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Overview

TeeTree provides built-in support for zooming and scrolling, allowing users to navigate large tree structures efficiently. You can control zoom levels programmatically and configure scrolling behavior.

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Zooming

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Set Zoom Level

Control the zoom level using the View3DOptions.Zoom property: 
// Set zoom to 150% (1.5x magnification)
Tree1.View3DOptions.Zoom := 150;

// Set zoom to 50% (0.5x reduction)
Tree1.View3DOptions.Zoom := 50;

// Reset to 100% (normal size)
Tree1.View3DOptions.Zoom := 100;

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Zoom with TrackBar

Create an interactive zoom control: 
procedure TForm1.TrackBarZoomChange(Sender: TObject);
begin
  // Change zoom based on trackbar position
  Tree1.View3DOptions.Zoom := TrackBarZoom.Position;
  
  // Display current zoom percentage
  LabelZoom.Caption := IntToStr(Tree1.View3DOptions.Zoom) + '%';
  
  // Enable/disable reset button
  ButtonReset.Enabled := TrackBarZoom.Position <> 100;
end;

​
Reset Zoom and View

procedure TForm1.ButtonResetClick(Sender: TObject);
begin
  // Reset to default view
  TrackBarZoom.Position := 100;
  Tree1.View3DOptions.Zoom := 100;
  Tree1.View3DOptions.HorizOffset := 0;
  Tree1.View3DOptions.VertOffset := 0;
end;

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OnZoom Event

Respond to zoom changes: 
procedure TForm1.Tree1Zoom(Sender: TObject);
begin
  // Update UI to reflect zoom change
  LabelZoom.Caption := IntToStr(Tree1.View3DOptions.Zoom) + '%';
  TrackBarZoom.Position := Tree1.View3DOptions.Zoom;
  ButtonReset.Enabled := Tree1.View3DOptions.Zoom <> 100;
end;

​
Centered Zooming

Control whether zooming is centered on the current view: 
// Enable centered zooming (zoom in/out from center)
Tree1.ZoomCentered := True;

// Disable centered zooming (zoom from top-left)
Tree1.ZoomCentered := False;

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Allow/Disallow Zooming

// Enable zoom functionality
Tree1.Zoom.Allow := True;

// Disable zoom functionality
Tree1.Zoom.Allow := False;

​
Scrolling (Panning)

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Enable Scrolling

Configure scrolling direction: 
// Enable horizontal scrolling only
Tree1.AllowPanning := pmHorizontal;

// Enable vertical scrolling only
Tree1.AllowPanning := pmVertical;

// Enable both horizontal and vertical scrolling
Tree1.AllowPanning := pmBoth;

// Disable scrolling
Tree1.AllowPanning := pmNone;

​
Set Scroll Mouse Button

Specify which mouse button activates scrolling: 
// Use left mouse button for scrolling
Tree1.ScrollMouseButton := mbLeft;

// Use middle mouse button for scrolling
Tree1.ScrollMouseButton := mbMiddle;

// Use right mouse button for scrolling
Tree1.ScrollMouseButton := mbRight;

​
OnScroll Event

Respond to scrolling changes: 
procedure TForm1.Tree1Scroll(Sender: TObject);
begin
  // Display current scroll position
  LabelScroll.Caption := Format(
    'Scroll: H=%d, V=%d',
    [Tree1.View3DOptions.HorizOffset, Tree1.View3DOptions.VertOffset]
  );
end;

​
Programmatic Scrolling

Set scroll position directly: 
// Scroll horizontally
Tree1.View3DOptions.HorizOffset := 100;

// Scroll vertically
Tree1.View3DOptions.VertOffset := 50;

// Reset scroll position
Tree1.View3DOptions.HorizOffset := 0;
Tree1.View3DOptions.VertOffset := 0;

​
Complete Zooming Example

Here’s a complete example with zoom controls: 
type
  TZoomingForm = class(TForm)
    Tree1: TTree;
    TrackBarZoom: TTrackBar;
    ButtonReset: TButton;
    LabelZoom: TLabel;
    CheckBoxCentered: TCheckBox;
    procedure FormCreate(Sender: TObject);
    procedure TrackBarZoomChange(Sender: TObject);
    procedure ButtonResetClick(Sender: TObject);
    procedure Tree1Zoom(Sender: TObject);
    procedure CheckBoxCenteredClick(Sender: TObject);
  private
    ChangingZoom: Boolean;
  end;

procedure TZoomingForm.FormCreate(Sender: TObject);
begin
  // Create sample tree structure
  with Tree1.Add('Root') do
  begin
    AddChild('Child 1');
    AddChild('Child 2').AddChild('Grandchild');
    AddChild('Child 3');
    Expanded := True;
  end;

  // Initialize zoom controls
  TrackBarZoom.Min := 10;   // 10% minimum
  TrackBarZoom.Max := 300;  // 300% maximum
  TrackBarZoom.Position := 100;
  
  LabelZoom.Caption := '100%';
  ButtonReset.Enabled := False;
end;

procedure TZoomingForm.TrackBarZoomChange(Sender: TObject);
begin
  ChangingZoom := True;

  // Change zoom
  Tree1.View3DOptions.Zoom := TrackBarZoom.Position;
  LabelZoom.Caption := IntToStr(Tree1.View3DOptions.Zoom) + '%';

