Split the concept of device scale and screen scale (#1811)

We now set deviceScale to always the mapping from logical window system pixels
to device independent pixels (which is what Ebiten API users expect), and
introduce a new concept of videoModeScale that maps from video mode to logical
window system pixels.

videoModeScale is now only used for computing full-screen resolutions, while
deviceScale is used for any other conversion.

Fixes window sizes on X11, should be a NOP otherwise.

Closes #1774.

internal/devicescale/devicescale.go

@@ -23,13 +23,13 @@ type pos struct {
 }
 
 var (
-	m     sync.Mutex
-	cache = map[pos]float64{}
+	m                   sync.Mutex
+	cache               = map[pos]float64{}
+	videoModeScaleCache = map[pos]float64{}
 )
 
-// GetAt returns the device scale at (x, y).
+// GetAt returns the device scale at (x, y), i.e. the number of device-dependent pixels per device-independent pixel.
 // x and y are in device-dependent pixels and must be the top-left coordinate of a monitor, or 0,0 to request a "global scale".
-// The device scale maps device dependent pixels to device independent pixels.
 func GetAt(x, y int) float64 {
 	m.Lock()
 	defer m.Unlock()
@@ -46,3 +46,16 @@ func GetAt(x, y int) float64 {
 
 	return s
 }
+
+// VideoModeScaleAt returns the video mode scale scale at (x, y), i.e. the number of video mode pixels per device-dependent pixel.
+// x and y are in device-dependent pixels and must be the top-left coordinate of a monitor, or 0,0 to request a "global scale".
+func VideoModeScaleAt(x, y int) float64 {
+	m.Lock()
+	defer m.Unlock()
+	if s, ok := videoModeScaleCache[pos{x, y}]; ok {
+		return s
+	}
+	s := videoModeScaleImpl(x, y)
+	videoModeScaleCache[pos{x, y}] = s
+	return s
+}

internal/devicescale/impl_android.go

@@ -103,3 +103,7 @@ func impl(x, y int) float64 {
 	}
 	return s
 }
+
+func videoModeScaleImpl(x, y int) float64 {
+	return 1
+}

internal/devicescale/impl_desktop.go

@@ -33,3 +33,8 @@ func monitorAt(x, y int) *glfw.Monitor {
 	}
 	return monitors[0]
 }
+
+func impl(x, y int) float64 {
+	sx, _ := monitorAt(x, y).GetContentScale()
+	return float64(sx)
+}

internal/devicescale/impl_ios.go

@@ -30,3 +30,7 @@ import "C"
 func impl(x, y int) float64 {
 	return float64(C.devicePixelRatio())
 }
+
+func videoModeScaleImpl(x, y int) float64 {
+	return 1
+}

internal/devicescale/impl_js.go

@@ -33,3 +33,7 @@ func impl(x, y int) float64 {
 	}
 	return ratio
 }
+
+func videoModeScaleImpl(x, y int) float64 {
+	return 1
+}

internal/devicescale/impl_notx.go

@@ -17,7 +17,6 @@
 
 package devicescale
 
-func impl(x, y int) float64 {
-	sx, _ := monitorAt(x, y).GetContentScale()
-	return float64(sx)
+func videoModeScaleImpl(x, y int) float64 {
+	return 1
 }

internal/devicescale/impl_x.go

@@ -25,9 +25,9 @@ import (
 	"github.com/jezek/xgb/xproto"
 )
 
-func impl(x, y int) float64 {
+func videoModeScaleImpl(x, y int) float64 {
 	// TODO: if https://github.com/glfw/glfw/issues/1961 gets fixed, this function may need revising.
-	// In case GLFW decides to switch to returning logical pixels, we can just return 1.0.
+	// In case GLFW decides to switch to returning logical pixels, we can just return 1.
 
