Add support for specifying widget alignment on layout level

4 files changed, 184 insertions, 13 deletions

diff --git a/boxlayout.go b/boxlayout.go
index d84a7bc0..a8b7dfdb 100644
--- a/boxlayout.go
+++ b/boxlayout.go
@@ -24,6 +24,7 @@ type BoxLayout struct {
 	margins            Margins
 	spacing            int
 	orientation        Orientation
+	alignment          Alignment2D
 	hwnd2StretchFactor map[win.HWND]int
 	size2MinSize       map[Size]Size
 	resetNeeded        bool
@@ -104,6 +105,24 @@ func (l *BoxLayout) SetOrientation(value Orientation) error {
 	return nil
 }
 
+func (l *BoxLayout) Alignment() Alignment2D {
+	return l.alignment
+}
+
+func (l *BoxLayout) SetAlignment(alignment Alignment2D) error {
+	if alignment != l.alignment {
+		if alignment < AlignHVDefault || alignment > AlignHFarVFar {
+			return newError("invalid Alignment value")
+		}
+
+		l.alignment = alignment
+
+		l.Update(false)
+	}
+
+	return nil
+}
+
 func (l *BoxLayout) Spacing() int {
 	return l.spacing
 }
@@ -230,7 +249,7 @@ func (l *BoxLayout) MinSizeForSize(size Size) Size {
 
 	bounds := Rectangle{Width: size.Width, Height: size.Height}
 
-	items, err := boxLayoutItems(widgetsToLayout(l.Container().Children()), l.orientation, bounds, l.margins, l.spacing, l.hwnd2StretchFactor)
+	items, err := boxLayoutItems(widgetsToLayout(l.Container().Children()), l.orientation, l.alignment, bounds, l.margins, l.spacing, l.hwnd2StretchFactor)
 	if err != nil {
 		return Size{}
 	}
@@ -302,7 +321,7 @@ func (l *BoxLayout) Update(reset bool) error {
 
 	ifContainerIsScrollViewDoCoolSpecialLayoutStuff(l)
 
-	items, err := boxLayoutItems(widgetsToLayout(l.Container().Children()), l.orientation, l.container.ClientBounds(), l.margins, l.spacing, l.hwnd2StretchFactor)
+	items, err := boxLayoutItems(widgetsToLayout(l.Container().Children()), l.orientation, l.alignment, l.container.ClientBounds(), l.margins, l.spacing, l.hwnd2StretchFactor)
 	if err != nil {
 		return err
 	}
@@ -360,7 +379,11 @@ func boxLayoutFlags(orientation Orientation, children *WidgetList) LayoutFlags {
 	return flags
 }
 
-func boxLayoutItems(widgets []Widget, orientation Orientation, bounds Rectangle, margins Margins, spacing int, hwnd2StretchFactor map[win.HWND]int) ([]layoutResultItem, error) {
+func boxLayoutItems(widgets []Widget, orientation Orientation, alignment Alignment2D, bounds Rectangle, margins Margins, spacing int, hwnd2StretchFactor map[win.HWND]int) ([]layoutResultItem, error) {
+	if len(widgets) == 0 {
+		return nil, nil
+	}
+
 	var greedyNonSpacerCount int
 	var greedySpacerCount int
 	var stretchFactorsTotal [3]int
@@ -498,10 +521,10 @@ func boxLayoutItems(widgets []Widget, orientation Orientation, bounds Rectangle,
 	results := make([]layoutResultItem, 0, len(widgets))
 
 	excessTotal := space1 - minSizesRemaining - spacingRemaining
-	excessShare := excessTotal / (len(widgets) + 1)
+	excessShare := excessTotal / len(widgets)
+	halfExcessShare := excessTotal / (len(widgets) * 2)
 	p1 := start1
 	for i, widget := range widgets {
-		p1 += excessShare
 		s1 := sizes[i]
 
 		var s2 int
@@ -511,15 +534,82 @@ func boxLayoutItems(widgets []Widget, orientation Orientation, bounds Rectangle,
 			s2 = prefSizes2[i]
 		}
 
