Add Emscripten/WebAssembly build target

Builds a browser-playable .html/.js/.wasm/.data via `./build-web.sh` (no
new CMake top-level target — Emscripten is detected at configure time and
takes the existing kobodl through a web-flavored pipeline).

Key pieces:
- CMakeLists.txt: route SDL3 through `--use-port=sdl3`; substitute
  `--use-port=libpng` for the missing sdl3_image port (Emscripten 5.0.7
  ships only sdl3 + sdl3_ttf). pthread (atomics+bulk-memory) lifted to
  kobo_deps so every TU agrees with wasm-ld's --shared-memory. Link with
  -sASYNCIFY (avoids rewriting kobo's blocking main loop around
  emscripten_set_main_loop), -sALLOW_MEMORY_GROWTH/-sMAXIMUM_MEMORY=1gb,
  -sPTHREAD_POOL_SIZE=4, -lidbfs.js, and --preload-file data@/data.
- graphics/img_compat.{h,c}: libpng-backed IMG_Load shim, used in
  sprite.c / gfxengine.cpp / filters.c via #include "img_compat.h".
  Native builds passthrough to <SDL3_image/SDL_image.h> unchanged.
- web/shell.html: HTML wrapper that mounts /home as IDBFS for persistent
  scores/config. Startup gated on addRunDependency until syncfs(true)
  finishes, then /home/scores is mkdir'd post-load (the game's addPlayer
  doesn't auto-create the score dir; see TODO in score.cpp).
  beforeunload + visibilitychange flushes /home back to IndexedDB.
- build-web.sh: emcmake wrapper + a static server that sets the
  COOP/COEP headers SharedArrayBuffer/pthreads require.

Source fixes needed to build under Emscripten's libc/libcxx:
- Renamed enemy_kind `pipe2` -> `pipe2k` (collided with libc pipe2(2)
  always declared in Emscripten's <unistd.h>).
- graphics/toolkit.cpp: added missing <stdio.h> for snprintf (Emscripten's
  libcxx headers don't pull it in transitively).
- states.cpp: gated the "Quit Kobo Deluxe" main-menu button on
  !__EMSCRIPTEN__; exit() on the web leaves a dead canvas.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CMakeLists.txt

@@ -14,6 +14,13 @@ option(KOBO_ENABLE_OSS "Build OSS audio backend (Linux)" OFF)
 option(KOBO_ENABLE_ALSA "Build ALSA audio backend (Linux)" OFF)
 option(KOBO_ENABLE_EPM "Extreme Pickyness Mode (-Wall -Werror)" OFF)
 
+# Emscripten target: SDL renderer maps to WebGL, no desktop GL needed.
+if(EMSCRIPTEN)
+    set(KOBO_ENABLE_OPENGL OFF CACHE BOOL "Use OpenGL rendering layer" FORCE)
+    set(KOBO_ENABLE_OSS    OFF CACHE BOOL "Build OSS audio backend"   FORCE)
+    set(KOBO_ENABLE_ALSA   OFF CACHE BOOL "Build ALSA audio backend"  FORCE)
+endif()
+
 # ---------------------------------------------------------------------------
 # Feature detection
 # ---------------------------------------------------------------------------
@@ -36,8 +43,21 @@ check_symbol_exists(_vsnprintf    stdio.h HAVE__VSNPRINTF)
 # Third-party libraries
 # ---------------------------------------------------------------------------
 # Migrating to SDL 3. Homebrew: `brew install sdl3 sdl3_image`.
+# Emscripten 5.x ships an sdl3 port but no sdl3_image yet — we substitute
+# libpng + a small shim (graphics/img_compat.c) for IMG_Load. The
+# `--use-port` flags must appear in both compile and link phases.
+if(EMSCRIPTEN)
+    add_library(SDL3::SDL3 INTERFACE IMPORTED)
+    target_compile_options(SDL3::SDL3 INTERFACE --use-port=sdl3)
+    target_link_options(SDL3::SDL3    INTERFACE --use-port=sdl3)
+
+    add_library(SDL3_image::SDL3_image INTERFACE IMPORTED)
+    target_compile_options(SDL3_image::SDL3_image INTERFACE --use-port=libpng)
+    target_link_options(SDL3_image::SDL3_image    INTERFACE --use-port=libpng)
+else()
     find_package(SDL3 CONFIG REQUIRED)
     find_package(SDL3_image CONFIG REQUIRED)
+endif()
 
