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TSVGDocument.DrawBeforeElement(TSVGGraphicElement,TSVGCanvas,TSVGRect,Boolean) Method

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Draw the sibling svg elements (and their children) of the specified element (i.e., the elements that have the same parent but are before the specified element in the parent's Items property) to the specified canvas inside the specified rectangle.

The ancestors of the specified element are also drawn. The svg sibling elements are drawn where they would be if the entire SVG was drawn.

Namespace: RSSVG

Parameters

Element

Type: TSVGGraphicElement

Draw "older" siblings (and ancestors)of this element

Canvas

Type: System.Void

Canvas to draw on

aRect

Type: System.Void

Rectangle to draw within

IncludeElement

Type: Boolean

Draw element and its children as well

The following example uses the DrawBeforeElement, DrawElement, and DrawAfterElement methods to optimize the drawing of an svg where one element may be changed often (such as in an editor):

Delphi

procedure TfrmSVGEditor.PaintBox1Paint(Sender: TObject; Canvas: TCanvas);
var
   aRect: TSVGRect;
begin
   // do we need to update the background (elements before) and foreground (elements
   // after) the current Element.  By creating a bitmap of the background and
   // foreground, we can optimize the drawing of the SVG as the current Element
   // changes
   if UpdateBackground then
   begin
     // draw background and foreground
     Background.Canvas.BeginScene;
     try
       Background.Clear(TAlphaColorRec.Null);
       if Element is TSVGGraphicElement then
         SVG.DrawBeforeElement(TSVGGraphicElement(Element), Background.Canvas, RectF(0,0,Background.Width, Background.Height));
     finally
       Background.Canvas.EndScene;
     end;
     Foreground.Canvas.BeginScene;
     try
       Foreground.Clear(TAlphaColorRec.Null);
       if Element is TSVGGraphicElement then
         SVG.DrawAfterElement(TSVGGraphicElement(Element), Foreground.Canvas, RectF(0,0,Foreground.Width, Foreground.Height));
     finally
       Foreground.Canvas.EndScene;
     end;
     FUpdateBackground := False;
   end;
   if Element is TSVGGraphicElement then
   begin
     // if current Element is a graphical element, draw the background
     aRect := RectF(0, 0, Background.Width, Background.Height);
     Canvas.DrawBitmap(Background, aRect, aRect, 1);
     // draw the element
     SVG.DrawElement(TSVGGraphicElement(Element), Canvas, PaintBox1.ClipRect);
     // draw the foreground
     Canvas.DrawBitmap(Foreground, aRect, aRect, 1);
   end
   else
     // just draw the entire SVG without any background/foreground caching
     SVG.Draw(Canvas, PaintBox1.ClipRect);
   // draw the focus rectangle
   Canvas.DrawFocusRect(SelectRect);
end;

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TSVGDocument.DrawBeforeElement(TSVGGraphicElement,TSVGCanvas,TSVGRect,Boolean) Method

Reference