initialization.go

package main

import (
    "fmt"
    "os"

    "github.com/jezek/xgb"
    "github.com/jezek/xgb/xinerama"
    "github.com/jezek/xgb/xproto"
)


// -----------------------------------------------------------------------------
// Note: Since functions in this file are related to initialization and thus
// execute at a time when the program is still building toward a viable state,
// these functions intentionally exit via a series of explicit commands,
// cleaning up only what has already been initialized rather than simply
// calling the normal illi die/restart functions.
// -----------------------------------------------------------------------------


// Note: The caller is responsible for tracking the lifetime of the returned X
// connection and calling connection.Close() when appropriate.
func connectToXServer() *xgb.Conn {
    connection, err := xgb.NewConn()
    if err != nil {
        fmt.Fprintf(os.Stderr, "ILLI: Failed to connect to X server: %s\n", err.Error())
        os.Exit(1)
    }
    return connection
}

func getAttachedScreens(conn *xgb.Conn) (screens []xinerama.ScreenInfo) {
    // Attempt to use xinerama to obtain screen information.
    err := xinerama.Init(conn)
    if err != nil {
        fmt.Fprintf(os.Stderr, "ILLI: Unable to initialize xinerama: %s\n", err.Error())
    } else { // Xinerama successfully initialized.
        reply, err := xinerama.QueryScreens(conn).Reply()
        if err != nil {
            fmt.Fprintf(os.Stderr, "ILLI: Unusable result when querying screens through xinerama: %s\n", err.Error())
        } else {
            screens = reply.ScreenInfo
            return
        }
    }

    // Since we were unable to obtain the screen information via xinerama, we
    // fall back to requesting ScreenInfo directly from the X server.
    setup := xproto.Setup(conn)
    if setup == nil || len(setup.Roots) < 1 {
        fmt.Fprintf(os.Stderr, "ILLI: Unusable ScreenInfo received from X server.\n")
        conn.Close()
        os.Exit(1)
    } else {
        screens = []xinerama.ScreenInfo{
            xinerama.ScreenInfo{
                Width:  setup.Roots[0].WidthInPixels,
                Height: setup.Roots[0].HeightInPixels,
            },
        }
        return
    }
    return // Should be unreachable
}

func getXRoot(conn *xgb.Conn) xproto.ScreenInfo {
    setup := xproto.Setup(conn)
    if setup == nil || len(setup.Roots) < 1 {
        fmt.Fprintf(os.Stderr, "ILLI: Failed to determine X root.\n")
        conn.Close()
        os.Exit(1)
    }
    return setup.Roots[0]
}

func getKeyboardMap(conn *xgb.Conn) (keymap [256][]xproto.Keysym) { // TODO: Why 256?
    const ( // TODO: Why? How does the keymap work under the hood?
        loKey = 8
        hiKey = 255
    )

    m := xproto.GetKeyboardMapping(conn, loKey, hiKey-loKey+1)
    r, err := m.Reply()
    if err != nil || r == nil {
        fmt.Fprintf(os.Stderr, "ILLI: Failed to load keymap from X server: %s\n.", err.Error())
        conn.Close()
        os.Exit(1)
    }

    for i := 0; i < hiKey-loKey+1; i++ {
        keymap[loKey+i] = r.Keysyms[i*int(r.KeysymsPerKeycode) : (i+1)*int(r.KeysymsPerKeycode)]
    }
    return keymap
}

func registerForKeyEvents(conn *xgb.Conn, root xproto.ScreenInfo, keymap [256][]xproto.Keysym) {
    // First we populate []grabs with the keysym and modifiers we seek.
    grabs := []struct {
        sym       xproto.Keysym
        modifiers uint16
        codes     []xproto.Keycode
    }{
        // TODO: Need to define a config table and do both keysym grabs and
        // main event loop using the config table rather than hardcoding key
        // assignments throughout the code.
        {
            sym:       XK_q,
            modifiers: xproto.ModMask1 | xproto.ModMaskShift,
        },
        {
            sym:       XK_Return,
            modifiers: xproto.ModMask1 | xproto.ModMaskShift,
        },
    }

    // Next we use the keymap provided by the X server to identify the keycodes
    // corresponding to the keysyms in []grabs.
    for i, syms := range keymap {
        for _, sym := range syms {
            for c := range grabs {
                if grabs[c].sym == sym {
                    grabs[c].codes = append(grabs[c].codes, xproto.Keycode(i))
                }
            }
        }
    }

    // Finally, we register with the X server for each combo of
    // keycode+modifiers in []grabs.
    for _, grabbed := range grabs {
        for _, code := range grabbed.codes {
            err := xproto.GrabKeyChecked(
                conn,
                false,
                root.Root,
                grabbed.modifiers,
                code,
                xproto.GrabModeAsync,
                xproto.GrabModeAsync,
            ).Check()
            if err != nil {
                fmt.Fprintf(os.Stderr,
                    "ILLI: Failed to register keycode 0x%X with modifier(s) 0x%X: %s\n",
                    code, grabbed.modifiers, err.Error())
            }

        }
    }
}

// In addition to the basic key/button press/release events, by registering for
// events like SubstructureRedirect, we are declaring our intent to act as
// window manager for this X server. Only one WM is allowed per X server, a
// policy enforced on the X server's side by refusing the registration request
// for events like SubstructureRedirect if an existing process already receives
// those events (i.e. is already the window manager).
func becomeWM(conn *xgb.Conn, root xproto.ScreenInfo) {
    err := xproto.ChangeWindowAttributesChecked(
            conn,
            root.Root,
            xproto.CwEventMask,
            []uint32{
                xproto.EventMaskKeyPress |
                xproto.EventMaskKeyRelease |
                xproto.EventMaskButtonPress |
                xproto.EventMaskButtonRelease |
                xproto.EventMaskStructureNotify |
                xproto.EventMaskSubstructureRedirect,
                // TODO: Should we also register for EventMaskSubstructureNotify ?
                //       Where is the authoritative list of events located?
            }).Check()
    if err != nil {
        fmt.Fprintf(os.Stderr, "ILLI: Unable to register as WM with X server: %s\n", err.Error())
        conn.Close()
        os.Exit(1)
    }
}