Why is this workaround for SaveToFile needed?
lazarus / 39-Graphics

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gwiesenekker · 2014-06-03 12:38

Hi,

I copy one bitmap to another using:

BitBlt(TImage-instance.Picture.Bitmap.Canvas.Handle, 0, 0, TImage-
instance.Picture.Bitmap.Width, TImage-instance.Picture.Bitmap.Height,
hdcSrc, SourceRect.Left, SourceRect.Top, SRCCOPY);

The Timage-instance is a component on the main form, and shows the
copied bitmap correctly. However, if I save this bitmap to a file
using:

TImage-instance.Picture.Bitmap.SaveToFile('Bitmap.bmp');

the resulting bitmap is always black. I found the workaround in
another thread:

pic := TPicture.Create;
pic.bitmap.width := TImage-instance.Picture.Bitmap.width;
pic.bitmap.height := TImage-instance.Picture.Bitmap.height;
pic.bitmap.Canvas.Draw(0, 0, TImage-instance.Picture.Bitmap);
pic.SaveToFile('Bitmap.bmp');
pic.Free;

But why is this workaround for SaveToFile needed?

Gijsbert

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engkin · 2014-06-09 02:49

Quote from: gwiesenekker on June 03, 2014, 02:38:28 pmBut why is this
workaround for SaveToFile needed?
It is not needed. When you deal with handles directly you need to call
Changed when you're done:
Code: [Select]BitBlt(TImage-instance.Picture.Bitmap.Canvas.Handle, 0,
0, TImage-instance.Picture.Bitmap.Width, TImage-
instance.Picture.Bitmap.Height, hdcSrc, SourceRect.Left,
SourceRect.Top, SRCCOPY);

TImage-instance.Picture.Bitmap.Canvas.Changed;  //<----