Dc Q!

[Arie]

Hi, Guys.

I have a question about DCs (Longs).
When I want to copy a DC into another DC and I do it like this:

FirstDC = SecondDC

So when I change the FirstDC the SecondDC changes too, and that's not what I wanted. I want to copy it.
Is there an API for this? or just a simple code?

Help please,
Arie.

[Sastraxi]

Try FirstDC = VarPtr(SecondDC). I dunno, sounds scary having Pointers in action in VB!

[CornedBee]

You cannot duplicate a dc. But you can use the SaveDC API to save the state of a device context, then restore it.

[CornedBee]

Sastraxi's code will most likely lead to an access violation.

[mlewis]

Use CreateDC to create a new DC, then BitBlt to copy the first onto the second. Do it all the time. Put the code into a function called CopyDC, put it into a module, and away you go.

[CornedBee]

But that's something different. What he wants is a copy of a screen dc so he can use two sets of settings (at least that's how I understand it), which you cannot. You can save a set of settings and later load it using SaveDC and RestoreDC.

[mlewis]

Originally posted by CornedBee
But that's something different. What he wants is a copy of a screen dc so he can use two sets of settings (at least that's how I understand it), which you cannot. You can save a set of settings and later load it using SaveDC and RestoreDC.

OK THIS is what he asked for:

So when I change the FirstDC the SecondDC changes too, and that's not what I wanted. I want to copy it.

He didn't ask for anything about copying DC settings; just contents...

[Sastraxi]

This is all too freaky for me... I'm outta here!

[CornedBee]

So when I change the FirstDC the SecondDC changes too, and that's not what I wanted. I want to copy it.

Does he mean the settings of SecondDC change too, or the content (what is displayed) change too?
Because you still cannot copy a DC. The return of CreateCompatibleDC will not draw to the screen, but to a memory location.

He didn't ask for anything about copying DC settings; just contents...

He asked for copying the DC, which is not possible. And maybe he doesn't know it, but to windows a DC is only a bunch of settings and a reference to a device, which stores the actual data (the device might be the screen or a printer or memory location or a DirectDraw surface, but the DC stores no data).

Arie, we need clarification.

[mlewis]

*sigh*

A Device Context stores a pointer to what roughly translates as image data. By using CreateCompatibleDC you can create a NEW DC that points to blank memory that is compatible with the screen DC. Then you copy the screen DC's image (i.e. contents) using BitBlt to the memory DC, and when you are done you copy them back and use DeleteObject on the memory DC.

[CornedBee]

Yeah, I know, but if you're a tech freak like I am the question means what I said.

Where's Arie anyway?

[Sastraxi]

Wouldn't it be ironic if he solved his problem on his own and just left

[mlewis]

Originally posted by CornedBee
Yeah, I know, but if you're a tech freak like I am the question means what I said.

Where's Arie anyway?

I've talked to dozens of other coders about DCs using the term "copy" to mean Blt'ing the contents. I've never heard anyone use the term like you do

[Arie]

Hey guys, relax.
I wasn't here a few days.

In the meanwhile I figured that what I need is to BitBlt from FirstDC into SecondDC. I needed only the image in it, nothing else.

I'll adapt the way that mlewis suggested.

Thank you all for helping,
Arie.

[CornedBee]

Ok, ok, I'm shutting up. I surely wouldn't use it that way, but it's now clear.