```{-# LANGUAGE FlexibleContexts #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  Diagrams.Trace
-- Copyright   :  (c) 2013 diagrams-lib team (see LICENSE)
-- License     :  BSD-style (see LICENSE)
-- Maintainer  :  diagrams-discuss@googlegroups.com
--
-- \"Traces\", aka embedded raytracers, for finding points on the edge
-- of a diagram.  See "Diagrams.Core.Trace" for internal
-- implementation details.
--
-----------------------------------------------------------------------------

module Diagrams.Trace
( -- * Types
Trace, Traced

-- * Diagram traces
, trace, setTrace, withTrace

-- * Querying traces
, traceV, traceP, maxTraceV, maxTraceP

-- * Subdiagram traces
, boundaryFrom, boundaryFromMay

) where

import           Diagrams.Core        (HasLinearMap, Point, Subdiagram,
location, origin, setTrace, trace)
import           Diagrams.Core.Trace

import           Data.Maybe
import           Data.VectorSpace     (Scalar, negateV)
import           Diagrams.Combinators (withTrace)

-- | Compute the furthest point on the boundary of a subdiagram,
--   beginning from the location (local origin) of the subdiagram and
--   moving in the direction of the given vector.  If there is no such
--   point, the origin is returned; see also 'boundaryFromMay'.
boundaryFrom :: (HasLinearMap v, Ord (Scalar v)) => Subdiagram b v m -> v -> Point v
boundaryFrom s v = fromMaybe origin \$ boundaryFromMay s v

-- | Compute the furthest point on the boundary of a subdiagram,
--   beginning from the location (local origin) of the subdiagram and
--   moving in the direction of the given vector, or @Nothing@ if
--   there is no such point.
boundaryFromMay :: (HasLinearMap v, Ord (Scalar v)) => Subdiagram b v m -> v -> Maybe (Point v)
boundaryFromMay s v = traceP (location s) (negateV v) s
```