-		p2 := start2 + (space2-s2)/2
-
-		var x, y, w, h int
+		var x, y, w, h, p2 int
 		if orientation == Horizontal {
+			switch alignment {
+			case AlignHNearVNear, AlignHNearVCenter, AlignHNearVFar:
+				// nop
+
+			case AlignHFarVNear, AlignHFarVCenter, AlignHFarVFar:
+				p1 += excessShare
+
+			default:
+				p1 += halfExcessShare
+			}
+
+			switch alignment {
+			case AlignHNearVNear, AlignHCenterVNear, AlignHFarVNear:
+				p2 = start2
+
+			case AlignHNearVFar, AlignHCenterVFar, AlignHFarVFar:
+				p2 = start2 + space2 - s2
+
+			default:
+				p2 = start2 + (space2-s2)/2
+			}
+
 			x, y, w, h = p1, p2, s1, s2
 		} else {
+			switch alignment {
+			case AlignHNearVNear, AlignHCenterVNear, AlignHFarVNear:
+				// nop
+
+			case AlignHNearVFar, AlignHCenterVFar, AlignHFarVFar:
+				p1 += excessShare
+
+			default:
+				p1 += halfExcessShare
+			}
+
+			switch alignment {
+			case AlignHNearVNear, AlignHNearVCenter, AlignHNearVFar:
+				p2 = start2
+
+			case AlignHFarVNear, AlignHFarVCenter, AlignHFarVFar:
+				p2 = start2 + space2 - s2
+
+			default:
+				p2 = start2 + (space2-s2)/2
+			}
+
 			x, y, w, h = p2, p1, s2, s1
 		}
 
+		if orientation == Horizontal {
+			switch alignment {
+			case AlignHNearVNear, AlignHNearVCenter, AlignHNearVFar:
+				p1 += excessShare
+
+			case AlignHFarVNear, AlignHFarVCenter, AlignHFarVFar:
+				// nop
+
+			default:
+				p1 += halfExcessShare
+			}
+
+		} else {
+			switch alignment {
+			case AlignHNearVNear, AlignHCenterVNear, AlignHFarVNear:
+				p1 += excessShare
+
+			case AlignHNearVFar, AlignHCenterVFar, AlignHFarVFar:
+				// nop
+
+			default:
+				p1 += halfExcessShare
+			}
+		}
+
 		p1 += s1 + spacing
 
 		results = append(results, layoutResultItem{widget: widget, bounds: Rectangle{X: x, Y: y, Width: w, Height: h}})
diff --git a/declarative/layouts.go b/declarative/layouts.go
index 601c3ffb..158a0cbb 100644
--- a/declarative/layouts.go
+++ b/declarative/layouts.go
@@ -61,6 +61,7 @@ func setLayoutSpacing(layout walk.Layout, spacing int, spacingZero bool) error {
 
 type HBox struct {
 	Margins     Margins
+	Alignment   Alignment2D
 	Spacing     int
 	MarginsZero bool
 	SpacingZero bool
@@ -77,11 +78,16 @@ func (hb HBox) Create() (walk.Layout, error) {
 		return nil, err
 	}
 
+	if err := l.SetAlignment(walk.Alignment2D(hb.Alignment)); err != nil {
+		return nil, err
+	}
+
 	return l, nil
 }
 
 type VBox struct {
 	Margins     Margins
+	Alignment   Alignment2D
 	Spacing     int
 	MarginsZero bool
 	SpacingZero bool
@@ -98,6 +104,10 @@ func (vb VBox) Create() (walk.Layout, error) {
 		return nil, err
 	}
 
+	if err := l.SetAlignment(walk.Alignment2D(vb.Alignment)); err != nil {
+		return nil, err
+	}
+
 	return l, nil
 }
 
@@ -105,6 +115,7 @@ type Grid struct {
 	Rows        int
 	Columns     int
 	Margins     Margins
+	Alignment   Alignment2D
 	Spacing     int
 	MarginsZero bool
 	SpacingZero bool
@@ -125,11 +136,16 @@ func (g Grid) Create() (walk.Layout, error) {
 		return nil, err
 	}
 
+	if err := l.SetAlignment(walk.Alignment2D(g.Alignment)); err != nil {
+		return nil, err
+	}
+
 	return l, nil
 }
 
 type Flow struct {
 	Margins     Margins
+	Alignment   Alignment2D
 	Spacing     int
 	MarginsZero bool
 	SpacingZero bool
@@ -146,5 +162,9 @@ func (f Flow) Create() (walk.Layout, error) {
 		return nil, err
 	}
 
+	if err := l.SetAlignment(walk.Alignment2D(f.Alignment)); err != nil {
+		return nil, err
+	}
+
 	return l, nil
 }
diff --git a/flowlayout.go b/flowlayout.go
index e85ef820..1cf2ec4e 100644
--- a/flowlayout.go
+++ b/flowlayout.go
@@ -16,6 +16,7 @@ type FlowLayout struct {
 	margins            Margins
 	size2MinSize       map[Size]Size
 	spacing            int
+	alignment          Alignment2D
 	resetNeeded        bool
 }
 
@@ -86,6 +87,24 @@ func (l *FlowLayout) SetSpacing(value int) error {
 	return nil
 }
 
