Modernize and bring up to date with JS pixelmatch

.clang-format

@@ -0,0 +1,8 @@
+BasedOnStyle: Google
+AccessModifierOffset: -4
+AllowShortFunctionsOnASingleLine: Inline
+BinPackArguments: false
+BinPackParameters: false
+ColumnLimit: 120
+IndentWidth: 4
+SpacesBeforeTrailingComments: 1

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install libpng
+        run: sudo apt-get update && sudo apt-get install -y libpng-dev
+      - name: Check formatting
+        run: clang-format --dry-run --Werror include/mapbox/*.hpp test/test.cpp test/bench.cpp test/png_decode.hpp
+      - run: cmake -B build -DCMAKE_BUILD_TYPE=Release
+      - run: cmake --build build
+      - run: ctest --test-dir build --output-on-failure

CMakeLists.txt

@@ -0,0 +1,37 @@
+cmake_minimum_required(VERSION 3.15)
+
+project(pixelmatch
+    VERSION 1.0.0
+    DESCRIPTION "C++ port of pixelmatch, a pixel-level image comparison library"
+    LANGUAGES CXX
+)
+
+add_library(pixelmatch INTERFACE)
+add_library(mapbox::pixelmatch ALIAS pixelmatch)
+
+target_include_directories(pixelmatch INTERFACE
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+    $<INSTALL_INTERFACE:include>
+)
+
+target_compile_features(pixelmatch INTERFACE cxx_std_11)
+
+if(PROJECT_IS_TOP_LEVEL)
+    enable_testing()
+    find_package(PNG REQUIRED)
+
+    add_executable(test_pixelmatch test/test.cpp)
+    target_link_libraries(test_pixelmatch PRIVATE pixelmatch PNG::PNG)
+    target_compile_options(test_pixelmatch PRIVATE -Wall -Wextra -Wshadow)
+    add_test(NAME pixelmatch
+        COMMAND test_pixelmatch
+        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+    )
+
+    add_executable(bench_pixelmatch test/bench.cpp)
+    target_link_libraries(bench_pixelmatch PRIVATE pixelmatch PNG::PNG)
+    target_compile_options(bench_pixelmatch PRIVATE -Wall -Wextra)
+endif()
+
+include(GNUInstallDirs)
+install(DIRECTORY include/ DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})

LICENSE.txt

@@ -1,4 +1,4 @@
-Copyright (c) 2015, Mapbox
+Copyright (c) 2026, Mapbox
 
 Permission to use, copy, modify, and/or distribute this software for any purpose
 with or without fee is hereby granted, provided that the above copyright notice

README.md

@@ -1,21 +1,35 @@
 ## pixelmatch-cpp
 
-[![Build Status](https://travis-ci.org/mapbox/pixelmatch-cpp.svg?branch=master)](https://travis-ci.org/mapbox/pixelmatch-cpp)
-
 A C++ port of [pixelmatch](https://github.com/mapbox/pixelmatch), the smallest, simplest and fastest JavaScript pixel-level image comparison library.
 
+This is a header-only library; add `include/` to your include path, use it as a CMake subdirectory, or install it and link against `mapbox::pixelmatch`.
+
+## Building & testing
+
+Requires CMake 3.15+ and a C++11 compiler.
+
+```bash
+cmake -B build
+cmake --build build
+ctest --test-dir build --output-on-failure
+```
+
+To generate an Xcode project: `cmake -B build -G Xcode && open build/pixelmatch.xcodeproj`.
+
 ## API
 
 ```cpp
 namespace mapbox {
 
-uint64_t pixelmatch(const uint8_t* img1,
-                    const uint8_t* img2,
-                    std::size_t width,
-                    std::size_t height,
-                    uint8_t* output = nullptr,
-                    double threshold = 0.1,
-                    bool includeAA = false);
+uint64_t pixelmatch(
+    const uint8_t* img1,
+    const uint8_t* img2,
+    std::size_t width,
+    std::size_t height,
+    uint8_t* output = nullptr,
+    double threshold = 0.1,
+    bool includeAA = false
+);
 
 }
 ```