driver: Use framebuffer's Y directions

internal/driver/graphics.go

@@ -32,7 +32,7 @@ type Graphics interface {
 	Reset() error
 	Draw(indexLen int, indexOffset int, mode CompositeMode, colorM *affine.ColorM, filter Filter, address Address) error
 	SetVsyncEnabled(enabled bool)
-	VDirection() VDirection
+	FramebufferYDirection() YDirection
 	NeedsRestoring() bool
 	IsGL() bool
 	HasHighPrecisionFloat() bool
@@ -59,9 +59,9 @@ type ReplacePixelsArgs struct {
 	Height int
 }
 
-type VDirection int
+type YDirection int
 
 const (
-	VUpward VDirection = iota
-	VDownward
+	Upward YDirection = iota
+	Downward
 )

internal/graphicsdriver/metal/graphics.go

@@ -684,8 +684,8 @@ func (g *Graphics) SetVsyncEnabled(enabled bool) {
 	g.view.setDisplaySyncEnabled(enabled)
 }
 
-func (g *Graphics) VDirection() driver.VDirection {
-	return driver.VUpward
+func (g *Graphics) FramebufferYDirection() driver.YDirection {
+	return driver.Downward
 }
 
 func (g *Graphics) NeedsRestoring() bool {

internal/graphicsdriver/monogame/graphics.go

@@ -91,8 +91,8 @@ func (g *Graphics) SetVsyncEnabled(enabled bool) {
 	panic("monogame: SetVsyncEnabled is not implemented yet")
 }
 
-func (g *Graphics) VDirection() driver.VDirection {
-	return driver.VUpward
+func (g *Graphics) FramebufferYDirection() driver.YDirection {
+	return driver.Downward
 }
 
 func (g *Graphics) NeedsRestoring() bool {

internal/graphicsdriver/opengl/graphics.go

@@ -129,8 +129,8 @@ func (g *Graphics) SetVsyncEnabled(enabled bool) {
 	// Do nothing
 }
 
-func (g *Graphics) VDirection() driver.VDirection {
-	return driver.VDownward
+func (g *Graphics) FramebufferYDirection() driver.YDirection {
+	return driver.Upward
 }
 
 func (g *Graphics) NeedsRestoring() bool {

uicontext.go

@@ -307,14 +307,14 @@ func (c *uiContext) draw() {
 	op := &DrawImageOptions{}
 
 	s := c.screenScale()
-	switch vd := uiDriver().Graphics().VDirection(); vd {
-	case driver.VDownward:
+	switch vd := uiDriver().Graphics().FramebufferYDirection(); vd {
+	case driver.Upward:
 		// c.screen is special: its Y axis is down to up,
 		// and the origin point is lower left.
 		op.GeoM.Scale(s, -s)
 		_, h := c.offscreen.Size()
 		op.GeoM.Translate(0, float64(h)*s)
-	case driver.VUpward:
+	case driver.Downward:
 		op.GeoM.Scale(s, s)
 	default:
 		panic(fmt.Sprintf("ebiten: invalid v-direction: %d", vd))