S2C - C API for S2 Geometry

This is a C API wrapper for Google's S2 geometry library, providing a C-compatible interface to S2's spherical geometry functionality.

Features

The C API provides access to core S2 functionality including:

• Basic Types: S2Point, S2LatLng, S2CellId, S1Angle
• Shapes: S2Cap, S2Cell, S2Loop, S2Polyline, S2Polygon
• Regions: S2LatLngRect, S2CellUnion
• Operations: Basic containment and intersection tests
• Utilities: S2RegionCoverer, S2Earth calculations

Building

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=Release -DBUILD_EXAMPLES=ON -DBUILD_TESTS=OFF
make -j8

Example Usage

#include "s2c.h"

// Create a point from latitude/longitude
S2CLatLng* latlng = s2c_latlng_from_degrees(40.7, -74.0);
S2CPoint* point = s2c_latlng_to_point(latlng);

// Create a polygon
S2CPoint* vertices[] = {v1, v2, v3};
S2CLoop* loop = s2c_loop_new_from_points(vertices, 3);
S2CPolygon* polygon = s2c_polygon_new_from_loop(loop);

// Test containment
bool contains = s2c_polygon_contains(polygon, point);

// Cleanup
s2c_polygon_destroy(polygon);
s2c_point_destroy(point);
s2c_latlng_destroy(latlng);

API Design

The API follows these conventions:

• All types are opaque pointers with S2C or S1C prefix
• Functions follow the pattern s2c_type_operation()
• Memory management uses explicit new/destroy functions
• Error handling through S2CError structure where applicable
• Boolean operations return bool directly

Implementation Status

Currently implemented:

• ✓ Basic geometric types (Point, LatLng, Angle, ChordAngle)
• ✓ Interval types (R1Interval, S1Interval)
• ✓ Shape types (Loop, Polygon, Polyline, Cap, Cell)
• ✓ Basic operations (containment, intersection tests)
• ✓ Region types (LatLngRect, CellUnion)
• ✓ Advanced Polygon operations (IntersectWithPolyline, GetOverlapFractions, etc.)
• ✓ Complete Polyline operations (Interpolate, Project, Subsample, etc.)
• ✓ S2Earth utility functions (distance calculations, conversions)
• ✓ Error handling system
• ✓ Memory management functions
• ✓ Basic test suite

Not yet implemented:

• Boolean operations with shape indexes
• S2Shape interface support
• S2BufferOperation implementation
• S2RegionCoverer GetCovering methods
• Encode/Decode for major types
• Full builder patterns for complex operations

Testing

The project includes a comprehensive test suite:

• tests/test_runner.c - Basic C test runner that doesn't require GoogleTest
• tests/test_basic_types.cc - Tests for basic types (requires GoogleTest)
• tests/test_geometry_types.cc - Tests for geometry types (requires GoogleTest)
• tests/test_utilities.cc - Tests for utility functions (requires GoogleTest)

To run tests:

cd build
make test_runner
./test_runner

Examples

See the examples/ directory for:

• polygon_operations.c - Creating and testing polygon operations
• simple_polygon_test.c - Basic polygon containment and intersection tests

License

This wrapper follows the same Apache 2.0 license as the S2 geometry library.