C / C++ / MFC

30-Oct-07 7:00

I am creating a small image viewer interface in MFC to do some processing on our research images which are very big in size (5000x3000). In that I am using StretchBlt to display image on DC, this works fine when I am using a scale of 1:1, but when I increase the scale, the display refresh is very slow when I use the scroll bar and the image becomes very bad when I compress an image (but I dont need to compress an image though). Is there any alternative to stretchblt().

Looking at CImage class, I can create an Image object from my current HBITMAP.
Looking at Image class from GDI+, I didnt see any constructor for Image object from HBITMAP.

Any suggestions???

thanks in advance,
-PNT

PKNT

led mike30-Oct-07 7:09

led mike

30-Oct-07 7:09

Have you look at the articles here on CodeProject?

Here is one example[^]

C^hris L^osinger30-Oct-07 7:19

30-Oct-07 7:19

instead of restretching with each redraw, you might be better off stretching once to a second bitmap, then re-blting that stretched bitmap for normal OnPaint handling.

Kiran Satish31-Oct-07 6:34

31-Oct-07 6:34

I tried this way, but it displays just a white page... here is how I did it

working version

CClientDC dc(this);<br />
dib->Draw(&dc,x,y);

where dib->Draw function is defined as below-

void DIBSection::Draw(CDC* pdcDest, int xs, int ys) <br />
{<br />
pdcDest->BitBlt( 0, 0, m_size.cx, m_size.cy, m_pdc, xs, ys, SRCCOPY);<br />
}

modified version

CDC* m_pdc = new CDC ;<br />
m_pdc->CreateCompatibleDC(NULL);<br />
dib->Draw(m_pdc, 0, 0, w*zoom_const, h*zoom_const, 0, 0, w, h);<br />
CClientDC dc(this);<br />
dc.SelectObject(m_pdc);<br />
dc.BitBlt(0, 0, w*zoom_const, h*zoom_const, m_pdc, 0, 0, SRCCOPY);

where w, h are width and height of my image and zoom const is the scaling factor. dib is an object of my DIBSection class. dib->Draw does nothing more except it calls the dc->BitBlt function with its own defined dc in the Blt function, which is created when the dib object is created with bitmap data.

am I doing something wrong here??

-PNT

PKNT

C^hris L^osinger31-Oct-07 7:28

31-Oct-07 7:28

Kiran Satish wrote:
dc.SelectObject(m_pdc);

you can't select a DC into another DC.

you need to create a compatibleDC, create a compatibleBitmap (of the scaled size), select that btimap into that DC, then BitBlt from your source DC onto the scaled DC/bitmap. then you can use that scaled bitmap to draw

Kiran Satish1-Nov-07 11:18

1-Nov-07 11:18

Thanks for the reply, I tried as you suggested...

<br />
CClientDC dc(this);<br />
CDC tempDC;<br />
tempDC.CreateCompatibleDC(NULL);<br />
CBitmap tempBMP;<br />
tempBMP.CreateCompatibleBitmap(&tempDC, w*zoom_const,h*zoom_const);<br />
tempDC.SelectObject(tempBMP);<br />
dib->Draw(&tempDC, 0,0,w*zoom_const,h*zoom_const,0,0,w,h);		<br />
dc.BitBlt( 0, 0, w*zoom_const,h*zoom_const, &tempDC, sp.x, sp.y, SRCCOPY);

it still shows me a black image.... am I still doing wrong??, sorry I am not soo familiar with CBitmaps and DCs. Just learning now Smile | :)

-PNT

PKNT

C^hris L^osinger1-Nov-07 12:09

1-Nov-07 12:09

Kiran Satish wrote:
dib->Draw(&tempDC

what is Draw expecting as its first parameter (CDC, HDC, CDC*) ?

as a test, you might try something simple like drawing a rectangle (CDC::FillSolidRect) on that tempBMP, just to see if maybe the problem is in the Draw function.

also tempDC.SelectObject(tempBMP); should probably be tempDC.SelectObject(&tempBMP);

Kiran Satish1-Nov-07 12:57

1-Nov-07 12:57

That draw function is same before...

<br />
void DIBSection::Draw(CDC* pdcDest, int x, int y, int nw, int nh, int xs, int ys, int w, int h)<br />
{<br />
pdcDest->StretchBlt( x, y, nw, nh, m_pdc, xs, ys, w, h, SRCCOPY);<br />
}

where m_pdc is the DC of dib where the actual pixel data is stored.

will try the simple fillrect function.

-PNT

PKNT

Kiran Satish1-Nov-07 13:45

1-Nov-07 13:45

I tried to fill the DC with RED color and it still shows up as 300x300 black image Confused | :confused:

...

tempDC.SelectObject(&tempBMP);<br />
tempDC.FillSolidRect(0,0,300,300,RGB(255,0,0));<br />
dc.BitBlt( 0, 0, 300,300, &tempDC, 300, 300, SRCCOPY);

-PNT

PKNT

C^hris L^osinger1-Nov-07 14:04

1-Nov-07 14:04

when you call CreateCompatibleBitmap, try giving it the DC you're going to BitBlt it to, not the temp DC.

Kiran Satish2-Nov-07 8:03

2-Nov-07 8:03

Yeh.. tht made it work... but if you dont mind, could you tell me why it is like tht??

thanks,
-PNT

PKNT

C^hris L^osinger2-Nov-07 8:15

2-Nov-07 8:15

the Bitmap needs to be compatible with the DC you're BitBlt'ing to. when you use the memory DC for the C*C*Bitmap call, the bitmap created will be monochrome. if you use an output DC, it will match the settings of that DC.

or, as Microsoft puts it:

Kiran Satish6-Nov-07 13:13