Cut tracked hands out of screens so you see them through it (work in progress)

Where frame-hands tracks a hand between an eye and a screen, that eye sees the
room through the screen. handcut.cpp draws the screen's buffer side by side
(one half per eye) with the hands cut out, only while a hand is in front of it.
The cutouts command turns it on or off. ft-handtest tries it on a test panel.

Not yet tested in the headset.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

screens/build.sh

@@ -1,5 +1,6 @@
 #!/usr/bin/env bash
-# Build ft-screens in the dev container on the Frame (screens/build/ft-screens).
+# Build ft-screens in the dev container on the Frame (screens/build/ft-screens), and
+# ft-handtest, which tries the hand cutouts (handcut.cpp) on a test panel of its own.
 # compositor.c is the wlroots side (C; wlroots headers aren't C++), vr.cpp the OpenVR side.
 # vr.cpp needs OpenVR's IVRIPCResourceManagerClient (ImportDmabuf), which the header
 # shipped with SteamVR on the Frame predates, so the build uses the public header from
@@ -12,8 +13,12 @@ openvr=v2.15.6
 [ -f build/include/openvr-$openvr ] || { curl -fsSL "https://raw.githubusercontent.com/ValveSoftware/openvr/$openvr/headers/openvr.h" -o build/include/openvr.h && touch build/include/openvr-$openvr; }
 gcc -std=c11 -O2 -Wall -Wno-unused-parameter -c -o build/compositor.o compositor.c \
   $(pkg-config --cflags wlroots-0.20 wayland-server xkbcommon libdrm pixman-1)
-g++ -std=c++17 -O2 -Wall -Wno-missing-field-initializers -Ibuild/include -c -o build/vr.o vr.cpp
-g++ -o build/ft-screens build/compositor.o build/vr.o \
-  $(pkg-config --libs wlroots-0.20 wayland-server xkbcommon) \
-  -L/opt/steamvr/bin/linuxarm64 -lopenvr_api -Wl,-rpath,/opt/steamvr/bin/linuxarm64
-echo "built build/ft-screens"'
+cxx="g++ -std=c++17 -O2 -Wall -Wno-missing-field-initializers -Ibuild/include $(pkg-config --cflags egl glesv2 gbm libdrm)"
+$cxx -c -o build/vr.o vr.cpp
+$cxx -c -o build/handcut.o handcut.cpp
+$cxx -c -o build/handtest.o handtest.cpp
+vrlibs="$(pkg-config --libs egl glesv2 gbm) -L/opt/steamvr/bin/linuxarm64 -lopenvr_api -Wl,-rpath,/opt/steamvr/bin/linuxarm64"
+g++ -o build/ft-screens build/compositor.o build/vr.o build/handcut.o \
+  $(pkg-config --libs wlroots-0.20 wayland-server xkbcommon) $vrlibs
+g++ -o build/ft-handtest build/handtest.o build/handcut.o $vrlibs
+echo "built build/ft-screens build/ft-handtest"'