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Better algo to calculate the segment count to convert a DRAWSEGMENT arc or circle to a set of segments. 

Currently, the max error between the arc/circle and a segment is set to 0.05 mm
This commit is contained in:
jean-pierre charras 2018-03-07 14:16:26 +01:00
parent ebd2b78f86
commit 8fcbb64a46
1 changed files with 18 additions and 10 deletions
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26
pcbnew/board_items_to_polygon_shape_transform.cpp
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@ -505,18 +505,26 @@ void DRAWSEGMENT::TransformShapeWithClearanceToPolygon( SHAPE_POLY_SET& aCornerB
if( m_Shape == S_CIRCLE || m_Shape == S_ARC )
{
// this is an ugly hack, but I don't want to change the file format now that we are in feature freeze.
// the circle to segment count parameter is essentially useless for larger circle/arc shapes as it doesn't provide
// sufficient approximation accuracy. Here we compute the necessary number of segments based on
// percentage accuracy required. This is currently mapped to the CircleToSegmentCount parameter: low value (16)
// means 1% accuracy, high - 0.33% acciracy.
// the circle to segment count parameter is essentially useless for larger circle/arc shapes as
// it doesn't provide sufficient approximation accuracy.
// Here we compute the necessary number of segments based on error between circle and segments
// The max error is the distance between the middle of a segment, and the circle
//
// Warning: too small values can create very long calculation time in zone filling
double error_max = Millimeter2iu( 0.05 );
// error relative to the radius value
double rel_error = error_max / GetRadius();
// best arc increment
double step = 180 / M_PI * acos( 1.0 - rel_error );
// the best seg count for a circle
int segCount = KiROUND( 360.0 / step );
double accuracy = aCircleToSegmentsCount == 16 ? 0.01 : 0.0033;
double r = GetRadius();
double step = 180.0 / M_PI * acos( r * ( 1.0 - accuracy ) / r );
aCircleToSegmentsCount = (int) ceil( 360.0 / step );
if( segCount > aCircleToSegmentsCount )
{
aCircleToSegmentsCount = segCount;
aCorrectionFactor = 1.0 / cos( M_PI / (aCircleToSegmentsCount * 2) );
}
}
switch( m_Shape )
{