Initial multi monitor HIDPI support

16 files changed, 275 insertions, 141 deletions

diff --git a/boxlayout.go b/boxlayout.go
index 0c261726..96d8afd2 100644
--- a/boxlayout.go
+++ b/boxlayout.go
@@ -26,7 +26,7 @@ type BoxLayout struct {
 	orientation        Orientation
 	alignment          Alignment2D
 	hwnd2StretchFactor map[win.HWND]int
-	size2MinSize       map[Size]Size
+	sizeAndDPI2MinSize map[sizeAndDPI]Size
 	resetNeeded        bool
 }
 
@@ -34,7 +34,7 @@ func newBoxLayout(orientation Orientation) *BoxLayout {
 	return &BoxLayout{
 		orientation:        orientation,
 		hwnd2StretchFactor: make(map[win.HWND]int),
-		size2MinSize:       make(map[Size]Size),
+		sizeAndDPI2MinSize: make(map[sizeAndDPI]Size),
 		margins:            Margins{9, 9, 9, 9},
 		spacing:            6,
 	}
@@ -243,18 +243,24 @@ func (l *BoxLayout) MinSizeForSize(size Size) Size {
 		return Size{}
 	}
 
-	if min, ok := l.size2MinSize[size]; ok {
+	dpi := l.container.DPI()
+
+	if min, ok := l.sizeAndDPI2MinSize[sizeAndDPI{size, dpi}]; ok {
 		return min
 	}
 
 	bounds := Rectangle{Width: size.Width, Height: size.Height}
 
-	items, err := boxLayoutItems(widgetsToLayout(l.Container().Children()), l.orientation, l.alignment, bounds, l.margins, l.spacing, l.hwnd2StretchFactor)
+	wb := l.container.AsWindowBase()
+	margins := wb.marginsFrom96DPI(l.margins)
+	spacing := wb.intFrom96DPI(l.spacing)
+
+	items, err := boxLayoutItems(widgetsToLayout(l.Container().Children()), l.orientation, l.alignment, bounds, margins, spacing, l.hwnd2StretchFactor)
 	if err != nil {
 		return Size{}
 	}
 
-	s := Size{l.margins.HNear + l.margins.HFar, l.margins.VNear + l.margins.VFar}
+	s := Size{margins.HNear + margins.HFar, margins.VNear + margins.VFar}
 
 	var maxSecondary int
 
@@ -280,15 +286,15 @@ func (l *BoxLayout) MinSizeForSize(size Size) Size {
 	}
 
 	if l.orientation == Horizontal {
-		s.Width += (len(items) - 1) * l.spacing
+		s.Width += (len(items) - 1) * spacing
 		s.Height += maxSecondary
 	} else {
-		s.Height += (len(items) - 1) * l.spacing
+		s.Height += (len(items) - 1) * spacing
 		s.Width += maxSecondary
 	}
 
 	if s.Width > 0 && s.Height > 0 {
-		l.size2MinSize[size] = s
+		l.sizeAndDPI2MinSize[sizeAndDPI{size, dpi}] = s
 	}
 
 	return s
@@ -299,7 +305,7 @@ func (l *BoxLayout) Update(reset bool) error {
 		return nil
 	}
 
-	l.size2MinSize = make(map[Size]Size)
+	l.sizeAndDPI2MinSize = make(map[sizeAndDPI]Size)
 
 	if reset {
 		l.resetNeeded = true
@@ -321,12 +327,16 @@ func (l *BoxLayout) Update(reset bool) error {
 
 	ifContainerIsScrollViewDoCoolSpecialLayoutStuff(l)
 
-	items, err := boxLayoutItems(widgetsToLayout(l.Container().Children()), l.orientation, l.alignment, l.container.ClientBounds(), l.margins, l.spacing, l.hwnd2StretchFactor)
+	items, err := boxLayoutItems(widgetsToLayout(l.Container().Children()), l.orientation, l.alignment, l.container.ClientBounds(), l.container.AsWindowBase().marginsFrom96DPI(l.margins), l.container.AsWindowBase().intFrom96DPI(l.spacing), l.hwnd2StretchFactor)
 	if err != nil {
 		return err
 	}
 
-	return applyLayoutResults(l.container, items)
+	if err := applyLayoutResults(l.container, items); err != nil {
+		return err
+	}
+
+	return nil
 }
 
 func boxLayoutFlags(orientation Orientation, children *WidgetList) LayoutFlags {
diff --git a/button.go b/button.go
index 53c07f74..83dac2c7 100644
--- a/button.go
+++ b/button.go
@@ -9,6 +9,7 @@ package walk
 import (
 	"fmt"
 	"strconv"
+	"unsafe"
 
 	"github.com/lxn/win"
 )
@@ -85,6 +86,14 @@ func (b *Button) init() {
 		b.textChangedPublisher.Event()))
 }
 
+func (b *Button) MinSizeHint() Size {
+	var s win.SIZE
+
+	b.SendMessage(win.BCM_GETIDEALSIZE, 0, uintptr(unsafe.Pointer(&s)))
+
+	return maxSize(Size{int(s.CX), int(s.CY)}, b.dialogBaseUnitsToPixels(Size{50, 14}))
+}
+
 func (b *Button) Image() Image {
 	return b.image
 }
diff --git a/canvas.go b/canvas.go
index 872bec7e..ef7709a5 100644
--- a/canvas.go
+++ b/canvas.go
@@ -101,7 +101,9 @@ func newCanvasFromHWND(hwnd win.HWND) (*Canvas, error) {
 		return nil, newError("GetDC failed")
 	}
 
