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TAChart: Fix drawing of empty transparent series with canvas drawer

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git-svn-id: trunk@38471 -
This commit is contained in:
ask 2012-09-01 13:27:58 +00:00
parent 1788289d4b
commit 51ae73b5dc
1 changed files with 11 additions and 6 deletions
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17
components/tachart/tadrawercanvas.pas
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@ -292,7 +292,7 @@ end;
procedure TCanvasDrawer.SetTransparency(ATransparency: TChartTransparency);
procedure FillAlpha(AAlpha: Byte);
function FillAlpha(AAlpha: Byte): Byte;
var
p: PRGBAQuad;
img: TRawImage;
@ -300,12 +300,14 @@ procedure TCanvasDrawer.SetTransparency(ATransparency: TChartTransparency);
FBuffer.BeginUpdate;
img := FBuffer.RawImage;
p := PRGBAQuad(img.Data);
Result := 0;
while PByte(p) < img.Data + img.DataSize do begin
// On the first pass, set all alpha values to AAlpha.
// Drawing will reset alpha of changed pixels to zero.
// On the second pass, flip unchanged pixels back to zero alpha,
// and changed ones to the desired alpha level.
p^.Alpha := p^.Alpha xor AAlpha;
Result := Result or p^.Alpha;
Inc(p);
end;
FBuffer.EndUpdate;
@ -316,11 +318,14 @@ begin
// then alpha-blend the bitmap to the canvas.
// This is slow, but currently seems the only way.
if (FTransparency <> ATransparency) and (FTransparency > 0) then begin
FillAlpha(255 - FTransparency);
StretchMaskBlt(
FCanvas.Handle, 0, 0, FCanvas.Width, FCanvas.Height,
FBuffer.Canvas.Handle, 0, 0, FCanvas.Width, FCanvas.Height,
0, 0, 0, SRCCOPY);
// StretchMaskBlt performs alpha blending only if the image contains
// at least one non-zero alpha value, so fully transparent image
// becomes black box. Workround: do not call StretchMaskBlt in this case.
if FillAlpha(255 - FTransparency) > 0 then
StretchMaskBlt(
FCanvas.Handle, 0, 0, FCanvas.Width, FCanvas.Height,
FBuffer.Canvas.Handle, 0, 0, FCanvas.Width, FCanvas.Height,
0, 0, 0, SRCCOPY);
end;
inherited;
if FTransparency > 0 then begin