How to paint 2 gradients together on a Canvas?

Question

Please look at this sample gradient image I did with a Paint program:

It c

Answer 1

Delphi 2005 and up:

Use GradientFillCanvas from the GraphUtil unit:

procedure TForm1.FormPaint(Sender: TObject);
var
  R: TRect;
begin
  SetRect(R, 0, 0, ClientWidth, ClientHeight div 2);
  GradientFillCanvas(Canvas, clWhite, $00056AFF, R, gdVertical);
  SetRect(R, 0, ClientHeight div 2, ClientWidth, ClientHeight); 
  GradientFillCanvas(Canvas, $000055FF, clWhite, R, gdVertical);
end;

---

Earlier Delphi versions:

Use GradientFill from Msimg32.dll. Add the following code to a global utilities unit:

type
  PTriVertex = ^TTriVertex;
  TTriVertex = record
    X, Y: DWORD;
    Red, Green, Blue, Alpha: WORD;
  end;

function GradientFill(DC: HDC; Vertex: PTriVertex; NumVertex: ULONG;
  Mesh: Pointer; NumMesh, Mode: ULONG): BOOL; stdcall; overload;
  external msimg32 name 'GradientFill';

function GradientFill(DC: HDC; const ARect: TRect; StartColor,
  EndColor: TColor; Vertical: Boolean): Boolean; overload;
const
  Modes: array[Boolean] of ULONG = (GRADIENT_FILL_RECT_H, GRADIENT_FILL_RECT_V);
var
  Vertices: array[0..1] of TTriVertex;
  GRect: TGradientRect;
begin
  Vertices[0].X := ARect.Left;
  Vertices[0].Y := ARect.Top;
  Vertices[0].Red := GetRValue(ColorToRGB(StartColor)) shl 8;
  Vertices[0].Green := GetGValue(ColorToRGB(StartColor)) shl 8;
  Vertices[0].Blue := GetBValue(ColorToRGB(StartColor)) shl 8;
  Vertices[0].Alpha := 0;
  Vertices[1].X := ARect.Right;
  Vertices[1].Y := ARect.Bottom;
  Vertices[1].Red := GetRValue(ColorToRGB(EndColor)) shl 8;
  Vertices[1].Green := GetGValue(ColorToRGB(EndColor)) shl 8;
  Vertices[1].Blue := GetBValue(ColorToRGB(EndColor)) shl 8;
  Vertices[1].Alpha := 0;
  GRect.UpperLeft := 0;
  GRect.LowerRight := 1;
  Result := GradientFill(DC, @Vertices, 2, @GRect, 1, Modes[Vertical]);
end;

Now, the painting code becomes:

procedure TForm1.FormPaint(Sender: TObject);
var
  R: TRect;
begin
  SetRect(R, 0, 0, ClientWidth, ClientHeight div 2);
  GradientFill(Canvas.Handle, R, clWhite, $00056AFF, True);
  SetRect(R, 0, ClientHeight div 2, ClientWidth, ClientHeight); 
  GradientFill(Canvas.Handle, R, $000055FF, clWhite, True);
end;

procedure TForm1.FormResize(Sender: TObject);
begin
  Invalidate;
end;