  // Enable or disable reset button
  ButtonReset.Enabled := TrackBarZoom.Position <> 100;

  ChangingZoom := False;
end;

procedure TZoomingForm.ButtonResetClick(Sender: TObject);
begin
  // Reset default view
  TrackBarZoom.Position := 100;
  Tree1.View3DOptions.Zoom := 100;
  Tree1.View3DOptions.HorizOffset := 0;
  Tree1.View3DOptions.VertOffset := 0;

  Tree1Zoom(Sender);  // Trigger OnZoom event
end;

procedure TZoomingForm.Tree1Zoom(Sender: TObject);
begin
  if not ChangingZoom then
  begin
    // Update UI when zoom changes externally
    LabelZoom.Caption := IntToStr(Tree1.View3DOptions.Zoom) + '%';
    TrackBarZoom.Position := Tree1.View3DOptions.Zoom;
    ButtonReset.Enabled := TrackBarZoom.Position <> 100;
  end;
end;

procedure TZoomingForm.CheckBoxCenteredClick(Sender: TObject);
begin
  Tree1.ZoomCentered := CheckBoxCentered.Checked;
end;

​
Complete Scrolling Example

Here’s a complete example with scroll controls: 
type
  TScrollingForm = class(TForm)
    Tree1: TTree;
    CheckBoxScrolling: TCheckBox;
    ComboBoxDirection: TComboBox;
    ComboBoxButton: TComboBox;
    LabelStatus: TLabel;
    procedure FormCreate(Sender: TObject);
    procedure Tree1Scroll(Sender: TObject);
    procedure CheckBoxScrollingClick(Sender: TObject);
    procedure ComboBoxDirectionChange(Sender: TObject);
    procedure ComboBoxButtonChange(Sender: TObject);
  end;

procedure TScrollingForm.FormCreate(Sender: TObject);
begin
  // Create sample nodes
  Tree1.Add('Node 1');
  Tree1.Add('Node 2');
  Tree1.Add('Node 3');
  Tree1.Add('Node 4');
  Tree1.Add('Node 5');

  // Disable zoom to focus on scrolling
  Tree1.Zoom.Allow := False;

  // Setup direction combo
  ComboBoxDirection.Items.Add('Horizontal');
  ComboBoxDirection.Items.Add('Vertical');
  ComboBoxDirection.Items.Add('Both');
  ComboBoxDirection.ItemIndex := 2;

  // Setup mouse button combo
  ComboBoxButton.Items.Add('Left');
  ComboBoxButton.Items.Add('Middle');
  ComboBoxButton.Items.Add('Right');
  ComboBoxButton.ItemIndex := 2;  // Right button

  // Enable scrolling
  Tree1.AllowPanning := pmBoth;
  Tree1.ScrollMouseButton := mbRight;
end;

procedure TScrollingForm.Tree1Scroll(Sender: TObject);
begin
  // Event called when tree is scrolled
  LabelStatus.Caption := Format(
    'Horizontal: %d, Vertical: %d',
    [Tree1.View3DOptions.HorizOffset, Tree1.View3DOptions.VertOffset]
  );
end;

procedure TScrollingForm.CheckBoxScrollingClick(Sender: TObject);
begin
  ComboBoxDirection.Enabled := CheckBoxScrolling.Checked;

  if CheckBoxScrolling.Checked then
  begin
    case ComboBoxDirection.ItemIndex of
      0: Tree1.AllowPanning := pmHorizontal;
      1: Tree1.AllowPanning := pmVertical;
      2: Tree1.AllowPanning := pmBoth;
    end;
  end
  else
    Tree1.AllowPanning := pmNone;  // Disable scrolling
end;

procedure TScrollingForm.ComboBoxDirectionChange(Sender: TObject);
begin
  // Change scrolling direction
  case ComboBoxDirection.ItemIndex of
    0: Tree1.AllowPanning := pmHorizontal;
    1: Tree1.AllowPanning := pmVertical;
    2: Tree1.AllowPanning := pmBoth;
  end;
end;

procedure TScrollingForm.ComboBoxButtonChange(Sender: TObject);
begin
  // Change scrolling mouse button
  case ComboBoxButton.ItemIndex of
    0: Tree1.ScrollMouseButton := mbLeft;
    1: Tree1.ScrollMouseButton := mbMiddle;
    2: Tree1.ScrollMouseButton := mbRight;
  end;
end;

​
Mouse Wheel Support

TeeTree automatically supports mouse wheel scrolling. Configure it with: 
// Enable mouse wheel for vertical scrolling
Tree1.MouseWheelScrolling := True;

​
Key Points

  • Use View3DOptions.Zoom to control zoom level (percentage)
  • Use ZoomCentered to control zoom behavior
  • Use AllowPanning to enable/disable scrolling
  • Use ScrollMouseButton to specify which button activates scrolling
  • Use OnZoom and OnScroll events to update UI
  • Use View3DOptions.HorizOffset and VertOffset for programmatic scrolling
  • Disable Zoom.Allow to prevent users from zooming
  • Mouse wheel scrolling is supported automatically
  • Reset view by setting zoom to 100 and offsets to 0

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