BGRABitmap tutorial 11

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This tutorial shows how to combine transformations.

Create a new project

Create a new project and add a reference to BGRABitmap, the same way as in the first tutorial.

Affine transformation of a radial gradient

Here is an affine transformation applied on a gradient like we did with textures :

uses BGRAGradientScanner, BGRATransform;   
 
procedure TForm1.FormPaint(Sender: TObject);
var image: TBGRABitmap;
    grad: TBGRAGradientScanner;
    affine: TBGRAAffineScannerTransform;
begin
  image := TBGRABitmap.Create(ClientWidth,ClientHeight, BGRABlack );
 
  grad := TBGRAGradientScanner.Create(BGRA(0,0,255),BGRAWhite,gtRadial,PointF(0,0),PointF(1,0),True,True);
 
  affine := TBGRAAffineScannerTransform.Create(grad);
  affine.Scale(150,80);
  affine.RotateDeg(-30);
  affine.Translate(ClientWidth/2, ClientHeight/2);
 
  image.Fill(affine);
 
  affine.free;
  grad.free;
 
  image.Draw(Canvas,0,0,True);
  image.free;
end;

The base gradient is radial, centered at origin (0,0), of radius 1.

The affine transformation does the following :

  • stretch the gradient to a size of 150x80
  • rotate 30 degrees in counterclockwise direction
  • center it in the form

The Fill instruction draws the result into the image.

Run the program

You should obtain a blue and white ellipse gradient.

BGRATutorial11a.png

Combine with a twirl

We can add another transformation to it like this :

var image: TBGRABitmap;
    grad: TBGRAGradientScanner;
    affine: TBGRAAffineScannerTransform;
    twirl: TBGRATwirlScanner;
begin
  image := TBGRABitmap.Create(ClientWidth,ClientHeight, BGRABlack );
 
  grad := TBGRAGradientScanner.Create(BGRA(0,0,255),BGRAWhite,gtRadial,PointF(0,0),PointF(1,0),True,True);
 
  affine := TBGRAAffineScannerTransform.Create(grad);
  affine.Scale(150,80);
  affine.RotateDeg(-30);
  affine.Translate(ClientWidth/2, ClientHeight/2);
 
  twirl := TBGRATwirlScanner.Create(affine,Point(ClientWidth div 2, ClientHeight div 2),100);
  image.Fill(twirl);
  twirl.Free;
 
  affine.free;
  grad.free;
 
  image.Draw(Canvas,0,0,True);
  image.free;
end;

Here, we simply create a twirl transformation applied to the previous one, and fill with it.

Run the program

Now the center of the gradient is twirled.

BGRATutorial11b.png

Use a custom scanner

We may want to create our own gradient generator. Here is for example a multiply gradient :

type
  { TBGRAMultiplyScanner }
 
  TBGRAMultiplyScanner = class(TBGRACustomScanner)
    function ScanAt(X, Y: Single): TBGRAPixel; override;
  end;
 
{ TBGRAMultiplyScanner }
 
function TBGRAMultiplyScanner.ScanAt(X, Y: Single): TBGRAPixel;
  function cycle512(value: integer): integer; inline;
  begin
    result := value and 511;
    if result >= 256 then result := 511-result;
  end;
 
var
  mul: integer;
begin
  mul := cycle512(round(x*y));
  result := BGRA(mul,mul,mul,255);
end;

It is derived from TBGRACustomScanner to be used for filling, and the ScanAt function is overridden. It computes the product of both coordinates and make a cycle of 512 with it (from 0 to 255 and then from 255 down to 0).

Let's draw it on the screen with a simple affine transformation :

var image: TBGRABitmap;
    grad: TBGRAMultiplyScanner;
    affine: TBGRAAffineScannerTransform;
begin
  image := TBGRABitmap.Create(ClientWidth,ClientHeight, BGRABlack );
 
  grad := TBGRAMultiplyScanner.Create;
  affine := TBGRAAffineScannerTransform.Create(grad);
  affine.Scale(6,4);
  affine.Translate(ClientWidth/2, ClientHeight/2);
  image.Fill(affine);
  affine.free;
  grad.free;
 
  image.Draw(Canvas,0,0,True);
  image.free;
end;

Run the program

It should look like this :

BGRATutorial11c.png

Make it beautiful

Add some colors by modifying the ScanAt procedure of the multiply gradient :

var
  mul: integer;
begin
  mul := round(x*y);
  result := BGRA(cycle512(round(x*10)),cycle512(mul),cycle512(round(y*10)),255);
end;

The red and blue intensities are filled with a cycle of x and y positions.

And add some rotation :

  affine := TBGRAAffineScannerTransform.Create(grad);
  affine.Scale(6,4);
  affine.RotateDeg(-30);
  affine.Translate(ClientWidth/2, ClientHeight/2);

BGRATutorial11d.png

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