KWin script to automatically move and resize windows to fit left or right half of the screen when switching windows.

kwin_two_panes.js

var to_the_left = true;
previous_active_client_id = null;

function resize_client(client) {
  geo = client.geometry;
  geo.width = workspace.workspaceWidth / 2;
  geo.height = workspace.workspaceHeight - 30;
  client.geometry = geo;
}

function move_client(fun) {
  for (var i = 0; i < 10; i++) {
    fun();
  }
}

workspace.clientActivated.connect(function(client) {
  if (client === null) {
    return;
  } else if (previous_active_client_id === null) {
    previous_active_client_id = client.windowId;
  } else if (previous_active_client_id === client.windowId) {
    return;
  }
  
  resize_client(client);
  if (to_the_left === true) {
    move_client(workspace.slotWindowPackLeft);
    to_the_left = false;
  } else {
    move_client(workspace.slotWindowPackRight);
    to_the_left = true;
  }
  move_client(workspace.slotWindowPackUp);
});