tools: add WebAssembly firmware text renderer

Signed-off-by: Joshua Jun <lets@throw.rocks>
Co-authored-by: GPT-6 <noreply@openai.com>
Signed-off-by: GPT-6 <noreply@openai.com>

Author: jplexer

tools/text2wasm/CMakeLists.txt

@@ -0,0 +1,130 @@
+# SPDX-FileCopyrightText: 2026 Core Devices LLC
+# SPDX-License-Identifier: Apache-2.0
+cmake_minimum_required(VERSION 3.21)
+project(pebble-text2wasm LANGUAGES C)
+
+if(NOT EMSCRIPTEN)
+  message(FATAL_ERROR "Configure with emcmake cmake to select the Emscripten toolchain")
+endif()
+find_package(Git REQUIRED)
+get_filename_component(PEBBLEOS_ROOT "${CMAKE_CURRENT_SOURCE_DIR}/../.." ABSOLUTE)
+set(DIST "${CMAKE_CURRENT_BINARY_DIR}/dist")
+set(OVERRIDES "${CMAKE_CURRENT_BINARY_DIR}/overrides")
+file(MAKE_DIRECTORY "${DIST}" "${OVERRIDES}/kernel" "${OVERRIDES}/resource")
+
+# The browser does not use events; its time ABI differs from the watch's.
+set(EVENTS_HEADER "${PEBBLEOS_ROOT}/src/fw/kernel/events.h")
+set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS "${EVENTS_HEADER}")
+file(READ "${EVENTS_HEADER}" events)
+string(REPLACE "#if __SIZEOF_POINTER__ == 4"
+  "#if __SIZEOF_POINTER__ == 4 && !defined(__EMSCRIPTEN__)" events "${events}")
+file(CONFIGURE OUTPUT "${OVERRIDES}/kernel/events.h" CONTENT "${events}" @ONLY)
+file(CONFIGURE OUTPUT "${OVERRIDES}/resource/resource_ids.auto.h"
+  CONTENT "#pragma once\n#define RESOURCE_ID_FONT_FALLBACK_INTERNAL 0xffffffff\n" @ONLY)
+
+add_executable(pebble_renderer
+  renderer.c
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/8_bit/framebuffer.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/framebuffer.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/gcolor_definitions.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/gtypes.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/gbitmap.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/graphics.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/gtransform.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/bitblt.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/8_bit/bitblt_private.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/text_render.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/utf8.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/text_layout.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/rtl_support.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/arabic_shaping.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/perimeter.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/text_resources.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/graphics_private.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/graphics_private_raw.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/graphics_circle.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/graphics/graphics_line.c"
+  "${PEBBLEOS_ROOT}/src/fw/applib/fonts/codepoint.c"
+  "${PEBBLEOS_ROOT}/lib/util/keyed_circular_cache.c"
+  "${PEBBLEOS_ROOT}/lib/util/math.c"
+  "${PEBBLEOS_ROOT}/lib/util/trig.c"
+  "${PEBBLEOS_ROOT}/lib/util/iterator.c"
+)
+set_target_properties(pebble_renderer PROPERTIES
+  OUTPUT_NAME renderer
+  SUFFIX .js
+  RUNTIME_OUTPUT_DIRECTORY "${DIST}"
+)
+target_include_directories(pebble_renderer PRIVATE
+  "${OVERRIDES}"
+  "${PEBBLEOS_ROOT}/src/fw/util/time"
+  "${PEBBLEOS_ROOT}/tests/overrides/dummy_board"
+  "${PEBBLEOS_ROOT}/tests/overrides/default"
+  "${PEBBLEOS_ROOT}/tests/stubs"
+  "${PEBBLEOS_ROOT}/tests/fakes"
+  "${PEBBLEOS_ROOT}/tests/test_includes"
+  "${PEBBLEOS_ROOT}/tests"
+  "${PEBBLEOS_ROOT}/include"
+  "${PEBBLEOS_ROOT}/include/pbl"
+  "${PEBBLEOS_ROOT}/kernel/arch/posix/include"
+  "${PEBBLEOS_ROOT}/subsys"
+  "${PEBBLEOS_ROOT}/src/fw"
+  "${PEBBLEOS_ROOT}/src/fw/applib/vendor/uPNG"
+  "${PEBBLEOS_ROOT}/src/fw/applib/vendor/tinflate"
+  "${PEBBLEOS_ROOT}/tests/fixtures"
+)
+target_compile_definitions(pebble_renderer PRIVATE
+  UNITTEST
+  CONFIG_SCREEN_COLOR_DEPTH_BITS=8
+  DISP_COLS=144
+  DISP_ROWS=168
+  DISPLAY_FRAMEBUFFER_BYTES=24192
+  PBL_COLOR
+  PBL_RECT
+  CONFIG_BOARD_OBELIX=1
+  CONFIG_PLATFORM_EMERY=1
+  CONFIG_FLASH_GD25Q256E=1
+  CONFIG_KERNEL_NUM_PRIORITIES=5
+  CONFIG_KERNEL_THREAD_TLS_SLOTS=2
+  CONFIG_KERNEL_STACK_ALIGN=8
+  CONFIG_KERNEL_TICK_HZ=1024
+)
+target_compile_options(pebble_renderer PRIVATE
+  -O2
+  -Wno-error=incompatible-pointer-types
+  -Wno-gnu-variable-sized-type-not-at-end
+)
+target_link_options(pebble_renderer PRIVATE
+  -O2
+  -Wl,--error-limit=0
+  -sSINGLE_FILE=1
+  -sMODULARIZE=1
+  -sEXPORT_NAME=createPebbleRenderer
+  -sALLOW_MEMORY_GROWTH=1
+  "-sEXPORTED_FUNCTIONS=['_render','_malloc','_free']"
+  "-sEXPORTED_RUNTIME_METHODS=['ccall','HEAPU8']"
+)
+
+set(font_outputs)
+foreach(directory normal common)
+  file(GLOB fonts CONFIGURE_DEPENDS "${PEBBLEOS_ROOT}/resources/${directory}/base/pbf/GOTHIC*.pbf")
+  foreach(font IN LISTS fonts)
+    get_filename_component(name "${font}" NAME)
+    set(output "${DIST}/${name}")
+    add_custom_command(OUTPUT "${output}"
+      COMMAND ${CMAKE_COMMAND} -E copy_if_different "${font}" "${output}"
+      DEPENDS "${font}"
+      VERBATIM)
+    list(APPEND font_outputs "${output}")
+  endforeach()
+endforeach()
+
+add_custom_target(text2wasm ALL
+  COMMAND ${CMAKE_COMMAND}
+    "-DGIT_EXECUTABLE=${GIT_EXECUTABLE}"
+    "-DPEBBLEOS_ROOT=${PEBBLEOS_ROOT}"
+    "-DOUTPUT=${DIST}/revision.txt"
+    -P "${CMAKE_CURRENT_SOURCE_DIR}/WriteRevision.cmake"
+  DEPENDS pebble_renderer ${font_outputs}
+  BYPRODUCTS "${DIST}/revision.txt"
+  VERBATIM)

