ofxBezierRs

An OpenFrameworks wrapper for bezier-rs providing a set geometrical functions on cartesian planar Beziér paths or shapes. In terms of algorithm, the Bezier-rs is quite close to bezier.js from Pomax's research work.

Early state

Bezier-rs provides plenty of functions, not all are implemented yet.
Right now, consider this addon as a proof-of-concept for using libBezierRs with C++ code.
Tested on osx 10.12 + OF 0.11.2 and linux + OF 0.11.2, the binaries are not yet bundled.

Functions :

• Shape offset
• Shape outline
• Shape rotation
• Reversing winding direction
• Computing the bounding box of a shape
• Shape hit testing
• Inflections
• Find shape self intersections
• Evaluate a point on the shape (t-value)
• Normal from t-value
• Tangent from t-value
• Curvature from t-value
• Find closest point on shape

Shapes

The shape object is close to the underlying one used in bezier-rs.
Their concept is quite simple :

• A point has a x and y.
• A bezier handle is a set of 3 points : 1 anchor and 2 (absolute) in/out bezier handles.
• A shape is a set of multiple bezier handles and can be closed (shape) or not (path).
  Note: Shapes work better if handles are winded clockwise.

Implementation notes

Bezier-rs is a library written in Rust which can build a C compatible library.

ofxBezierRs relies on 3 essential components :

• bezier-rs-ffi : A rust crate to build a library that provides API for communicating with C (an ffi in Rust's terms).
• bezier-rs-ffi.h : C++ bindings for the compiled library, generated from the rust crate.
• ofxBezierRs.h : Some glue to make it work better with OF.

Usage

#include "ofxBezierRs.h"
int main(){

	// Build an array-compatible list of beziers handles.
	// Must remain accessible when calling bez_rs_shape_create.
	std::vector<bezrsBezierHandle> bezierHandles = { ... }; // <-- Fill this with your vector drawing
	// Make raw handle
	bezrsShapeRaw bezRsShapeInput = { bezierHandles.data(), bezierHandles.size(), true };
	// Build internal/opaque shape from raw input
	bezrsShape* bezRsShape = bezrs_shape_create( &bezRsShapeInput, true);
	// Transform the shape
	bezrs_cubic_bezier_offset(bezRsShape, 10, bezrsJoinType::Round, 0);
	// Retrieve resulting shape
	bezrsShapeRaw offsetShapeRaw = bezrs_shape_return_handle_data(bezRsShape);
	// Use result
	size_t bhi = 0;
	for (const bezrsBezierHandle* bh = offsetShapeRaw.data; bhi < offsetShapeRaw.len; bh++){
		ofDrawCircle(bh->pos.x, bh->pos.y, 5.f); // draw
		// or copy to own variable

		bhi++;
	}
	// Destroy shape handle
	bezrs_shape_destroy(bezRsShape);

	return 0;
}

There's a set of ImGui helpers available, to opt-in, define OFXBEZRS_DEFINE_IMGUI_HELPERS.

Development

To build a new library binary for your platform, make sure that you have Rust installed.

• curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Build the library :

• cd ./bezier-rs-ffi/
• cargo build --release
• Copy lib files to ofxBezierRs/libs/bezier-rs-ffi/lib/PLATFORM/libbezier_rs_ffi.a|dylib|so (PLATFORM: osx, linux64, etc.)

Generate bindings :

• Install or update cbindgen : cargo install --force cbindgen
• cd ./bezier-rs-ffi/
• Run : cbindgen --config ./cbindgen.toml --crate bezier-rs-ffi --output include/bezier-rs-ffi.h.
• Copy bezier-rs-ffi.h to libs/bezier-rs-ffi/include.

You can run the above instructions automatically :

• cd ./libs/bezier-rs-ffi && ./Build.sh

License

The bezier-rs crate is licensed MIT or Apache-2.0. The bezier-rs crate is made by the team behind Graphite.rs. ofxBezierRs and bezier-rs-ffi are MIT and made by Daan de Lange.