internal/uidriver/glfw, internal/devicescale: Add comments

internal/devicescale/devicescale.go

@@ -27,6 +27,8 @@ var (
 	cache = map[pos]float64{}
 )
 
+// GetAt returns the device scale at (x, y).
+// x and y are in device-dependent pixels.
 func GetAt(x, y int) float64 {
 	m.Lock()
 	defer m.Unlock()

internal/uidriver/glfw/ui_unix.go

@@ -25,6 +25,7 @@ import (
 
 // fromGLFWMonitorPixel must be called from the main thread.
 func fromGLFWMonitorPixel(x float64, deviceScale float64) float64 {
+	// deviceScaleFactor is sometimes an unnice value (e.g., 1.502361). Use math.Ceil to clean the vaule.
 	return math.Ceil(x / deviceScale)
 }
 
@@ -45,6 +46,7 @@ func (u *UserInterface) toGLFWPixel(x float64) float64 {
 // toFramebufferPixel must be called from the main thread.
 func (u *UserInterface) toFramebufferPixel(x float64) float64 {
 	s, _ := currentMonitor(u.window).GetContentScale()
+	// deviceScaleFactor is sometimes an unnice value (e.g., 1.502361). Use math.Ceil to clean the vaule.
 	return math.Ceil(x * float64(s) / u.deviceScaleFactor())
 }