🚀 go-pugleaf

"UO" <uo@uott> wrote in message news:489877b5$1@newsgroups.borland.com...

> Here, does the word "CreateDC" include "CreateCompatibleDC?"

CreateDC() and CreateCompatibleDC() are unique and unrelated functions.  But 
in this particular context, you are being warned the same thing.  Do not 
hold on to any HDC that you do not explicitally create yourself.

> What about GetDC/GetWindowDC?

Do not hold on to those HDCs between messages.

> Until I started reading Petzold's book I had used SelectObject() as:

That is the correct way to use it.  Always re-select any previous GDI 
resources you replace when you are done using them.

> case WM_PAINT:
>    hdc = GetDC(hwnd);

You should be looking at the wParam value.  If not 0, it contains an HDC 
that you need to draw to instead.

>    SelectObject(hdc, hBrushOld); //1

> When do I have to save / restore old attributes, here the hBrushOld?

When you are done using them before exiting.

> Is the line marked with //1 necessary?

Yes.

> Another book gives the following code for BitBlt function as an example:
<snip>
> Is the line marked with //2 necessary?

Yes, for the same reason.

> This book restores all GDI objects, not just bitmaps.

That is the correct thing to do.  If you replace any GDI object with your 
own, restore the old one when you are done.

> Another material, a tutorial actually, gives the following code:
<snip>
> The default bitmap is restored again.

As it should be.

> So, when is it necessary to restore default attributes?

Always.

> Assume the following code:
<snip>
> Is it ok to delete hdcMem while hBitmap is selected into hdcMem

No.

> or should I use the following code?

Yes.


Gambit 

"Remy Lebeau (TeamB)" <no.spam@no.spam.com> wrote in message 
news:489892df$1@newsgroups.borland.com...


>Do not hold on to any HDC that you do not explicitally create yourself.

Then, yes, CreateCompatibleDC/DeleteDC can be used between messages


> That is the correct way to use it.  Always re-select any previous GDI 
> resources you replace when you are done using them.
>
>> case WM_PAINT:
>>    hdc = GetDC(hwnd);
>
> You should be looking at the wParam value.  If not 0, it contains an HDC 
> that you need to draw to instead.

Sorry, my mistake. The code should be:

case WM_PAINT:
    hdc = BeginPaint(hdc, &ps);
    hBrushOld = SelectObject(hdc, hBrush);
    GetClientRect(&rect);
    Rectangle(hdc, 10, 20, 30, 40);
    SelectObject(hdc, hBrushOld); //1
    EndPaint(hdc, &ps);
break;


>> So, when is it necessary to restore default attributes?
>
> Always.

It's quite weird that a textbook which is considered as "classic" or "best" 
by many people,
can contain so arguable material.

Thanks again... 

"UO" <uo@uott> wrote in message news:4898a6fd$1@newsgroups.borland.com...

> Sorry, my mistake. The code should be:

Your code is still not looking at the wParam value.  And it is passing an 
invalid HWND to both BeginPaint() and EndPaint() as well.  Try this instead:

    case WM_PAINT:
        if( wParam == 0 )
            hdc = BeginPaint(hwnd, &ps);

        else
            hdc = reinterpret_cast<HDC>(wParam);
        ...
        if( wParam == 0 )
            EndPaint(hwnd, &ps);
        break;


Gambit 

"UO" <uo@uott> wrote:

>It's quite weird that a textbook which is considered as "classic" or "best" 
>by many people, can contain so arguable material.

Petzold (at least the earliest editions) were the best purely by dint of
being pretty much the *only* books with the requisite information in.
They were lousy so far as the quality of their C++ went, but they did
give examples which worked, even if the results were not production code
quality. 

(Once you've got something which makes the APIs work, it's your job to
see how it works, and then produce the good stuff. Not everyone did ...)

Alan Bellingham
-- 
Team Browns
<url:http://www.borland.com/newsgroups/> Borland newsgroup descriptions
<url:http://www.borland.com/newsgroups/netiquette.html>      netiquette

"Alan Bellingham" <alanb@episys.com>, haber iletisinde sunlari 
yazdi:brkh94lo4g60fric1ii9g9uki4af7bul9m@4ax.com...
> "UO" <uo@uott> wrote:
>
> (Once you've got something which makes the APIs work, it's your job to
> see how it works, and then produce the good stuff. Not everyone did ...)

The main concern of my messages was gdi memory leak. I think it is
quite hard to produce a memory leak and "see how it works" in recent
Windows systems. So, I still think everyone needs theoretical-correct
information, a theoretical-correct book.

UO 

"Remy Lebeau (TeamB)" <no.spam@no.spam.com>, haber iletisinde �unlar� 
yazd�:4898bd3c$1@newsgroups.borland.com...
>
> "UO" <uo@uott> wrote in message news:4898a6fd$1@newsgroups.borland.com...
>
>> Sorry, my mistake. The code should be:
>
> Your code is still not looking at the wParam value.  And it is passing an 
> invalid HWND to both BeginPaint() and EndPaint() as well.  Try this 
> instead:
>
>    case WM_PAINT:
>        if( wParam == 0 )
>            hdc = BeginPaint(hwnd, &ps);
>
>        else
>            hdc = reinterpret_cast<HDC>(wParam);
>        ...
>        if( wParam == 0 )
>            EndPaint(hwnd, &ps);
>        break;
>
>
> Gambit

Sorry, I've made a typing mistake again. It should:
case WM_PAINT:
    hdc = BeginPaint(hwnd, &ps);
    hBrushOld = SelectObject(hdc, hBrush);
    GetClientRect(&rect);
    Rectangle(hdc, 10, 20, 30, 40);
    SelectObject(hdc, hBrushOld); //1
    EndPaint(hwnd, &ps);
break;
(But appearently  you understood what I meant)

I'm not using common controls currently.

Anyway, should I use a ReleaseDC() or something after
"hdc = reinterpret_cast<HDC>(wParam);" ?

UO 

"UO" <uo@uott> wrote in message news:48995465$1@newsgroups.borland.com...

> Anyway, should I use a ReleaseDC() or something after
> "hdc = reinterpret_cast<HDC>(wParam);" ?

No.  The sender of the message owns that HDC and will release it accordingly 
after the WM_PAINT message handler exits.


Gambit