::CreateFramesAndRender(bool insideReentrantCall)
// return immediately, but it doesn't when resizing the window!
// Instead, you have to subscribe to a kind of special "mid-resize" event,
// and then call the render function yourself.
// As a consequence,
auto fnHandleIdlingAndPollEvents_MayReRenderDuringResize_GotchaReentrant = [this]()
// As a consequence, this function is not called inside reentrant calls
//
// Under emscripten, the idling implementation is different:
// we cannot sleep (which would lead to a busy wait), so we skip rendering the frame if needed
// => we return true if we should not render this frame
auto fnHandleIdlingAndPollEvents_MayReRenderDuringResize_GotchaReentrant = [this]()-> bool
{
// This will be our return value: can only be true under emscripten, when idling is needed
bool shallSkipRenderingThisFrame = false;

double now = Internal::ClockSeconds();

auto fnShallIdle = [&]() -> bool
{
assert(params.fpsIdling.fpsIdle >= 0.f && "fpsIdle must be >= 0");

// If the last event is recent, do not idle
bool hasRecentEvent = (now - gStatics.timeLastEvent) < (double)params.fpsIdling.timeActiveAfterLastEvent;
// If idling is disabled by params, do not idle
bool isIdlingDisabledByParams = (! params.fpsIdling.enableIdling || (params.fpsIdling.fpsIdle <= 0.f) );

// If the test engine is running, do not idle
bool isTestEngineRunning = false;
#ifdef HELLOIMGUI_WITH_TEST_ENGINE
if (params.useImGuiTestEngine && TestEngineCallbacks::IsRunningTest())
isTestEngineRunning = true;
#endif

// If the app started recently, do not idle
bool startedRecently = mIdxFrame < 12;

bool preventIdling = isIdlingDisabledByParams || hasRecentEvent || isTestEngineRunning || ShouldRemoteDisplay() || startedRecently;
return ! preventIdling;
};

bool shallIdle = fnShallIdle();
params.fpsIdling.isIdling = shallIdle;

// Keep track of the time of the last event,
// by counting the number of events in the input queue
int nbEventsBefore = ImGui::GetCurrentContext()->InputEventsQueue.size();
// If the last event is recent, do not idle
double now = ImGui::GetTime();
bool preventIdling = (now - gStatics.timeLastEvent < (double)params.fpsIdling.timeActiveAfterLastEvent);

#ifndef __EMSCRIPTEN__
// Idling for non emscripten, where HelloImGui is responsible for the main loop.
// This form of idling will call WaitForEventTimeout(), which may call sleep():
if (!preventIdling)
IdleBySleeping();
if (shallIdle)
{
double waitTimeout = 1. / (double) params.fpsIdling.fpsIdle;
mBackendWindowHelper->WaitForEventTimeout(waitTimeout);
}
#endif

// Poll Events (this fills GImGui.InputEventsQueue)
Expand All @@ -1044,20 +1079,19 @@ void AbstractRunner::CreateFramesAndRender(bool insideReentrantCall)
// defined during the window creation)
Impl_PollEvents();

#ifdef __EMSCRIPTEN__
// Idling for emscripten: early exit if idling
// This test should be done after calling Impl_PollEvents() since it checks the event queue for incoming events!
if ( ! preventIdling && ShallIdleThisFrame_Emscripten())
{
mIdxFrame += 1;
return;
}
#endif

int nbEventsAfter = ImGui::GetCurrentContext()->InputEventsQueue.size();
if (nbEventsAfter > nbEventsBefore)
gStatics.timeLastEvent = ImGui::GetTime();
gStatics.timeLastEvent = now;

#ifdef __EMSCRIPTEN__
// Idling for emscripten: we cannot sleep, so we skip rendering the frame if needed
bool wasLastFrameRenderedInTimeForDesiredFps = ((now - gStatics.lastRefreshTime) < 1. / params.fpsIdling.fpsIdle);
shallSkipRenderingThisFrame = shallIdle && wasLastFrameRenderedInTimeForDesiredFps;
#endif

if (! shallSkipRenderingThisFrame)
gStatics.lastRefreshTime = now;
return shallSkipRenderingThisFrame;
};


Expand Down Expand Up @@ -1226,6 +1260,15 @@ void AbstractRunner::CreateFramesAndRender(bool insideReentrantCall)
// Will display on remote server if needed
mRemoteDisplayHandler.Heartbeat_PreImGuiNewFrame();

if (ShouldRemoteDisplay()) // FIXME, unrelated
{
// if displaying remote, the FPS is limited on the server to a value between 30 and 60 fps
// We cannot idle too slow, other the GUI becomes really sluggish
// Ideally, we should ask the server about it current refresh rate
// (At the moment, we can only deliver 30fps)
params.fpsIdling.fpsIdle = 30.f;
}

