Merlin's Delphi Forge

In setup programs or sometimes in AboutBoxes you can find gradient forms.

It sure looks as if it were a lot of work but it’s really very easy. All you have to do is add this code to your program.
This example will create a gradient rectangle on the whole form Canvas. To change it’s size just change the parameters of the Rectangle() function.

Add this code to your form’s OnPaint event:

1) Constant number of steps:

const
  btN = 100; { Number of steps }
var
  iI: Integer;
  Col: TColor;
begin
  for iI := 0 to btN - 1 do
    with Canvas do begin
      Col := RGB(0, 0, Round(50 + 205 * (iI / btN)));
      Pen.Color := Col;
      Brush.Color := Col;
      Rectangle(0, Round(ClientHeight * (iI / btN)), ClientWidth, Round(ClientHeight * ((iI + 1) / btN)));
    end;
end;

To get rid of problems when resizing the form just add this code to the form’s OnResize event:

...
Invalidate;
...

2) It calculates the number of steps:

var
  wHeight, wRow: Word;
begin
  wHeight := (ClientHeight + 255) div 256;
  for Row := 0 to 255 do
    with Canvas do begin
      Brush.Color := RGB(wRow, 0, 0); { Modify this for a different color }
      FillRect(Rect(0, wRow * wHeight, ClientWidth, (wRow + 1) * wHeight)) ;
    end;
end;

3) Hacking our way around…
This function works in Delphi 3 but not in Delphi 4.

uses
  Charts;
...
  GradientFill(Canvas, ClientRect, clBlack, clBlue, False);
...