Add TextView, improved Scrollbar

scrollbar.go

@@ -173,15 +173,15 @@ func (this *Scrollbar) handleMouseDown (button input.Button) {
 		}
 	case input.ButtonMiddle:
 		if above {
-			this.SetValue(0)
+			this.scrollBy(-this.pageSize())
 		} else {
-			this.SetValue(1)
+			this.scrollBy(this.pageSize())
 		}
 	case input.ButtonRight:
 		if above {
-			this.SetValue(this.Value() - 0.05)
+			this.scrollBy(-this.stepSize())
 		} else {
-			this.SetValue(this.Value() + 0.05)
+			this.scrollBy(this.stepSize())
 		}
 	}
 }
@@ -229,6 +229,34 @@ func (this *Scrollbar) fallbackDragOffset () image.Point {
 	}
 }
 
+func (this *Scrollbar) pageSize () int {
+	if this.layout.linked == nil { return 0 }
+	viewport := this.layout.linked.InnerBounds()
+	if this.layout.vertical {
+		return viewport.Dy()
+	} else {
+		return viewport.Dx()
+	}
+}
+
+func (this *Scrollbar) stepSize () int {
+	// FIXME: this should not be hardcoded, need to get base font metrics
+	// from theme somehow. should be (emspace, lineheight)
+	return 16
+}
+
+func (this *Scrollbar) scrollBy (distance int) {
+	if this.layout.linked == nil { return }
+	var vector image.Point; if this.layout.vertical {
+		vector.Y = distance
+	} else {
+		vector.X = distance
+	}
+	this.layout.linked.ScrollTo (
+		this.layout.linked.ContentBounds().Min.
+		Add(vector))
+}
+
 type scrollbarCookie struct {
 	owner *Scrollbar
 	subCookies []event.Cookie