{
SCOPED_RELEASE_GIL_ON_MAIN_THREAD;
fnReloadFontsIfDpiScaleChanged();
Expand All @@ -1249,8 +1292,12 @@ void AbstractRunner::CreateFramesAndRender(bool insideReentrantCall)
if (!insideReentrantCall) // Do not poll events again in a reentrant call!
{
// We cannot release the GIL here, since we may have a reentrant call!
if (!insideReentrantCall)
fnHandleIdlingAndPollEvents_MayReRenderDuringResize_GotchaReentrant();
bool shallSkipThisFrame = fnHandleIdlingAndPollEvents_MayReRenderDuringResize_GotchaReentrant();
if (shallSkipThisFrame)
{
mIdxFrame += 1;
return;
}
}

{
Expand Down Expand Up @@ -1305,84 +1352,6 @@ void AbstractRunner::CreateFramesAndRender(bool insideReentrantCall)
mIdxFrame += 1;
}

// Idling for non emscripten, where HelloImGui is responsible for the main loop.
// This form of idling will call WaitForEventTimeout(), which may call sleep():
void AbstractRunner::IdleBySleeping()
{
#ifdef HELLOIMGUI_WITH_TEST_ENGINE
if (params.useImGuiTestEngine && TestEngineCallbacks::IsRunningTest())
return;
#endif

if (ShouldRemoteDisplay())
{
// if displaying remote, the FPS is limited on the server to a value between 30 and 60 fps
// We cannot idle too slow, other the GUI becomes really sluggish
// Ideally, we should ask the server about it current refresh rate
// (At the moment, we can only deliver 30fps)
params.fpsIdling.fpsIdle = 30.f;
}

assert(params.fpsIdling.fpsIdle >= 0.f);
params.fpsIdling.isIdling = false;
if ((params.fpsIdling.fpsIdle > 0.f) && params.fpsIdling.enableIdling)
{
double beforeWait = Internal::ClockSeconds();
double waitTimeout = 1. / (double) params.fpsIdling.fpsIdle;
mBackendWindowHelper->WaitForEventTimeout(waitTimeout);

double afterWait = Internal::ClockSeconds();
double waitDuration = (afterWait - beforeWait);
double waitIdleExpected = 1. / params.fpsIdling.fpsIdle;
params.fpsIdling.isIdling = (waitDuration > waitIdleExpected * 0.9);
}
}

// Logic for idling under emscripten
// (this is adapted for emscripten, since CreateFramesAndRender is called 60 times per second by the browser,
// and a sleep would actually could a javascript busy loop!)
// This test should be done after calling Impl_PollEvents() since it checks the event queue for incoming events!
bool AbstractRunner::ShallIdleThisFrame_Emscripten()
{
#ifdef HELLOIMGUI_WITH_TEST_ENGINE
if (params.useImGuiTestEngine && TestEngineCallbacks::IsRunningTest())
return false;
#endif

ImGuiContext& g = *GImGui;
bool hasInputEvent = ! g.InputEventsQueue.empty();

if (! params.fpsIdling.enableIdling || (params.fpsIdling.fpsIdle <= 0.f) )
{
params.fpsIdling.isIdling = false;
return false;
}

double now = Internal::ClockSeconds();

bool shallIdleThisFrame;
{
if (hasInputEvent)
{
params.fpsIdling.isIdling = false;
shallIdleThisFrame = false;
}
else
{
params.fpsIdling.isIdling = true;
if ((now - gStatics.lastRefreshTime) < 1. / params.fpsIdling.fpsIdle)
shallIdleThisFrame = true;
else
shallIdleThisFrame = false;
}
}

if (! shallIdleThisFrame)
gStatics.lastRefreshTime = now;

return shallIdleThisFrame;
}

void AbstractRunner::OnPause()
{
#ifdef HELLOIMGUI_MOBILEDEVICE
Expand Down
3 changes: 0 additions & 3 deletions src/hello_imgui/internal/backend_impls/abstract_runner.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -94,9 +94,6 @@ class AbstractRunner
void MakeWindowSizeRelativeTo96Ppi_IfRequired();
bool ShallSizeWindowRelativeTo96Ppi();
bool WantAutoSize();
// Logic for idling
void IdleBySleeping();
bool ShallIdleThisFrame_Emscripten();

void SetLayoutResetIfNeeded();

Expand Down

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