Commit f3a98206 authored by Paul Asmuth's avatar Paul Asmuth
Browse files

test if two lines are parallel

parent 0af465b9

core/graphics/geometry.cc

+9 −0
Original line number Diff line number Diff line
@@ -50,6 +50,15 @@ vec2 vec2_mul(const vec2& v, double s) { 
  return {v.x * s, v.y * s};

}



double vec2_dot(const vec2& a, const vec2& b) {

  return a.x * b.x + a.y * b.y;

}



vec2 vec2_from_deg(double deg) {

  double a = (deg - 180.0) / 180.0 * M_PI;

  return {cos(a), sin(a)};

}



std::ostream& operator <<(std::ostream& os, const Point& p) {

  os << "Point(";

  os << p.x;

core/graphics/geometry.h

+2 −0
Original line number Diff line number Diff line
@@ -42,6 +42,8 @@ vec2 vec2_normalize(const vec2& v); 
vec2 vec2_add(const vec2& a, const vec2& b);

vec2 vec2_sub(const vec2& a, const vec2& b);

vec2 vec2_mul(const vec2& v, double s);

double vec2_dot(const vec2& a, const vec2& b);

vec2 vec2_from_deg(double deg);



std::ostream& operator <<(std::ostream& os, const Point& c);

std::ostream& operator <<(std::ostream& os, const Rectangle& c);

core/graphics/intersect.cc

0 → 100644
+46 −0
Original line number Diff line number Diff line 
/**

 * This file is part of the "fviz" project

 *   Copyright (c) 2018 Paul Asmuth

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

#include "intersect.h"



namespace fviz {



/**

 * Check if two lines intersect and if they do, return the intersection

 * point

 */

bool intersect_line_line(

    vec2 o0,

    vec2 v0,

    vec2 o1,

    vec2 v1,

    vec2* x /* = nullptr */) {

  // ensure the direction vectors are normalized

  v0 = vec2_normalize(v0);

  v1 = vec2_normalize(v1);



  // consider lines as parallel if the angle between them is smaller than some

  // threshold

  const double a_epsilon = 0.001;

  double a = acos(vec2_dot(v0, v1));

  double a_norm = fmod(M_PI - a, M_PI);



  if (a_norm < a_epsilon) {

    return false;

  }



  return true;

}



} // namespace fviz

core/graphics/intersect.h

0 → 100644
+39 −0
Original line number Diff line number Diff line 
/**

 * This file is part of the "fviz" project

 *   Copyright (c) 2018 Paul Asmuth

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

#pragma once

#include <unordered_map>

#include <optional>



#include "graphics/color.h"

#include "graphics/layer.h"

#include "graphics/geometry.h"

#include "return_code.h"

#include "sexpr.h"



namespace fviz {



/**

 * Given two (infinite) lines defined by a point on each of the the lines o0, o1

 * (their 'origins') and their normal direction vectors v0, v1, compute the point

 * of intersection. Returns false if the two lines are parallel.

 */

bool intersect_line_line(

    vec2 o0,

    vec2 v0,

    vec2 o1,

    vec2 v1,

    vec2* x = nullptr);



} // namespace fviz

tests/unit/test_graphics_intersect.cc

0 → 100644
+152 −0
Original line number Diff line number Diff line 
/**

 * This file is part of the "fviz" project

 *   Copyright (c) 2018 Paul Asmuth

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

#include "graphics/intersect.h"

#include "unittest.h"



using namespace fviz;



void test_intersect_parallel() {

  // some slope but offset in y -> parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 1},

          vec2_from_deg(45),

          nullptr),

      false);



  // some slope but offset in x -> parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 1},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(45),

          nullptr),

      false);



  // coincident -> parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(45),

          nullptr),

      false);



  // 180 degree shifted angles -> parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(45 + 180),

          nullptr),

     false);



  // -180 degree shifted angles -> parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(45 - 180),

          nullptr),

      false);



  // 360 degree shifted angles -> parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(45 + 360),

          nullptr),

      false);



  // -360 degree shifted angles -> parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(45 + -360),

          nullptr),

      false);



  // angles very close to each other -> "parallel"

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(45.0000001),

          nullptr),

      false);



  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(44.9999999),

          nullptr),

      false);



  // angles less close to each other -> not parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(45.01),

          nullptr),

      true);



  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 0},

          vec2_from_deg(44.99),

          nullptr),

      true);



  // angles different and x offset -> not parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {1, 0},

          vec2_from_deg(45.1),

          nullptr),

      true);



  // angles different and x offset -> not parallel

  EXPECT_EQ(

      intersect_line_line(

          {0, 0},

          vec2_from_deg(45),

          {0, 1},

          vec2_from_deg(45.1),

          nullptr),

      true);

}



int main(int argc, char** argv) {

  test_intersect_parallel();

}

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