Is this how I make custom controls both transparent and flicker-free in Windows? Or do I have one of these steps wrong?

Question

I could begin by asking the question outright or by citing my sources (this, this, this, and this) descriptively, but I'll walk you ll through what I'm trying to do instead.

Let's start with a main window. It has its own window class whose hbrBackground is set to COLOR_BTNFACE + 1. Now let's do

EnableThemeDialogTexture(hwnd, ETDT_ENABLE | ETDT_USETABTEXTURE)

so the tab control we're about to add will be drawn with visual styles. (Try Windows XP with the standard Luna theme for best results.) Now let's add a tab control and two tabs.

On the first tab, we create an instance (let's call it container) of a new window class. This window class is going to hold various controls. I could set hbrBackground to COLOR_BTNFACE + 1, but then it will draw over the tab background. So I want this new child window to be transparent. So what I do is

1. set the class hbrBackground to GetStockObject(HOLLOW_BRUSH)
2. set container's extended style to WS_EX_TRANSPARENT
3. set the class WM_ERASEBKGND handler to do SetBkMode((HDC) wParam, TRANSPARENT); return 0; to set the device context and have Windows draw the transparent background.

So far so good, right? I'm not sure if I'm really doing all this correctly, and I'd like this to also be flicker-free, which doesn't seem to happen: when I resize the window (at least in wine) I get either flicker or garbage drawn (even in child controls, somehow!). Windows XP in a VM just shows flicker. I tried tweaking some settings but to no avail.

But wait, now I want to have another control, one that just draws some bitmap data. On the next tab, create another container, then have a third window class area as a child of that. area only draws in the upper-left 100x100 area and has scrollbars; the rest of the window area should be transparent.

Right now, what I have for area is:

1. the window class hbrBackground set to NULL and styles CS_HREDRAW and CS_VREDRAW set
2. the extended window style being 0
3. the WM_ERASEBKGND simply doing return 1;
4. the WM_PAINT filling the entire update rect with COLOR_BTNFACE + 1 before drawing, and rendering all of it

This is flicker-free, but obviously not transparent. NOW I'm really not sure what to do, because I want the area to be transparent in such a way that it shows the tab control background. Again, I tried tweaking settings to bring them closer to what I tried above with container, but I got either flicker or invalidation leftovers when I tried.

So how do I get both of these custom control types (the container and the drawing area) to be both flicker-free and transparent?

I presently must target Windows XP at a minimum, though if the solution would be easier with Vista+ only I'd be happy to keep that solution on the side in case I ever drop XP support (unfortunately Stack Overflow doesn't let me hand out silver medals...).

Thanks!

Answer 1

To paint your window in a manner that is "flicker free", you will need to paint your window to a bitmap, then copy the bitmap to the destination device context. On Windows XP, you will need to create a bitmap, adjust the origin of the drawing DC and then paint your window. On Vista and later you can use BeginBufferedPaint and its associated routines to do the buffering for you.

Once you have buffered painting working, you can then use WM_PRINTCLIENT to paint your window's parent window into the your drawing DC before you do any actual drawing. Unfortunately, not all windows will support WM_PRINTCLIENT.

You could consider using DrawThemeParentBackground, rather than WM_PRINTCLIENT directly.

Combining these two methods together will leave you with transparent flicker-free drawing.