feat(webgl): Add GAL native test harness for visual regression testing

Add a standalone test application that compiles KiCad's actual OPENGL_GAL
against system wxWidgets to generate baseline screenshots for comparing
native OpenGL rendering against WebGL rendering in the browser.

Architecture:
- Compiles 18 KiCad GAL source files from the kicad submodule
- Uses template-based private member accessor (safer than #define private public)
- Generates shader C++ files from GLSL (10 shader pairs for SMAA AA)
- Minimal stubs for KiCad dependencies (PGM_BASE, ADVANCED_CFG, etc.)

Test coverage:
- 11 scenarios testing ~19% of GAL API
- basic-lines, line-widths, circles, arcs, rectangles, polygons
- alpha-blending, transforms, grid-cursor, segments, complex-scene

Key insights documented:
- GAL uses world-to-screen transformation requiring 1:1 pixel mapping
- FBO reading required for clean screenshots on macOS
- Layer depth needed for proper z-ordering in complex scenes

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/gal-regression/native/CMakeLists.txt

@@ -0,0 +1,120 @@
+cmake_minimum_required(VERSION 3.16)
+project(gal_native_test)
+
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+# Suppress deprecation warnings on macOS
+if(APPLE)
+    add_compile_definitions(GL_SILENCE_DEPRECATION)
+endif()
+
+# Find wxWidgets (system installation)
+set(wxWidgets_CONFIG_EXECUTABLE "/opt/homebrew/bin/wx-config")
+find_package(wxWidgets REQUIRED COMPONENTS core base gl)
+include(${wxWidgets_USE_FILE})
+
+# Find other required packages
+find_package(OpenGL REQUIRED)
+find_package(GLEW REQUIRED)
+
+# KiCad source root
+set(KICAD_ROOT ${CMAKE_SOURCE_DIR}/../../../kicad)
+
+# Generated shader files
+set(SHADER_SOURCES
+    ${CMAKE_SOURCE_DIR}/generated/glsl_kicad_frag.cpp
+    ${CMAKE_SOURCE_DIR}/generated/glsl_kicad_vert.cpp
+    ${CMAKE_SOURCE_DIR}/generated/glsl_smaa_base.cpp
+    ${CMAKE_SOURCE_DIR}/generated/glsl_smaa_pass_1_frag_color.cpp
+    ${CMAKE_SOURCE_DIR}/generated/glsl_smaa_pass_1_frag_luma.cpp
+    ${CMAKE_SOURCE_DIR}/generated/glsl_smaa_pass_1_vert.cpp
+    ${CMAKE_SOURCE_DIR}/generated/glsl_smaa_pass_2_frag.cpp
+    ${CMAKE_SOURCE_DIR}/generated/glsl_smaa_pass_2_vert.cpp
+    ${CMAKE_SOURCE_DIR}/generated/glsl_smaa_pass_3_frag.cpp
+    ${CMAKE_SOURCE_DIR}/generated/glsl_smaa_pass_3_vert.cpp
+)
+
+# KiCad OpenGL GAL sources
+set(KICAD_GAL_SOURCES
+    ${KICAD_ROOT}/common/gal/opengl/opengl_gal.cpp
+    ${KICAD_ROOT}/common/gal/opengl/gl_context_mgr.cpp
+    ${KICAD_ROOT}/common/gal/opengl/shader.cpp
+    ${KICAD_ROOT}/common/gal/opengl/vertex_manager.cpp
+    ${KICAD_ROOT}/common/gal/opengl/vertex_item.cpp
+    ${KICAD_ROOT}/common/gal/opengl/vertex_container.cpp
+    ${KICAD_ROOT}/common/gal/opengl/cached_container.cpp
+    ${KICAD_ROOT}/common/gal/opengl/cached_container_gpu.cpp
+    ${KICAD_ROOT}/common/gal/opengl/cached_container_ram.cpp
+    ${KICAD_ROOT}/common/gal/opengl/noncached_container.cpp
+    ${KICAD_ROOT}/common/gal/opengl/gpu_manager.cpp
+    ${KICAD_ROOT}/common/gal/opengl/opengl_compositor.cpp
+    ${KICAD_ROOT}/common/gal/opengl/antialiasing.cpp
+    ${KICAD_ROOT}/common/gal/opengl/utils.cpp
+    ${KICAD_ROOT}/common/gal/opengl/gl_resources.cpp
+    ${KICAD_ROOT}/common/gal/graphics_abstraction_layer.cpp
+    ${KICAD_ROOT}/common/gal/color4d.cpp
+    ${KICAD_ROOT}/common/gal/gal_display_options.cpp
+    ${KICAD_ROOT}/common/gal/hidpi_gl_canvas.cpp
+)
+
+# Our stub and test files
+set(STUB_SOURCES
+    ${CMAKE_SOURCE_DIR}/kicad_stubs.cpp
+    ${CMAKE_SOURCE_DIR}/gal_test_accessor.cpp
+    ${CMAKE_SOURCE_DIR}/../scenarios/gal_test_scenarios.cpp
+)
+
+# Main executable
+add_executable(gal_native_test
+    gal_native_test.cpp
+    ${STUB_SOURCES}
+    ${KICAD_GAL_SOURCES}
+    ${SHADER_SOURCES}
+)
+
+# Include directories - our stubs first, then KiCad, then wxWidgets
+target_include_directories(gal_native_test PRIVATE
+    # Our stubs (for KiCad-specific types not in wxWidgets)
+    ${CMAKE_SOURCE_DIR}
+    ${CMAKE_SOURCE_DIR}/../scenarios
+    ${CMAKE_SOURCE_DIR}/generated
+
+    # KiCad includes
+    ${KICAD_ROOT}/include
+    ${KICAD_ROOT}/include/gal
+    ${KICAD_ROOT}/include/gal/opengl
+    ${KICAD_ROOT}/common     # For gal/opengl/antialiasing.h
+
+    # KiCad libs
+    ${KICAD_ROOT}/libs/kimath/include
+    ${KICAD_ROOT}/libs/kimath/include/math
+    ${KICAD_ROOT}/libs/kimath/include/geometry
+    ${KICAD_ROOT}/libs/core/include
+
+    # KiCad thirdparty
+    ${KICAD_ROOT}/thirdparty/thread-pool
+
+    # System includes
+    ${OPENGL_INCLUDE_DIR}
+    ${GLEW_INCLUDE_DIRS}
+
+    # Homebrew dependencies
+    /opt/homebrew/include   # nlohmann-json, clipper2
+)
+
+# Link libraries
+target_link_libraries(gal_native_test
+    ${wxWidgets_LIBRARIES}
+    OpenGL::GL
+    GLEW::GLEW
+)
+
+# Compile definitions
+target_compile_definitions(gal_native_test PRIVATE
+    GAL_TEST_BUILD=1
+)
+
+message(STATUS "KiCad root: ${KICAD_ROOT}")
+message(STATUS "wxWidgets libraries: ${wxWidgets_LIBRARIES}")
+message(STATUS "Building GAL native test with actual KiCad OPENGL_GAL sources")