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[Andrej Mitrovic]

On 7/9/11, Johannes Pfau <spam at example.com> wrote:
> I'm not sure if cairo's win32 backend uses some kind of
> acceleration? http://cairographics.org/threaded_animation_with_cairo/
> talks about performance & animations, it's quite gtk specific, but
> maybe there's some useful information in there.

I'm already using multithreading. The performance issue I'm having is
related to constantly creating and deleting a cairo surface and the
cairo context.

Here cairo uses a backbuffer, draws to it, and then I do a blit via a
GDI function:

case WM_PAINT:
            _buffer    = CreateCompatibleDC(hdc);
            hBitmap    = CreateCompatibleBitmap(hdc, width, height);
            hOldBitmap = SelectObject(_buffer, hBitmap);

            surf = cairo_win32_surface_create(_buffer);
            ctx = cairo_create(surf);

            DrawStuff(ctx, rc);

            BitBlt(hdc, 0, 0, width, height, _buffer, x, y, SRCCOPY);
            SelectObject(_buffer, hOldBitmap);
            DeleteObject(hBitmap);
            DeleteDC(_buffer);
            EndPaint(hwnd, &ps);

I'm trying to remove the calls to create/delete functions, I only
really need them in two cases: when I initialize the window, and when
the window is resized. If I do that I will still get performance
issues when resizing because I get numerous WM_SIZE messages very
rapidly as the window is resized, and just calling Create/Delete takes
about 10% CPU time.

Probably a more clever way to do this is to initially create a big
buffer that can fit the entire screen, and then just limit painting to
the visible rectangle. This way I could avoid calling create/delete.
But that wastes memory.

I'll look around the cairo newsgroups/websites to see how people
handle window resizing.