tools/text2wasm/README.md

@@ -0,0 +1,26 @@
+<!-- SPDX-FileCopyrightText: 2026 Core Devices LLC -->
+<!-- SPDX-License-Identifier: Apache-2.0 -->
+
+# Firmware text rendering in WebAssembly
+
+With Emscripten on PATH:
+
+```sh
+emcmake cmake -S tools/text2wasm -B build-text2wasm
+cmake --build build-text2wasm --target text2wasm
+```
+
+`dist/renderer.js` contains WASM and its loader. The output also includes Gothic
+base fonts and the firmware revision. Load with `createPebbleRenderer()`, pass a
+UTF-8 string, base PBF pointer/length, and extension PBF pointer/length to `render`, then copy the returned 144×168
+RGBA framebuffer before the next call. The caller retains ownership of inputs.
+
+The target compiles firmware glyph decoding, layout, RTL/shaping, and drawing
+sources unchanged. Resource reads are served from memory. Test adapters supply
+application state and heap services. A generated header disables the on-watch
+event-size assertion for Emscripten's different time ABI; events are not used.
+
+This is a text-box demo, not a full firmware emulator. It has no emoji font,
+or system-screen layout support yet. Optional extension PBFs use firmware glyph fallback. Input fonts must be
+trusted, compiler-produced PBF files; malformed PBF handling is not hardened.
+The browser host should cap text length and recreate the module after a trap.

