CODEWITHSUNDEEP
c++winapi
Sossenbinder
Sossenbinder

Reputation: 5282

How can I erase the window background in an owner drawn static control?

I am currently developing a kind of "WinMerge" clone, and currently I am trying to implement a custom scrollbar which should later represent both compared files as a rectangle in the background each.

This is what it looks like at the startup:

enter image description here

However, after scrolling around a little bit, this is what I end up with:

enter image description here

As you can clearly see, only those parts look correct which I explicitely paint over in my paint routine:

void LocationPane::OnPaint(CDCHandle dc)
{
    DefWindowProc();

    dc = GetDC();

    DrawLocationPaneFigures(dc);
}

This is how my control is configured in my .rc file:

CONTROL         "",IDC_LOCATIONPANE,"Static",SS_OWNERDRAW | SS_NOTIFY | WS_BORDER | WS_GROUP,7,21,91,541

As you can see, it is an owner drawn control.

How can I erase the background for this control while repainting it?

Upvotes: 0

Views: 340

Answers (1)

zett42
zett42

Reputation: 27756

A static control with SS_OWNERDRAW style receives a WM_DRAWITEM message when it needs to be redrawn.

So first you need to replace your OnPaint() handler by a handler for WM_DRAWITEM. Instead of calling GetDC() use the device context supplied to you in the DRAWITEMSTRUCT.

To erase the background it's generally best to do it as part of the regular painting code to reduce flickering (by calling FillRect() for instance).

I suggest to always draw the whole client area of your control. Then you may handle WM_ERASEBKGND to return TRUE without calling DefWindowProc() to reduce flickering even more.

Upvotes: 1

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