src/ui/scenic/lib/gfx/resources/shapes/planar_shape.cc

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/ui/scenic/lib/gfx/resources/shapes/planar_shape.h"

namespace scenic_impl {
namespace gfx {

PlanarShape::PlanarShape(Session* session, SessionId session_id, ResourceId id,
                         const ResourceTypeInfo& type_info)
    : Shape(session, session_id, id, type_info) {}

bool PlanarShape::GetIntersection(const escher::ray4& ray, float* out_distance) const {
  // Reject if the ray origin is behind the Z=0 plane.
  if (ray.origin.z > 0.f)
    return false;

  // Reject if the ray is not pointing down towards the Z=0 plane.
  float delta_z = ray.direction.z;
  if (delta_z < std::numeric_limits<float>::epsilon())
    return false;

  // Compute the distance to the plane in multiples of the ray's direction
  // vector and the point of intersection.
  //
  // TODO(40161): Right now, this must be "* (1 / delta_z)" instead of "/ delta_z" for floating
  // point behavior consistent with bounding box tests. We can change this to be the more direct "/
  // delta_z" if we drop best-effort support for hit tests coplanar with view bounds.
  float distance = -ray.origin.z * (1 / delta_z);
  escher::vec2 point =
      (escher::vec2(ray.origin) + distance * escher::vec2(ray.direction)) / ray.origin.w;

  // Reject if the shape does not contain the point of intersection.
  if (!ContainsPoint(point))
    return false;

  *out_distance = distance;
  return true;
}

}  // namespace gfx
}  // namespace scenic_impl