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Hotfixed bizzare non-monotonically-increasing SDL_GetPerformanceCounter bug #6189

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Hotfixed bizzare non-monotonically-increasing SDL_GetPerformanceCounter bug #6189

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11 changes: 11 additions & 0 deletions backends/imgui_impl_sdl2.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -612,6 +612,17 @@ void ImGui_ImplSDL2_NewFrame()
// Setup time step (we don't use SDL_GetTicks() because it is using millisecond resolution)
static Uint64 frequency = SDL_GetPerformanceFrequency();
Uint64 current_time = SDL_GetPerformanceCounter();

// If SDL_GetPerformanceCounter doesn't return a monotonically increasing value,
// "fake" the time this frame.
//
// This bizzare edge-case bug seems to happen when using the SDL backend in a VirtualBox
// VM, it also seems to happen in emscripten backends (#6114, #3644) - might be related to
// a Spectre mitigation?
if (current_time <= bd->Time)
{
current_time = bd->Time + 1;
}
io.DeltaTime = bd->Time > 0 ? (float)((double)(current_time - bd->Time) / frequency) : (float)(1.0f / 60.0f);
bd->Time = current_time;

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