StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

POBitmap rotation in winapi
text
Body
copied!<p>I have a BitMap (a little sprite) that i have to rotate at a certain angle. I found this code, and i tried to adapt it for my application, but it doesn't seem to work. The sprite doesn't rotate at all, instead it moves a little bit.</p> <p>Here's the function code:</p> <pre><code>void Sprite::Rotate(float radians, const char* szImageFile) { // Create a memory DC compatible with the display HDC sourceDC, destDC; sourceDC = CreateCompatibleDC( mpBackBuffer->getDC() ); destDC = CreateCompatibleDC( mpBackBuffer->getDC() ); // Get logical coordinates HBITMAP hBitmap = (HBITMAP)LoadImage(g_hInst, szImageFile, IMAGE_BITMAP, 0, 0, LR_CREATEDIBSECTION | LR_LOADFROMFILE); BITMAP bm; ::GetObject( hBitmap, sizeof( bm ), &bm ); float cosine = (float)cos(radians); float sine = (float)sin(radians); // Compute dimensions of the resulting bitmap // First get the coordinates of the 3 corners other than origin int x1 = (int)(bm.bmHeight * sine); int y1 = (int)(bm.bmHeight * cosine); int x2 = (int)(bm.bmWidth * cosine + bm.bmHeight * sine); int y2 = (int)(bm.bmHeight * cosine - bm.bmWidth * sine); int x3 = (int)(bm.bmWidth * cosine); int y3 = (int)(-bm.bmWidth * sine); int minx = min(0,min(x1, min(x2,x3))); int miny = min(0,min(y1, min(y2,y3))); int maxx = max(0,max(x1, max(x2,x3))); int maxy = max(0,max(y1, max(y2,y3))); int w = maxx - minx; int h = maxy - miny; // Create a bitmap to hold the result HBITMAP hbmResult = ::CreateCompatibleBitmap(mpBackBuffer->getDC(), w, h); HBITMAP hbmOldSource = (HBITMAP)::SelectObject( sourceDC, hBitmap ); HBITMAP hbmOldDest = (HBITMAP)::SelectObject( destDC, hbmResult ); // Draw the background color before we change mapping mode HBRUSH hbrBack = CreateSolidBrush( mcTransparentColor ); HBRUSH hbrOld = (HBRUSH)::SelectObject( destDC, hbrBack ); PatBlt( destDC, 0, 0, w, h, PATCOPY); ::DeleteObject( ::SelectObject( destDC, hbrOld ) ); // We will use world transform to rotate the bitmap SetGraphicsMode(destDC, GM_ADVANCED); XFORM xform; xform.eM11 = cosine; xform.eM12 = -sine; xform.eM21 = sine; xform.eM22 = cosine; xform.eDx = (float)-minx; xform.eDy = (float)-miny; SetWorldTransform( destDC, &xform ); // Now do the actual rotating - a pixel at a time BitBlt(destDC, 0, 0, w, h, sourceDC, 0, 0, SRCCOPY ); // Restore DCs ::SelectObject( sourceDC, hbmOldSource ); ::SelectObject( destDC, hbmOldDest ); BITMAP btm; ::GetObject( hbmResult, sizeof( mImageBM ), &mImageBM ); } </code></pre> <p><strong>I can't figure out why it doesn't rotate the image, but instead it moves it. Also if you know another method to do this, i'm open for suggestions, but keep in mind that i can use only winapi, no additional libraries and i'm a beginner in windows programming.</strong> </p> <p>edit: Here is where i got the code: <a href="http://www.codeguru.com/cpp/g-m/bitmap/specialeffects/article.php/c1743/" rel="nofollow">http://www.codeguru.com/cpp/g-m/bitmap/specialeffects/article.php/c1743/</a> . I had to change it a bit, but i don't think it was because of that, i only changed the CDCs to HDCs. One important thing i've ommited is that the (0, 0) coord. for the image in that code is considered in the corner, but in my application it is in the center of the sprite. Even if that's a problem, i think it is a problem of calculating the new dimensions of the bitmap, i don't see the connection with the rotation.</p>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload