MFC: how to reduce the time cost of OnInitialUpdate() for scrolling?

3
votes

I need to print data of many lines. Each line could have text wrapping so the height varies. To do scrolling, I need to derive the total height. Since each line could have different height, I can only go through every line to add up the heights, like below.

void CMyScrollView::OnInitialUpdate()
{
    ...
    for (auto &l: lines)
    {
        DrawText(dc, l.text, &rc, DT_EDITCONTROL | DT_WORDBREAK | DT_CALCRECT);
        total_height += rc.Height();
    }
    SetScrollSizes(MM_TEXT, CRect(..., total_height));
}

What I've found is that "DrawText(... DT_CALCRECT)" is pretty costly even without actual drawing. Is there way to accelerate the process in such case?

c++visual-c++mfc
Not an actual acceleration but doing this calculation in chunks would at least make your program responsive. This would involve defining a custom message and processing some number of lines each time the message is received, keep posting the message so long as you haven't reached the end of your data. – SoronelHaetir
Thanks, it works well! – user180574
I should add that if this is going to take more than a second or two that it would be a good idea to add some sort of progress indicator to the status bar. – SoronelHaetir
@SoronelHaetir, Good point, I am adding it... – user180574
@SoronelHaetir, chunks are new for me, can you add this comment to answer with a little codefragment. Thanks. – Tom Tom