 if(KOBO_ENABLE_OPENGL)
     find_package(OpenGL)
@@ -65,7 +85,17 @@ endif()
 # ---------------------------------------------------------------------------
 # Platform-specific install layout (matches the old autotools behavior)
 # ---------------------------------------------------------------------------
-if(APPLE)
+if(EMSCRIPTEN)
+    # In the browser, "data" is preloaded into Emscripten's virtual FS at /.
+    # Config/scores live under /home which we mount as IDBFS for persistence
+    # (see Module.preRun in the HTML shell / build-web.sh).
+    set(KOBO_BUNDLE_STYLE "web")
+    set(KOBO_EXEFILE       "kobodl.html")
+    set(KOBO_DATA_DIR      "/data")
+    set(KOBO_SCORE_DIR     "/home/scores")
+    set(KOBO_CONFIG_DIR    "/home")
+    set(KOBO_CONFIG_FILE   ".kobodlrc")
+elseif(APPLE)
     set(KOBO_BUNDLE_STYLE "macosx")
     set(KOBO_EXEFILE       "kobodl")
     set(KOBO_DATA_DIR      "EXE>>../Resources")
@@ -139,6 +169,13 @@ if(UNIX AND NOT APPLE)
     target_link_libraries(kobo_deps INTERFACE m)
 endif()
 
+if(EMSCRIPTEN)
+    # -pthread enables wasm atomics+bulk-memory; every TU must agree on it or
+    # wasm-ld rejects --shared-memory.
+    target_compile_options(kobo_deps INTERFACE -pthread)
+    target_link_options(kobo_deps    INTERFACE -pthread)
+endif()
+
 if(KOBO_ENABLE_EPM)
     target_compile_options(kobo_deps INTERFACE
         -Wall -Werror -Wwrite-strings -fno-builtin
@@ -168,6 +205,32 @@ target_include_directories(kobodl PRIVATE ${CMAKE_SOURCE_DIR}/data/sfx)
 target_link_libraries(kobodl PRIVATE graphics sound eel kobo_deps)
 set_target_properties(kobodl PROPERTIES OUTPUT_NAME ${KOBO_EXEFILE})
 
+if(EMSCRIPTEN)
+    # ASYNCIFY lets the existing blocking main loop (gengine->run(), SDL_Delay)
+    # yield to the browser without rewriting it around emscripten_set_main_loop.
+    # pthread (atomics+bulk-memory) is applied via kobo_deps for every TU.
+    # The data directory is baked into the .data sidecar via --preload-file.
+    target_link_options(kobodl PRIVATE
+        -sASYNCIFY=1
+        -sALLOW_MEMORY_GROWTH=1
+        -sINITIAL_MEMORY=128MB
+        -sMAXIMUM_MEMORY=1gb
+        -sPTHREAD_POOL_SIZE=4
+        -sEXIT_RUNTIME=1
+        -sFORCE_FILESYSTEM=1
+        -sEXPORTED_RUNTIME_METHODS=FS,callMain
+        -lidbfs.js
+        --preload-file ${CMAKE_SOURCE_DIR}/data@/data
+    )
+    # Generate index.html alongside kobodl.html so it can be served as the
+    # default document. The shell file mounts /home as IDBFS for persistence.
+    if(EXISTS ${CMAKE_SOURCE_DIR}/web/shell.html)
+        target_link_options(kobodl PRIVATE
+            --shell-file ${CMAKE_SOURCE_DIR}/web/shell.html)
+    endif()
+    set_target_properties(kobodl PROPERTIES SUFFIX "")
+endif()
+
 # ---------------------------------------------------------------------------
 # Install rules
 # ---------------------------------------------------------------------------
@@ -189,6 +252,14 @@ elseif(KOBO_BUNDLE_STYLE STREQUAL "simple")
     install(TARGETS kobodl RUNTIME DESTINATION KoboDeluxe)
     install(DIRECTORY data/gfx data/sfx DESTINATION KoboDeluxe)
     install(FILES COPYING COPYING.LIB README ChangeLog TODO DESTINATION KoboDeluxe)
+elseif(KOBO_BUNDLE_STYLE STREQUAL "web")
+    # Emscripten emits kobodl.html / .js / .wasm / .data — install all four.
+    install(TARGETS kobodl RUNTIME DESTINATION web)
+    install(FILES
+        ${CMAKE_CURRENT_BINARY_DIR}/kobodl.js
+        ${CMAKE_CURRENT_BINARY_DIR}/kobodl.wasm
+        ${CMAKE_CURRENT_BINARY_DIR}/kobodl.data
+        DESTINATION web OPTIONAL)
 else()
     include(GNUInstallDirs)
     install(TARGETS kobodl RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})

