<div dir="ltr">From what I can see, my issue boils down to CAIRO_OPERATOR_SOURCE not behaving as I would expect, with the use of an xcb backed surface. Namely, after doing a cairo_pop_group_to_source(), if I cairo_set_operator(cairo, CAIRO_OPERATOR_SOURCE), based on the docs I would expect the alpha channel to be copied from the intermediate pattern/surface as-is to the destination, with no blending. I actually observe this when the destination is *not* an xcb derived surface (I'm playing with a png one now, using the sample program I included). With an xcb backed surface like in my original program, setting the operator to CAIRO_OPERATOR_SOURCE results in a solid black background. Specifically, my case is this: // BEGIN render loop <div> cairo_push_group(cairo); cairo_set_source_rgba(cairo, 0.8, 0, 0, 0.1); // draw (lots of) stuff // END render loop cairo_pop_group_to_source(cairo); cairo_set_operator(cairo, CAIRO_OPERATOR_SOURCE); cairo_paint(cairo); // reset operator to CAIRO_OPERATOR_OVER xcb_flush(xcon); sleep(1); I've been looking into cairo-xcb / xcb specifics regarding this, but any cluesticks that could be provided would be appreciated. Cheers, -Ryan <blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex" class="gmail_quote">Hello, I've recently been using cairo + xcb to build a new application. I've hit a problem supporting transparency / alpha-blending, where I want to allow users to set the background window with an alpha value and have the root x11 window show through that. The raw transparency piece works fine and is easy in cairo + xcb, but I'm struggling with my main render loop -- it seems to add / accumulate the alpha values with each render, and doesn't remove previously drawn content with alpha values. I have more details below including a fully functioning prototype with my layout setup (also below and in a gist), but here's what I've been trying after much google'ing and searching the archives: My main render loop looks roughly like this (and I understand why this would accumulate opaqueness over time): // BEGIN render loop cairo_push_group(cairo); clear_background(); // draw (lots of) stuff // END render loop cairo_pop_group_to_source(cairo); cairo_paint(cairo); xcb_flush(xcon); sleep(1); where clear_background() is: cairo_set_source_rgba(cairo, 0.8, 0, 0, 0.1); cairo_paint(cairo); With that loop, as-is, I can see why the alpha values are accumulating with each render. To compensate, I've tried the following based on the cairo site's documentation, and browsing the archives, but with no success: 1. cairo_set_operator(cairo, CAIRO_OPERATOR_SOURCE); (and subsequent resets to *_OVER) I've tried this before the cairo_paint() at the END of the loop, as well as in the BEGIN loop (both before and after the cairo_push_group()). My understanding is that this copies the alpha from SOURCE as-is, with no blending, but I'm not observing that in the results, regardless of where I place it (and tweak the timing to confirm each step). Use of it *always* results in a black background, which makes me think I have something larger out-of-whack. 2. I've looked at other operators, but none seem applicable (and I've tested most in various setups like the above). 3. Using cairo_mask() / cairo_mask_surface() when using cairo_pop_group() (the raw one, returning a cairo_pattern_t) to render after the pop, but that also fails. My ultimate goals are basically these: 1. Have the window always reset to a consistent background of rgba = 0.8/0/0/0.1 2. Don't 'accumulate' alpha artifacts from the widgets drawn in the loop each time My sample code below illustrates what I'm trying and my setup. It draws a 200 x 200 pixel window (at x,y = 200,200). It has an initial background of rgba = 0.8/0/0/0.1, and a 50x50 pixel green square in the top left (rgba=0/1/0/0.5). Every second it redraws, and moves the square towards the bottom right. IDEALLY: 1. The background is *always* rgba = 0.8/0/0/0.1 2. Only one square (the most recent) is shown with rgba = 0/1/0/0.5 BUT what I observe (trying lots of variants): 1. The background gets more opaque with each render, eventually becoming solid 2. The previous renders of the green square persist and aren't cleared The code is below, along with build instructions, and available at: <a href="https://gist.github.com/ryanflannery/1649ce3dd45cb6e16088931262283386" target="_blank" style="color:rgb(17,85,204);font-family:monospace,monospace;font-size:12.8px">https://gist.github.com/ryanflannery/1649ce3dd45cb6e16088931262283386</a> Note the example includes a great deal of XCB setup, including logic to handle tiling window managers (my use case). I doubt that's of interest here, but I'm including it for completeness (but below the main cairo logic). Any feedback appreciated (on this or other conventions I have!) Cheers, -Ryan</blockquote></div></div>