C / C++ / MFC

2-Mar-11 4:14

Ok, so here is the thing. I got a window, simple win32 window with a black background which was applied with FillRect function to fill whole client rectangle with black color. Now i am trying to paint some picture on this window with StretchBlt. Basically, here is my function:

void PaintBkgImage(__in HWND hWnd, 
		__in HDC PaintDC, 
		__in BITMAP bmp, 
		__in HDC prevDC,
		__in int StretchFromLeft,
		__in int StretchFromRight,
		__in int StretchFromTop,
	        __in int StretchFromBottom)
{
	SetStretchBltMode(PaintDC, HALFTONE);
	StretchBlt(PaintDC, 
			   StretchFromLeft, 
			   StretchFromTop, 
			   _client_rect.right, 
			   _client_rect.bottom - StretchFromBottom,
			   prevDC, 
			   StretchFromRight, 
			   0, 
			   bmp.bmWidth, 
			   bmp.bmHeight, 
			   SRCCOPY);
}

and now StretchFromLeft = 10 for example, so the pic should be stretched from left by 10 units. Ok, StretchBlt does this, but it leaves a nasty white rectangle on left side. Same thing with any other parameter =/
I have tried filling window with black color yet again but it has no effect at all after calling StretchBlt. How can i make it work? So basically i need my window to remain black and only picture should be stretched from every side (left , right, bottom ,top)?
Thanks

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Hans Dietrich2-Mar-11 4:26

Hans Dietrich

2-Mar-11 4:26

The second parameter of StretchBlt (StretchFromLeft in your code) is the x-offset in destination dc. So, no surprise you're getting a margin on left.

Best wishes,
Hans

[Hans Dietrich Software]

csrss2-Mar-11 7:02

2-Mar-11 7:02

Margin on left is what i need to get, as well as margin on right , margin from top and bottom. And my code is fine, the deal here was a white rectangle, but after some look into it, - there was a need to paint over these white rects inside wm_paint, while i was painting over in wm_erasebkg and that was the mistake.

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CPallini2-Mar-11 4:57

CPallini

2-Mar-11 4:57

Do you paint your background inside the WM_PAINT handler?

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-- Alfonso the Wise, 13th Century King of Castile.

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[My articles]

csrss2-Mar-11 5:14

2-Mar-11 5:14

Yup, image is drawn in wm_paint, and filling with black goes in WM_ERASEBKGND.

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Re: StretchBlt problem [Solved]

Chris Meech2-Mar-11 6:15

Chris Meech

2-Mar-11 6:15

You might have to call InvalidateRect for the area that is exposed by the StretchBlt call. Smile | :)

Chris Meech
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csrss2-Mar-11 6:58

How to calculate to get new pixel color by mix alpha value with r, g and b value [modified]

2-Mar-11 6:58

Alright, i got it. The deal is actually to erase these while fields in wm_paint after call StretchBlt

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Amrit Agr2-Mar-11 2:11

Amrit Agr

2-Mar-11 2:11

Hi, I want to use AlphaBlend() method to display transparent shadow. I requires some sort of calculation to mix color value from bitmap( for which I have to display shadow ) with other color( shadow color ).
I have referred caculation method from msdn it's not giving me proper result. I am giving the code. Pls help me out.

DWORD destRedColor   = 0;
DWORD destBlueColor  = 0;
DWORD destGreenColor = 0;
DWORD destAlphaColor = 0;
DWORD SrcRedColor     = 0;
DWORD SrcBlueColor    = 0;
DWORD SrcGreenColor   = 0;
DWORD SrcAlphaColor   = 0;
int src_const_alpha   = 0;

// After all the inits we can do the job : Replace Color
for ( int i = ( ( bm.bmWidth * bm.bmHeight ) - 1 ); i >= 0; --i )
 {
	COLORREF clrRef =  ptPixels[i]; //Bitmap pixel color taken with CreateDIBSection's void* lpBits;
	clrRef = COLORREF2RGB( clrRef );
        
        //taking alpha,red,green and blue values.
	DWORD redDest   = GetRValue( clrRef );
	DWORD greenDest = GetGValue( clrRef);
        DWORD blueDest  = GetBValue( clrRef);
	BYTE *ptrAlphaDest = reinterpret_cast<BYTE*>( &clrRef );
	DWORD alphaDest;
	alphaDest = ptrAlphaDest[0];

