How to draw TTreeView's styled selection rectangle during AdvancedCustomDrawItem? - delphi

Question

I'm doing custom TTreeView drawing from scratch using OnAdvancedCustomDrawItem event, and I wonder how to render these selection and hot rectangles correctly in the background of my owner-draw items? They are Vista/7 styled so I cannot simply fill the background in some solid color.
I tried to draw my items at cdPostPaint stage, but if I leave DefaultDraw := True atcdPrePaint stage to draw selection background, the complete default drawing occurs, including text of items.
procedure TForm1.TreeView1AdvancedCustomDrawItem(Sender: TCustomTreeView;
Node: TTreeNode; State: TCustomDrawState; Stage: TCustomDrawStage; var PaintImages,
DefaultDraw: Boolean);
begin
case Stage of
cdPreErase:
begin
DefaultDraw := True;
end;
cdPostErase:
begin
DefaultDraw := True;
end;
cdPrePaint:
begin
// I thought this will paint only the selected/hot backgrounds,
// however this will paint whole item, including text.
DefaultDraw := True;
end;
cdPostPaint:
begin
DefaultDraw := False;
// painting my owner-draw text
// .........
end;
end;
PaintImages := False;
end;

Answer 1

Here is my solution (tested).
Note the TreeView must have HotTrack := True to draw hot items normally.
There also must be additional drawing when themes not enabled.
uses
UxTheme,
Themes;
const
TreeExpanderSpacing = 6;
procedure TForm1.DrawExpander(ACanvas: TCanvas; ATextRect: TRect; AExpanded: Boolean;
AHot: Boolean);
var
ExpanderRect: TRect;
Graphics: IGPGraphics;
Points: array of TGPPoint;
Brush: IGPBrush;
Pen: IGPPen;
ThemeData: HTHEME;
ElementPart: Integer;
ElementState: Integer;
ExpanderSize: TSize;
UnthemedColor: TColor;
begin
if ThemeServices.ThemesEnabled then
begin
if AHot then
ElementPart := TVP_HOTGLYPH
else
ElementPart := TVP_GLYPH;
if AExpanded then
ElementState := GLPS_OPENED
else
ElementState := GLPS_CLOSED;
ThemeData := OpenThemeData(TreeView1.Handle, VSCLASS_TREEVIEW);
GetThemePartSize(ThemeData, ACanvas.Handle, ElementPart, ElementState, nil,
TS_TRUE, ExpanderSize);
ExpanderRect.Left := ATextRect.Left - TreeExpanderSpacing - ExpanderSize.cx;
ExpanderRect.Right := ExpanderRect.Left + ExpanderSize.cx;
ExpanderRect.Top := ATextRect.Top + (ATextRect.Bottom - ATextRect.Top - ExpanderSize.cy) div 2;
ExpanderRect.Bottom := ExpanderRect.Top + ExpanderSize.cy;
DrawThemeBackground(ThemeData, ACanvas.Handle, ElementPart, ElementState, ExpanderRect, nil);
CloseThemeData(ThemeData);
end
else
begin
// Drawing expander without themes enabled
Graphics := TGPGraphics.Create(ACanvas.Handle);
Graphics.SmoothingMode := SmoothingModeHighQuality;
ExpanderRect := ATextRect;
ExpanderRect.Right := ATextRect.Left - TDPIAware.GetScaledSize(TreeExpanderSpacing96dpi);
ExpanderRect.Left := ATextRect.Left - TDPIAware.GetScaledSize(TreeExpanderSpacing96dpi) -
TDPIAware.GetScaledSize(Max(TreeExpanderCollapsedWidth96dpi, TreeExpanderExpandedWidth96dpi));
if ASelected then
UnthemedColor := ColorToRGB(clHighlightText)
else
if AExpanded then
UnthemedColor := clBlack
else
UnthemedColor := clGray;
SetLength(Points, 3);
if AExpanded then
begin
Points[0] := TGPPoint.Create(ExpanderRect.Right, ExpanderRect.Top +
(ExpanderRect.Bottom - ExpanderRect.Top - TreeExpanderExpandedHeight96dpi) div 2);
Points[1] := TGPPoint.Create(ExpanderRect.Right, ExpanderRect.Top +
(ExpanderRect.Bottom - ExpanderRect.Top + TreeExpanderExpandedHeight96dpi) div 2);
Points[2] := TGPPoint.Create(ExpanderRect.Right - TreeExpanderExpandedWidth96dpi,
ExpanderRect.Top + (ExpanderRect.Bottom - ExpanderRect.Top +
TreeExpanderExpandedHeight96dpi) div 2);
Brush := TGPSolidBrush.Create(TGPColor.CreateFromColorRef(UnthemedColor));
Graphics.FillPolygon(Brush, Points);
end
else
begin
Points[0] := TGPPoint.Create(ExpanderRect.Right - TreeExpanderCollapsedWidth96dpi,
ExpanderRect.Top + (ExpanderRect.Bottom - ExpanderRect.Top -
TreeExpanderCollapsedHeight96dpi) div 2);
Points[1] := TGPPoint.Create(ExpanderRect.Right,
ExpanderRect.Top + (ExpanderRect.Bottom - ExpanderRect.Top) div 2);
Points[2] := TGPPoint.Create(ExpanderRect.Right - TreeExpanderCollapsedWidth96dpi,
ExpanderRect.Top + (ExpanderRect.Bottom - ExpanderRect.Top +
TreeExpanderCollapsedHeight96dpi) div 2);
Pen := TGPPen.Create(TGPColor.CreateFromColorRef(UnthemedColor));
Graphics.DrawPolygon(Pen, Points);
end;
end;
end;
procedure TForm1.TreeView1AdvancedCustomDrawItem(Sender: TCustomTreeView;
Node: TTreeNode; State: TCustomDrawState; Stage: TCustomDrawStage; var PaintImages,
DefaultDraw: Boolean);
var
NodeRect: TRect;
NodeTextRect: TRect;
Text: string;
ThemeData: HTHEME;
TreeItemState: Integer;
begin
if Stage = cdPrePaint then
begin
NodeRect := Node.DisplayRect(False);
NodeTextRect := Node.DisplayRect(True);
// Drawing background
if (cdsSelected in State) and Sender.Focused then
TreeItemState := TREIS_SELECTED
else
if (cdsSelected in State) and (cdsHot in State) then
TreeItemState := TREIS_HOTSELECTED
else
if cdsSelected in State then
TreeItemState := TREIS_SELECTEDNOTFOCUS
else
if cdsHot in State then
TreeItemState := TREIS_HOT
else
TreeItemState := TREEITEMStateFiller0;
if TreeItemState <> TREEITEMStateFiller0 then
begin
ThemeData := OpenThemeData(Sender.Handle, VSCLASS_TREEVIEW);
DrawThemeBackground(ThemeData, Sender.Canvas.Handle, TVP_TREEITEM, TreeItemState,
NodeRect, nil);
CloseThemeData(ThemeData);
end;
// Drawing expander
if Node.HasChildren then
DrawExpander(Sender.Canvas, NodeTextRect, Node.Expanded, cdsHot in State);
// Drawing main text
SetBkMode(Sender.Canvas.Handle, TRANSPARENT);
SetTextColor(Sender.Canvas.Handle, clBlue);
Text := Node.Text;
Sender.Canvas.TextRect(NodeTextRect, Text,
[tfVerticalCenter, tfSingleLine, tfEndEllipsis, tfLeft]);
// Some extended drawing...
end;
PaintImages := False;
DefaultDraw := False;
end;