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Simplify the winding calculation 

This algorithm is more robust against points and cheaper to execute.
This commit is contained in:
Seth Hillbrand 2023-01-25 13:12:47 -08:00
parent cf52bfcc55
commit 33bef16376
1 changed files with 11 additions and 85 deletions
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94
common/font/outline_decomposer.cpp
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@ -221,97 +221,23 @@ int OUTLINE_DECOMPOSER::winding( const GLYPH_POINTS& aContour ) const
return 0;
}
unsigned int i_lowest_vertex = 0;
double lowest_y = std::numeric_limits<double>::max();
double sum = 0.0;
size_t len = aContour.size();
for( unsigned int i = 0; i < aContour.size(); i++ )
for( size_t i = 0; i < len - 1; i++ )
{
VECTOR2D p = aContour[i];
VECTOR2D p1 = aContour[ i ];
VECTOR2D p2 = aContour[ i + 1 ];
if( p.y < lowest_y )
{
i_lowest_vertex = i;
lowest_y = p.y;
// note: we should also check for p.y == lowest_y and then choose the point with
// leftmost.x, but as p.x is a double, equality is a dubious concept; however
// this should suffice in the general case
}
sum += ( ( p2.x - p1.x ) * ( p2.y + p1.y ) );
}
unsigned int i_prev_vertex = ( i_lowest_vertex + aContour.size() - 1 ) % aContour.size();
unsigned int i_next_vertex = ( i_lowest_vertex + 1 ) % aContour.size();
sum += ( ( aContour[0].x - aContour[len - 1].x ) * ( aContour[0].y + aContour[len - 1].y ) );
const VECTOR2D& lowest = aContour[i_lowest_vertex];
VECTOR2D prev( aContour[i_prev_vertex] );
while( prev == lowest )
{
if( i_prev_vertex == 0 )
i_prev_vertex = aContour.size() - 1;
else
i_prev_vertex--;
if( i_prev_vertex == i_lowest_vertex )
{
// ERROR: degenerate contour (all points are colinear with equal Y coordinate)
// TODO: signal error
// for now let's just return something at random
if( sum > 0.0 )
return cw;
}
prev = aContour[i_prev_vertex];
}
VECTOR2D next( aContour[i_next_vertex] );
while( next == lowest )
{
if( i_next_vertex == aContour.size() - 1 )
i_next_vertex = 0;
else
i_next_vertex++;
if( i_next_vertex == i_lowest_vertex )
{
// ERROR: degenerate contour (all points are equal)
// TODO: signal error
// for now let's just return something at random
return cw;
}
next = aContour[i_next_vertex];
}
// winding is figured out based on the angle between the lowest
// vertex and its neighbours
//
// prev.x < lowest.x && next.x > lowest.x -> ccw
//
// prev.x > lowest.x && next.x < lowest.x -> cw
//
// prev.x < lowest.x && next.x < lowest.x:
// ?
//
// prev.x > lowest.x && next.x > lowest.x:
// ?
//
if( prev.x < lowest.x && next.x > lowest.x )
if( sum < 0.0 )
return ccw;
if( prev.x > lowest.x && next.x < lowest.x )
return cw;
double prev_deltaX = prev.x - lowest.x;
double prev_deltaY = prev.y - lowest.y;
double next_deltaX = next.x - lowest.x;
double next_deltaY = next.y - lowest.y;
double prev_atan = atan2( prev_deltaY, prev_deltaX );
double next_atan = atan2( next_deltaY, next_deltaX );
if( prev_atan > next_atan )
return ccw;
else
return cw;
return 0;
}