transparent areas panel hack

BlitzMax Forums/BlitzMax Module Tweaks/transparent areas panel hack

Chris C

(Posted 2006) [#1]

I was reading this http://www.flipcode.com/articles/article_win32skins.shtml

and thought that would be handy for panels with images!
(this should work on anything that has a window handle hWnd)

in win32panel.h add 2 new helper method declerations


	LRESULT wndProc( HWND hwnd,UINT msg,WPARAM wp,LPARAM lp,WNDPROC proc );
	
	HRGN ScanRegion(HBITMAP pBitmap, BYTE jTranspR, BYTE jTranspG, BYTE jTranspB);
	BYTE* Get24BitPixels(HBITMAP pBitmap, WORD *pwWidth, WORD *pwHeight);
};

#endif

then in win32panel.cpp setBackgroundImage needs

void Win32Panel::setBackgroundImage( BBGraphics *g,int flags ){

	if( _bitmap ){ DeleteObject( _bitmap );_bitmap=0; }
	if (g){
		_bgw=g->width();
		_bgh=g->height();
		_bitmap=win32GuiDriver.createBitmap( g );
		_bitmapflags=flags;
	}else{
		_bgw=0;
		_bgh=0;
		_bitmapflags=0;
	}
	
	HRGN hRegion1=ScanRegion(_bitmap,255,0,0);
	SetWindowRgn(_panel.hwnd(), hRegion1, true);
	InvalidateRect( _panel.hwnd(),0,true );
	DeleteObject(hRegion1);
}

then finally at the end of the same file add this code


// -------------------------------------------------------------------------------------
// Scan a bitmap and return a perfect fit region.
// The caller must release the region object...
// (this method starts with a full region and excludes inside the loop)
// -------------------------------------------------------------------------------------
// from <a href="http://www.flipcode.com/articles/article_win32skins.shtml" target="_blank">http://www.flipcode.com/articles/article_win32skins.shtml</a>
HRGN Win32Panel::ScanRegion(HBITMAP pBitmap, BYTE jTranspR, BYTE jTranspG, BYTE jTranspB)
{
  // bitmap width and height
  WORD wBmpWidth,wBmpHeight;

  // the final region and a temporary region
  HRGN hRgn, hTmpRgn;

  // 24bit pixels from the bitmap
  BYTE *pPixels = Get24BitPixels(pBitmap, &wBmpWidth, &wBmpHeight);
  if (!pPixels) return NULL;

  // create our working region
  hRgn = CreateRectRgn(0,0,wBmpWidth,wBmpHeight);
  if (!hRgn) { delete pPixels; return NULL; }

  // ---------------------------------------------------------
  // scan the bitmap
  // ---------------------------------------------------------
  DWORD p=0;
  for (WORD y=0; y<wBmpHeight; y++)
  {
    for (WORD x=0; x<wBmpWidth; x++)
    {
      BYTE jRed   = pPixels[p+2];
      BYTE jGreen = pPixels[p+1];
      BYTE jBlue  = pPixels[p+0];

      if (jRed == jTranspR && jGreen == jTranspG && jBlue == jTranspB)
      {
        // remove transparent color from region
        hTmpRgn = CreateRectRgn(x,y,x+1,y+1);
        CombineRgn(hRgn, hRgn, hTmpRgn, RGN_XOR);
        DeleteObject(hTmpRgn);
      }

      // next pixel
      p+=3;
    }
  }

  // release pixels
  delete pPixels;

  // return the region
  return hRgn;
}

// -------------------------------------------------------------------------------------
// Return bitmap pixels in 24bits format.
// The caller must release the memory...
// -------------------------------------------------------------------------------------
BYTE* Win32Panel::Get24BitPixels(HBITMAP pBitmap, WORD *pwWidth, WORD *pwHeight)
{
  // a bitmap object just to get bitmap width and height
	BITMAP bmpBmp;

  // pointer to original bitmap info
	LPBITMAPINFO pbmiInfo;

  // bitmap info will hold the new 24bit bitmap info
  BITMAPINFO bmiInfo;

  // width and height of the bitmap
  WORD wBmpWidth, wBmpHeight;

  // ---------------------------------------------------------
  // get some info from the bitmap
  // ---------------------------------------------------------
	GetObject(pBitmap, sizeof(bmpBmp),&bmpBmp);
  pbmiInfo   = (LPBITMAPINFO)&bmpBmp;

  // get width and height
	wBmpWidth  = (WORD)pbmiInfo->bmiHeader.biWidth;
	wBmpWidth -= (wBmpWidth%4);                       // width is 4 byte boundary aligned.
	wBmpHeight = (WORD)pbmiInfo->bmiHeader.biHeight;

  // copy to caller width and height parms
  *pwWidth  = wBmpWidth;
  *pwHeight = wBmpHeight;
  // ---------------------------------------------------------

	// allocate width * height * 24bits pixels
  BYTE *pPixels = new BYTE[wBmpWidth*wBmpHeight*3];
	if (!pPixels) return NULL;

  // get user desktop device context to get pixels from
	HDC hDC = GetWindowDC(NULL);

  // fill desired structure
	bmiInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
	bmiInfo.bmiHeader.biWidth = wBmpWidth;
	bmiInfo.bmiHeader.biHeight = -wBmpHeight;
	bmiInfo.bmiHeader.biPlanes = 1;
	bmiInfo.bmiHeader.biBitCount = 24;
	bmiInfo.bmiHeader.biCompression = BI_RGB;
	bmiInfo.bmiHeader.biSizeImage = wBmpWidth*wBmpHeight*3;
	bmiInfo.bmiHeader.biXPelsPerMeter = 0;
	bmiInfo.bmiHeader.biYPelsPerMeter = 0;
	bmiInfo.bmiHeader.biClrUsed = 0;
	bmiInfo.bmiHeader.biClrImportant = 0;

  // get pixels from the original bitmap converted to 24bits
  int iRes = GetDIBits(hDC,pBitmap,0,wBmpHeight,(LPVOID)pPixels,&bmiInfo,DIB_RGB_COLORS);

  // release the device context
	ReleaseDC(NULL,hDC);

  // if failed, cancel the operation.
	if (!iRes)
  {
    delete pPixels;
    return NULL;
  };

  // return the pixel array
	return pPixels;
}

now any time you add an image to a panel any pure red pixels
will be 100% see through like this

the rather bad drawing of a cross hair is an image on a max gui panel