 	// Note: GLFW currently returns physical pixel sizes,
 	// but we need to predict the window system-side size of the fullscreen window
@@ -35,7 +35,6 @@ func impl(x, y int) float64 {
 	// Also at the moment we need this prior to switching to fullscreen, but that might be replacable.
 	// So this function computes the ratio of physical per logical pixels.
 	m := monitorAt(x, y)
-	sx, _ := m.GetContentScale()
 	monitorX, monitorY := m.GetPos()
 	xconn, err := xgb.NewConn()
 	defer xconn.Close()
@@ -43,19 +42,19 @@ func impl(x, y int) float64 {
 		// No X11 connection?
 		// Assume we're on pure Wayland then.
 		// GLFW/Wayland shouldn't be having this issue.
-		return float64(sx)
+		return 1
 	}
 	if err = randr.Init(xconn); err != nil {
 		// No RANDR extension?
 		// No problem.
-		return float64(sx)
+		return 1
 	}
 	root := xproto.Setup(xconn).DefaultScreen(xconn).Root
 	res, err := randr.GetScreenResourcesCurrent(xconn, root).Reply()
 	if err != nil {
 		// Likely means RANDR is not working.
 		// No problem.
-		return float64(sx)
+		return 1
 	}
 	for _, crtc := range res.Crtcs[:res.NumCrtcs] {
 		info, err := randr.GetCrtcInfo(xconn, crtc, res.ConfigTimestamp).Reply()
@@ -75,9 +74,9 @@ func impl(x, y int) float64 {
 			// Return one scale, even though there may be separate X and Y scales.
 			// Return the _larger_ scale, as this would yield a letterboxed display on mismatch, rather than a cut-off one.
 			scale := math.Max(float64(physWidth)/float64(xWidth), float64(physHeight)/float64(xHeight))
-			return float64(sx) * scale
+			return scale
 		}
 	}
 	// Monitor not known to XRandR. Weird.
-	return float64(sx)
+	return 1
 }

internal/uidriver/glfw/input.go

@@ -305,8 +305,8 @@ func (i *Input) update(window *glfw.Window, context driver.UIContext) {
 	cx, cy := window.GetCursorPos()
 	// TODO: This is tricky. Rename the function?
 	s := i.ui.deviceScaleFactor()
-	cx = fromGLFWMonitorPixel(cx, s)
-	cy = fromGLFWMonitorPixel(cy, s)
+	cx = i.ui.fromGLFWPixel(cx)
+	cy = i.ui.fromGLFWPixel(cy)
 	cx, cy = context.AdjustPosition(cx, cy, s)
 
 	// AdjustPosition can return NaN at the initialization.

internal/uidriver/glfw/ui.go

@@ -189,9 +189,10 @@ func initialize() error {
 	m := currentMonitor(w)
 	theUI.initMonitor = m
 	v := m.GetVideoMode()
-	scale := devicescale.GetAt(currentMonitor(w).GetPos())
-	theUI.initFullscreenWidthInDP = int(fromGLFWMonitorPixel(float64(v.Width), scale))
-	theUI.initFullscreenHeightInDP = int(fromGLFWMonitorPixel(float64(v.Height), scale))
+	mx, my := currentMonitor(w).GetPos()
+	scale := devicescale.VideoModeScaleAt(mx, my)
+	theUI.initFullscreenWidthInDP = int(theUI.fromGLFWMonitorPixel(float64(v.Width), scale))
+	theUI.initFullscreenHeightInDP = int(theUI.fromGLFWMonitorPixel(float64(v.Height), scale))
 
 	// Create system cursors. These cursors are destroyed at glfw.Terminate().
 	glfwSystemCursors[driver.CursorShapeDefault] = nil
@@ -528,10 +529,12 @@ func (u *UserInterface) ScreenSizeInFullscreen() (int, int) {
 
 	var w, h int
 	_ = u.t.Call(func() error {
-		v := currentMonitor(u.window).GetVideoMode()
-		s := u.deviceScaleFactor()
-		w = int(fromGLFWMonitorPixel(float64(v.Width), s))
-		h = int(fromGLFWMonitorPixel(float64(v.Height), s))
+		m := currentMonitor(u.window)
+		v := m.GetVideoMode()
+		mx, my := m.GetPos()
+		s := devicescale.VideoModeScaleAt(mx, my)
+		w = int(u.fromGLFWMonitorPixel(float64(v.Width), s))
+		h = int(u.fromGLFWMonitorPixel(float64(v.Height), s))
 		return nil
 	})
 	return w, h
@@ -707,7 +710,7 @@ func (u *UserInterface) SetCursorShape(shape driver.CursorShape) {
 func (u *UserInterface) DeviceScaleFactor() float64 {
 	if !u.isRunning() {
 		// TODO: Use the initWindowPosition. This requires to convert the units correctly (#1575).
-		return devicescale.GetAt(u.initMonitor.GetPos())
+		return u.deviceScaleFactor()
 	}
 
 	f := 0.0
@@ -724,7 +727,8 @@ func (u *UserInterface) deviceScaleFactor() float64 {
 	if u.window != nil {
 		m = currentMonitor(u.window)
 	}
-	return devicescale.GetAt(m.GetPos())
+	mx, my := m.GetPos()
+	return devicescale.GetAt(mx, my)
 }
 
 func init() {
@@ -933,11 +937,13 @@ func (u *UserInterface) updateSize() (float64, float64, bool) {
 
