working on tracing

Readme.md

@@ -4,6 +4,29 @@ A lightweight half-edge data structure.
 
 Best used with glm and glow.
 
+
+## Function parameter order guide
+
+The following types of parameters exist:
+
+* M (`Mesh const& m` or `Mesh& m`) reference to mesh (depending on topology is modified)
+* RO-A (`attribute<T> const&`) read-only attributes such as position
+* RW-A (`attribute<T>&`) read-write attributes
+* OPT-A (`attribute<T>* = nullptr` or `attribute<T> const* = nullptr`) optional attributes
+* H (`handle h`) handle
+* M-P: other mandatory parameters
+* OPT-P: other optional parameters
+* OUT-P: output parameters (that don't fit in the return value)
+
+Free functions that perform mesh-related algorithms follow these rules for their parameters:
+
+* Mesh (M) or handle (H) is first parameter ("what does this function operates on?")
+* Followed by all required RO-A such as `position`
+* Followed by all mandatory parameters M-P
+* Followed by all additional outputs RW-A and OUT-P
+* Finalized by all optional parameters OPT-A and OPT-P (least frequently used parameter should be last)
+
+
 ## TODO
 
 * Properties

src/polymesh/algorithms/tracing.hh

+#pragma once
+
+#include "../Mesh.hh"
+#include "../fields.hh"
+
+namespace polymesh
+{
+
+/**
+ * Traces a ray inside the triangle stopping at the next edge
+ */
+
+/// Traces from halfedge h into its triangle
+/// Start point is given by interpolating h.from and h.to given x
+/// Direction is given by virtual source with SQUARED distance d1_sqr from h.from and d2_sqr from h.to
+/// Returns intersecting half-edge and new x parameter
+template <class Scalar = float, class EdgeLengthF>
+std::pair<halfedge_handle, float> trace_step(halfedge_handle h, EdgeLengthF&& edge_length, Scalar x, Scalar d1_sqr, Scalar d2_sqr);
+
+/// ======== IMPLEMENTATION ========
+
+template <class Scalar, class EdgeLengthF>
+std::pair<halfedge_handle, float> trace_step(halfedge_handle h, EdgeLengthF&& edge_length, Scalar x, Scalar d1_sqr, Scalar d2_sqr)
+{
+    assert(!h.is_boundary() && "cannot trace into boundary");
+    auto f = h.face();
+    assert(f.vertices().size() == 3 && "only supports triangles");
+
+    // TODO
+}
+
+}