Extracting Single Images from a CImageList object

Introduction

While working on a project of mine using skinned buttons, I ran into problems when I tried to use a CImageList as the source of the state images.

The CImageList does not provide any direct access to the separate images within the list. I searched, and searched and searched and search... well you get the idea... Anyway after banging my head against the keyboard for 4 days, I finally found a solution.

The GetImageFromList function

The result of my headaches is the GetImageFromList function. If you are familiar with using CDCs then you are probably already calling this an obvious solution - but then, why are you reading this article in the first place?

Here is the function I managed to come up with (with the help of sites like this):

It takes 3 parameters, and returns nothing.

• lstImages: A pointer to the CImageList object containing all of the images.
• nImage: The index of the image that is going to be extracted.
• destBitmap: A pointer to the CBitmap object that is going to contain the extracted image.

The function makes a copy of the image list, and moves the requested image to the front of that list.

It then draws the requested image into the destination bitmap.

void CMyWindowClass::GetImageFromList(CImageList *lstImages, 
                             int nImage, CBitmap* destBitmap)
{    
     //First we want to create a temporary image list we can manipulate
     CImageList tmpList;
     tmpList.Create(lstImages);
     
    //Then swap the requested image to the first spot in the list 
    tmpList.Copy( 0, nImage, ILCF_SWAP );
    
    //Now we need to get som information about the image 
    IMAGEINFO lastImage;
    tmpList.GetImageInfo(0,&lastImage);
    
    //Heres where it gets fun
    //Create a Compatible Device Context using 
    //the valid DC of your calling window
    CDC dcMem; dcMem.CreateCompatibleDC (GetWindowDC()); 
    
    //This rect simply stored the size of the image we need
    CRect rect (lastImage.rcImage);
    
    //Using the bitmap passed in, Create a bitmap 
    //compatible with the window DC
    //We also know that the bitmap needs to be a certain size.
    destBitmap->CreateCompatibleBitmap (this->GetWindowDC(), 
                                      rect.Width (), rect.Height ());
    
    //Select the new destination bitmap into the DC we created above
    CBitmap* pBmpOld = dcMem.SelectObject (destBitmap);
    
    //This call apparently "draws" the bitmap from the list, 
    //onto the new destination bitmap
    tmpList.DrawIndirect (&dcMem, 0, CPoint (0, 0), 
           CSize (rect.Width (), rect.Height ()), CPoint (0, 0));
    
    
    //cleanup by reselecting the old bitmap object into the DC
    dcMem.SelectObject (pBmpOld);
}

It looks big, but remove the comments and you have a mere 12 lines of code.

Conclusion

I hope that this article can save at least one person from going through what I went through to find the answer.

Good Luck, and Happy Coding!!