ui: Center the screen on fullscreen mode (#374)

graphicscontext.go

@@ -19,6 +19,7 @@ import (
 
 	"github.com/hajimehoshi/ebiten/internal/graphics"
 	"github.com/hajimehoshi/ebiten/internal/restorable"
+	"github.com/hajimehoshi/ebiten/internal/ui"
 )
 
 func newGraphicsContext(f func(*Image) error) *graphicsContext {
@@ -64,7 +65,8 @@ func (c *graphicsContext) SetSize(screenWidth, screenHeight int, screenScale flo
 
 	w = int(float64(screenWidth) * screenScale)
 	h = int(float64(screenHeight) * screenScale)
-	c.screen = newImageWithScreenFramebuffer(w, h)
+	ox, oy := ui.ScreenOffset()
+	c.screen = newImageWithScreenFramebuffer(w, h, ox, oy)
 	_ = c.screen.Clear()
 
 	c.offscreen = offscreen

image.go

@@ -275,9 +275,9 @@ func NewImageFromImage(source image.Image, filter Filter) (*Image, error) {
 	return i, nil
 }
 
-func newImageWithScreenFramebuffer(width, height int) *Image {
+func newImageWithScreenFramebuffer(width, height int, offsetX, offsetY float64) *Image {
 	checkSize(width, height)
-	r := restorable.NewScreenFramebufferImage(width, height)
+	r := restorable.NewScreenFramebufferImage(width, height, offsetX, offsetY)
 	i := &Image{r}
 	runtime.SetFinalizer(i, (*Image).Dispose)
 	return i

internal/graphics/command.go

@@ -357,9 +357,11 @@ func (c *newImageCommand) Exec(indexOffsetInBytes int) error {
 }
 
 type newScreenFramebufferImageCommand struct {
-	result *Image
-	width  int
-	height int
+	result  *Image
+	width   int
+	height  int
+	offsetX float64
+	offsetY float64
 }
 
 func (c *newScreenFramebufferImageCommand) Exec(indexOffsetInBytes int) error {
@@ -370,8 +372,10 @@ func (c *newScreenFramebufferImageCommand) Exec(indexOffsetInBytes int) error {
 		return errors.New("graphics: height must be equal or more than 1.")
 	}
 	f := &framebuffer{
-		native: opengl.GetContext().ScreenFramebuffer(),
-		flipY:  true,
+		native:  opengl.GetContext().ScreenFramebuffer(),
+		flipY:   true,
+		offsetX: c.offsetX,
+		offsetY: c.offsetY,
 	}
 	c.result.framebuffer = f
 	return nil

internal/graphics/framebuffer.go

@@ -36,6 +36,8 @@ type framebuffer struct {
 	native    opengl.Framebuffer
 	flipY     bool
 	proMatrix []float32
+	offsetX   float64
+	offsetY   float64
 }
 
 func newFramebufferFromTexture(texture *texture) (*framebuffer, error) {
@@ -65,6 +67,8 @@ func (f *framebuffer) projectionMatrix(height int) []float32 {
 		m[4*1+1] *= -1
 		m[4*3+1] += float32(height) / float32(viewportSize) * 2
 	}
+	m[4*3+0] += float32(f.offsetX) / float32(viewportSize) * 2
+	m[4*3+1] += float32(f.offsetY) / float32(viewportSize) * 2
 	f.proMatrix = m
 	return f.proMatrix
 }

internal/graphics/image.go

@@ -107,15 +107,17 @@ func NewImageFromImage(img *image.RGBA, width, height int, filter opengl.Filter)
 	return i
 }
 
-func NewScreenFramebufferImage(width, height int) *Image {
+func NewScreenFramebufferImage(width, height int, offsetX, offsetY float64) *Image {
 	i := &Image{
 		width:  width,
 		height: height,
 	}
 	c := &newScreenFramebufferImageCommand{
-		result: i,
-		width:  width,
-		height: height,
+		result:  i,
+		width:   width,
+		height:  height,
+		offsetX: offsetX,
+		offsetY: offsetY,
 	}
 	theCommandQueue.Enqueue(c)
 	return i

internal/restorable/image.go

@@ -52,6 +52,9 @@ type Image struct {
 
 	// screen indicates whether the image is used as an actual screen.
 	screen bool
+
+	offsetX float64
+	offsetY float64
 }
 
 func NewImage(width, height int, filter opengl.Filter, volatile bool) *Image {
@@ -81,11 +84,13 @@ func NewImageFromImage(source *image.RGBA, width, height int, filter opengl.Filt
 	return i
 }
 
-func NewScreenFramebufferImage(width, height int) *Image {
+func NewScreenFramebufferImage(width, height int, offsetX, offsetY float64) *Image {
 	i := &Image{
-		image:    graphics.NewScreenFramebufferImage(width, height),
+		image:    graphics.NewScreenFramebufferImage(width, height, offsetX, offsetY),
 		volatile: true,
 		screen:   true,
+		offsetX:  offsetX,
+		offsetY:  offsetY,
 	}
 	theImages.add(i)
 	runtime.SetFinalizer(i, (*Image).Dispose)
@@ -249,7 +254,7 @@ func (p *Image) restore() error {
 	if p.screen {
 		// The screen image should also be recreated because framebuffer might
 		// be changed.
-		p.image = graphics.NewScreenFramebufferImage(w, h)
+		p.image = graphics.NewScreenFramebufferImage(w, h, p.offsetX, p.offsetY)
 		p.basePixels = nil
 		p.baseColor = color.RGBA{}
 		p.drawImageHistory = nil

internal/ui/ui_glfw.go

@@ -194,6 +194,26 @@ func IsFullscreen() bool {
 	return f
 }
 
+func ScreenOffset() (float64, float64) {
+	u := currentUI
+	if !u.isRunning() {
+		return 0, 0
+	}
+	if !IsFullscreen() {
+		return 0, 0
+	}
+	ox := 0.0
+	oy := 0.0
+	m := glfw.GetPrimaryMonitor()
+	v := m.GetVideoMode()
+	_ = u.runOnMainThread(func() error {
+		ox = (float64(v.Width)*u.deviceScale/u.glfwScale - float64(u.width)*u.actualScreenScale()) / 2
+		oy = (float64(v.Height)*u.deviceScale/u.glfwScale - float64(u.height)*u.actualScreenScale()) / 2
+		return nil
+	})
+	return ox, oy
+}
+
 func SetCursorVisibility(visible bool) {
 	// This can be called before Run: change the state asyncly.
 	go func() {

internal/ui/ui_js.go

@@ -66,6 +66,10 @@ func IsFullscreen() bool {
 	return false
 }
 
+func ScreenOffset() (float64, float64) {
+	return 0, 0
+}
+
 func SetCursorVisibility(visibility bool) {
 	if visibility {
 		canvas.Get("style").Set("cursor", "auto")

internal/ui/ui_mobile.go

@@ -106,6 +106,10 @@ func ScreenScale() float64 {
 	return currentUI.scale
 }
 
+func ScreenOffset() (float64, float64) {
+	return 0, 0
+}
+
 func SetCursorVisibility(visibility bool) {
 	// Do nothing
 }