C / C++ / MFC

23-Mar-09 0:24

Hi everyone Smile | :)

I'm stuck with the code which renders a preview of a Camera using VFW.

The thing is that i want to do TextOut on this image within FrameCallback,
but the textout comes some kind of a bottom-up ?

The idea is to store avi sequence with a text drawn inside (generally a date).

Here is the code:

I enumerate available devices, and connect to the one i choose.
Then i do

BOOL SetVideoFormatRGB()<br />
{<br />
    DWORD size = capGetVideoFormatSize(ghWndCap);<br />
<br />
    if ( size <= 0 )<br />
    {<br />
     <br />
        return FALSE;<br />
    }<br />
<br />
    void* pBuffer = new BYTE[size];<br />
    BITMAPINFO* pBitmapInfo = (BITMAPINFO*) pBuffer;<br />
<br />
    if ( capGetVideoFormat(ghWndCap, pBuffer, size) <= 0 )<br />
    {<br />
      <br />
        return FALSE;<br />
    }<br />
<br />
    pBitmapInfo->bmiHeader.biBitCount = 24;<br />
    pBitmapInfo->bmiHeader.biCompression = 0;<br />
    pBitmapInfo->bmiHeader.biSizeImage = pBitmapInfo->bmiHeader.biWidth * pBitmapInfo->bmiHeader.biHeight * 3;<br />
 <br />
<br />
    if ( ! capSetVideoFormat(ghWndCap, pBitmapInfo, size) )<br />
    {<br />
      <br />
        return FALSE;<br />
    }<br />
<br />
    <br />
    g_nBitCount = pBitmapInfo->bmiHeader.biBitCount;<br />
    g_nBitsPerPixel = pBitmapInfo->bmiHeader.biBitCount;<br />
<br />
    <br />
    return TRUE;<br />
}

Next thing - i create a Callback for VFW:

capSetCallbackOnFrame(ghWndCap, (FARPROC)FrameCallbackProc);

And process each frame :

<br />
 LRESULT PASCAL FrameCallbackProc(HWND hWnd, LPVIDEOHDR lpVHdr)<br />
{	<br />
  <br />
    if ( g_nBitCount != 24 )   // only RGB format !<br />
        return 0;<br />
<br />
     <br />
    if ( ! g_hFrameBitmap )   // failed<br />
        return 0;<br />
 <br />
	BeginPaint(hWnd,&ps);<br />
 <br />
    <br />
	<br />
SetBitmapBits(g_hFrameBitmap, g_nImageWidth*g_nImageHeight*3, lpVHdr->lpData);<br />
 <br />
<br />
<br />
<br />
 <br />
 <br />
	<br />
SetBkMode(g_hFrameDC,TRANSPARENT);<br />
SelectObject(g_hFrameDC, FONTmain);<br />
SetTextColor(g_hFrameDC,RGB(0,0,0));<br />
hPen = CreatePen(0, 1, RGB(210,210,210));<br />
SelectObject(g_hFrameDC, hPen);<br />
Rectangle(g_hFrameDC,  0,0,  320,100);<br />
TextOut(g_hFrameDC,2,2,"AAAAAAAAAAA",10);<br />
 <br />
 GetBitmapBits(g_hFrameBitmap, g_nImageWidth*g_nImageHeight*3, lpVHdr->lpData);<br />
 <br />
<br />
<br />
		EndPaint(hWnd,&ps); <br />
return (LRESULT)true;<br />
 }

This code does the trick but all i draw on g_hFrameBitmap is bottom-up, so point:

0,0 is on the bottom left side of whole image. The string "AAAAA..." also comes
bottom up.

g_hFrameBitmap is created as:

<br />
void CreateGraphicObjects(HWND hWnd)<br />
{<br />
  <br />
    g_hFrameDC = CreateCompatibleDC(GetDC(hWnd));<br />
     <br />
 <br />
	 <br />
    <br />
    memset(&lpbi, 0, sizeof(lpbi));<br />
    lpbi = (LPBITMAPINFO) new BYTE[sizeof(BITMAPINFOHEADER) + (256 * sizeof(RGBQUAD))];<br />
    lpbi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);<br />
    lpbi->bmiHeader.biWidth = g_nImageWidth;<br />
    lpbi->bmiHeader.biHeight = -240;<br />
    lpbi->bmiHeader.biPlanes = 1;<br />
    lpbi->bmiHeader.biBitCount = 24;<br />
    lpbi->bmiHeader.biCompression = BI_RGB;<br />
    lpbi->bmiHeader.biSizeImage = WIDTHBYTES((DWORD)g_nImageWidth * 8) * g_nImageHeight;<br />
    lpbi->bmiHeader.biXPelsPerMeter = 0;<br />
    lpbi->bmiHeader.biYPelsPerMeter = 0;<br />
    lpbi->bmiHeader.biClrUsed = 0;<br />
    lpbi->bmiHeader.biClrImportant = 0;<br />
    <br />
 <br />
<br />
    g_hFrameBitmap=  CreateDIBSection( <br />
        NULL,                       // DC - we don't need it here <br />
        lpbi,                       // BITMAPINFOHEADER pointer<br />
        DIB_RGB_COLORS,             // palette is in BITMAPINFO, contains RGBQUAD entries (doesn't matter for RGB)<br />
        (void **)&pBits,             // output pointer to bitmap bits<br />
        NULL, <br />
        0 ); <br />
 <br />
	<br />
    delete[] lpbi;<br />
    SelectObject(g_hFrameDC, (HBITMAP)g_hFrameBitmap);<br />
<br />
	<br />
}<br />

Any chance to get this resolved? I've tried to pass negative values to bitmap header - no luck.