build-web.sh

@@ -0,0 +1,48 @@
+#!/bin/sh
+# Build Kobo Deluxe as a WebAssembly app via Emscripten.
+#
+# Prereq: install and activate emsdk so emcmake / emcc are on PATH.
+#   git clone https://github.com/emscripten-core/emsdk ~/emsdk
+#   ~/emsdk/emsdk install latest && ~/emsdk/emsdk activate latest
+#   . ~/emsdk/emsdk_env.sh
+#
+# Output: build-web/kobodl.{html,js,wasm,data}
+# Serve from build-web/ with any static server that sets the COOP/COEP headers
+# required for SharedArrayBuffer (pthreads). Example:
+#   ./build-web.sh && ./build-web.sh serve
+
+set -e
+
+HERE="$(cd "$(dirname "$0")" && pwd)"
+BUILD="$HERE/build-web"
+
+case "${1:-build}" in
+    serve)
+        cd "$BUILD"
+        exec python3 -c "
+import http.server, socketserver
+class H(http.server.SimpleHTTPRequestHandler):
+    def end_headers(self):
+        self.send_header('Cross-Origin-Opener-Policy', 'same-origin')
+        self.send_header('Cross-Origin-Embedder-Policy', 'require-corp')
+        super().end_headers()
+socketserver.TCPServer(('', 8000), H).serve_forever()
+"
+        ;;
+    clean)
+        rm -rf "$BUILD"
+        ;;
+    build|*)
+        command -v emcmake >/dev/null 2>&1 || {
+            echo "emcmake not found. Source emsdk_env.sh first." >&2
+            exit 1
+        }
+        mkdir -p "$BUILD"
+        cd "$BUILD"
+        emcmake cmake -DCMAKE_BUILD_TYPE=Release "$HERE"
+        cmake --build . -j
+        echo
+        echo "Built: $BUILD/kobodl.html"
+        echo "Serve: ./build-web.sh serve  (then open http://localhost:8000/kobodl.html)"
+        ;;
+esac

enemies.h

@@ -72,7 +72,7 @@ extern const enemy_kind bombdeto;
 extern const enemy_kind cannon;
 extern const enemy_kind pipe1;
 extern const enemy_kind core;
-extern const enemy_kind pipe2;
+extern const enemy_kind pipe2k;
 extern const enemy_kind rock;
 extern const enemy_kind ring;
 extern const enemy_kind enemy_m1;
@@ -434,7 +434,7 @@ inline int _enemy::realize()
 
 inline int _enemy::is_pipe()
 {
-	return ((_state != notuse) && ((ek == &pipe1) || (ek == &pipe2)));
+	return ((_state != notuse) && ((ek == &pipe1) || (ek == &pipe2k)));
 }
 
 

enemy.cpp

@@ -755,10 +755,10 @@ void _enemy::move_core()
 
 void _enemy::kill_core()
 {
-	enemies.make(&pipe2, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 3);
+	enemies.make(&pipe2k, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 3);
-	enemies.make(&pipe2, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 7);
+	enemies.make(&pipe2k, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 7);
-	enemies.make(&pipe2, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 1);
+	enemies.make(&pipe2k, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 1);
-	enemies.make(&pipe2, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 5);
+	enemies.make(&pipe2k, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 5);
 	enemies.make(&explosion4, CS2PIXEL(x), CS2PIXEL(y));
 	sound.g_base_core_explo(x, y);
 	release();
@@ -978,19 +978,19 @@ void _enemy::move_pipe2()
 	}
 	p ^= a;
 	if(p & U_MASK)
-		enemies.make(&pipe2, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 1);
+		enemies.make(&pipe2k, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 1);
 	if(p & R_MASK)
-		enemies.make(&pipe2, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 3);
+		enemies.make(&pipe2k, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 3);
 	if(p & D_MASK)
-		enemies.make(&pipe2, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 5);
+		enemies.make(&pipe2k, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 5);
 	if(p & L_MASK)
-		enemies.make(&pipe2, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 7);
+		enemies.make(&pipe2k, CS2PIXEL(x), CS2PIXEL(y), 0, 0, 7);
 	manage.add_score(10);
 	release();
 }
 
