internal/ui: bug fix: need nil check at dipFromGLFWMonitorPixel

Updates #1878

internal/ui/monitor_glfw.go

@@ -33,7 +33,7 @@ type Monitor struct {
 	x               int
 	y               int
 	contentScale    float64
-	videoModeScale float64
+	videoModeScale_ float64
 }
 
 // Name returns the monitor's name.
@@ -50,6 +50,15 @@ func (m *Monitor) deviceScaleFactor() float64 {
 	return m.contentScale
 }
 
+func (m *Monitor) videoModeScale() float64 {
+	// It is rare, but monitor can be nil when glfw.GetPrimaryMonitor returns nil.
+	// In this case, return 1 as a tentative scale (#1878).
+	if m == nil {
+		return 1
+	}
+	return m.videoModeScale_
+}
+
 type monitors struct {
 	// monitors is the monitor list cache for desktop glfw compile targets.
 	// populated by 'updateMonitors' which is called on init and every
@@ -141,7 +150,7 @@ func (m *monitors) update() {
 			x:               x,
 			y:               y,
 			contentScale:    contentScale,
-			videoModeScale: videoModeScale(m),
+			videoModeScale_: videoModeScale(m),
 		})
 	}
 

internal/ui/ui_glfw_linbsd.go

@@ -111,7 +111,7 @@ func videoModeScale(m *glfw.Monitor) float64 {
 }
 
 func dipFromGLFWMonitorPixel(x float64, monitor *Monitor) float64 {
-	return x / (monitor.videoModeScale * monitor.deviceScaleFactor())
+	return x / (monitor.videoModeScale() * monitor.deviceScaleFactor())
 }
 
 func dipFromGLFWPixel(x float64, monitor *Monitor) float64 {