Mega Code Archive
Draw a gradient on a canvas with an arbitrary number of colors
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Title: draw a gradient on a canvas with an arbitrary number of colors?
{
The following code allows you to draw a gradient on a canvas with
an arbitrary number of colors (minimum 2).
To draw a gradient on a form's canvas,
call the DrawGradient() in the OnPaint and OnResize-event handlers.
}
{
Mit dieser Prozedur kann man auf einen Canvas einen Farbverlauf mit
beliebig vielen Farben (min. 2) zeichnen.
Z.B. wenn auf eine Form ein Farbverlauf gezeichnet werden soll,
rufe die DrawGradient() Funktion im OnPaint-Ereignis und
im OnResize-Ereignis der Form auf.
}
procedure DrawGradient(ACanvas: TCanvas; Rect: TRect;
Horicontal: Boolean; Colors: array of TColor);
type
RGBArray = array[0..2] of Byte;
var
x, y, z, stelle, mx, bis, faColorsh, mass: Integer;
Faktor: double;
A: RGBArray;
B: array of RGBArray;
merkw: integer;
merks: TPenStyle;
merkp: TColor;
begin
mx := High(Colors);
if mx 0 then
begin
if Horicontal then
mass := Rect.Right - Rect.Left
else
mass := Rect.Bottom - Rect.Top;
SetLength(b, mx + 1);
for x := 0 to mx do
begin
Colors[x] := ColorToRGB(Colors[x]);
b[x][0] := GetRValue(Colors[x]);
b[x][1] := GetGValue(Colors[x]);
b[x][2] := GetBValue(Colors[x]);
end;
merkw := ACanvas.Pen.Width;
merks := ACanvas.Pen.Style;
merkp := ACanvas.Pen.Color;
ACanvas.Pen.Width := 1;
ACanvas.Pen.Style := psSolid;
faColorsh := Round(mass / mx);
for y := 0 to mx - 1 do
begin
if y = mx - 1 then
bis := mass - y * faColorsh - 1
else
bis := faColorsh;
for x := 0 to bis do
begin
Stelle := x + y * faColorsh;
faktor := x / bis;
for z := 0 to 3 do
a[z] := Trunc(b[y][z] + ((b[y + 1][z] - b[y][z]) * Faktor));
ACanvas.Pen.Color := RGB(a[0], a[1], a[2]);
if Horicontal then
begin
ACanvas.MoveTo(Rect.Left + Stelle, Rect.Top);
ACanvas.LineTo(Rect.Left + Stelle, Rect.Bottom);
end
else
begin
ACanvas.MoveTo(Rect.Left, Rect.Top + Stelle);
ACanvas.LineTo(Rect.Right, Rect.Top + Stelle);
end;
end;
end;
b := nil;
ACanvas.Pen.Width := merkw;
ACanvas.Pen.Style := merks;
ACanvas.Pen.Color := merkp;
end
else
// Please specify at least two colors
raise EMathError.Create('Es müssen mindestens zwei Farben angegeben werden.');
end;
// Example Calls:
// Aufrufbeispiele:
DrawGradient(Image1.Canvas, Rect(0, 0, 100, 200), False, [clRed, $00FFA9B4]);
DrawGradient(Canvas, GetClientRect, True, [121351, clBtnFace, clBlack, clWhite]);
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