Chapter 31: Software Drawing and Graphical Gameslinear-chapter31linear

Co-authored-by: Hsiang-Ying Fu <66062782+fuhsnn@users.noreply.github.com>
Co-authored-by: fuhsnn <66062782+fuhsnn@users.noreply.github.com>
Co-authored-by: Symious <14933944+symious@users.noreply.github.com>
Co-authored-by: Jun Kawasaki <jun784@gmail.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

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+# Chapter 31: Software Drawing and Graphical Games
+
+English | [日本語](README.ja.md)
+
+[Previous: Chapter 30 — Text Formatting and Diagnostics](../chapter30/README.md)
+
+Small graphical games drive this chapter's language and library work, starting
+with a pixel window for a Simple-written 2-D graphics library. MiniFB supplies
+the optional native window/input backend; drawing stays in Simple.
+
+The [drawing library](drawing.md) provides a pixel canvas, colors,
+rectangles, circles, thick lines, and bitmap labels. The
+[graphical tic-tac-toe game](examples/TicTacToeGraphical.smp) uses it for
+mouse/keyboard play against the terminal game's CPU strategy.
+The optional [audio library](audio.md) adds soft move sounds and rising
+or falling win/loss cues, played in the background by miniaudio.
+Hexadecimal colors (`0xe47b57`) and leading-zero octal font masks (`025755`)
+are supported by this chapter's integer literal syntax.
+
+```sh
+make -C chapter31 libs CTAGS=     # Once while online (also: init or lib).
+make -C chapter31 run-graphical-tictactoe CTAGS=
+```
+
+This explicitly builds the optional graphics/audio backends and opens a window. Use
+`graphical-tictactoe` instead to build the executable without starting it or
+requiring MiniFB.
+Dependencies stay cached under `chapter31/lib`, including across `make clean`.
+Only explicit `libs`/`init`/`lib` setup targets access the internet; other
+targets use local files and fail promptly if something needs downloading.
+
+The default build and test suite need no graphics dependencies. See
+[optional graphics](graphics.md) for building MiniFB, running the pixel
+example, and handling a missing backend. `make tests_nographics CTAGS=` runs
+all ordinary tests with graphics explicitly disabled.
+
+The inherited language and library are described in [Chapter 30](../chapter30/README.md).
+The [grammar and code map](31-grammar.md),
+[source layout](../../src/main/java/com/seaofnodes/simple/README.md), and
+[runnable examples](examples/) describe this snapshot.
+
+From the repository root:
+
+```sh
+make lib tests release CHAPTERS=chapter31 CTAGS=
+make -C chapter31 tictactoe CTAGS=
+```
+
+The game binary is `chapter31/build/examples/x86_64_v2_win64/TicTacToe.exe`
+on Windows and `chapter31/build/examples/x86_64_v2_SystemV/TicTacToe` on Linux.
+For a WSL build in the same checkout, use `CLZDIR=build/classes-linux` to keep
+Linux Java outputs separate from Windows outputs.
+
+IntelliJ has a `chapter31` module and a **chapter31 tests** run configuration.
+Inherited Java test names retain their historical chapter numbers.