-	return (&Canvas{hdc: hdc, hwnd: hwnd}).init()
+	dpi := int(win.GetDpiForWindow(hwnd))
+
+	return (&Canvas{hdc: hdc, hwnd: hwnd, dpix: dpi, dpiy: dpi}).init()
 }
 
 func newCanvasFromHDC(hdc win.HDC) (*Canvas, error) {
@@ -113,8 +115,10 @@ func newCanvasFromHDC(hdc win.HDC) (*Canvas, error) {
 }
 
 func (c *Canvas) init() (*Canvas, error) {
-	c.dpix = int(win.GetDeviceCaps(c.hdc, win.LOGPIXELSX))
-	c.dpiy = int(win.GetDeviceCaps(c.hdc, win.LOGPIXELSY))
+	if c.dpix == 0 || c.dpiy == 0 {
+		c.dpix = int(win.GetDeviceCaps(c.hdc, win.LOGPIXELSX))
+		c.dpiy = int(win.GetDeviceCaps(c.hdc, win.LOGPIXELSY))
+	}
 
 	if win.SetBkMode(c.hdc, win.TRANSPARENT) == 0 {
 		return nil, newError("SetBkMode failed")
diff --git a/checkbox.go b/checkbox.go
index 778ecbbe..dbfc3a76 100644
--- a/checkbox.go
+++ b/checkbox.go
@@ -8,7 +8,6 @@ package walk
 
 import (
 	"strconv"
-	"syscall"
 
 	"github.com/lxn/win"
 )
@@ -65,39 +64,6 @@ func (*CheckBox) LayoutFlags() LayoutFlags {
 	return 0
 }
 
-func (cb *CheckBox) MinSizeHint() Size {
-	if checkBoxCheckSize.Width == 0 {
-		if win.IsAppThemed() {
-			hTheme := win.OpenThemeData(cb.hWnd, syscall.StringToUTF16Ptr("Button"))
-			defer win.CloseThemeData(hTheme)
-
-			hdc := win.GetDC(cb.hWnd)
-			defer win.ReleaseDC(cb.hWnd, hdc)
-
-			var s win.SIZE
-			if win.S_OK == win.GetThemePartSize(hTheme, hdc, win.BP_CHECKBOX, win.CBS_UNCHECKEDNORMAL, nil, win.TS_TRUE, &s) {
-				checkBoxCheckSize.Width = int(s.CX)
-				checkBoxCheckSize.Height = int(s.CY)
-			}
-		} else {
-			checkBoxCheckSize.Width = 12
-			checkBoxCheckSize.Height = 12
-		}
-	}
-
-	if cb.Text() == "" {
-		return checkBoxCheckSize
-	}
-
-	defaultSize := cb.dialogBaseUnitsToPixels(Size{50, 10})
-	textSize := cb.calculateTextSizeImpl("n" + cb.text())
-
-	w := textSize.Width + checkBoxCheckSize.Width
-	h := maxi(defaultSize.Height, textSize.Height)
-
-	return Size{w, h}
-}
-
 func (cb *CheckBox) SizeHint() Size {
 	return cb.MinSizeHint()
 }
diff --git a/combobox.go b/combobox.go
index 0548d30b..ff70d7f5 100644
--- a/combobox.go
+++ b/combobox.go
@@ -244,7 +244,7 @@ func (cb *ComboBox) MinSizeHint() Size {
 	}
 
 	// FIXME: Use GetThemePartSize instead of guessing
-	w := maxi(defaultSize.Width, cb.maxItemTextWidth+30)
+	w := maxi(defaultSize.Width, cb.maxItemTextWidth+int(win.GetSystemMetricsForDpi(win.SM_CXVSCROLL, uint32(cb.DPI())))+8)
 	h := defaultSize.Height + 1
 
 	return Size{w, h}
@@ -542,7 +542,7 @@ func (cb *ComboBox) calculateMaxItemTextWidth() int {
 	}
 	defer win.ReleaseDC(cb.hWnd, hdc)
 
-	hFontOld := win.SelectObject(hdc, win.HGDIOBJ(cb.Font().handleForDPI(0)))
+	hFontOld := win.SelectObject(hdc, win.HGDIOBJ(cb.Font().handleForDPI(cb.DPI())))
 	defer win.SelectObject(hdc, hFontOld)
 
 	var maxWidth int
diff --git a/container.go b/container.go
index 4af7f28c..b94bccda 100644
--- a/container.go
+++ b/container.go
@@ -100,6 +100,11 @@ type Layout interface {
 	Update(reset bool) error
 }
 
+type sizeAndDPI struct {
+	size Size
+	dpi  int
+}
+
 type HeightForWidther interface {
 	HeightForWidth(width int) int
 }
diff --git a/flowlayout.go b/flowlayout.go
index 1cf2ec4e..e5c79cce 100644
--- a/flowlayout.go
+++ b/flowlayout.go
@@ -14,7 +14,7 @@ type FlowLayout struct {
 	container          Container
 	hwnd2StretchFactor map[win.HWND]int
 	margins            Margins
-	size2MinSize       map[Size]Size
+	sizeAndDPI2MinSize map[sizeAndDPI]Size
 	spacing            int
 	alignment          Alignment2D
 	resetNeeded        bool
@@ -32,7 +32,7 @@ type flowLayoutSectionItem struct {
 }
 
 func NewFlowLayout() *FlowLayout {
-	return &FlowLayout{size2MinSize: make(map[Size]Size)}
+	return &FlowLayout{sizeAndDPI2MinSize: make(map[sizeAndDPI]Size)}
 }
 
 func (l *FlowLayout) Container() Container {
@@ -163,7 +163,9 @@ func (l *FlowLayout) MinSizeForSize(size Size) Size {
 		return Size{}
 	}
 
