In addition to drawing GDI+ onto a control canvas via TGPGraphics (which has been working fine), I'm also trying to draw onto a TBitmap using GDI+ as well, and then drawing that bitmap to the control canvas. However, nothing actually appears to get drawn.
The following code is within the WM_PAINT message handler, which again works for the actual control canvas, but when creating an equivalent TGPGraphics object and passing this TBitmap handle, nothing gets drawn:
FBitmapCanvas:= CreateGPCanvas(FBitmap.Handle);
try
FBitmapCanvas.DrawLine(FSomePen, P1, P2); //Same pen used to successfully draw to control canvas
finally
FreeAndNil(FBitmapCanvas);
end;
Canvas.Draw(0, 0, FBitmap); //Draw this bitmap to control canvas
CreateGPCanvas looks like so, and is used for both this bitmap and the control:
function CreateGPCanvas(const DC: HDC): TGPGraphics;
begin
Result:= TGPGraphics.Create(DC);
Result.SetInterpolationMode(InterpolationMode.InterpolationModeHighQuality);
Result.SetSmoothingMode(SmoothingMode.SmoothingModeHighQuality);
Result.SetCompositingQuality(CompositingQuality.CompositingQualityHighQuality);
end;
On the other hand, if I don't try to use the TGPGraphics and instead draw a line directly via the TBitmap.Canvas property, it works fine (but of course looks ugly because it's not GDI+). So I know the actual bitmap gets drawn correctly to the control canvas.
FBitmap.Canvas.MoveTo(P1.X, P1.Y);
FBitmap.Canvas.LineTo(P2.X, P2.Y);
What am I doing wrong here, and how do I make the TGPGraphics work on this bitmap canvas?
PS - The only reason I'm using a TBitmap at all is because what I'm actually writing needs to "remember" a portion of what was previously drawn and retain it, rather than repainting it over and over.
