On Mon, Nov 9, 2020 at 4:30 PM Per Dalgas Jakobsen <p...@knaldgas.dk> wrote: > > Hi, > > I'm trying to learn coding with XCB and found an issue the XCB people > think should be placed her. > Drawing a diamond seems to render correctly only if started (end ended) > at the right-most corner, drawing from any other corner causes the > right-most pixel not to be rendered.
libxcb has no involvement with actual drawing or rendering. It's sole function is to transmit requests, and all their parameters, to the X server which then executes them. libxcb is really just a very thin mapping layer between a functional API and X protocol messages. What you want to do is investigate the formal X protocol specification, which defines how various coordinates and parameters get interpreted. > xcb_poly_line (connection, XCB_COORD_MODE_ORIGIN, window, > foreground, 5, diamond); This would be the PolyLine request: https://www.x.org/releases/X11R7.7/doc/xproto/x11protocol.html#requests:PolyLine Note the nuanced detail of how various coordinates get interpreted and the meticulous detail in defining the actual drawn pixels. Elsewhere in this specification you will find the formal definition of the low level data points. For example, in general, line drawing-related requests specify the coordinates for the center of the drawn line. A question then arises, if the line's width is given as an even number of pixels, what actual pixels get drawn? If the line's width is given as 1, 3 or 5 pixels, for example, and it's a vertical line, which pixels get drawn is not such a big mystery. But what if it's 2 or 4 pixels, then what? You're going to have to sift through the specification, to get the details of what happens. That's just one example (whose answer I don't recall off the top of my head), you'll have to decipher what's happening in your case similarly. _______________________________________________ xorg@lists.x.org: X.Org support Archives: http://lists.freedesktop.org/archives/xorg Info: https://lists.x.org/mailman/listinfo/xorg Your subscription address: %(user_address)s
