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Thread: rotate by angle



Permlink Replies: 2 - Last Post: Feb 25, 2016 1:16 PM Last Post By: Goran Ekstrom
Alain Bastien

Posts: 153
Registered: 11/12/01
rotate by angle
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  Posted: Dec 7, 2015 2:27 AM
Hi,

How to I rotate a .JPG image on a Canvas by angle or 90cw or ccw ?

Thanks
Mario Sassone

Posts: 12
Registered: 10/28/06
Re: rotate by angle
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  Posted: Feb 25, 2016 12:26 PM   in response to: Alain Bastien in response to: Alain Bastien
Alain Bastien wrote:
Hi,

How to I rotate a .JPG image on a Canvas by angle or 90cw or ccw ?

Thanks

I dont know libraries doing that work, but Im sure they exist, in some place.
If you prefer to do it yourself, you could:
1) load the images in a Graphics::TBitmap structure;
2) access the pixels colors through the ScanLine method:
	
        for (int y = 0; y < myBitmap->Height; ++y)	{
		RGBQUAD* const pRow  = static_cast <RGBQUAD*> (myBitmap ->ScanLine[y]);
		for (int x = 0; x < myBitmap->Width; ++x)	{
			int redValue  = pRowOut[x].rgbRed;
			int greenValue = pRowOut[x].rgbGreen;
			int blueValue  = pRowOut[x].rgbBlue;
		}
	}

3) manipulate the pixels with a rotation matrix algorythm (you can rotate 90 and flip by inverting rows and columns)
4) recreate the modified TBitmap:

Edited by: Mario Sassone on Feb 25, 2016 9:26 PM

Edited by: Mario Sassone on Feb 25, 2016 9:27 PM
Goran Ekstrom

Posts: 149
Registered: 1/10/04
Re: rotate by angle
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  Posted: Feb 25, 2016 1:16 PM   in response to: Alain Bastien in response to: Alain Bastien
Alain Bastien wrote:
Hi,

How to I rotate a .JPG image on a Canvas by angle or 90cw or ccw ?

Thanks

Maybe some of these links may help:

http://www.codeguru.com/cpp/g-m/bitmap/specialeffects/article.php/c1743/Rotate-a-bitmap-image.htm

https://msdn.microsoft.com/en-us/library/windows/desktop/dd183389(v=vs.85).aspx

Google "winapi rotate bitmap" for more info.
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