How to get Transparent Color on Bitmap (coding should be in separate functions, not should be in the same function)

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Hi All,
I am trying to get transparent color on bitmap. I am trying it for several ways and several hours. (I know the way to load bitmap and load color in the same function. But I would like to get it in separate functions.)
Until now, I can't get simple solution yet. Please help me if possible.
I use MFC CDialog. The coding is as follow:

C++

BOOL CTestingDlg::OnInitDialog(){ //Load base bitmap
//To do
  LoadFileBitmap(&m_bmpPLmain, _T("C:\\Test\\testbitmap.bmp");
}
================
void CTestingDlg::OnPaint(){ //Load color on bitmap, Actually, I want transparent color, but my problem is the following code can't get transparent one.
//To do
		CDC hdcMem;
		BITMAP bmpInfo;
		m_bmpPLmain.GetBitmap(&bmpInfo);
		CDC* pDC = this->GetDC();
		hdcMem.CreateCompatibleDC(pDC);
		CBitmap* pOldBmp = hdcMem.SelectObject(&m_bmpPLmain);
		
		for (int i = 0; i < 150; i++) {
			for(int j = 0; j < 150; j++) {
				hdcMem.SetPixel(j, i, RGB(200,60,20));
			}
		}
		pDC->BitBlt(0, 0, bmpInfo.bmWidth, bmpInfo.bmHeight, &hdcMem, 10, 10, SRCAND);
		CDialogEx::OnPaint();
}
================
BOOL CTestingDlg::LoadFileBitmap(CBitmap* pBmp, LPCTSTR szFilename){
   pBmp->DeleteObject();
   return pBmp->Attach(LoadImage(NULL, szFilename, IMAGE_BITMAP, 0, 0,
                     LR_LOADFROMFILE | LR_DEFAULTSIZE | LR_LOADTRANSPARENT));
}
================

I don't know why I can't get transparent color. Please help me for that problem.
Thank you very much.

Best Regards,
April2004

Posted 22-Apr-12 5:35am

April2004

Updated 22-Apr-12 5:52am

Code-o-mat

v2

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Code-o-mat 22-Apr-12 11:59am

Explain what you mean by "transparent color". Usually transparent color in relation with a bitmap means the color on the bitmap that indicates "holes" in the bitmap, so when you render the bitmap to some surface, the pixels on the "target surface" would stay unchanged if they would be overwritten by the specified transparent color. But i get the feeling you are not talking about this.

Nelek 22-Apr-12 12:27pm

OP wrote a comment to answer you, but didn't wrote it as "reply" to you. Have a look below

Code-o-mat 22-Apr-12 12:32pm

I noticed, but thank you very much for telling me.

Nelek 22-Apr-12 17:34pm

You are welcome :)

April2004 22-Apr-12 12:06pm

Suppose, I load Circle shape bitmap in OnInitDialog. Then, I paint the red color on it. I would like to see the Circle even after the red color is painted. With the above code, I just can see the red color as the red color is covered on the circle.
That is the meaning of transparent that I want. Thank you very much for care of my problem.

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April2004 · Answer 1 · 2012-04-23T03:26:00

Solution 3

Hello All,
Thank you very much for your helps. I got the output that I want after controlling Invalidate(TRUE) and Invalidate(FALSE).
From all of your answers, I got a lot of knowledge. I will study more about the keywords that you are guiding. Again, thank you very much.

Posted 23-Apr-12 3:26am

April2004

Code-o-mat · Answer 2 · 2012-04-22T06:40:00

Still not completely sure what you mean, but try something like this:

C++

int Red, Green, Blue;
COLORREF Color;
for (int i = 0; i < 150; i++) {
    for(int j = 0; j < 150; j++) {
        Color = hdcMem.GetPixel(j, i);
        Red   = GetRValue(Color);
        Green = GetGValue(Color);
        Blue  = GetBValue(Color);
        Red   += (200 - Red  ) / 2;
        Green += ( 60 - Green) / 2;
        Blue  += ( 20 - Blue ) / 2;
        hdcMem.SetPixel(j, i, RGB((UCHAR)Red, (UCHAR)Green, (UCHAR)Blue));
    }
}

But manupulating a picture using GetPixel/SetPixel can be very time consuming, you might consider using GDI+ or maybe directly accessing the pixel-data in the bitmap.

E.g somethig like:

C++

...
Gdiplus::Graphics Gp(hdcMem);
Gp.SetPageUnit(Gdiplus::UnitPixel);
Gdiplus::SolidBrush GBr(Gdiplus::Color(128, 200, 60, 20));
Gp.FillRectangle(&GBr, 0, 0, 150, 150);
...

You might need to change the code here or there, i'm writing this by heart.

nv3 · Answer 3 · 2012-04-22T08:50:00

If you override the OnPaint function of a picture control you take full responsibility for the drawing. And your BitBlt does not do transparent drawing.

Look into what TransparentBlt does and AlphaBlend. They probably produce the result that you want. Lookup the reference information on MSDN for these two functions and that will get you on track.

How to get Transparent Color on Bitmap (coding should be in separate functions, not should be in the same function)

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