        //taking alpha,red,green and blue values.
	DWORD redSrc   = GetRValue( _cNewColor ); //Shadow Color ( of user's choice )
	DWORD greensrc = GetGValue( _cNewColor );
        DWORD blueSrc  = GetBValue( _cNewColor );
	BYTE *ptrAlphaSrc = reinterpret_cast<BYTE*>( &_cNewColor );
	DWORD alphaSrc;
	alphaSrc = ptrAlphaSrc[0];

	src_const_alpha  = int( m_intensity * 2.55 );
	SrcRedColor   = redSrc   * src_const_alpha / 255.0;
        SrcGreenColor = greensrc * src_const_alpha / 255.0;
	SrcBlueColor  = blueSrc  * src_const_alpha / 255.0;
	SrcAlphaColor = alphaSrc * src_const_alpha / 255.0;

        destRedColor   = SrcRedColor    + ( 1 - SrcAlphaColor ) * redDest;
	destGreenColor = SrcGreenColor  + ( 1 - SrcAlphaColor ) * greenDest;
	destBlueColor  = SrcBlueColor   + ( 1 - SrcAlphaColor ) * blueDest;
	destAlphaColor = SrcAlphaColor  + ( 1 - SrcAlphaColor ) * alphaDest;

	ptPixels[i]
	= (destAlphaColor << 24 ) |                       
	  (destRedColor   << 16 ) |  
	  (destGreenColor << 8  ) | 
	  (destBlueColor);
}

modified on Wednesday, March 2, 2011 10:19 PM

Re: How to calculate to get new pixel color by mix alpha value with r, g and b value

«_Superman_»2-Mar-11 2:43

«_Superman_»

2-Mar-11 2:43

If you do not post any code or indicate the exact problem, all we can help you with is to wish you good luck.

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

Microsoft MVP (Visual C++)

Polymorphism in C

Re: How to calculate to get new pixel color by mix alpha value with r, g and b value

Amrit Agr3-Mar-11 0:17

Amrit Agr

3-Mar-11 0:17

DWORD destRedColor   = 0;
DWORD destBlueColor  = 0;
DWORD destGreenColor = 0;
DWORD destAlphaColor = 0;
DWORD SrcRedColor     = 0;
DWORD SrcBlueColor    = 0;
DWORD SrcGreenColor   = 0;
DWORD SrcAlphaColor   = 0;
int src_const_alpha   = 0;

// After all the inits we can do the job : Replace Color
for ( int i = ( ( bm.bmWidth * bm.bmHeight ) - 1 ); i >= 0; --i )
 {
	COLORREF clrRef =  ptPixels[i]; //Bitmap pixel color taken with CreateDIBSection's void* lpBits;
	clrRef = COLORREF2RGB( clrRef );
        
        //taking alpha,red,green and blue values.
	DWORD redDest   = GetRValue( clrRef );
	DWORD greenDest = GetGValue( clrRef);
        DWORD blueDest  = GetBValue( clrRef);
	BYTE *ptrAlphaDest = reinterpret_cast<BYTE*>( &clrRef );
	DWORD alphaDest;
	alphaDest = ptrAlphaDest[0];

        //taking alpha,red,green and blue values.
	DWORD redSrc   = GetRValue( _cNewColor ); //Shadow Color ( of user's choice )
	DWORD greensrc = GetGValue( _cNewColor );
        DWORD blueSrc  = GetBValue( _cNewColor );
	BYTE *ptrAlphaSrc = reinterpret_cast<BYTE*>( &_cNewColor );
	DWORD alphaSrc;
	alphaSrc = ptrAlphaSrc[0];

	src_const_alpha  = int( m_intensity * 2.55 );
	SrcRedColor   = redSrc   * src_const_alpha / 255.0;
        SrcGreenColor = greensrc * src_const_alpha / 255.0;
	SrcBlueColor  = blueSrc  * src_const_alpha / 255.0;
	SrcAlphaColor = alphaSrc * src_const_alpha / 255.0;

        destRedColor   = SrcRedColor    + ( 1 - SrcAlphaColor ) * redDest;
	destGreenColor = SrcGreenColor  + ( 1 - SrcAlphaColor ) * greenDest;
	destBlueColor  = SrcBlueColor   + ( 1 - SrcAlphaColor ) * blueDest;
	destAlphaColor = SrcAlphaColor  + ( 1 - SrcAlphaColor ) * alphaDest;

	ptPixels[i]
	= (destAlphaColor << 24 ) |                       
	  (destRedColor   << 16 ) |  
	  (destGreenColor << 8  ) | 
	  (destBlueColor);
}

