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

I like to use class helpers on TCanvas so I revised the code in the other answer.

type
  TTriVertex = record
  public
    type
      P = ^TTriVertex;
  public
    X, Y: DWORD;
    Red, Green, Blue, Alpha: WORD;
    constructor Create(APoint: TPoint; AColor: TColor; AAlpha: Word = 0);
  end;

  TTriVertexRect = record
  public
    TopLeft: TTriVertex;
    LowerRight: TTriVertex;
    constructor Create(ARect: TRect; Color1,Color2; AAlpha1: Word = 0; AAlpha2: Word = 0);
  end;
 {Enumerate the constants so they will show up on alt space in the IDE}
 TGradientFillType = (
     gftRectH = GRADIENT_FILL_RECT_H
    ,gftRectV = GRADIENT_FILL_RECT_V
    ,gftTriangle = GRADIENT_FILL_TRIANGLE);

 TCavas_Helper = class helper for TCanvas
  public
    function GradientFill(const Vertexes: array of TTriVertexRect; FillType: TGradientFillType): Boolean; overload;
  end;

{ TTriVertex }

constructor TTriVertex.Create(APoint: TPoint; AColor: TColor; AAlpha: Word = 0);
begin
  X := APoint.X;
  Y := APoint.Y;
  Red := GetRValue(ColorToRGB(AColor)) SHL 8;
  Green := GetGValue(ColorToRGB(AColor)) SHL 8;
  Blue := GetBValue(ColorToRGB(AColor)) SHL 8;
  Alpha := 0;
end;

{ TTriVertexRect }

constructor TTriVertexRect.Create(ARect: TRect; Color1, Color2: TColor; AAlpha1,
  AAlpha2: Word);
begin
  TopLeft.Create(ARect.TopLeft,Color1,AAlpha1);
  LowerRight.Create(ARect.BottomRight,Color2,AAlpha2);
end;

{ TCavas_Helper }

function TCavas_Helper.GradientFill(const Vertexes: array of TTriVertexRect; FillType: TGradientFillType): Boolean;
var
  GRect: array of TGradientRect;
  Index: Integer;
begin
  SetLength(GRect,Length(Vertexes));
  for Index := 0 to Length(GRect) do begin
    GRect[Index].UpperLeft := Index*2;
    GRect[Index].LowerRight := Index*2 + 1;
  end;
  Result := WIndows.GradientFill(Handle,@Vertexes[0],Length(Vertexes)*2,@GRect[0],Length(GRect),Ord(FillType))
end;

So the actual call looks like this

procedure TForm56.FormPaint(Sender: TObject);
begin
  Canvas.GradientFill([
      TTriVertexRect.Create(Rect(0,0,ClientWidth,ClientHeight DIV 2),clWhite,$00056AFF)
     ,TTriVertexRect.Create(Rect(0,ClientHeight DIV 2,ClientWidth,ClientHeight),$00056AFF,clWhite)
    ],gftRectV);
end;

Sample: