TIEBitmap.RenderToCanvasWithAlpha

Declaration

procedure RenderToCanvasWithAlpha(Dest: TCanvas; xDst, yDst, dxDst, dyDst: integer; xSrc, ySrc, dxSrc, dySrc: integer; Transparency: integer = 255; Filter: TResampleFilter = rfNone; RenderOperation: TIERenderOperation = ielNormal; Opacity: double = 1.0);

Description

Draws the rectangle, xSrc, ySrc, dxSrc (width), dySrc (height), within the destination rectangle, xDst, yDst, dxDst (width), dyDst (height), of Dest TCanvas object.
Transparency specifies the transparency value (0=Fully Transparent to 255=Fully Opaque).
Filter the resampling filter.
RenderOperation the rendering operation.
Opacity specifies the opacity (0=Fully Transparent to 1.0=Fully Opaque).

This function reads the destination canvas pixels and merges them with image using the alpha channel mask, i.e. painting will not occur for pixels of < 255 in the AlphaChannel

Opacity vs Transparency

Both the Opacity and Transparency parameters provide the same functionality. Transparency is the traditional ImageEn value, whereas Opacity provides easier PSD compatibility.
While they can be used in combination, generally only one will be used, i.e. leave Opacity=1 and make use of transparency, or alternatively, leave Transparency=255 and make use of Opacity. For example, for 50% opacity: Transparency = 255 and Opacity = 0.5, or Transparency = 128 and Opacity = 1.0

Examples

// Draw aIEBitmap within aRect while maintaining the aspect ratio of the image
aRect := GetImageRectWithinArea( aIEBitmap.Width, aIEBitmap.Height, aRect );
aIEBitmap.RenderToCanvasWithAlpha( aCanvas, aRect.Left, aRect.Top, aRect.Right - aRect.Left, aRect.Bottom - aRect.Top, 0, 0, aIEBitmap.Width, aIEBitmap.Height, 255, rfFastLinear );

// Draw a transparent PNG onto a canvas
var
  bmp: TBitmap;
  ieb: TIEBitmap;
  aRect: TRect;
begin
  bmp := TBitmap.Create();
  ieb := TIEBitmap.Create();
  try
    bmp.LoadFromFile( 'D:\Background.bmp' );

    ieb.LoadFromFile( 'AlphaImage.png' );
    if ieb.HasAlphaChannel( True ) = False then
      raise Exception.create( 'Image has no alpha!' );

    // Calculate destination rect so PNG is centered on our background image
    aRect := GetImageRectWithinArea( ieb.Width, ieb.Height, Rect( 0, 0, bmp.Width, bmp.Height ));
    ieb.RenderToCanvasWithAlpha( bmp.Canvas,
                                 aRect.Left, aRect.Top, aRect.Right - aRect.Left, aRect.Bottom - aRect.Top,
                                 0, 0, ieb.Width, ieb.Height,
                                 255, rfFastLinear );
  finally
    bmp.Free;
    ieb.Free;
  end;
end;

See Also

◼DrawToCanvasWithAlpha
◼RenderToCanvas

TIEBitmap Assignment and Drawing Methods

TBitmap Methods

TCanvas Methods

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