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

6-Nov-07 13:13

It working definitely better than before, but what I am trying to do now is, rather than doing this work everytime I update/refresh the window, is there any way I can reduce this work, but doing this only once for each zoom constant? For now, this is how it goes..

CClientDC dc(this);<br />
CDC tempDC;<br />
tempDC.CreateCompatibleDC(NULL);<br />
CBitmap tempBMP;<br />
tempBMP.CreateCompatibleBitmap(&dc, 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);

where sp is the scroll position. But lets say I scrolled the image, in this case the zoom constant is still the same, I just need to update the position of the image wrt view window. I see stretching the bitmap all the time is very time consuming Unsure | :~

.

thanks,
-PNT

PKNT

C^hris L^osinger6-Nov-07 14:49

6-Nov-07 14:49

create a CBitmap object member of your window class. every time your zoom level changes:

1. delete the contents of that CBitmap
2. create a new (compatible) bitmap of the appropriate size
3. do your StretchBlt onto that

the code to do that is basically the same as what you have above, but you drawing into m_zoomedBitmap (or whatever) instead of tempBMP, and you use StretchBlt there.

then, when it's time to do the OnPaint/OnDraw, draw that member CBitmap with a normal BitBlt.

Kiran Satish7-Nov-07 6:50

7-Nov-07 6:50

I tried exactly what you said (I hope), declared a CBitmap member in Document class and using it instead of tempBMP like below..

CClientDC dc(this);<br />
if (zoom_const >1)<br />
{<br />
CDC tempDC;<br />
tempDC.CreateCompatibleDC(NULL);<br />
if (m_bZoomUpdate)//update bitmap for the first time when zoom_const changes<br />
{<br />
GetDocument()->m_zoomedBMP.CreateCompatibleBitmap(&dc, w*zoom_const,h*zoom_const);<br />
tempDC.SelectObject(&GetDocument()->m_zoomedBMP);<br />
dib->Draw(&tempDC, 0,0,w*GetDocument()->zoom_const,h*GetDocument()->zoom_const,0,0,w,h);		<br />
m_bZoomUpdate = false;<br />
}<br />
else<br />
tempDC.SelectObject(&GetDocument()->m_zoomedBMP);<br />
dc.BitBlt( 0, 0, w*zoom_const,h*zoom_const, &tempDC, sp.x, sp.y, SRCCOPY);<br />
}<br />
else //zoom_const =1<br />
dib->Draw(&dc, 0,0,w*zoom_const,h*zoom_const,sp.x,sp.y,w,h);

It works... and the drawing is as normal with no delays... Now time for getting the exact location of a pixel in zoom mode D'Oh! | :doh:

.

thanks,
-PNT.

PKNT

Kiran Satish8-Nov-07 7:17