+func (l *FlowLayout) Alignment() Alignment2D {
+	return l.alignment
+}
+
+func (l *FlowLayout) SetAlignment(alignment Alignment2D) error {
+	if alignment != l.alignment {
+		if alignment < AlignHVDefault || alignment > AlignHFarVFar {
+			return newError("invalid Alignment value")
+		}
+
+		l.alignment = alignment
+
+		l.Update(false)
+	}
+
+	return nil
+}
+
 func (l *FlowLayout) StretchFactor(widget Widget) int {
 	if factor, ok := l.hwnd2StretchFactor[widget.Handle()]; ok {
 		return factor
@@ -176,7 +195,7 @@ func (l *FlowLayout) MinSizeForSize(size Size) Size {
 			margins.VFar = 0
 		}
 
-		layoutItems, err := boxLayoutItems(widgets, Horizontal, bounds, margins, l.spacing, l.hwnd2StretchFactor)
+		layoutItems, err := boxLayoutItems(widgets, Horizontal, l.alignment, bounds, margins, l.spacing, l.hwnd2StretchFactor)
 		if err != nil {
 			return Size{}
 		}
@@ -258,7 +277,7 @@ func (l *FlowLayout) Update(reset bool) error {
 			margins.VFar = 0
 		}
 
-		layoutItems, err := boxLayoutItems(widgets, Horizontal, bounds, margins, l.spacing, l.hwnd2StretchFactor)
+		layoutItems, err := boxLayoutItems(widgets, Horizontal, l.alignment, bounds, margins, l.spacing, l.hwnd2StretchFactor)
 		if err != nil {
 			return err
 		}
@@ -277,7 +296,7 @@ func (l *FlowLayout) Update(reset bool) error {
 
 		bounds.Height = maxSecondary + margins.VNear + margins.VFar
 
-		if layoutItems, err = boxLayoutItems(widgets, Horizontal, bounds, margins, l.spacing, l.hwnd2StretchFactor); err != nil {
+		if layoutItems, err = boxLayoutItems(widgets, Horizontal, l.alignment, bounds, margins, l.spacing, l.hwnd2StretchFactor); err != nil {
 			return err
 		}
 
diff --git a/gridlayout.go b/gridlayout.go
index 313c8e60..5a3032b9 100644
--- a/gridlayout.go
+++ b/gridlayout.go
@@ -33,6 +33,7 @@ type GridLayout struct {
 	container            Container
 	margins              Margins
 	spacing              int
+	alignment            Alignment2D
 	resetNeeded          bool
 	rowStretchFactors    []int
 	columnStretchFactors []int
@@ -102,6 +103,24 @@ func (l *GridLayout) SetSpacing(value int) error {
 	return nil
 }
 
+func (l *GridLayout) Alignment() Alignment2D {
+	return l.alignment
+}
+
+func (l *GridLayout) SetAlignment(alignment Alignment2D) error {
+	if alignment != l.alignment {
+		if alignment < AlignHVDefault || alignment > AlignHFarVFar {
+			return newError("invalid Alignment value")
+		}
+
+		l.alignment = alignment
+
+		l.Update(false)
+	}
+
+	return nil
+}
+
 func (l *GridLayout) sufficientStretchFactors(stretchFactors []int, required int) []int {
 	oldLen := len(stretchFactors)
 	if oldLen < required {
@@ -595,8 +614,11 @@ func (l *GridLayout) Update(reset bool) error {
 			}
 		}
 
-		w := l.spannedWidth(info, widths)
-		h := l.spannedHeight(info, heights)
+		width := l.spannedWidth(info, widths)
+		height := l.spannedHeight(info, heights)
+
+		w := width
+		h := height
 
 		if lf := widget.LayoutFlags(); lf&GrowableHorz == 0 || lf&GrowableVert == 0 {
 			s := widget.SizeHint()
@@ -616,6 +638,26 @@ func (l *GridLayout) Update(reset bool) error {
 			}
 		}
 
+		if w != width {
+			switch l.alignment {
+			case AlignHCenterVNear, AlignHCenterVCenter, AlignHCenterVFar:
+				x += (width - w) / 2
+
+			case AlignHFarVNear, AlignHFarVCenter, AlignHFarVFar:
+				x += width - w
+			}
+		}
+
+		if h != height {
+			switch l.alignment {
+			case AlignHNearVCenter, AlignHCenterVCenter, AlignHFarVCenter:
+				y += (height - h) / 2
+
+			case AlignHNearVFar, AlignHCenterVFar, AlignHFarVFar:
+				y += height - h
+			}
+		}
+
 		items = append(items, layoutResultItem{widget: widget, bounds: Rectangle{X: x, Y: y, Width: w, Height: h}})
 	}