Fix TextBox scroll behavior

textbox.go

@@ -222,7 +222,7 @@ func (this *textBox) drawDot (can canvas.Canvas) {
 
 func (this *textBox) textOffset () image.Point {
 	return this.InnerBounds().Min.
-		Sub(this.scroll).
+		Add(this.scroll).
 		Sub(this.drawer.LayoutBoundsSpace().Min)
 }
 
@@ -294,6 +294,7 @@ func (this *textBox) doLayout () {
 	this.contentBounds = this.normalizedLayoutBoundsSpace()
 	this.constrainScroll()
 	this.contentBounds = this.contentBounds.Add(this.scroll)
+	// println(this.InnerBounds().String(), this.contentBounds.String())
 
 	if previousContentBounds != this.contentBounds {
 		this.on.contentBoundsChange.Broadcast()
@@ -308,19 +309,19 @@ func (this *textBox) constrainScroll () {
 	// X
 	if width <= innerBounds.Dx() {
 		this.scroll.X = 0
-	} else if this.scroll.X < 0 {
+	} else if this.scroll.X > 0 {
 		this.scroll.X = 0
-	} else if this.scroll.X > width - innerBounds.Dx() {
+	} else if this.scroll.X < innerBounds.Dx() - width  {
-		this.scroll.X = width - innerBounds.Dx()
+		this.scroll.X =  innerBounds.Dx() - width
 	}
 
 	// Y
 	if height <= innerBounds.Dy() {
 		this.scroll.Y = 0
-	} else if this.scroll.Y < 0 {
+	} else if this.scroll.Y > 0 {
 		this.scroll.Y = 0
-	} else if this.scroll.Y > height - innerBounds.Dy() {
+	} else if this.scroll.Y < innerBounds.Dy() - height {
-		this.scroll.Y = height - innerBounds.Dy()
+		this.scroll.Y = innerBounds.Dy() - height
 	}
 }
 
@@ -333,16 +334,16 @@ func (this *textBox) scrollToDot () {
 
 	// X
 	if dot.X < innerBounds.Min.X + em {
-		scroll.X -= innerBounds.Min.X - dot.X + em
+		scroll.X += innerBounds.Min.X - dot.X + em
 	} else if dot.X > innerBounds.Max.X - em {
-		scroll.X += dot.X - innerBounds.Max.X + em
+		scroll.X -= dot.X - innerBounds.Max.X + em
 	}
 
 	// Y
 	if dot.Y < innerBounds.Min.Y + lineHeight {
-		scroll.Y -= innerBounds.Min.Y - dot.Y + lineHeight
+		scroll.Y += innerBounds.Min.Y - dot.Y + lineHeight
 	} else if dot.Y > innerBounds.Max.Y - lineHeight {
-		scroll.Y += dot.Y - innerBounds.Max.Y + lineHeight
+		scroll.Y -= dot.Y - innerBounds.Max.Y + lineHeight
 	}
 	
 	this.ScrollTo(scroll)