Make each Zed instance use half the screen in 'start-local-collaboration' script

script/start-local-collaboration

@@ -17,23 +17,32 @@ MESSAGE
   exit 1
 fi
 
-github_login=$(curl -sH "Authorization: bearer $GITHUB_TOKEN" https://api.github.com/user | jq -r .login)
-
-other_github_login=nathansobo
-if [[ $github_login == $other_github_login ]]; then
-  other_github_login=as-cii
+# Start one Zed instance as the current user and a second instance with a different user.
+username_1=$(curl -sH "Authorization: bearer $GITHUB_TOKEN" https://api.github.com/user | jq -r .login)
+username_2=nathansobo
+if [[ $username_1 == $username_2 ]]; then
+  username_2=as-cii
 fi
 
+# Make each Zed instance take up half of the screen.
+screen_size=($(system_profiler SPDisplaysDataType | grep Resolution | head -n1 | egrep -o '[0-9]+'))
+width=$(expr ${screen_size[0]} / 2)
+height=${screen_size[1]}
+position_1=0,0
+position_2=${width},0
+
+# Authenticate using the collab server's admin secret.
 export ZED_ADMIN_API_TOKEN=secret
 export ZED_SERVER_URL=http://localhost:8080
-export ZED_WINDOW_SIZE=800,600
+export ZED_WINDOW_SIZE=${width},${height}
 
 cargo build
 sleep 0.1
 
+# Start the two Zed child processes. Open the given paths with the first instance.
 trap "trap - SIGTERM && kill -- -$$" SIGINT SIGTERM EXIT
-ZED_WINDOW_POSITION=0,0   ZED_IMPERSONATE=${github_login}       target/debug/Zed $@ &
+ZED_IMPERSONATE=${username_1} ZED_WINDOW_POSITION=${position_1} target/debug/Zed $@ &
 sleep 0.1
-ZED_WINDOW_POSITION=800,0 ZED_IMPERSONATE=${other_github_login} target/debug/Zed &
+ZED_IMPERSONATE=${username_2} ZED_WINDOW_POSITION=${position_2} target/debug/Zed &
 sleep 0.1
 wait