Can I combine 2 BitBlt into 1

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Hi,

My question is can I combine 2 BitBlt into 1 time?

I use BitBlt one time to show Base Bitmap on screen. Then, I use BitBlt one time again to show Pixels on Base Bitmap. In current code, the Base Bitmap is shown and after that Pixels are shown on Base Bitmap.

My desire is to show the user Base Bitmap and Pixels in one time.
I think I need to combine it before I show on the screen. But I don't know the way to do it. Could anyone help me for my problem?

The current code is as the following.

C++

void TestDlg::ShowData() {
    CBitmap bmp;
    bmp.LoadBitmap(IDB_BITMAP_TESTBITMAP);
    BITMAP bmpInfo;
    bmp.GetBitmap(&bmpInfo);
    CDC* pDC = this->GetDC();
    CDC dc;
    dc.CreateCompatibleDC(pDC);
    pDC->BitBlt(0, 0, bmpInfo.bmWidth, bmpInfo.bmHeight, &dc, 0, 0, SRCCOPY);//show Base Bitmap

    for (int i = 0; i < bmpInfo.bmHeight; i++) {
	for(int j = 0; j < bmpInfo.bmWidth; j++) {
	     dc.SetPixel(j, i, RGB(rand()%100, rand()%50, rand()%100)); //just example, actually pixel colors are reading from file
	}
    }
    pDC->BitBlt(0, 0, bmpInfo.bmWidth, bmpInfo.bmHeight, &dc, 0, 0, SRCAND); //show pixel colors data on Base Bitmap
    dc.SelectObject(pOldBmp);
    bmp.DeleteObject();
    dc.DeleteDC();
    ReleaseDC(pDC);
}

Is there the way to combine Base Bitmap and Pixel colors before showing to user? Thank you very much for your great help.

[EDIT] Added pre-tags for better readability - Code-o-mat [/EDIT]

Posted 14-May-12 4:35am

April2004

Updated 14-May-12 5:16am

Code-o-mat

v2

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enhzflep 14-May-12 11:19am

Yeah, of course there is. It's in your code already, in fact.
a) Comment-out the first BitBlt
b) Make the 2nd BitBlt SRCCOPY instead of SRCAND

There's no need to show a bitmap if you're immediately going to modify it and reshow it once more. Just load it, modify it and display it.

April2004 14-May-12 12:11pm

Thank you very much for your advice.
May be my misunderstanding. I tested as you said. If I comment out the first BitBlt, the Base Bitmap can be shown on screen. Any idea on it ?
Thanks again.

2 solutions

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Code-o-mat · Answer 1 · 2012-05-14T05:23:00

I personally don't think there's an easy way of doing that (if i understand your "desire" correctly), it would probably be possible with going DirectX/Direct3D and doing somekind of multisampling or with some shader code.
What you could try to do is creating an intermediate buffer, do those blits and pixel modifications on this buffer, and then blit this buffer onto the screen.

Something similar to this should do it (writing this by hearth so it might need some fixups here or there, so don't just blindly copy-paste it):

C++

void TestDlg::ShowData() {
    CBitmap bmp;
    bmp.LoadBitmap(IDB_BITMAP_TESTBITMAP);
    BITMAP bmpInfo;
    bmp.GetBitmap(&bmpInfo);
    CDC* pDC = this->GetDC();
    CDC dc;
    dc.CreateCompatibleDC(pDC);
    CBitmap *pOldBml = dc.SelectObject(bmp);

    //Create intermediate buffer and DC
    CBitmap interBitmap;
    CDC     interDC;

    interBitmap.CreateCompatibleBitmap(pDC, bmpInfo.bmWidth, bmpInfo.bmHeight);
    interDC.CreatecompartibleDC(pDC);
    Cbitmap *oldInterBitmap = interDC.SelectObject(&interBitmap);

    interDC.BitBlt(0, 0, bmpInfo.bmWidth, bmpInfo.bmHeight, &dc, 0, 0, SRCCOPY);//move Base Bitmap to intermediate buffer

    for (int i = 0; i < bmpInfo.bmHeight; i++) {
	for(int j = 0; j < bmpInfo.bmWidth; j++) {
	     dc.SetPixel(j, i, RGB(rand()%100, rand()%50, rand()%100)); //just example, actually pixel colors are reading from file
	}
    }
    interDC.BitBlt(0, 0, bmpInfo.bmWidth, bmpInfo.bmHeight, &dc, 0, 0, SRCAND); //show pixel colors data on intermediate buffer
    pDC->BitBlt(0, 0, bmpInfo.bmWidth, bmpInfo.bmHeight, &interDC, 0, 0, SRCCOPY); //finally, show result on screen

    //Free up resources
    interDC.SelectObject(oldInterBitmap);
    interDC.DeleteDC();
    interBitmap.DeleteObject();

    dc.SelectObject(pOldBmp);
    bmp.DeleteObject();
    dc.DeleteDC();
    ReleaseDC(pDC);
}

JackDingler · Answer 2 · 2012-05-14T05:45:00

Solution 2

Code-o-mat might have the ultimate answer...

But AlphaBlend() may serve your purposes.

To do pixel blending, you'll need an alpha channel. This is just another channel, to add to RGB, for RGBA. It will *often* (there are exceptions), the same type as your red, blue and green colors.

This channel determines how much weight that pixel has. 0 is considered completely transparent and 0xff or 1.0 is completely opaque.

Posted 14-May-12 5:45am

JackDingler

Updated 14-May-12 5:48am

v2

Comments

April2004 14-May-12 12:21pm

AlphaBlend() is totally new for me. Thank you very much for your advice. I will study about it. If you have an example or reference links, could you please point it out for me? Thank you again JackDingler.

JackDingler 14-May-12 12:23pm

I don't have a current example. MSDN may have one.

April2004 14-May-12 12:35pm

Ok. I will study it. Thank you for your guideline.