fix for overview panel

internal/hoststats/cpu_windows.go

@@ -0,0 +1,65 @@
+//go:build windows
+
+package hoststats
+
+import (
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+// GetSystemTimes isn't wrapped by x/sys/windows either -- same manual
+// kernel32.dll binding as GlobalMemoryStatusEx in mem_windows.go.
+var procGetSystemTimes = modkernel32.NewProc("GetSystemTimes")
+
+// cpuSampler computes CPU busy% from successive cumulative GetSystemTimes
+// snapshots, mirroring cpu_unix.go's /proc/stat delta approach: the kernel
+// time value already includes idle time on Windows, so busy = (kernel -
+// idle) + user, and total = kernel + user.
+type cpuSampler struct {
+	prevIdle, prevKernel, prevUser uint64
+	have                           bool
+}
+
+func (c *cpuSampler) sample() float64 {
+	idle, kernel, user, ok := getSystemTimes()
+	if !ok {
+		return 0
+	}
+	if !c.have {
+		c.prevIdle, c.prevKernel, c.prevUser = idle, kernel, user
+		c.have = true
+		return 0
+	}
+	deltaIdle := idle - c.prevIdle
+	deltaTotal := (kernel - c.prevKernel) + (user - c.prevUser)
+	c.prevIdle, c.prevKernel, c.prevUser = idle, kernel, user
+	if deltaTotal == 0 {
+		return 0
+	}
+	pct := (1 - float64(deltaIdle)/float64(deltaTotal)) * 100
+	switch {
+	case pct < 0:
+		pct = 0
+	case pct > 100:
+		pct = 100
+	}
+	return pct
+}
+
+func getSystemTimes() (idle, kernel, user uint64, ok bool) {
+	var idleFT, kernelFT, userFT windows.Filetime
+	r, _, _ := procGetSystemTimes.Call(
+		uintptr(unsafe.Pointer(&idleFT)),
+		uintptr(unsafe.Pointer(&kernelFT)),
+		uintptr(unsafe.Pointer(&userFT)),
+	)
+	if r == 0 {
+		return 0, 0, 0, false
+	}
+	return filetimeToUint64(idleFT), filetimeToUint64(kernelFT), filetimeToUint64(userFT), true
+}
+
+func filetimeToUint64(ft windows.Filetime) uint64 {
+	return uint64(ft.HighDateTime)<<32 | uint64(ft.LowDateTime)
+}