 
-const enemy_kind pipe2 = {
+const enemy_kind pipe2k = {
 	0,
 	&_enemy::make_pipe2,
 	&_enemy::move_pipe2,

graphics/CMakeLists.txt

@@ -9,6 +9,7 @@ add_library(graphics STATIC
     toolkit.cpp
     vidmodes.c
     region.c
+    img_compat.c
 )
 
 target_include_directories(graphics

graphics/filters.c

@@ -23,7 +23,7 @@
 #include <math.h>
 #include "logger.h"
 #include "sdl_compat.h"
-#include <SDL3_image/SDL_image.h>
+#include "img_compat.h"
 #include "sprite.h"
 #include "filters.h"
 

graphics/gfxengine.cpp

@@ -28,7 +28,7 @@
 
 #include "gfxengine.h"
 #include "filters.h"
-#include <SDL3_image/SDL_image.h>
+#include "img_compat.h"
 #include "sdl_compat.h"
 #include "sofont.h"
 #include "window.h"

graphics/img_compat.c

@@ -0,0 +1,92 @@
+/*
+ * img_compat.c — libpng-backed IMG_Load for the Emscripten build.
+ *
+ * Returns an RGBA8 SDL_Surface. Handles palette, grayscale, tRNS, and 16-bit
+ * inputs by normalizing to 8-bit RGBA in the read pipeline.
+ */
+#ifdef __EMSCRIPTEN__
+
+#include "img_compat.h"
+
+#include <png.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+SDL_Surface *IMG_Load(const char *file)
+{
+    FILE *fp = fopen(file, "rb");
+    if(!fp)
+        return NULL;
+
+    unsigned char hdr[8];
+    if(fread(hdr, 1, 8, fp) != 8 || png_sig_cmp(hdr, 0, 8))
+    {
+        fclose(fp);
+        return NULL;
+    }
+
+    png_structp png = png_create_read_struct(PNG_LIBPNG_VER_STRING,
+                                             NULL, NULL, NULL);
+    if(!png) { fclose(fp); return NULL; }
+    png_infop info = png_create_info_struct(png);
+    if(!info)
+    {
+        png_destroy_read_struct(&png, NULL, NULL);
+        fclose(fp);
+        return NULL;
+    }
+
+    SDL_Surface *surf = NULL;
+    png_bytep *rows = NULL;
+
+    if(setjmp(png_jmpbuf(png)))
+    {
+        if(rows) free(rows);
+        if(surf) SDL_DestroySurface(surf);
+        png_destroy_read_struct(&png, &info, NULL);
+        fclose(fp);
+        return NULL;
+    }
+
+    png_init_io(png, fp);
+    png_set_sig_bytes(png, 8);
+    png_read_info(png, info);
+
+    png_uint_32 w, h;
+    int depth, ctype;
+    png_get_IHDR(png, info, &w, &h, &depth, &ctype, NULL, NULL, NULL);
+
+    if(depth == 16) png_set_strip_16(png);
+    if(ctype == PNG_COLOR_TYPE_PALETTE) png_set_palette_to_rgb(png);
+    if(ctype == PNG_COLOR_TYPE_GRAY && depth < 8)
+        png_set_expand_gray_1_2_4_to_8(png);
+    if(png_get_valid(png, info, PNG_INFO_tRNS))
+        png_set_tRNS_to_alpha(png);
+    if(ctype == PNG_COLOR_TYPE_GRAY || ctype == PNG_COLOR_TYPE_GRAY_ALPHA)
+        png_set_gray_to_rgb(png);
+    if(ctype == PNG_COLOR_TYPE_RGB || ctype == PNG_COLOR_TYPE_GRAY
+            || ctype == PNG_COLOR_TYPE_PALETTE)
+        png_set_filler(png, 0xFF, PNG_FILLER_AFTER);
+
+    png_read_update_info(png, info);
+
+    surf = SDL_CreateSurface((int)w, (int)h, SDL_PIXELFORMAT_RGBA32);
+    if(!surf)
+        png_error(png, "SDL_CreateSurface failed");
+
+    rows = (png_bytep *)malloc(sizeof(png_bytep) * h);
+    if(!rows)
+        png_error(png, "row table alloc failed");
+    for(png_uint_32 y = 0; y < h; ++y)
+        rows[y] = (png_bytep)((unsigned char *)surf->pixels + y * surf->pitch);
+
+    png_read_image(png, rows);
+    png_read_end(png, NULL);
+
+    free(rows);
+    png_destroy_read_struct(&png, &info, NULL);
+    fclose(fp);
+    return surf;
+}
+
+#endif /* __EMSCRIPTEN__ */