 	var w, h float64
 	if u.isFullscreen() {
-		v := currentMonitor(u.window).GetVideoMode()
+		m := currentMonitor(u.window)
+		v := m.GetVideoMode()
 		ww, wh := v.Width, v.Height
-		s := u.deviceScaleFactor()
-		w = fromGLFWMonitorPixel(float64(ww), s)
-		h = fromGLFWMonitorPixel(float64(wh), s)
+		mx, my := m.GetPos()
+		s := devicescale.VideoModeScaleAt(mx, my)
+		w = u.fromGLFWMonitorPixel(float64(ww), s)
+		h = u.fromGLFWMonitorPixel(float64(wh), s)
 	} else {
 		// Instead of u.windowWidth and u.windowHeight, use the actual window size here.
 		// On Windows, the specified size at SetSize and the actual window size might not
@@ -946,9 +952,6 @@ func (u *UserInterface) updateSize() (float64, float64, bool) {
 		w = u.fromGLFWPixel(float64(ww))
 		h = u.fromGLFWPixel(float64(wh))
 	}
-	// On Linux/UNIX, further adjusting is required (#1307).
-	w = u.toFramebufferPixel(w)
-	h = u.toFramebufferPixel(h)
 
 	return w, h, true
 }

internal/uidriver/glfw/ui_darwin.go

@@ -81,22 +81,27 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/internal/glfw"
 )
 
-func fromGLFWMonitorPixel(x float64, deviceScale float64) float64 {
-	return x
+// fromGLFWMonitorPixel must be called from the main thread.
+func (u *UserInterface) fromGLFWMonitorPixel(x float64, videoModeScale float64) float64 {
+	// videoModeScale is always 1 on macOS,
+	// however leaving the divison in place for consistency.
+	return x / videoModeScale
 }
 
+// fromGLFWPixel must be called from the main thread.
 func (u *UserInterface) fromGLFWPixel(x float64) float64 {
+	// NOTE: On macOS, GLFW exposes the device independent coordinate system.
+	// Thus, the conversion functions are unnecessary,
+	// however we still need the deviceScaleFactor internally
+	// so we can create and maintain a HiDPI frame buffer.
 	return x
 }
 
+// toGLFWPixel must be called from the main thread.
 func (u *UserInterface) toGLFWPixel(x float64) float64 {
 	return x
 }
 
-func (u *UserInterface) toFramebufferPixel(x float64) float64 {
-	return x
-}
-
 func (u *UserInterface) adjustWindowPosition(x, y int) (int, int) {
 	return x, y
 }

internal/uidriver/glfw/ui_unix.go

@@ -19,37 +19,23 @@
 package glfw
 
 import (
-	"math"
-
 	"github.com/hajimehoshi/ebiten/v2/internal/driver"
 	"github.com/hajimehoshi/ebiten/v2/internal/glfw"
 )
 
 // 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)
+func (u *UserInterface) fromGLFWMonitorPixel(x float64, videoModeScale float64) float64 {
+	return x / (videoModeScale * u.deviceScaleFactor())
 }
 
 // fromGLFWPixel must be called from the main thread.
 func (u *UserInterface) fromGLFWPixel(x float64) float64 {
-	// deviceScaleFactor() is a scale by desktop environment (e.g., Cinnamon), while GetContentScale() is X's scale.
-	// They are different things and then need to be treated in different ways (#1350).
-	s, _ := currentMonitor(u.window).GetContentScale()
-	return x / float64(s)
+	return x / u.deviceScaleFactor()
 }
 
 // toGLFWPixel must be called from the main thread.
 func (u *UserInterface) toGLFWPixel(x float64) float64 {
-	s, _ := currentMonitor(u.window).GetContentScale()
-	return x * float64(s)
-}
-
-// 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())
+	return x * u.deviceScaleFactor()
 }
 
 func (u *UserInterface) adjustWindowPosition(x, y int) (int, int) {

internal/uidriver/glfw/ui_windows.go

@@ -99,8 +99,8 @@ func getMonitorInfoW(hMonitor uintptr, lpmi *monitorInfo) error {
 }
 
 // fromGLFWMonitorPixel must be called from the main thread.
-func fromGLFWMonitorPixel(x float64, deviceScale float64) float64 {
-	return x / deviceScale
+func (u *UserInterface) fromGLFWMonitorPixel(x float64, videoModeScale float64) float64 {
+	return x / (videoModeScale * u.deviceScaleFactor())
 }
 
 // fromGLFWPixel must be called from the main thread.
@@ -113,11 +113,6 @@ func (u *UserInterface) toGLFWPixel(x float64) float64 {
 	return x * u.deviceScaleFactor()
 }
 
-// toFramebufferPixel must be called from the main thread.
-func (u *UserInterface) toFramebufferPixel(x float64) float64 {
-	return x
-}
-
 func (u *UserInterface) adjustWindowPosition(x, y int) (int, int) {
 	mx, my := currentMonitor(u.window).GetPos()
 	// As the video width/height might be wrong,