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Add methods to determine orientation of PolyLine #1411

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merged 1 commit into from Oct 21, 2016
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Add methods to determine orientation of PolyLine #1411

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5 changes: 5 additions & 0 deletions include/cinder/PolyLine.h
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Expand Up @@ -51,6 +51,11 @@ class PolyLineT {
void setClosed( bool aClosed = true ) { mClosed = aClosed; }
bool isClosed() const { return mClosed; }

//! Returns \c true if PolyLine is clockwise-oriented. If \a isColinear is non-null, it receives \c true if all points are colinear
bool isClockwise( bool *isColinear = nullptr ) const;
//! Returns \c true if PolyLine is counterclockwise-oriented. If \a isColinear is non-null, it receives \c true if all points are colinear
bool isCounterClockwise( bool *isColinear = nullptr ) const;

T getPosition( float t ) const;
T getDerivative( float t ) const;

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45 changes: 45 additions & 0 deletions src/cinder/PolyLine.cpp
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Expand Up @@ -29,6 +29,51 @@

namespace cinder {


template<typename T>
bool PolyLineT<T>::isClockwise( bool *isColinear ) const
{
if( mPoints.size() < 3 ) {
if( isColinear != nullptr ) *isColinear = true;
return false;
}

size_t last = mPoints.size() - 1;
// If the first and last point are the same (on a closed polygon), ignore one.
if( mPoints.front() == mPoints.back() ) --last;

// Find an extreme point since we know it will be on the hull...
size_t smallest = 0;
for( size_t i = 1; i <= last; ++i ) {
if( mPoints[i].x < mPoints[smallest].x ) {
smallest = i;
} else if( mPoints[i].x == mPoints[smallest].x && mPoints[i].y < mPoints[smallest].y ) {
smallest = i;
}
};
// ...then get the next and previous point
size_t prev = ( smallest == 0 ) ? last : ( smallest - 1 );
size_t next = ( smallest == last ) ? 0 : ( smallest + 1 );
vec2 a = mPoints[next], b = mPoints[smallest], c = mPoints[prev];

// The sign of the determinate indicates the orientation:
// positive is clockwise
// zero is colinear
// negative is counterclockwise
double determinate = ( b.x - a.x ) * ( c.y - a.y ) - ( c.x - a.x ) * ( b.y - a.y );
if( isColinear != nullptr ) *isColinear = determinate == 0.0;
return determinate > 0.0;
}

template<typename T>
bool PolyLineT<T>::isCounterClockwise( bool *isColinear ) const
{
bool colinear;
bool clockwise = this->isClockwise( &colinear );
if( isColinear != nullptr ) *isColinear = colinear;
return colinear ? false : !clockwise;
}

template<typename T>
T PolyLineT<T>::getPosition( float t ) const
{
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96 changes: 96 additions & 0 deletions test/unit/src/PolyLineTest.cpp
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@@ -0,0 +1,96 @@
#include "cinder/app/App.h"
#include "cinder/PolyLine.h"

#include "catch.hpp"


using namespace ci;
using namespace ci::app;
using namespace std;

TEST_CASE("PolyLine", "Orientation")
{
SECTION("Just two points")
{
vector<vec2> input({
vec2( 294.641, 105.359 ),
vec2( 387.617, 12.3833 ),
});

PolyLine2f p1 = PolyLine2f( input );
bool colinear;
REQUIRE( ! p1.isClockwise() );
REQUIRE( ! p1.isClockwise( &colinear ) );
REQUIRE( colinear );

REQUIRE( ! p1.isCounterClockwise() );
REQUIRE( ! p1.isCounterClockwise( &colinear ) );
REQUIRE( colinear );
}

SECTION("Three in a row")
{
vector<vec2> input({
vec2( 0, 0 ),
vec2( 100, 0 ),
vec2( -29, 0 )
});
PolyLine2f p1 = PolyLine2f( input );
bool colinear;

REQUIRE( ! p1.isClockwise() );
REQUIRE( ! p1.isClockwise( &colinear ) );
REQUIRE( colinear );

REQUIRE( ! p1.isCounterClockwise() );
REQUIRE( ! p1.isCounterClockwise( &colinear ) );
REQUIRE( colinear );
}

SECTION("Open Polygon")
{
vector<vec2> input({
vec2( 294.641, 105.359 ),
vec2( 387.617, 12.3833 ),
vec2( 412.967, 2.96674 ),
vec2( 417.987, -7.98667 ),
vec2( 386.023, -94.0354 )
});
PolyLine2f p1 = PolyLine2f( input );
reverse( input.begin(), input.end() );
PolyLine2f p2 = PolyLine2f( input );
bool colinear;

REQUIRE( p1.isClockwise() );
REQUIRE( p1.isClockwise( &colinear ) );
REQUIRE( ! colinear );

REQUIRE( ! p2.isClockwise() );
REQUIRE( ! p2.isClockwise( &colinear ) );
REQUIRE( ! colinear );
}

SECTION("Closed Polygon")
{
vector<vec2> input({
vec2( 294.641, 105.359 ),
vec2( 387.617, 12.3833 ),
vec2( 412.967, 2.96674 ),
vec2( 417.987, -7.98667 ),
vec2( 386.023, -94.0354 ),
vec2( 294.641, 105.359 )
});
PolyLine2f p1 = PolyLine2f( input );
bool colinear;
reverse( input.begin(), input.end() );
PolyLine2f p2 = PolyLine2f( input );

REQUIRE( p1.isClockwise() );
REQUIRE( p1.isClockwise( &colinear ) );
REQUIRE( ! colinear );

REQUIRE( ! p2.isClockwise() );
REQUIRE( ! p2.isClockwise( &colinear ) );
REQUIRE( ! colinear );
}
}
4 changes: 4 additions & 0 deletions test/unit/xcode/UnitTests.xcodeproj/project.pbxproj
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Expand Up @@ -10,6 +10,7 @@
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9CA851C01C1F74000049358B /* Base64Test.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 9CA851B61C1F74000049358B /* Base64Test.cpp */; };
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9CA851C21C1F74000049358B /* ObjLoaderTest.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 9CA851B91C1F74000049358B /* ObjLoaderTest.cpp */; };
Expand Down Expand Up @@ -61,6 +62,7 @@
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Expand Down Expand Up @@ -207,6 +209,7 @@
9CA851B71C1F74000049358B /* catch.hpp */,
9CA851B81C1F74000049358B /* JsonTest.cpp */,
9CA851B91C1F74000049358B /* ObjLoaderTest.cpp */,
4989E06B1DB6889500503C9A /* PolyLineTest.cpp */,
9CA851BA1C1F74000049358B /* RandTest.cpp */,
9CA851BD1C1F74000049358B /* SystemTest.cpp */,
9CA851BE1C1F74000049358B /* TestMain.cpp */,
Expand Down Expand Up @@ -285,6 +288,7 @@
9CA851C01C1F74000049358B /* Base64Test.cpp in Sources */,
9CA851C31C1F74000049358B /* RandTest.cpp in Sources */,
11E4FC4D1C267DB70082A67E /* FftUnit.cpp in Sources */,
4989E06C1DB6889500503C9A /* PolyLineTest.cpp in Sources */,
9CA851C11C1F74000049358B /* JsonTest.cpp in Sources */,
11E4FC4E1C26801E0082A67E /* RingBufferUnit.cpp in Sources */,
9CA851C51C1F74000049358B /* SystemTest.cpp in Sources */,
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