ImageEn, unit imageenview




property OnDrawLayer: TIEDrawLayerExEvent;


Occurs immediately after a layer is painted.

Parameter Description
Dest The destination bitmap (usually the back buffer)
LayerIndex The layer index that we are drawing
DestRect Specifies the rectangle where the layer will be drawn on Dest (same as Layers[].ClientAreaBox)

Note: With TImageEnView.OnDrawLayer, Dest is the entire image the layer has been painted to. With OnBeforeDrawLayer, Dest is only the layer as an image

ImageEnView Paint Events

The main paint events of TImageEnView are OnDrawBackBuffer which occurs when the back buffer is painted and OnDrawCanvas which occurs every time the canvas is painted. Generally OnDrawBackBuffer is used for better performance, because the back buffer painting only occurs after the content is updated. If you need constant custom drawing (e.g. to draw a marker at the current cursor position) then use OnDrawCanvas.

In layer applications, OnBeforeDrawLayer and OnDrawLayer will occur while painting each individual layer. Use these methods if you need easy custom drawing upon each individual layer (e.g. a layer title). Generally OnBeforeDrawLayer is best, unless you need to paint to the whole image (i.e. outside the area of the layer).

Other drawing events:
 OnDrawBackground occurs when the background (area behind the image is painted) is painted to allow custom background styling
 OnDrawLayerBox occurs when the box around a layer is painted to allow custom styling of the box
 OnDrawLayerGrip occurs when the grips of the selected layer are drawn to allow custom grip styling
 OnTransitionPaint occurs while transitioning from one image to the next
 OnPaint notifies whenever there is a paint event. It is not used for custom drawing
 OnDrawPolygon notifies whenever a point of a polygonal selection is drawn


Demo  Demos\LayerEditing\Layers_CustomDraw\LayersDraw.dpr


// Display the index over the layer
procedure Tfmain.ImageEnView1DrawLayer(Sender: TObject; Dest: TIEBitmap; LayerIndex: Integer; DestRect: TRect);
  txtRect: TRect;
  txtRect := Rect( DestRect.Left + 10, DestRect.Top + 10, DestRect.Left + 40, DestRect.Top + 40 );
  with Dest.Canvas do
    // Simple example: Would be better to center text in filled rect
    Brush.Color := clBlue;
    FillRect( aRect );

    Font.Color  := clWhite;
    Font.Height := 12;
    Font.Style  := [fsBold];

    TextRect( txtRect, DestRect.Left + 20, DestRect.Top + 20, IntToStr( LayerIndex ));