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Vladimir Stefanovic
Guest
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 Posted: Sun Jan 25, 2004 5:01 pm Post subject: Some questions about TImage... |
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Hello,
I have some misunderstanding about TImage. Suppose I
have two TImage objects: SrcImage and DstImage.
I can load some image into SrcImage...
SrcImage->Picture->LoadFromFile()
....if the file type is supported:
* JPEG Image File (*.jpg, *.jpeg),
* Bitmaps (*.bmp),
* Icons (*.ico),
* Metafiles (*.wmf) and
* Enhanced Metafiles (*.emf).
.... after loading sometimes I have a need to Assign()
SrcImage to some other image (DstImage) object.
Here is my first question. Should I always use:
SrcImage->Picture->Assign( DstImage->Picture );
or, depending of a file type (*.bmp, ...)
SrcImage->Picture->Bitmap->Assign( DstImage->Picture->Bitmap );
Sometimes I grab image from screen:
HDC dc = GetDC( hSomeWindow );
Graphics::TCanvas *ScreenCanvas = new Graphics::TCanvas;
ScreenCanvas->Handle = dc;
TRect MRectangle = ScreenCanvas->ClipRect;
MRectangle.Top = 0;
MRectangle.Left = 0;
MRectangle.Right = MRectangle.Right - MRectangle.Left;
MRectangle.Bottom = MRectangle.Bottom - MRectangle.Top;
SrcImage->Picture->Bitmap->Width = MRectangle.Right;
SrcImage->Picture->Bitmap->Height= MRectangle.Bottom;
SrcImage->Picture->Bitmap->Canvas->CopyRect( MRectangle, ScreenCanvas,
ScreenCanvas->ClipRect );
delete ScreenCanvas;
ReleaseDC( hSomeWindow, dc );
Here is my second question. Should I in this case take care of
how TImage object was filled with data because of assigning:
SrcImage->Picture->Bitmap->Assign( DstImage->Picture->Bitmap )
In these two cases I loaded image into SrcImage the two different ways,
so should I keep track of how I got data because of latter assigning.
Vladimir.
P. S. Sorry for my bad English (and worse VCL C++ :)
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Remy Lebeau (TeamB)
Guest
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| Posted: Sun Jan 25, 2004 10:36 pm Post subject: Re: Some questions about TImage... |
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"Vladimir Stefanovic" <spam (AT) not (DOT) needed> wrote
| Quote: | Should I always use:
SrcImage->Picture->Assign( DstImage->Picture );
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Yes, except that you have it backwards. You are assigning the DstImage to
the SrcImage instead of the other way around:
DstImageSrcImage->Picture->Assign( SrcImage->Picture );
Or simply:
DstImage->Picture = SrcImage->Picture;
Which calls Assign() internally.
| Quote: | or, depending of a file type (*.bmp, ...)
SrcImage->Picture->Bitmap->Assign( DstImage->Picture->Bitmap );
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No. As soon as you reference the Bitmap property for any reason whatsoever,
the contained image will be converted to a bitmap. Thus you will lose your
original image format.
| Quote: | TRect MRectangle = ScreenCanvas->ClipRect;
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If you are trying to get the dimensions of the window, use the
GetWindowRect() function instead:
RECT MRectangle;
::GetWindowRect(hSomeWindow, &MRectangle);
| Quote: | MRectangle.Right = MRectangle.Right - MRectangle.Left;
MRectangle.Bottom = MRectangle.Bottom - MRectangle.Top;
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That code has no effect. You set the Left and Top values to 0 beforehand,
so those statements are the same as the following:
MRectangle.Right = MRectangle.Right - 0;
MRectangle.Bottom = MRectangle.Bottom - 0;
aka:
MRectangle.Right = MRectangle.Right;
MRectangle.Bottom = MRectangle.Bottom;
Thus, you are assigning the same values back to themselves without any
change.
Try this code instead:
HDC hdc = NULL;
Graphics::TCanvas *ScreenCanvas = new Graphics::TCanvas;
try
{
hdc = GetDC( hSomeWindow );
ScreenCanvas->Handle = hdc;
RECT r;
GetWindowRect( hSomeWindow, &r );
Graphics::TBitmap *bmp = SrcImage->Picture->Bitmap;
bmp->Width = (r.right - r.left);
bmp->Height = (r.bottom - r.top);
bmp->Canvas->CopyRect( r, ScreenCanvas, r );
}
__finally
{
if( hdc )
ReleaseDC( hSomeWindow, hdc );
delete ScreenCanvas;
}
| Quote: | Should I in this case take care of how TImage object was
filled with data because of assigning:
SrcImage->Picture->Bitmap->Assign( DstImage->Picture->Bitmap )
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For what purpose exactly? Please elaborate. You shouldn't really care how
the TImage is being loaded, it is making a copy of the image data either
way. Once loaded, the data is separate from whatever source it came from.
Gambit
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