graphics/img_compat.h

@@ -0,0 +1,32 @@
+/*
+ * img_compat.h — SDL3_image shim.
+ *
+ * On native builds, this is just a passthrough to <SDL3_image/SDL_image.h>.
+ * On Emscripten there is no SDL3_image port yet (only sdl3 and sdl3_ttf), so
+ * we provide an IMG_Load implementation backed by the libpng port. Only PNG
+ * decoding is needed — Kobo Deluxe's assets are all .png.
+ */
+#ifndef KOBO_IMG_COMPAT_H
+#define KOBO_IMG_COMPAT_H
+
+#ifdef __EMSCRIPTEN__
+
+#include <SDL3/SDL.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+SDL_Surface *IMG_Load(const char *file);
+
+#ifdef __cplusplus
+}
+#endif
+
+#else  /* native */
+
+#include <SDL3_image/SDL_image.h>
+
+#endif
+
+#endif /* KOBO_IMG_COMPAT_H */

graphics/sprite.c

@@ -30,7 +30,7 @@ TODO: tables as needed when loading banks.
 #include <string.h>
 #include "logger.h"
 #include "sdl_compat.h"
-#include <SDL3_image/SDL_image.h>
+#include "img_compat.h"
 #include "sprite.h"
 #include "filters.h"
 

graphics/toolkit.cpp

@@ -23,6 +23,7 @@
 
 #include <string.h>
 #include <stdlib.h>
+#include <stdio.h>
 
 #include "window.h"
 #include "toolkit.h"

states.cpp

@@ -1286,7 +1286,11 @@ void main_menu_t::build()
 		button("Return to Intro", 0);
 	else
 		button("Abort Current Game", 101);
+#ifndef __EMSCRIPTEN__
+	// In the browser, exit() leaves the page on a dead canvas. Drop the
+	// option entirely; reloading the tab is the user's exit.
 	button("Quit Kobo Deluxe", MENU_TAG_CANCEL);
+#endif
 }
 
 void main_menu_t::rebuild()

web/shell.html

@@ -0,0 +1,62 @@
+<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<title>Kobo Deluxe</title>
+<style>
+  html, body { margin: 0; height: 100%; background: #000; color: #ccc;
+               font-family: monospace; }
+  #wrap { display: flex; flex-direction: column; align-items: center;
+          justify-content: center; height: 100%; }
+  canvas { background: #000; image-rendering: pixelated; outline: none;
+           max-width: 100%; max-height: 100vh; }
+  #status { padding: 8px; font-size: 13px; }
+</style>
+</head>
+<body>
+<div id="wrap">
+  <canvas id="canvas" tabindex="-1" oncontextmenu="event.preventDefault()"></canvas>
+  <div id="status">Loading…</div>
+</div>
+<script>
+  var statusEl = document.getElementById('status');
+  var Module = {
+    canvas: (function () {
+      var c = document.getElementById('canvas');
+      c.addEventListener('webglcontextlost', function (e) {
+        alert('WebGL context lost. Reload to continue.'); e.preventDefault();
+      }, false);
+      return c;
+    })(),
+    print: function (t) { console.log(t); },
+    printErr: function (t) { console.warn(t); },
+    setStatus: function (t) { statusEl.textContent = t; },
+    preRun: [function () {
+      // Persist config + high scores across reloads via IndexedDB.
+      // syncfs(true) is async and replaces /home with whatever's in IDBFS,
+      // so we (1) gate startup on it via addRunDependency, and (2) re-mkdir
+      // /home/scores *after* the load (the game's addPlayer doesn't auto-
+      // create the score dir; see the TODO in score.cpp:504).
+      try { FS.mkdir('/home'); } catch (e) {}
+      FS.mount(IDBFS, {}, '/home');
+      Module.addRunDependency('idbfs');
+      FS.syncfs(true, function (err) {
+        if (err) console.warn('IDBFS load failed:', err);
+        try { FS.mkdir('/home/scores'); } catch (e) {}
+        Module.removeRunDependency('idbfs');
+      });
+    }],
+    postRun: [function () {
+      // Push the in-memory /home back to IndexedDB on tab close. visibility-
+      // change covers mobile, where beforeunload is unreliable.
+      var flush = function () { FS.syncfs(false, function () {}); };
+      window.addEventListener('beforeunload', flush);
+      document.addEventListener('visibilitychange', function () {
+        if (document.visibilityState === 'hidden') flush();
+      });
+    }],
+  };
+</script>
+{{{ SCRIPT }}}
+</body>
+</html>