Best reagards!

Jonathan Davies23-Mar-09 2:52

Jonathan Davies

23-Mar-09 2:52

Hi,
The line: lpbi->bmiHeader.biHeight = -240; indicates, by the used of a negative value, that this is a top-down bitmap. That is 0,0 is at the top-left corner. You say you'd tried to "pass negative values to bitmap header", did you mean by altering the sign of this? If this is the case when you then say "no luck" do you mean the video did'nt change from top-down to bottom-up or the text stayed displayed as: "some kind of bottom-up?

I have come across 'fixes' to get bitmaps/video displayed 'the right way up' in the past. These only tend to come to light when further work is done. Are yuu sure there is'nt such a fix somewhere you are not looking?

Jonathan Davies23-Mar-09 3:32

Jonathan Davies

23-Mar-09 3:32

Hi again,
On browsing through some of my code I came across:

// MM_TEXT maps 1 logical unit to 1 pixel, +x to the right and +y down
int OldMode = ::SetMapMode(hCrossesDC, MM_TEXT);

Could this be what you need?

pabloesso23-Mar-09 3:40

23-Mar-09 3:40

Jonathan,

yes i have altered the

lpbi->bmiHeader.biHeight = -240;

to +240 and -240 - but this does not make any change.
The TextOut 0,0 position is at bottom left side of the video preview and the letters
are drawn bottom-up.

I will look at your above code later on to see if this sorts this out.

Many thanks for your reply!

pabloesso24-Mar-09 1:23

24-Mar-09 1:23

Damn still nothing.

Have a look at this screen below:

http://www.fileden.com/files/2009/3/19/2370332/image.jpg

After applying SetMapMode(g_hFrameDC, MM_TEXT); - still the same issue.

Look at the TEXTOUT - it is rendered as:

TextOut(g_hFrameDC,2,2,"AAAAAAAAAAA",10);

And comes bottom-up in the wrong coordinates... ://

pabloesso29-Mar-09 7:02

29-Mar-09 7:02

Still noone?

So how do they do that in other capture video programs?

It is just a matter of adding a Label to the video stream and it is such a pain?

Damn ;/

pabloesso29-Mar-09 7:16

Doubt in Run time polymerphisim

29-Mar-09 7:16

Ok,
below is the screenshot of my application. You can see the camera stream on the left side of the window and the TextOut results.

http://www.fileden.com/files/2009/3/19/2370332/aaa.jpg

And the code below:

 BeginPaint(hWnd,&ps);
SetBitmapBits(g_hFrameBitmap, g_nImageWidth*g_nImageHeight*3, lpVHdr->lpData);
SetBkMode(g_hFrameDC,TRANSPARENT);
SelectObject(g_hFrameDC, FONTmain);
SetTextColor(g_hFrameDC,RGB(0,0,0));
hPen = CreatePen(0, 1, RGB(210,210,210));
SelectObject(g_hFrameDC, hPen);
Rectangle(g_hFrameDC,  0,0,  320,20);
TextOut(g_hFrameDC,2,2,"AAAAAAAAAAA",10);
GetBitmapBits(g_hFrameBitmap,320*240*3,lpVHdr->lpData);
EndPaint(hWnd,&ps);

Cool_Phillip23-Mar-09 0:04

Cool_Phillip

23-Mar-09 0:04

Hi All
Suppose I've a class

Class Parent
{
public:
virtual void V();
};

Class Child: public Parent
{
public:
void V();
}

main()
{
Child obj;
obj.V();
}

Q:-If we create a derive class object and call the function V(), is is runtime polymerphisim?

Regards
Phillip

«_Superman_»23-Mar-09 0:06

«_Superman_»

23-Mar-09 0:06

No. That would be only compile time binding that happens.

«_Superman_»
I love work. It gives me something to do between weekends.

CPallini23-Mar-09 0:11

CPallini

23-Mar-09 0:11

Nope.
The following code use polymorphism:

void main(void)
{
  Parent * p = new Child();
  p->V();
}

Cool_Phillip23-Mar-09 1:08

Cool_Phillip

23-Mar-09 1:08

thank you very much. I faced this question in an interview and replied same answer. But i was confused wheather my ans is correct or not. Smile | :)

Regards
Phillip