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Issue 4557. CFAbsoluteTimeGetCurrent can jump backwards. Use mach_abs… #4563

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Issue 4557. CFAbsoluteTimeGetCurrent can jump backwards. Use mach_abs… #4563

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25 changes: 21 additions & 4 deletions backends/imgui_impl_osx.mm
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@
#include "imgui.h"
#include "imgui_impl_osx.h"
#import <Cocoa/Cocoa.h>
#include <mach/mach_time.h>

// CHANGELOG
// (minor and older changes stripped away, please see git history for details)
Expand All @@ -37,7 +38,8 @@
@class ImFocusObserver;

// Data
static CFAbsoluteTime g_Time = 0.0;
static double g_HostClockPeriod;
static double g_Time = 0.0;
static NSCursor* g_MouseCursors[ImGuiMouseCursor_COUNT] = {};
static bool g_MouseCursorHidden = false;
static bool g_MouseJustPressed[ImGuiMouseButton_COUNT] = {};
Expand All @@ -52,6 +54,19 @@ + (id)_windowResizeNorthSouthCursor;
+ (id)_windowResizeEastWestCursor;
@end

static void InitHostClockPeriod()
{
struct mach_timebase_info info;
mach_timebase_info(&info);
// Period is the reciprocal of frequency.
g_HostClockPeriod = 1e-9 * ((double)info.denom / (double)info.numer);
}

static double GetMachAbsoluteTimeInSeconds()
{
return (double)mach_absolute_time() * g_HostClockPeriod;
}

static void resetKeys()
{
ImGuiIO& io = ImGui::GetIO();
Expand Down Expand Up @@ -231,9 +246,11 @@ void ImGui_ImplOSX_NewFrame(NSView* view)
}

// Setup time step
if (g_Time == 0.0)
g_Time = CFAbsoluteTimeGetCurrent();
CFAbsoluteTime current_time = CFAbsoluteTimeGetCurrent();
if (g_Time == 0.0) {
InitHostClockPeriod();
g_Time = GetMachAbsoluteTimeInSeconds();
}
double current_time = GetMachAbsoluteTimeInSeconds();
io.DeltaTime = (float)(current_time - g_Time);
g_Time = current_time;

Expand Down