-	if min, ok := l.size2MinSize[size]; ok {
+	dpi := l.container.DPI()
+
+	if min, ok := l.sizeAndDPI2MinSize[sizeAndDPI{size, dpi}]; ok {
 		return min
 	}
 
@@ -174,6 +176,9 @@ func (l *FlowLayout) MinSizeForSize(size Size) Size {
 	var s Size
 	var maxPrimary int
 
+	wb := l.container.AsWindowBase()
+	spacing := wb.intFrom96DPI(l.spacing)
+
 	for i, section := range sections {
 		var widgets []Widget
 		var sectionMinWidth int
@@ -182,12 +187,12 @@ func (l *FlowLayout) MinSizeForSize(size Size) Size {
 
 			sectionMinWidth += item.minSize.Width
 		}
-		sectionMinWidth += (len(section.items) - 1) * l.spacing
+		sectionMinWidth += (len(section.items) - 1) * spacing
 		maxPrimary = maxi(maxPrimary, sectionMinWidth)
 
 		bounds.Height = section.secondaryMinSize
 
-		margins := l.margins
+		margins := wb.marginsFrom96DPI(l.margins)
 		if i > 0 {
 			margins.VNear = 0
 		}
@@ -195,7 +200,8 @@ func (l *FlowLayout) MinSizeForSize(size Size) Size {
 			margins.VFar = 0
 		}
 
-		layoutItems, err := boxLayoutItems(widgets, Horizontal, l.alignment, bounds, margins, l.spacing, l.hwnd2StretchFactor)
+
+		layoutItems, err := boxLayoutItems(widgets, Horizontal, l.alignment, bounds, margins, spacing, l.hwnd2StretchFactor)
 		if err != nil {
 			return Size{}
 		}
@@ -216,16 +222,16 @@ func (l *FlowLayout) MinSizeForSize(size Size) Size {
 
 		s.Height += maxSecondary
 
-		bounds.Y += maxSecondary + l.spacing
+		bounds.Y += maxSecondary + spacing
 	}
 
 	s.Width = maxPrimary
 
-	s.Width += l.margins.HNear + l.margins.HFar
-	s.Height += l.margins.VNear + l.margins.VFar + (len(sections)-1)*l.spacing
+	s.Width += wb.intFrom96DPI(l.margins.HNear + l.margins.HFar)
+	s.Height += wb.intFrom96DPI(l.margins.VNear + l.margins.VFar + (len(sections)-1)*l.spacing)
 
 	if s.Width > 0 && s.Height > 0 {
-		l.size2MinSize[size] = s
+		l.sizeAndDPI2MinSize[sizeAndDPI{size, dpi}] = s
 	}
 
 	return s
@@ -236,7 +242,7 @@ func (l *FlowLayout) Update(reset bool) error {
 		return nil
 	}
 
-	l.size2MinSize = make(map[Size]Size)
+	l.sizeAndDPI2MinSize = make(map[sizeAndDPI]Size)
 
 	if reset {
 		l.resetNeeded = true
@@ -261,6 +267,8 @@ func (l *FlowLayout) Update(reset bool) error {
 	bounds := l.container.ClientBounds()
 	sections := l.sectionsForPrimarySize(bounds.Width)
 
+	wb := l.container.AsWindowBase()
+
 	for i, section := range sections {
 		var widgets []Widget
 		for _, item := range section.items {
@@ -269,7 +277,7 @@ func (l *FlowLayout) Update(reset bool) error {
 
 		bounds.Height = section.secondaryMinSize
 
-		margins := l.margins
+		margins := wb.marginsFrom96DPI(l.margins)
 		if i > 0 {
 			margins.VNear = 0
 		}
@@ -277,7 +285,9 @@ func (l *FlowLayout) Update(reset bool) error {
 			margins.VFar = 0
 		}
 
-		layoutItems, err := boxLayoutItems(widgets, Horizontal, l.alignment, bounds, margins, l.spacing, l.hwnd2StretchFactor)
+		spacing := wb.intFrom96DPI(l.spacing)
+
+		layoutItems, err := boxLayoutItems(widgets, Horizontal, l.alignment, bounds, margins, spacing, l.hwnd2StretchFactor)
 		if err != nil {
 			return err
 		}
@@ -296,7 +306,7 @@ func (l *FlowLayout) Update(reset bool) error {
 
 		bounds.Height = maxSecondary + margins.VNear + margins.VFar
 
-		if layoutItems, err = boxLayoutItems(widgets, Horizontal, l.alignment, bounds, margins, l.spacing, l.hwnd2StretchFactor); err != nil {
+		if layoutItems, err = boxLayoutItems(widgets, Horizontal, l.alignment, bounds, margins, spacing, l.hwnd2StretchFactor); err != nil {
 			return err
 		}
 
