ebiten: DeviceScaleFactor before RunGame can return a wrong value when SetWindowPosition is called

[hajimehoshi]

When SetWindowPosition is called and the position is in another monitor, DeviceScaleFactor should be affected.

[hajimehoshi]

DeviceScaleFactor should not be called before RunGame, due to Android?

[hajimehoshi]

Probably we have to keep a temporary window created at init and detect the monitor correctly. This is not an easy task.

[aprchen]

Is there any plan for this issue?

[hajimehoshi]

No so far, but is this an urgent issue for you?

[aprchen]

No so far, but is this an urgent issue for you?

Yes, I made a function of dragging the window. When using DeviceScaleFactor, the window will shake when it moves, and it will be normal without using DeviceScaleFactor.

[hajimehoshi]

I don't understand what you are doing. Could you show a (pseudo) code?

[aprchen]

the demo like this

package main

import (
	"fmt"

	"github.com/hajimehoshi/ebiten/v2"
	"github.com/hajimehoshi/ebiten/v2/inpututil"
)

type Test struct {
	isHighDPI bool
	c         WindowDragCoordinator
}

func (t *Test) Update() error {
	t.c.Update()
	return nil
}

func (t *Test) Draw(screen *ebiten.Image) {
	return
}

func (t *Test) Layout(outsideWidth, outsideHeight int) (screenWidth, screenHeight int) {
	if t.isHighDPI {
		s := ebiten.DeviceScaleFactor()
		return int(s) * outsideWidth, int(s) * outsideHeight
	}
	return outsideWidth, outsideHeight
}

func NewTest() *Test {
	return &Test{}
}

func main() {
	g := NewTest()
	g.isHighDPI = true
	ebiten.SetWindowSize(200, 200)
	err := ebiten.RunGame(g)
	if err != nil {
		panic(err)
	}
}

type Point struct {
	x, y int
}

type mouse struct {
	current, init Point
}

func (m mouse) String() string {
	return fmt.Sprintf("x %d y %d  fx %d fy %d", m.current.x, m.current.y, m.init.x, m.init.y)
}

func (m mouse) Diff() (dx, dy int) {
	return m.current.x - m.init.x, m.current.y - m.init.y
}

func (m *mouse) SetInitPosition() {
	m.init.x, m.init.y = ebiten.CursorPosition()
}

func (m *mouse) RefreshCurrentPosition() {
	m.current.x, m.current.y = ebiten.CursorPosition()
}

type window struct {
	current, init Point
}

func (w *window) RefreshCurrentPosition() {
	w.current.x, w.current.y = ebiten.WindowPosition()
}

func (w *window) GetSize() (width, height int) {
	return ebiten.WindowSize()
}

func (w *window) SetInitPosition() {
	w.init.x, w.init.y = ebiten.WindowPosition()
}

func (w *window) GetMax() (x, y int) {
	wWidth, wHeight := w.GetSize()
	mx, my := ebiten.ScreenSizeInFullscreen()
	return mx - wWidth, my - wHeight
}

func (w *window) MoveBy(dx, dy int) {
	w.current.x += dx
	w.current.y += dy
	maxX, maxy := w.GetMax()
	if w.current.x < 0 {
		w.current.x = 0
	}
	if w.current.x > maxX {
		w.current.x = maxX
	}
	if w.current.y < 0 {
		w.current.y = 0
	}
	if w.current.y > maxy {
		w.current.y = maxy
	}
	ebiten.SetWindowPosition(w.current.x, w.current.y)
}

type WindowDragCoordinator struct {
	mouse  mouse
	window window
	isHold bool
}

func (c *WindowDragCoordinator) Update() {
	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButtonLeft) {
		c.mouse.SetInitPosition()
		c.window.SetInitPosition()
		c.isHold = true
		return
	}
	if inpututil.IsMouseButtonJustReleased(ebiten.MouseButtonLeft) {
		c.isHold = false
		return
	}
	if !c.isHold {
		return
	}
	c.mouse.RefreshCurrentPosition()
	fmt.Println(c.mouse)
	c.window.RefreshCurrentPosition()
	c.window.MoveBy(c.mouse.Diff())
}

[hajimehoshi]

Thanks, but is this related to this issue? This issue focuses on DeviceScaleFactor before RunGame.

[aprchen]

Thanks, but is this related to this issue? This issue focuses on DeviceScaleFactor before RunGame.

sorry, I followed the method comment
this should be another issue

[hajimehoshi]

How about not enabling to specify a monitor by SetWindowPosition? Then we can assume DeviceScaleFactor always returns the scale of the default monitor.

[hajimehoshi]

Solved this issue by not letting users change the initial monitor.