Title: Drawing a Shaded Rectangle
Question: Using GradientFill API function
Answer:
The GradientFill function fills rectangle and triangle structures. To add smooth shading to a triangle, call the GradientFill function with the three triangle endpoints. GDI will linearly interpolate and fill the triangle.
To add smooth shading to a rectangle, call GradientFill with the upper-left and lower-right coordinates of the rectangle. There are two shading modes used when drawing a rectangle. In horizontal mode, the rectangle is shaded from left-to-right. In vertical mode, the rectangle is shaded from top-to-bottom. First, you need the GradientFill function declaration (Windows.pas contains wrong dectaration of GradientFill function):
type
TRIVERTEX = packed record
X, Y : DWORD;
Red, Green, Blue, Alpha : Word;
end;
function GradientFill(DC : hDC; pVertex : Pointer; dwNumVertex : DWORD;
pMesh : Pointer; dwNumMesh, dwMode: DWORD) : DWord; stdcall;
external 'msimg32.dll';
The following example shows a horizontal rectangle call.
procedure TForm1.Button1Click(Sender: TObject);
var
vert : array[0..1] of TRIVERTEX;
gRect : GRADIENT_RECT;
begin
vert [0] .x := 0;
vert [0] .y := 0;
vert [0] .Red := $0000;
vert [0] .Green := $0000;
vert [0] .Blue := $0000;
vert [0] .Alpha := $0000;
vert [1] .x := 100;
vert [1] .y := 32;
vert [1] .Red := $0000;
vert [1] .Green := $0000;
vert [1] .Blue := $ff00;
vert [1] .Alpha := $0000;
gRect.UpperLeft := 0;
gRect.LowerRight := 1;
GradientFill(Form1.Canvas.Handle, @vert,2,@gRect,1,GRADIENT_FILL_RECT_H);
end;