This one create color gradient white to yellow. But this one has more features than previous example.

     You can select the gradient color and direction to fill.

         This is the main procedure doing entire color gradient according to selected colors and direction.

procedure TForm1.Update(Sender: TObject);
Var
   Xo, Yo, Max, RC, GC, BC, R, H, W : Integer;
   Angle, Radius, XStep, YStep, RStep, GStep, BStep : Real;
   Red, Green, Blue, Red1, Green1, Blue1,
   Red2, Green2, Blue2 : Integer;
begin
   { Get form size }
   H:=Image1.Height;
   W:=Image1.Width;

   { Set pen width }
   Image1.Canvas.Pen.Width:=1;

   { Set Max count }
   Case ComboBox1.ItemIndex Of
      0:Max:=H;
      1:Max:=W;
      2:Begin
            Max:=Round(Sqrt((W+1)*(W+1)+(H+1)*(H+1)))+110;
            Image1.Canvas.Pen.Width:=2;

            { Set diagonal step size }
            If H>W Then
            Begin
               XStep:=1.0;
               YStep:=2*H/Max;
            End Else
            Begin
               YStep:=1.0;
               XStep:=2*W/Max;
            End;
         End;
      3:Begin
            Max:=360*4;
            Image1.Canvas.Pen.Width:=2;

            { Set circle coodinates }
            Xo:=W Div 2;
            Yo:=H Div 2;
            Radius:=Round(Sqrt(Xo*Xo+Yo*Yo));
         End;
   End;

{ The GetRValue macro retrieves an intensity value for
the Red component of a 32-bit red, green, blue (RGB) value. }
Red1:=GetRValue(Shape1.Brush.Color);
{ The GetRValue macro retrieves an intensity value for
the Green component of a 32-bit red, green, blue (RGB) value. }
Green1:=GetGValue(Shape1.Brush.Color);
{ The GetRValue macro retrieves an intensity value for
the Blue component of a 32-bit red, green, blue (RGB) value. }
Blue1:=GetBValue(Shape1.Brush.Color);

Red2:=GetRValue(Shape2.Brush.Color);
Green2:=GetGValue(Shape2.Brush.Color);
Blue2:=GetBValue(Shape2.Brush.Color);

RStep:=(Red1-Red2)/Max;
GStep:=(Green1-Green2)/Max;
BStep:=(Blue1-Blue2)/Max;

{ Select starting color }
{ Call ColorToRGB to obtain an RGB representation
of a color for using with Windows API calls. }
If ColorToRGB(Shape1.Brush.Color)>ColorToRGB(Shape2.Brush.Color) Then
Begin
   Red:=Red1;
   Green:=Green1;
   Blue:=Blue1;
End Else
Begin
   Red:=Red2;
   Green:=Green2;
   Blue:=Blue2;
End;

{ Set starting color }
RC:=Red;
GC:=Green;
BC:=Blue;

Angle:=0;
For R:=0 To Max Do
Begin
{ set fill color }

{ The RGB macro selects a red, green, blue (RGB) color
based on the arguments supplied and the color capabilities
of the output device.

The intensity for each argument is in the range 0 through 255.
If all three intensities are zero, the result is black.
If all three intensities are 255, the result is white.}
Image1.Canvas.Pen.Color:=RGB(RC,GC,BC);

{ Fill area by drawing lines }
Case ComboBox1.ItemIndex Of
   0:Begin
         Image1.Canvas.MoveTo(0,R);
         Image1.Canvas.LineTo(W,R);
      End;
   1:Begin
         Image1.Canvas.MoveTo(R,0);
         Image1.Canvas.LineTo(R,H);
      End;
   2:Begin
         Image1.Canvas.MoveTo(0,Round(R*YStep));
         Image1.Canvas.LineTo(Round(R*XStep),0);
      End;
   3:Begin
         Image1.Canvas.MoveTo(Xo,Yo);   Image1.Canvas.LineTo(Xo+Round(Radius*Sin(Angle*(Pi/180))),
         Yo-Round(Radius*Cos(Angle*(Pi/180))));
      End;
End;

{ Change fill color for each color }
RC:=Round(Red+R*RStep);
GC:=Round(Green+R*GStep);
BC:=Round(Blue+R*BStep);

{ Increase angle }
Angle:=Angle+0.25;
End;
End;

 

 

     Use this one to select color by clicking on shape. And also this will call Update procedure and update color gradient.

procedure TForm1.Shape1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
     ColorDialog1.Color:=Shape1.Brush.Color;
     If ColorDialog1.Execute Then
     Begin
          Shape1.Brush.Color:=ColorDialog1.Color;
          Update(Self);
     End;
end;

procedure TForm1.Shape2MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
     ColorDialog1.Color:=Shape2.Brush.Color;
     If ColorDialog1.Execute Then
     Begin
          Shape2.Brush.Color:=ColorDialog1.Color;
          Update(Self);
     End;
end;

 

     Use this one to update color gradient if user changes direction.

procedure TForm1.ComboBox1Change(Sender: TObject);
begin
     Update(Self);
end;

 

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