Basic predicate skeleton

Project.toml

@@ -5,6 +5,7 @@ version = "0.1.3"
 
 [deps]
 CoordinateTransformations = "150eb455-5306-5404-9cee-2592286d6298"
+ExactPredicates = "429591f6-91af-11e9-00e2-59fbe8cec110"
 GeoInterface = "cf35fbd7-0cd7-5166-be24-54bfbe79505f"
 GeometryBasics = "5c1252a2-5f33-56bf-86c9-59e7332b4326"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"

src/GeometryOps.jl

@@ -26,6 +26,7 @@ include("methods/barycentric.jl")
 include("methods/centroid.jl")
 include("methods/distance.jl")
 include("methods/equals.jl")
+include("methods/clipping/predicates.jl")
 include("methods/clipping/clipping_processor.jl")
 include("methods/clipping/coverage.jl")
 include("methods/clipping/cut.jl")

src/methods/clipping/predicates.jl

@@ -0,0 +1,49 @@
+module Predicates
+
+    using ExactPredicates
+    using ExactPredicates.Codegen
+    using ExactPredicates.Codegen: group!, coord, @genpredicate
+
+    using ExactPredicates: ext, inp
+
+    # This is the implementation of r_cross_s from 2 points in the `_intersection_points` file.
+    # 0 == parallel
+    @genpredicate function isparallel(a1 :: 2, a2 :: 2, b1 :: 2, b2 :: 2)
+        r = a2 - a1
+        s = b2 - b1
+        group!(r...)
+        group!(s...)
+        ext(r, s)
+    end
+    # This is the implementation of `iscollinear` from `intersection_points`.
+    # 0 == parallel.
+    @genpredicate function iscollinear(a1::2, a2::2, b1::2, b2::2)
+        Δqp = b1 - a1
+        s = b2 - b1
+        group!(Δqp...)
+        group!(s...)
+        ext(s, Δqp)
+    end
+
+end
+
+import .Predicates
+
+# Predicates.r_cross_s(...)
+
+#=
+# If we want to inject adaptivity, we would do:
+using MultiFloats
+function isparallel_adaptive(a1, a2, b1, b2)
+    r = Float64x2.(a2) - Float64x2.(a1)
+    s = Float64x2.(b2) - Float64x2.(b1)
+    return sign(Predicates.ext(r, s))
+end
+function isparallel(a1, a2, b1, b2)
+    # try Predicates.isparallel_naive(a1, a2, b1, b2)
+    # check the error bound there
+    # then try isparallel_adaptive(a1, a2, b1, b2)
+    # then try Predicates.isparallel_slow
+    # then try isparallel
+end
+=#