ui: Adjust fullscreen scale (#267)

internal/ui/ui_glfw.go

@@ -37,6 +37,7 @@ type userInterface struct {
 	deviceScale     float64
 	glfwScale       float64
 	fullscreen      bool
+	fullscreenScale float64
 	funcs           chan func()
 	running         bool
 	sizeChanged     bool
@@ -243,6 +244,20 @@ func (u *userInterface) actualScreenScale() float64 {
 	if u.deviceScale == 0 {
 		u.deviceScale = deviceScale()
 	}
+	if u.fullscreen {
+		if u.fullscreenScale == 0 {
+			m := glfw.GetPrimaryMonitor()
+			v := m.GetVideoMode()
+			sw := float64(v.Width) / float64(u.width)
+			sh := float64(v.Height) / float64(u.height)
+			s := sw
+			if s > sh {
+				s = sh
+			}
+			u.fullscreenScale = s
+		}
+		return u.fullscreenScale * u.deviceScale
+	}
 	return u.scale * u.deviceScale
 }