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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "pdf/draw_utils/page_boundary_intersect.h"
#include "base/check.h"
#include "ui/gfx/geometry/point_f.h"
#include "ui/gfx/geometry/rect.h"
#include "ui/gfx/geometry/rect_f.h"
namespace chrome_pdf {
namespace {
// gfx::Rect considers points on its bottom and right border to be not contained
// within the rect. So to make sure CalculatePageBoundaryIntersectPoint()
// returns points within the page, use this constant to move them inwards a bit.
constexpr float kBoundaryEpsilon = 0.0001f;
} // namespace
gfx::PointF CalculatePageBoundaryIntersectPoint(
const gfx::Rect& page_rect,
const gfx::PointF& inside_point,
const gfx::PointF& outside_point) {
const gfx::RectF rect(page_rect);
CHECK(!rect.IsEmpty());
CHECK(rect.Contains(inside_point));
CHECK(!rect.Contains(outside_point));
const float x_diff = outside_point.x() - inside_point.x();
const float y_diff = outside_point.y() - inside_point.y();
// Handle the special case where calculating the slope would divide by 0.
if (x_diff == 0) {
if (y_diff > 0) {
return {inside_point.x(), rect.bottom() - kBoundaryEpsilon};
}
return {inside_point.x(), rect.y()};
}
// Handle the special case where dividing by the slope would be dividing by 0.
if (y_diff == 0) {
if (x_diff > 0) {
return {rect.right() - kBoundaryEpsilon, inside_point.y()};
}
return {rect.x(), inside_point.y()};
}
// For all other cases, calculate where the line between `inside_point` and
// `outside_point` would intersect `rect` on its horizontal and vertical
// boundaries, assuming the line going towards `outside_point` is infinitely
// long in that direction, and the boundary lines also extends infinitely.
const float slope = y_diff / x_diff;
gfx::PointF left_or_right_boundary_intersection_point;
if (x_diff > 0) {
float y_distance = (rect.right() - inside_point.x()) * slope;
left_or_right_boundary_intersection_point = {
rect.right() - kBoundaryEpsilon, inside_point.y() + y_distance};
} else {
float y_distance = (inside_point.x() - rect.x()) * slope;
left_or_right_boundary_intersection_point = {rect.x(),
inside_point.y() - y_distance};
}
gfx::PointF top_or_bottom_boundary_intersection_point;
if (y_diff > 0) {
float x_distance = (rect.bottom() - inside_point.y()) / slope;
top_or_bottom_boundary_intersection_point = {
inside_point.x() + x_distance, rect.bottom() - kBoundaryEpsilon};
} else {
float x_distance = (inside_point.y() - rect.y()) / slope;
top_or_bottom_boundary_intersection_point = {inside_point.x() - x_distance,
rect.y()};
}
// Then return the result closest to `inside_point`.
float left_or_right_point_length =
(left_or_right_boundary_intersection_point - inside_point).Length();
float top_or_bottom_point_length =
(top_or_bottom_boundary_intersection_point - inside_point).Length();
return left_or_right_point_length < top_or_bottom_point_length
? left_or_right_boundary_intersection_point
: top_or_bottom_boundary_intersection_point;
}
} // namespace chrome_pdf
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