@@ -304,7 +314,7 @@ func (l *FlowLayout) Update(reset bool) error {
 			return err
 		}
 
-		bounds.Y += bounds.Height + l.spacing
+		bounds.Y += bounds.Height + spacing
 	}
 
 	return nil
@@ -316,14 +326,17 @@ func (l *FlowLayout) sectionsForPrimarySize(primarySize int) []flowLayoutSection
 
 	var sections []flowLayoutSection
 
+	margins := l.container.AsWindowBase().marginsFrom96DPI(l.margins)
+	spacing := l.container.AsWindowBase().intFrom96DPI(l.spacing)
+
 	section := flowLayoutSection{
-		primarySpaceLeft: primarySize - l.margins.HNear - l.margins.HFar,
+		primarySpaceLeft: primarySize - margins.HNear - margins.HFar,
 	}
 
 	addSection := func() {
 		sections = append(sections, section)
 		section.items = nil
-		section.primarySpaceLeft = primarySize - l.margins.HNear - l.margins.HFar
+		section.primarySpaceLeft = primarySize - margins.HNear - margins.HFar
 		section.secondaryMinSize = 0
 	}
 
@@ -341,7 +354,7 @@ func (l *FlowLayout) sectionsForPrimarySize(primarySize int) []flowLayoutSection
 		addItem := func() {
 			section.items = append(section.items, item)
 			if len(section.items) > 1 {
-				section.primarySpaceLeft -= l.spacing
+				section.primarySpaceLeft -= spacing
 			}
 			section.primarySpaceLeft -= item.minSize.Width
 
@@ -351,7 +364,7 @@ func (l *FlowLayout) sectionsForPrimarySize(primarySize int) []flowLayoutSection
 		if section.primarySpaceLeft < item.minSize.Width && len(section.items) == 0 {
 			addItem()
 			addSection()
-		} else if section.primarySpaceLeft < l.spacing+item.minSize.Width && len(section.items) > 0 {
+		} else if section.primarySpaceLeft < spacing+item.minSize.Width && len(section.items) > 0 {
 			addSection()
 			addItem()
 		} else {
@@ -364,8 +377,8 @@ func (l *FlowLayout) sectionsForPrimarySize(primarySize int) []flowLayoutSection
 	}
 
 	if len(sections) > 0 {
-		sections[0].secondaryMinSize += l.margins.VNear
-		sections[len(sections)-1].secondaryMinSize += l.margins.VFar
+		sections[0].secondaryMinSize += margins.VNear
+		sections[len(sections)-1].secondaryMinSize += margins.VFar
 	}
 
 	return sections
diff --git a/form.go b/form.go
index 6b7e3e0c..ba4cdda2 100644
--- a/form.go
+++ b/form.go
@@ -683,8 +683,8 @@ func (fb *FormBase) WndProc(hwnd win.HWND, msg uint32, wParam, lParam uintptr) u
 		}
 
 		mmi.PtMinTrackSize = win.POINT{
-			int32(maxi(min.Width, fb.minSize.Width)),
-			int32(maxi(min.Height, fb.minSize.Height)),
+			int32(fb.intFrom96DPI(maxi(min.Width, fb.minSize.Width))),
+			int32(fb.intFrom96DPI(maxi(min.Height, fb.minSize.Height))),
 		}
 		return 0
 
@@ -704,6 +704,16 @@ func (fb *FormBase) WndProc(hwnd win.HWND, msg uint32, wParam, lParam uintptr) u
 	case win.WM_SIZE:
 		fb.clientComposite.SetBounds(fb.window.ClientBounds())
 
+	case win.WM_DPICHANGED:
+		wasSuspended := fb.Suspended()
+		fb.SetSuspended(true)
+		defer fb.SetSuspended(wasSuspended)
+
+		rc := (*win.RECT)(unsafe.Pointer(lParam))
+		fb.window.SetBounds(rectangleFromRECT(*rc))
+
+		fb.applyFont(fb.Font())
+
 	case win.WM_SYSCOMMAND:
 		if wParam == win.SC_CLOSE {
 			fb.closeReason = CloseReasonUser
diff --git a/gridlayout.go b/gridlayout.go
index a4e1a826..82938c81 100644
--- a/gridlayout.go
+++ b/gridlayout.go
@@ -34,18 +34,18 @@ type GridLayout struct {
 	margins              Margins
 	spacing              int
 	alignment            Alignment2D
-	resetNeeded          bool
 	rowStretchFactors    []int
 	columnStretchFactors []int
 	widgetBase2Info      map[*WidgetBase]*gridLayoutWidgetInfo
 	cells                [][]gridLayoutCell
-	size2MinSize         map[Size]Size
+	sizeAndDPI2MinSize   map[sizeAndDPI]Size
+	resetNeeded          bool
 }
 
 func NewGridLayout() *GridLayout {
 	l := &GridLayout{
-		widgetBase2Info: make(map[*WidgetBase]*gridLayoutWidgetInfo),
-		size2MinSize:    make(map[Size]Size),
+		widgetBase2Info:    make(map[*WidgetBase]*gridLayoutWidgetInfo),
+		sizeAndDPI2MinSize: make(map[sizeAndDPI]Size),
 	}
 
 	return l
@@ -397,7 +397,9 @@ func (l *GridLayout) MinSizeForSize(size Size) Size {
 		return Size{}
 	}
 
