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Image with round corner - Graphics32

Posted on 2010-09-14
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Last Modified: 2013-11-22
I would like to know the best way to create smooth round corners in one image (with different radius; from small up to half width/height) and make this corner transparent.

I found one procedure to draw a rectangle with rounded corners from Kieran Foster (December 7th, 2007), but as explained I need to cut the corners from image in a way that they are smooth and with a rounded shape. The part removed to create the round corner should be transparent.
Thx
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Question by:andrefm
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Expert Comment

by:epasquier
ID: 33671219
On which kind of canvas do you want to draw ?
In a Timage ? a custom component ? Maybe the form itself ?

I ask this because of the "transparency" which is not achieved the same way in all cases. Forms shapes, for example, can have transparent zones thanks to "regions" that are cut out from the normal form rectangle.
For images, it is merely a specific color that is stated as the transparent color, so it is just a matter of painting the outside of the rounded corner with that color.
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Accepted Solution

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epasquier earned 500 total points
ID: 33671535
Here is an example with TImage :
put a TImage and trackbar. The trackbar have a Min property of 0, and a Max of 100. It will change the percentage of the width/height taken by the rounded corners. 0 = perfect rectangle, 100=ellipse

Add the following code to draw a rounded rectangle, fill it with white, and the corners are transparent (filled with a constant color that is not likely going to be used for the drawing.
To better view the transparency, add a Timage with a loaded image and set it behind the first TImage


type
  TForm1 = class(TForm)
    trckbr1: TTrackBar;
    img1: TImage;
    img2: TImage;
    procedure FormCreate(Sender: TObject);
    procedure trckbr1Change(Sender: TObject);
  private
    procedure PaintCorner;
  public

var
  Form1: TForm1;

implementation

Const
 clTransp=$111213; // transparent color

procedure TForm1.FormCreate(Sender: TObject);
begin
 img1.Picture.Bitmap:=TBitmap.Create;
 img1.Picture.Bitmap.Width:=img1.Width;
 img1.Picture.Bitmap.Height:=img1.Height;
 img1.Picture.Bitmap.TransparentColor:=clTransp;
 img1.Transparent:=True;
 PaintCorner;
end;


procedure TForm1.trckbr1Change(Sender: TObject);
begin
 PaintCorner;
end;

procedure TForm1.PaintCorner;
Var
 W,H,RW,RH:Integer;
begin
 With img1.Picture.Bitmap,Canvas do
  begin
   Pen.Color:=clRed;
   Brush.Color:=clTransp;
   FillRect(ClipRect);
   RW:=Width-1;
   RH:=Height-1;
   W:=Width*trckbr1.Position Div 200;
   H:=Height*trckbr1.Position Div 200;
   Arc(0,0,2*W,2*H,W,0,0,H+1);
   MoveTo(W,0);
   LineTo(RW-W,0);
   Arc(RW,0,RW-2*W,2*H,RW,H,RW-W-1,0);
   MoveTo(RW,H);
   LineTo(RW,RH-H);
   Arc(RW,RH-2*H,RW-2*W,RH,RW-W,RH,RW,RH-H-1);
   MoveTo(W,RH);
   LineTo(RW-W,RH);
   Arc(0,RH,2*W,RH-2*H,0,RH-H,W+2,RH);
   MoveTo(0,H);
   LineTo(0,RH-H);
   Brush.Color:=clWhite;
   FloodFill(RW Div 2, RH Div 2,clRed, fsBorder);
  end;
end;

end.

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Author Closing Comment

by:andrefm
ID: 33688675
Expected solution using Graphics32, but could easily adapt.
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