evince: disable all keyboard shortcuts except PageDown, PageUp

Question

I have file ~/.config/evince/accels but it is empty. what is the syntax for disabling the idiotic default keyboard shortcuts?

Can I perhaps "dump" the current shorcuts, and then edit?

I constantly lose my position on page by accidentally pressing some key.

I just want to keep PageDown and PageUp so that I can scroll the pages.

I am using Evince 43 on Debian

Answer 1

If we look at the sources, in NEWS we find

Evince 45.alpha

• Remove loading and saving of custom accels file

so I don't think that is supported anymore. Also in the sources, we have the code in ev-application.c

ev_application_startup (GApplication *gapplication)
 const gchar *action_accels[] = {
  "win.open",       "<Ctrl>O", NULL,
  "win.open-copy",  "<Ctrl>N", NULL,
...
 for (it = action_accels; it[0]; it += g_strv_length ((gchar **)it) + 1)
   gtk_application_set_accels_for_action (GTK_APPLICATION (application), it[0], &it[1]);

where we see the fixed bindings being set up.

To change or remove a binding we can edit this code and recompile the application, or more simply we can interpose a shim between the application and the dynamically loaded gtk library. The shim could, for example, not call the gtk_application_set_accels_for_action() function for win.open, and so remove the binding <Ctrl>O for that action. Or we could change the binding to make <Ctrl>Z work instead. Here's a suitable file shim_gtk.c:

/*
 * capture calls to a routine and replace with your code
 * gcc -Wall -O2 -fpic -shared -ldl -o shim_gtk.so shim_gtk.c
 * LD_PRELOAD=/.../shim_gtk.so /bin/evince
 * https://unix.stackexchange.com/q/787459/119298
 */
#define _GNU_SOURCE /* needed to get RTLD_NEXT defined in dlfcn.h */
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <dlfcn.h>

void gtk_application_set_accels_for_action(char *app, char *action, char **accels){
    static char *(*real_fn)(char *app, char *action, char **accels) = NULL;

    if (!real_fn) {
        real_fn = dlsym(RTLD_NEXT, "gtk_application_set_accels_for_action");
        char *error = dlerror();
        if (error != NULL) {
            fprintf(stderr, "%s\n", error);
            exit(1);
        }
    }
#if 0
    if(strcmp(action, "win.open")==0){
        fprintf(stderr, "not calling for %s\n", action);
    }else{
        fprintf(stderr, "doing call for %s\n", action);
        real_fn(app, action, accels);
    }
#endif
#if 1
    if(strcmp(action, "win.open")==0){
        fprintf(stderr, "binding for %s\n", action);
        static char *mybinding[] = { "<Ctrl>Z", 0 }; // nul terminated utf8
        real_fn(app, action, mybinding);
    }else{
        real_fn(app, action, accels);
    }
#endif
}

Here the #if 0 is used to disable some code, and #if 1 to enable some other example code to do as described above. Compile with

gcc -Wall -O2 -fpic -shared -ldl -o shim_gtk.so shim_gtk.c

and run with

LD_PRELOAD=/.../shim_gtk.so /bin/evince ...

replacing ... appropriately. You should remove the debugging fprintf() calls as they might interfere with the real use of stderr by the application.

Answer 2

Give these a try. Be sure to chmod +x filename to give them execute access. only_direction_keys.sh will turn off most of the keymap leaving the arrow and PgUp and PgDn keys and launches evince. Launch this first!

Key_reset.sh resets your keybindings to the settings you had before. You will want to run this after you are finished.

Please look through the code before running and make any changes you feel suit your needs. Evince is kind of a pain to change keybindings but this workaround seemed to work pretty well when I ran it through some tests. Not perfect, but gets the job done. Also, it is a good idea to check code before blindly running it from a stranger on the web :)

First, install xbindkeys:

sudo apt install xbindkeys

And the shell scripts:

1. only_direction_keys.sh:

#!/bin/bash

# Create a default xbindkeys configuration file if it doesn't exist
if [ ! -f ~/.xbindkeysrc ]; then
  touch ~/.xbindkeysrc
fi

# Backup the current xbindkeys config before we modify it
cp ~/.xbindkeysrc ~/.xbindkeysrc.bak

# Disable all keys except arrow keys and PageUp/PageDown

# Start by clearing the current xbindkeys configuration
> ~/.xbindkeysrc

# Define keybindings for the allowed keys (arrow keys and PgUp/PgDn)
# We will bind these keys to "do nothing" commands so they are active

# Up arrow
echo "'echo'" >> ~/.xbindkeysrc
echo "  m:0x0 + c:111" >> ~/.xbindkeysrc

# Down arrow
echo "'echo'" >> ~/.xbindkeysrc
echo "  m:0x0 + c:116" >> ~/.xbindkeysrc

# Left arrow
echo "'echo'" >> ~/.xbindkeysrc
echo "  m:0x0 + c:113" >> ~/.xbindkeysrc

# Right arrow
echo "'echo'" >> ~/.xbindkeysrc
echo "  m:0x0 + c:114" >> ~/.xbindkeysrc

# Page Up
echo "'echo'" >> ~/.xbindkeysrc
echo "  m:0x0 + c:112" >> ~/.xbindkeysrc

# Page Down
echo "'echo'" >> ~/.xbindkeysrc
echo "  m:0x0 + c:117" >> ~/.xbindkeysrc

# Now we will block all other keys by binding them to a dummy action
# Disable the remaining keys (this is a simple solution, not an exhaustive list)
for keycode in {1..255}; do
  # Skip the allowed keys (up, down, left, right, PgUp, PgDn)
  if [[ "$keycode" != "111" && "$keycode" != "116" && "$keycode" != "113" && "$keycode" != "114" && "$keycode" != "112" && "$keycode" != "117" ]]; then
  echo "'xdotool key --clearmodifiers F13'" >> ~/.xbindkeysrc
  echo "  m:0x0 + c:$keycode" >> ~/.xbindkeysrc
fi
done

# Apply the new xbindkeys configuration
xbindkeys -p

# Launch evince
evince

2. key_reset.sh:

#!/bin/sh
cp ~/.xbindkeysrc.bak ~/.xbindkeysrc
xbindkeys -p