-	if min, ok := l.size2MinSize[size]; ok {
+	dpi := l.container.DPI()
+
+	if min, ok := l.sizeAndDPI2MinSize[sizeAndDPI{size, dpi}]; ok {
 		return min
 	}
 
@@ -465,13 +467,17 @@ func (l *GridLayout) MinSizeForSize(size Size) Size {
 		heights[row] = maxHeight
 	}
 
-	width := l.margins.HNear + l.margins.HFar
-	height := l.margins.VNear + l.margins.VFar
+	margins := l.container.AsWindowBase().marginsFrom96DPI(l.margins)
+
+	width := margins.HNear + margins.HFar
+	height := margins.VNear + margins.VFar
+
+	spacing := l.container.AsWindowBase().intFrom96DPI(l.spacing)
 
 	for i, w := range ws {
 		if w > 0 {
 			if i > 0 {
-				width += l.spacing
+				width += spacing
 			}
 			width += w
 		}
@@ -479,14 +485,14 @@ func (l *GridLayout) MinSizeForSize(size Size) Size {
 	for i, h := range heights {
 		if h > 0 {
 			if i > 0 {
-				height += l.spacing
+				height += spacing
 			}
 			height += h
 		}
 	}
 
 	if width > 0 && height > 0 {
-		l.size2MinSize[size] = Size{width, height}
+		l.sizeAndDPI2MinSize[sizeAndDPI{size, dpi}] = Size{width, height}
 	}
 
 	return Size{width, height}
@@ -494,12 +500,13 @@ func (l *GridLayout) MinSizeForSize(size Size) Size {
 
 func (l *GridLayout) spannedWidth(info *gridLayoutWidgetInfo, widths []int) int {
 	width := 0
+	spacing := l.container.AsWindowBase().intFrom96DPI(l.spacing)
 
 	for i := info.cell.column; i < info.cell.column+info.spanHorz; i++ {
 		if w := widths[i]; w > 0 {
 			width += w
 			if i > info.cell.column {
-				width += l.spacing
+				width += spacing
 			}
 		}
 	}
@@ -509,12 +516,13 @@ func (l *GridLayout) spannedWidth(info *gridLayoutWidgetInfo, widths []int) int
 
 func (l *GridLayout) spannedHeight(info *gridLayoutWidgetInfo, heights []int) int {
 	height := 0
+	spacing := l.container.AsWindowBase().intFrom96DPI(l.spacing)
 
 	for i := info.cell.row; i < info.cell.row+info.spanVert; i++ {
 		if h := heights[i]; h > 0 {
 			height += h
 			if i > info.cell.row {
-				height += l.spacing
+				height += spacing
 			}
 		}
 	}
@@ -564,7 +572,7 @@ func (l *GridLayout) Update(reset bool) error {
 		return nil
 	}
 
-	l.size2MinSize = make(map[Size]Size)
+	l.sizeAndDPI2MinSize = make(map[sizeAndDPI]Size)
 
 	if reset {
 		l.resetNeeded = true
@@ -593,6 +601,9 @@ func (l *GridLayout) Update(reset bool) error {
 
 	items := make([]layoutResultItem, 0, len(l.widgetBase2Info))
 
+	margins := l.container.AsWindowBase().marginsFrom96DPI(l.margins)
+	spacing := l.container.AsWindowBase().intFrom96DPI(l.spacing)
+
 	for wb, info := range l.widgetBase2Info {
 		widget := wb.window.(Widget)
 
@@ -600,17 +611,17 @@ func (l *GridLayout) Update(reset bool) error {
 			continue
 		}
 
-		x := l.margins.HNear
+		x := margins.HNear
 		for i := 0; i < info.cell.column; i++ {
 			if w := widths[i]; w > 0 {
-				x += w + l.spacing
+				x += w + spacing
 			}
 		}
 
-		y := l.margins.VNear
+		y := margins.VNear
 		for i := 0; i < info.cell.row; i++ {
 			if h := heights[i]; h > 0 {
-				y += h + l.spacing
+				y += h + spacing
 			}
 		}
 
@@ -666,7 +677,11 @@ func (l *GridLayout) Update(reset bool) error {
 		items = append(items, layoutResultItem{widget: widget, bounds: Rectangle{X: x, Y: y, Width: w, Height: h}})
 	}
 
-	return applyLayoutResults(l.container, items)
+	if err := applyLayoutResults(l.container, items); err != nil {
+		return err
+	}
+
+	return nil
 }
 
 func (l *GridLayout) sectionSizesForSpace(orientation Orientation, space int, widths []int) []int {
@@ -785,20 +800,24 @@ func (l *GridLayout) sectionSizesForSpace(orientation Orientation, space int, wi
 
 	sort.Stable(sortedSections)
 
+	margins := l.container.AsWindowBase().marginsFrom96DPI(l.margins)
+
 	if orientation == Horizontal {
-		space -= l.margins.HNear + l.margins.HFar
+		space -= margins.HNear + margins.HFar
 	} else {
-		space -= l.margins.VNear + l.margins.VFar
+		space -= margins.VNear + margins.VFar
 	}
 