Problem with SetWindowExtEx()

ashtwin2-Mar-11 1:30

ashtwin

2-Mar-11 1:30

Hi all,
the function SetWindowExtEx() is returning false for me sometimes. I am using MM_ANISOTROPIC mapping mode.
GetLastError() is returning error code 50(The request is not supported).
This is happening very rarely and only during print operation.
Can size may be a problem.

Re: Problem with SetWindowExtEx()

Luc Pattyn2-Mar-11 1:37

Luc Pattyn

2-Mar-11 1:37

Hi,

I don't know, however what I would do is this:
add some code to log all parameter values and the return value and the GetLastError value (only when it failed!) to a file when it succeeds and when it fails. Looking at those numbers is likely to tell you what is going on.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

ReadFile overlapped i\o

sawerr2-Mar-11 0:39

sawerr

2-Mar-11 0:39

Hi
I am using ReadFile with overlapped i\o in synchronous mode. I have 2 questions.

while (true)
{
    BOOL b = ReadFile(hSource, &buffer, 200, &k, &ov);
    if ((b && k ) == 0)
    {
        break;
    }

    ov.Offset = ov.Offset + k;

}
    }

The file that program reads is bigger than 200 byte so it must not return EOF. But it does.
When it reads first phase
b = 0 (TRUE), k == 0 which means synchronous read operation gets to the end of a file as described here:
http://msdn.microsoft.com/en-us/library/aa365690%28v=vs.85%29.aspx[^]

My first question is, why does program return EOF even though file 6KB.

My second question is,
I want to read file in a loop as seen here:
ov.Offset = ov.Offset + k;

But i don't understand what is the differences between offset and offsethigh. I mean which one must be increased? I don't really understand the effect of offset and offsethigh. First i thought offset must be beginning and offsethigh is the ending so i must advanced both of them but i think this is not true.

Thanks...

Luc Pattyn2-Mar-11 1:31

Luc Pattyn

2-Mar-11 1:31

Hi,

I'm only handling the second question: the file offset once was simply a 32-bit number; later on it had to become a 64-bit number (in order to handle very large files), and MS has chosen to represent such 64-bit number as a struct containing two 32-bit numbers called xyzHigh and xyz. Their combined value equals (xyzHigh<<32)+xyz, so what you need to do is add to the lower part, and if an overflow occurs, add that to the higher part.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

«_Superman_»2-Mar-11 2:57

«_Superman_»

2-Mar-11 2:57

I believe the way you're making the check is not right.

For an overlapped operation, no. of bytes read, k in this case will always be 0.
The actual bytes read is taken using GetOverlappedResult.

Now assume ReadFile returns TRUE, in which case b will be 1.
So now we have k with a value of 0 and b with a value of 1, which is a perfect result for an overlapped read.

Consider the check if ((b && k) == 0).
This translates to if ((1 && 0) == 0).
Which further translates to if (0 == 0).
Now this becomes true and the program thinks it has reached EOF.

Here is an excerpt from the documentation on how to check for EOF in a overlapped read operation -
if the file is opened with FILE_FLAG_OVERLAPPED and lpOverlapped is not NULL, the return value is zero (0) and GetLastError returns ERROR_HANDLE_EOF when the file pointer goes beyond the current end of file

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

Microsoft MVP (Visual C++)

Polymorphism in C

Richard MacCutchan2-Mar-11 3:05

Richard MacCutchan

2-Mar-11 3:05

Are you sure that the initial values in your OVERLAPPED structure are correct? Have you checked the error code when ReadFile() returns FALSE? Lastly, are you sure it is a good idea to use overlapped IO for what is such a simple file read?

I must get a clever new signature for 2011.

CPallini2-Mar-11 3:13

CPallini

2-Mar-11 3:13

Richard MacCutchan wrote:
Lastly, are you sure it is a good idea to use overlapped IO for what is such a simple file read?

Good point, indeed.
Smile | :)