Take the tutorial figures out of the games themselves

Both examples gain --screenshot PATH and --screenshot-frame N. The capture sits
between the world being drawn and the frame being presented, because
SDL_RenderPresent is where the target stops being readable, and it works under
the dummy video driver and the software renderer like the rest of the headless
path does.

`cmake --build build --target docs_game_figures` regenerates
docs/images/sidescroller.png and docs/images/jrpg.png by running each game to a
chosen frame. Same contract as docs_screenshots: deliberate, never part of a
build, because the PNGs are tracked. There is no --check counterpart, and the
target says why -- the sidescroller drives its physics from the wall clock, so a
byte comparison would fail for reasons that have nothing to do with the
documentation.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KzBDV2fqgnUAcqCKqKvc71

CMakeLists.txt

@@ -807,6 +807,35 @@ add_custom_target(${AKGL_DOCS_SCREENSHOTS_TARGET}
 # examples/CMakeLists.txt, one game at a time, for the same reason.
 if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/examples/CMakeLists.txt")
   add_subdirectory(examples)
+
+  # The figures at the top of chapters 20 and 21 are frames out of the games
+  # themselves, taken by --screenshot between the world being drawn and the
+  # frame being presented. Same contract as docs_screenshots above: deliberate,
+  # never part of a build, because the PNGs are tracked.
+  #
+  # There is no --check counterpart. docs_screenshots can compare because its
+  # figures are one deterministic frame of drawing calls; a game frame is not.
+  # The sidescroller drives its physics from the wall clock, so which pixel the
+  # player occupies depends on how fast the machine ran, and a byte comparison
+  # would fail for reasons that have nothing to do with the documentation.
+  add_custom_target(docs_game_figures
+    COMMAND ${CMAKE_COMMAND} -E env
+            SDL_VIDEODRIVER=dummy SDL_RENDER_DRIVER=software SDL_AUDIODRIVER=dummy
+            $<TARGET_FILE:sidescroller>
+            --assets "${CMAKE_CURRENT_SOURCE_DIR}/docs/tutorials/assets/sidescroller"
+            --autoplay --frames 110
+            --screenshot "${CMAKE_CURRENT_SOURCE_DIR}/docs/images/sidescroller.png"
+            --screenshot-frame 100
+    COMMAND ${CMAKE_COMMAND} -E env
+            SDL_VIDEODRIVER=dummy SDL_RENDER_DRIVER=software SDL_AUDIODRIVER=dummy
+            $<TARGET_FILE:jrpg>
+            --demo --frames 240
+            --screenshot "${CMAKE_CURRENT_SOURCE_DIR}/docs/images/jrpg.png"
+            --screenshot-frame 230
+    DEPENDS sidescroller jrpg
+    COMMENT "Regenerating the tutorial figures in docs/images"
+    VERBATIM
+  )
 endif()
 
 # Mutation testing copies the repository to scratch space, applies one small