+	spacing := l.container.AsWindowBase().intFrom96DPI(l.spacing)
+
 	var spacingRemaining int
 	for _, max := range maxSizes {
 		if max > 0 {
-			spacingRemaining += l.spacing
+			spacingRemaining += spacing
 		}
 	}
 	if spacingRemaining > 0 {
-		spacingRemaining -= l.spacing
+		spacingRemaining -= spacing
 	}
 
 	offsets := [3]int{0, sectionCountWithGreedyNonSpacer, sectionCountWithGreedyNonSpacer + sectionCountWithGreedySpacer}
@@ -832,8 +851,8 @@ func (l *GridLayout) sectionSizesForSpace(orientation Orientation, space int, wi
 			minSizesRemaining -= min
 			stretchFactorsRemaining -= stretch
 
-			space -= (size + l.spacing)
-			spacingRemaining -= l.spacing
+			space -= (size + spacing)
+			spacingRemaining -= spacing
 		}
 	}
 
diff --git a/lineedit.go b/lineedit.go
index da4c1251..7016bdc7 100644
--- a/lineedit.go
+++ b/lineedit.go
@@ -270,7 +270,6 @@ func (le *LineEdit) sizeHintForLimit(limit int) (size Size) {
 }
 
 func (le *LineEdit) initCharWidth() {
-
 	font := le.Font()
 	if font == le.charWidthFont {
 		return
@@ -285,7 +284,7 @@ func (le *LineEdit) initCharWidth() {
 	}
 	defer win.ReleaseDC(le.hWnd, hdc)
 
-	defer win.SelectObject(hdc, win.SelectObject(hdc, win.HGDIOBJ(font.handleForDPI(0))))
+	defer win.SelectObject(hdc, win.SelectObject(hdc, win.HGDIOBJ(font.handleForDPI(le.DPI()))))
 
 	buf := []uint16{'M'}
 
diff --git a/pushbutton.go b/pushbutton.go
index 088dbe4e..f16c21cd 100644
--- a/pushbutton.go
+++ b/pushbutton.go
@@ -7,10 +7,6 @@
 package walk
 
 import (
-	"unsafe"
-)
-
-import (
 	"github.com/lxn/win"
 )
 
@@ -42,14 +38,6 @@ func (*PushButton) LayoutFlags() LayoutFlags {
 	return GrowableHorz
 }
 
-func (pb *PushButton) MinSizeHint() Size {
-	var s win.SIZE
-
-	pb.SendMessage(win.BCM_GETIDEALSIZE, 0, uintptr(unsafe.Pointer(&s)))
-
-	return maxSize(Size{int(s.CX), int(s.CY)}, pb.dialogBaseUnitsToPixels(Size{50, 14}))
-}
-
 func (pb *PushButton) SizeHint() Size {
 	return pb.MinSizeHint()
 }
diff --git a/radiobutton.go b/radiobutton.go
index 3fb36dc2..59947b5e 100644
--- a/radiobutton.go
+++ b/radiobutton.go
@@ -97,17 +97,6 @@ func (*RadioButton) LayoutFlags() LayoutFlags {
 	return 0
 }
 
-func (rb *RadioButton) MinSizeHint() Size {
-	defaultSize := rb.dialogBaseUnitsToPixels(Size{50, 10})
-	textSize := rb.calculateTextSizeImpl("n" + rb.text())
-
-	// FIXME: Use GetThemePartSize instead of GetSystemMetrics?
-	w := textSize.Width + int(win.GetSystemMetrics(win.SM_CXMENUCHECK))
-	h := maxi(defaultSize.Height, textSize.Height)
-
-	return Size{w, h}
-}
-
 func (rb *RadioButton) SizeHint() Size {
 	return rb.MinSizeHint()
 }
diff --git a/tableview.go b/tableview.go
index d7140990..e84ec667 100644
--- a/tableview.go
+++ b/tableview.go
@@ -366,7 +366,7 @@ func (tv *TableView) applyEnabled(enabled bool) {
 func (tv *TableView) applyFont(font *Font) {
 	tv.WidgetBase.applyFont(font)
 
-	hFont := uintptr(font.handleForDPI(0))
+	hFont := uintptr(font.handleForDPI(tv.DPI()))
 
 	win.SendMessage(tv.hwndFrozenLV, win.WM_SETFONT, hFont, 0)
 	win.SendMessage(tv.hwndNormalLV, win.WM_SETFONT, hFont, 0)
diff --git a/toolbar.go b/toolbar.go
index 8d5f735c..82570646 100644
--- a/toolbar.go
+++ b/toolbar.go
@@ -124,6 +124,15 @@ func (tb *ToolBar) SizeHint() Size {
 
 	return Size{width, height}
 }
+
+func (tb *ToolBar) applyFont(font *Font) {
+	tb.WidgetBase.applyFont(font)
+
+	tb.applyDefaultButtonWidth()
+
+	tb.updateParentLayout()
+}
+
 func (tb *ToolBar) Orientation() Orientation {
 	style := win.GetWindowLong(tb.hWnd, win.GWL_STYLE)
 
@@ -143,8 +152,9 @@ func (tb *ToolBar) applyDefaultButtonWidth() error {
 		return nil
 	}
 
-	lParam := uintptr(
-		win.MAKELONG(uint16(tb.defaultButtonWidth), uint16(tb.defaultButtonWidth)))
+	width := tb.intFrom96DPI(tb.defaultButtonWidth)
+
+	lParam := uintptr(win.MAKELONG(uint16(width), uint16(width)))
 	if 0 == tb.SendMessage(win.TB_SETBUTTONWIDTH, 0, lParam) {
 		return newError("SendMessage(TB_SETBUTTONWIDTH)")
 	}
diff --git a/widget.go b/widget.go
index 13b76b90..e67e90bd 100644
--- a/widget.go
+++ b/widget.go
@@ -470,20 +470,20 @@ func (wb *WidgetBase) updateParentLayoutWithReset(reset bool) error {
 
 	layout := parent.Layout()
 
