How would I go about rotating a Bitmap in Windows GDI,C++?
+1
A:
Sounds like you have to use PlgBlt. Take your rectangle's 4 corners as 2D Points, rotate them, then call PlgBlt.
From MSDN Bitmap Rotation:
To copy a bitmap into a parallelogram; use the PlgBlt function, which performs a bit-block transfer from a rectangle in a source device context into a parallelogram in a destination device context. To rotate the bitmap, an application must provide the coordinates, in world units, to be used for the corners of the parallelogram.
Frank Krueger
2010-02-16 01:43:05
The PlgBlt docs specifically mention that rotation transformations are not supported. That's accurate. Link: http://msdn.microsoft.com/en-us/library/dd162804%28VS.85%29.aspx
Hans Passant
2010-02-16 02:48:46
nobugz: Please read the post and the link before voting something down. I am suggesting that he pass in a **pre-rotated** parallelogram, just as the docs say to do. PlgBlt does not support **rotation transformations on the context**. That means that the context rotation won't be applied. **But he can apply it himself to the rectangle to get a parallelogram**.
Frank Krueger
2010-02-16 04:20:24
I didn't vote you down.
Hans Passant
2010-02-16 04:41:37
+3
A:
You can do it with GDI+ (#include <gdiplus.h>). The Graphics class has the RotateTransform method. That allows arbitrary rotations. Use Image::RotateFlip() if you only need to rotate by 90 degree increments, that's a lot more efficient.
Hans Passant
2010-02-16 02:55:42
@Frank Krueger - you have to be able to mind-read on this site. Either that, or throw pasta at the wall and see what sticks.
Mark Ransom
2010-02-16 05:05:51
A:
Another possibility (beyond those already suggested) is to use SetWorldTransform(). This is different in that it is modal and applies to the DC as a whole, not just a single operation. If you want to rotate one bitmap rotated, but other things without rotation, it's probably not your best choice. If you want to draw a number of things rotated, or (especially) if you want to rotate everything you draw (at least into one DC) it can work quite nicely though.
Jerry Coffin
2010-02-16 04:38:26
I tried SetWorldTransform () and it had absolutely no effect. The documentation says that the device context's graphics mode must be set to GM_ADVANCED. I tried it, and it resulted in a totally black bitmap.This is what usually happens when trying a Microsoft feature; it doesn't work, and you spend the other 90% of your time trying to figure out why. .NET is noticeably better, but it's so slow.
2010-07-13 19:56:47
+1
A:
I saw a promising and efficient solution that only uses GDI here: http://www.codeguru.com/cpp/g-m/gdi/print.php/c3693
Haven't tried it yet.