tools/text2wasm/WriteRevision.cmake

@@ -0,0 +1,7 @@
+# SPDX-FileCopyrightText: 2026 Core Devices LLC
+# SPDX-License-Identifier: Apache-2.0
+
+execute_process(COMMAND "${GIT_EXECUTABLE}" -C "${PEBBLEOS_ROOT}" rev-parse HEAD
+  OUTPUT_VARIABLE revision
+  COMMAND_ERROR_IS_FATAL ANY)
+file(CONFIGURE OUTPUT "${OUTPUT}" CONTENT "${revision}" @ONLY)

tools/text2wasm/renderer.c

@@ -0,0 +1,91 @@
+/* SPDX-FileCopyrightText: 2026 Core Devices LLC */
+/* SPDX-License-Identifier: Apache-2.0 */
+#include <stdlib.h>
+#include <string.h>
+#include "applib/graphics/graphics.h"
+#include "applib/graphics/framebuffer.h"
+#include "applib/graphics/text.h"
+#include "applib/graphics/text_resources.h"
+#include "stubs_app_state.h"
+#include "stubs_applib_resource.h"
+#include "stubs_compiled_with_legacy2_sdk.h"
+#include "stubs_logging.h"
+#include "stubs_pebble_tasks.h"
+#include "stubs_heap.h"
+#include "stubs_pbl_malloc.h"
+#include "stubs_memory_layout.h"
+
+static const uint8_t *font_bytes;
+static const uint8_t *extension_bytes;
+static size_t extension_size;
+static size_t font_size;
+static FrameBuffer framebuffer;
+static GContext context;
+static uint8_t pixels[144 * 168 * 4];
+size_t sys_resource_load_range(ResAppNum app, uint32_t id, uint32_t offset, uint8_t *buffer,
+                               size_t size) {
+  const uint8_t *bytes = id == 2 ? extension_bytes : font_bytes;
+  size_t length = id == 2 ? extension_size : font_size;
+  if (!bytes || offset > length || size > length - offset) return 0;
+  memcpy(buffer, bytes + offset, size);
+  return size;
+}
+bool sys_resource_is_valid(ResAppNum app, uint32_t id) {
+  return id == 1 || (id == 2 && extension_size);
+}
+uint32_t sys_resource_get_and_cache(ResAppNum app, uint32_t id) {
+  return id;
+}
+ResourceCallbackHandle resource_watch(ResAppNum app, uint32_t id, ResourceChangedCallback cb,
+                                      void *data) {
+  return NULL;
+}
+FontInfo *fonts_get_system_emoji_font_for_size(unsigned int size) {
+  return NULL;
+}
+void passert_failed(const char *file, int line, const char *message, ...) {
+  abort();
+}
+void passert_failed_no_message(const char *file, int line) {
+  abort();
+}
+void passert_failed_no_message_with_lr(const char *file, int line, uint32_t lr) {
+  abort();
+}
+uint8_t *render(const char *text, const uint8_t *font, size_t length, const uint8_t *extension,
+                size_t extension_length) {
+  font_bytes = font;
+  font_size = length;
+  extension_bytes = extension;
+  extension_size = extension_length;
+  FontInfo info = {0};
+  if (!text_resources_init_font(0, 1, extension_length ? 2 : 0, &info)) return NULL;
+  framebuffer_init(&framebuffer, &(GSize){144, 168});
+  graphics_context_init(&context, &framebuffer, GContextInitializationMode_App);
+  s_app_state_get_graphics_context = &context;
+  framebuffer_clear(&framebuffer);
+  graphics_context_set_text_color(&context, GColorBlack);
+  graphics_draw_text(&context, text, &info, GRect(4, 4, 136, 160),
+                     GTextOverflowModeTrailingEllipsis, GTextAlignmentLeft, NULL);
+  for (int i = 0; i < 144 * 168; i++) {
+    uint8_t c = framebuffer.buffer[i];
+    pixels[4 * i] = ((c >> 4) & 3) * 85;
+    pixels[4 * i + 1] = ((c >> 2) & 3) * 85;
+    pixels[4 * i + 2] = (c & 3) * 85;
+    pixels[4 * i + 3] = 255;
+  }
+  return pixels;
+}
+
+uint8_t fonts_get_font_height(GFont font) {
+  return ((FontInfo *)font)->max_height;
+}
+void sys_font_reload_font(FontInfo *font) {
+  abort();
+}
+GFont sys_font_get_system_font(const char *key) {
+  return NULL;
+}
+void util_assertion_failed(const char *file, int line) {
+  abort();
+}