-	var size2MinSize map[Size]Size
+	var sizeAndDPI2MinSize map[sizeAndDPI]Size
 	switch l := layout.(type) {
 	case *BoxLayout:
-		size2MinSize = l.size2MinSize
+		sizeAndDPI2MinSize = l.sizeAndDPI2MinSize
 
 	case *GridLayout:
-		size2MinSize = l.size2MinSize
+		sizeAndDPI2MinSize = l.sizeAndDPI2MinSize
 
 	case *FlowLayout:
-		size2MinSize = l.size2MinSize
+		sizeAndDPI2MinSize = l.sizeAndDPI2MinSize
 	}
-	if size2MinSize != nil {
-		for k := range size2MinSize {
-			delete(size2MinSize, k)
+	if sizeAndDPI2MinSize != nil {
+		for k := range sizeAndDPI2MinSize {
+			delete(sizeAndDPI2MinSize, k)
 		}
 	}
 
diff --git a/window.go b/window.go
index 9f030a07..b15b79a1 100644
--- a/window.go
+++ b/window.go
@@ -86,6 +86,9 @@ type Window interface {
 	// of.
 	Disposing() *Event
 
+	// DPI returns the current DPI value of the Window.
+	DPI() int
+
 	// Enabled returns if the Window is enabled for user interaction.
 	Enabled() bool
 
@@ -292,6 +295,7 @@ type calcTextSizeInfo struct {
 	font  fontInfo
 	text  string
 	size  Size
+	dpi   int
 }
 
 // WindowBase implements many operations common to all Windows.
@@ -776,6 +780,87 @@ func (wb *WindowBase) SetDoubleBuffering(enabled bool) error {
 	return wb.ensureExtendedStyleBits(win.WS_EX_COMPOSITED, enabled)
 }
 
+// DPI returns the current DPI value of the WindowBase.
+func (wb *WindowBase) DPI() int {
+	return int(win.GetDpiForWindow(wb.hWnd))
+}
+
+func (wb *WindowBase) intFrom96DPI(value int) int {
+	return wb.scaleInt(value, float64(wb.DPI()) / 96.0)
+}
+
+func (wb *WindowBase) intTo96DPI(value int) int {
+	return wb.scaleInt(value, 96.0 / float64(wb.DPI()))
+}
+
+func (wb *WindowBase) scaleInt(value int, scale float64) int {
+	return int(float64(value) * scale)
+}
+
+func (wb *WindowBase) marginsFrom96DPI(value Margins) Margins {
+	return wb.scaleMargins(value, float64(wb.DPI()) / 96.0)
+}
+
+func (wb *WindowBase) marginsTo96DPI(value Margins) Margins {
+	return wb.scaleMargins(value, 96.0 / float64(wb.DPI()))
+}
+
+func (wb *WindowBase) scaleMargins(value Margins, scale float64) Margins {
+	return Margins{
+		HNear: int(float64(value.HNear) * scale),
+		VNear: int(float64(value.VNear) * scale),
+		HFar: int(float64(value.HFar) * scale),
+		VFar: int(float64(value.VFar) * scale),
+	}
+}
+
+func (wb *WindowBase) pointFrom96DPI(value Point) Point {
+	return wb.scalePoint(value, float64(wb.DPI()) / 96.0)
+}
+
+func (wb *WindowBase) pointTo96DPI(value Point) Point {
+	return wb.scalePoint(value, 96.0 / float64(wb.DPI()))
+}
+
+func (wb *WindowBase) scalePoint(value Point, scale float64) Point {
+	return Point{
+		X: int(float64(value.X) * scale),
+		Y: int(float64(value.Y) * scale),
+	}
+}
+
+func (wb *WindowBase) rectangleFrom96DPI(value Rectangle) Rectangle {
+	return wb.scaleRectangle(value, float64(wb.DPI()) / 96.0)
+}
+
+func (wb *WindowBase) rectangleTo96DPI(value Rectangle) Rectangle {
+	return wb.scaleRectangle(value, 96.0 / float64(wb.DPI()))
+}
+
+func (wb *WindowBase) scaleRectangle(value Rectangle, scale float64) Rectangle {
+	return Rectangle{
+		X: int(float64(value.X) * scale),
+		Y: int(float64(value.Y) * scale),
+		Width: int(float64(value.Width) * scale),
+		Height: int(float64(value.Height) * scale),
+	}
+}
+
+func (wb *WindowBase) sizeFrom96DPI(value Size) Size {
+	return wb.scaleSize(value, float64(wb.DPI()) / 96.0)
+}
+
+func (wb *WindowBase) sizeTo96DPI(value Size) Size {
+	return wb.scaleSize(value, 96.0 / float64(wb.DPI()))
+}
+
+func (wb *WindowBase) scaleSize(value Size, scale float64) Size {
+	return Size{
+		Width: int(float64(value.Width) * scale),
+		Height: int(float64(value.Height) * scale),
+	}
+}
+
 // Enabled returns if the *WindowBase is enabled for user interaction.
 func (wb *WindowBase) Enabled() bool {
 	return wb.enabled
@@ -845,11 +930,19 @@ func (wb *WindowBase) applyFont(font *Font) {
 }
 
