src/ui/lib/escher/geometry/bounding_box.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/lib/escher/geometry/bounding_box.h"

#include <array>

#include "src/lib/fxl/logging.h"
#include "src/ui/lib/escher/geometry/intersection.h"
#include "src/ui/lib/escher/geometry/plane_ops.h"

namespace escher {

namespace {

static const size_t kNumPlanes = 6;

bool PlanesAreValid(const std::array<vec4, kNumPlanes>& planes) {
  for (size_t i = 0; i < kNumPlanes; ++i) {
    if (std::abs(glm::length(vec3(planes[i])) - 1.f) > kEpsilon) {
      return false;
    }
  }
  return true;
}

}  // namespace

BoundingBox::BoundingBox(vec3 min, vec3 max) : min_(min), max_(max) {
#ifndef NDEBUG
  FXL_DCHECK(min.x <= max.x) << min << " " << max;
  FXL_DCHECK(min.y <= max.y) << min << " " << max;
  FXL_DCHECK(min.z <= max.z) << min << " " << max;
  int dimensions = (min.x != max.x ? 1 : 0) + (min.y != max.y ? 1 : 0) + (min.z != max.z ? 1 : 0);
  // Should use empty bounding-box if box is 1D or 0D.
  FXL_DCHECK(dimensions >= 2);
#endif
}

BoundingBox BoundingBox::NewChecked(vec3 min, vec3 max, uint32_t max_degenerate_dimensions) {
  vec3 diff = max - min;
  if (diff.x < 0.f || diff.y < 0.f || diff.z < 0.f)
    return BoundingBox();

  uint32_t degenerate_dimensions =
      (diff.x == 0.f ? 1 : 0) + (diff.y == 0.f ? 1 : 0) + (diff.z == 0.f ? 1 : 0);
  return degenerate_dimensions > max_degenerate_dimensions ? BoundingBox() : BoundingBox(min, max);
}

BoundingBox& BoundingBox::Join(const BoundingBox& box) {
  if (is_empty()) {
    min_ = box.min_;
    max_ = box.max_;
  } else if (!box.is_empty()) {
    min_ = glm::min(min_, box.min_);
    max_ = glm::max(max_, box.max_);
  }
  return *this;
}

BoundingBox& BoundingBox::Intersect(const BoundingBox& box) {
  if (is_empty()) {
    return *this;
  } else if (box.is_empty()) {
    *this = BoundingBox();
  } else {
    min_ = glm::max(min_, box.min_);
    max_ = glm::min(max_, box.max_);
    if (min_.x > max_.x || min_.y > max_.y || min_.z > max_.z) {
      *this = BoundingBox();
    } else {
      int dimensions =
          (min_.x != max_.x ? 1 : 0) + (min_.y != max_.y ? 1 : 0) + (min_.z != max_.z ? 1 : 0);
      if (dimensions < 2) {
        // We consider the intersection between boxes that touch at only one
        // point or an edge to be empty.
        *this = BoundingBox();
      }
    }
  }
  return *this;
}

BoundingBox operator*(const mat4& matrix, const BoundingBox& box) {
  FXL_DCHECK(matrix[3][3] == 1.f);  // No perspective allowed.

  if (box.is_empty()) {
    return box;
  }

  // Fancy trick to transform an AABB.
  // See http://dev.theomader.com/transform-bounding-boxes/
  vec4 xa = box.min().x * matrix[0];
  vec4 xb = box.max().x * matrix[0];
  vec4 ya = box.min().y * matrix[1];
  vec4 yb = box.max().y * matrix[1];
  vec4 za = box.min().z * matrix[2];
  vec4 zb = box.max().z * matrix[2];
  vec3 min = glm::min(vec3(xa), vec3(xb)) + glm::min(vec3(ya), vec3(yb)) +
             glm::min(vec3(za), vec3(zb)) + vec3(matrix[3]);
  vec3 max = glm::max(vec3(xa), vec3(xb)) + glm::max(vec3(ya), vec3(yb)) +
             glm::max(vec3(za), vec3(zb)) + vec3(matrix[3]);

  return BoundingBox(min, max);
}

std::vector<plane3> BoundingBox::CreatePlanes() const {
  std::array<glm::vec4, kNumPlanes> planes;
  std::vector<escher::plane3> result;
  result.resize(kNumPlanes);

  planes[0] = glm::vec4(1, 0, 0, min_.x);
  planes[1] = glm::vec4(0, 1, 0, min_.y);
  planes[2] = glm::vec4(0, 0, 1, min_.z);
  planes[3] = glm::vec4(-1, 0, 0, -max_.x);
  planes[4] = glm::vec4(0, -1, 0, -max_.y);
  planes[5] = glm::vec4(0, 0, -1, -max_.z);

  FXL_DCHECK(PlanesAreValid(planes));

  for (size_t i = 0; i < kNumPlanes; i++) {
    glm::vec4 plane = planes[i];
    result[i] = plane3(glm::vec3(plane), plane.w);
  }
  return result;
}

mat4 BoundingBox::CreateTransform() const {
  mat4 transform = glm::translate(mat4(), min_);
  transform = glm::scale(transform, vec3(width(), height(), depth()));
  return transform;
}

uint32_t BoundingBox::NumClippedCorners(const plane2& plane, const float_t& epsilon) const {
  uint32_t count = 0;
  float_t adjusted_epsilon = std::max(epsilon, 0.f);
  count += PlaneClipsPoint(plane, vec2(min_.x, min_.y), adjusted_epsilon) ? 2 : 0;
  count += PlaneClipsPoint(plane, vec2(min_.x, max_.y), adjusted_epsilon) ? 2 : 0;
  count += PlaneClipsPoint(plane, vec2(max_.x, max_.y), adjusted_epsilon) ? 2 : 0;
  count += PlaneClipsPoint(plane, vec2(max_.x, min_.y), adjusted_epsilon) ? 2 : 0;
  return count;
}

uint32_t BoundingBox::NumClippedCorners(const plane3& plane, const float_t& epsilon) const {
  uint32_t count = 0;
  float_t adjusted_epsilon = std::max(epsilon, 0.f);
  count += PlaneClipsPoint(plane, vec3(min_.x, min_.y, min_.z), adjusted_epsilon) ? 1 : 0;
  count += PlaneClipsPoint(plane, vec3(min_.x, min_.y, max_.z), adjusted_epsilon) ? 1 : 0;
  count += PlaneClipsPoint(plane, vec3(min_.x, max_.y, min_.z), adjusted_epsilon) ? 1 : 0;
  count += PlaneClipsPoint(plane, vec3(min_.x, max_.y, max_.z), adjusted_epsilon) ? 1 : 0;
  count += PlaneClipsPoint(plane, vec3(max_.x, min_.y, min_.z), adjusted_epsilon) ? 1 : 0;
  count += PlaneClipsPoint(plane, vec3(max_.x, min_.y, max_.z), adjusted_epsilon) ? 1 : 0;
  count += PlaneClipsPoint(plane, vec3(max_.x, max_.y, min_.z), adjusted_epsilon) ? 1 : 0;
  count += PlaneClipsPoint(plane, vec3(max_.x, max_.y, max_.z), adjusted_epsilon) ? 1 : 0;

  return count;
}

}  // namespace escher