 func SetWindowFont(hwnd win.HWND, font *Font) {
-	win.SendMessage(hwnd, win.WM_SETFONT, uintptr(font.handleForDPI(0)), 1)
+	setWindowFont(hwnd, font)
 }
 
 func setWindowFont(hwnd win.HWND, font *Font) {
-	win.SendMessage(hwnd, win.WM_SETFONT, uintptr(font.handleForDPI(0)), 1)
+	dpi := int(win.GetDpiForWindow(hwnd))
+
+	win.SendMessage(hwnd, win.WM_SETFONT, uintptr(font.handleForDPI(dpi)), 1)
+
+	if window := windowFromHandle(hwnd); window != nil {
+		if widget, ok := window.(Widget); ok {
+			widget.AsWidgetBase().updateParentLayoutWithReset(false)
+		}
+	}
 }
 
 // Suspended returns if the *WindowBase is suspended for layout and repainting
@@ -1119,24 +1212,35 @@ func (wb *WindowBase) SetMinMaxSize(min, max Size) error {
 	return nil
 }
 
+type fontInfoAndDPI struct {
+	fontInfo
+	dpi int
+}
+
 var (
 	dialogBaseUnitsUTF16StringPtr = syscall.StringToUTF16Ptr("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz")
-	fontInfo2DialogBaseUnits      = make(map[fontInfo]Size)
+	fontInfoAndDPI2DialogBaseUnits      = make(map[fontInfoAndDPI]Size)
 )
 
 func (wb *WindowBase) dialogBaseUnits() Size {
 	// The window may use a font different from that in WindowBase,
 	// like e.g. NumberEdit does, so we try to use the right one.
 	font := wb.window.Font()
-	fi := fontInfo{family: font.Family(), pointSize: font.PointSize(), style: font.Style()}
-	if s, ok := fontInfo2DialogBaseUnits[fi]; ok {
+	fi := fontInfoAndDPI{
+		fontInfo: fontInfo{
+			family: font.Family(),
+			pointSize: font.PointSize(), 
+			style: font.Style(), 
+		},
+		dpi: wb.DPI()}
+	if s, ok := fontInfoAndDPI2DialogBaseUnits[fi]; ok {
 		return s
 	}
 
 	hdc := win.GetDC(wb.hWnd)
 	defer win.ReleaseDC(wb.hWnd, hdc)
 
-	hFont := font.handleForDPI(0)
+	hFont := font.handleForDPI(wb.DPI())
 	hFontOld := win.SelectObject(hdc, win.HGDIOBJ(hFont))
 	defer win.SelectObject(hdc, win.HGDIOBJ(hFontOld))
 
@@ -1156,7 +1260,7 @@ func (wb *WindowBase) dialogBaseUnits() Size {
 
 	s := Size{int((size.CX/26 + 1) / 2), int(tm.TmHeight)}
 
-	fontInfo2DialogBaseUnits[fi] = s
+	fontInfoAndDPI2DialogBaseUnits[fi] = s
 
 	return s
 }
@@ -1177,15 +1281,22 @@ func (wb *WindowBase) calculateTextSizeImpl(text string) Size {
 func (wb *WindowBase) calculateTextSizeImplForWidth(text string, width int) Size {
 	font := wb.window.Font()
 
+	dpi := wb.DPI()
+
 	if wb.calcTextSizeInfoPrev != nil &&
 		width == wb.calcTextSizeInfoPrev.width &&
 		font.family == wb.calcTextSizeInfoPrev.font.family &&
 		font.pointSize == wb.calcTextSizeInfoPrev.font.pointSize &&
 		font.style == wb.calcTextSizeInfoPrev.font.style &&
-		text == wb.calcTextSizeInfoPrev.text {
+		text == wb.calcTextSizeInfoPrev.text &&
+		dpi == wb.calcTextSizeInfoPrev.dpi {
 		return wb.calcTextSizeInfoPrev.size
 	}
 
+	if wb.calcTextSizeInfoPrev != nil && dpi != wb.calcTextSizeInfoPrev.dpi {
+		width = int(float64(width) * float64(dpi) / float64(wb.calcTextSizeInfoPrev.dpi))
+	}
+
 	var size Size
 	if width > 0 {
 		canvas, err := wb.CreateCanvas()
@@ -1208,7 +1319,7 @@ func (wb *WindowBase) calculateTextSizeImplForWidth(text string, width int) Size
 		}
 		defer win.ReleaseDC(wb.hWnd, hdc)
 
-		hFontOld := win.SelectObject(hdc, win.HGDIOBJ(font.handleForDPI(0)))
+		hFontOld := win.SelectObject(hdc, win.HGDIOBJ(font.handleForDPI(dpi)))
 		defer win.SelectObject(hdc, hFontOld)
 
 		lines := strings.Split(text, "\n")
@@ -1237,6 +1348,7 @@ func (wb *WindowBase) calculateTextSizeImplForWidth(text string, width int) Size
 	wb.calcTextSizeInfoPrev.font.style = font.style
 	wb.calcTextSizeInfoPrev.text = text
 	wb.calcTextSizeInfoPrev.size = size
+	wb.calcTextSizeInfoPrev.dpi = dpi
 
 	return size
 }