65 lines
1.5 KiB
Go
65 lines
1.5 KiB
Go
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package render
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// MidpointEllipse implements an ellipse plotting algorithm.
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func MidpointEllipse(center, radius Point) chan Point {
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yield := make(chan Point)
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go func() {
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var (
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pos = NewPoint(radius.X, 0)
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delta = NewPoint(
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2*radius.Y*radius.Y*pos.X,
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2*radius.X*radius.X*pos.Y,
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)
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err = radius.X*radius.X -
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radius.Y*radius.Y*radius.X +
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(radius.Y*radius.Y)/4
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)
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for delta.Y < delta.X {
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yield <- NewPoint(center.X+pos.X, center.Y+pos.Y)
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yield <- NewPoint(center.X+pos.X, center.Y-pos.Y)
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yield <- NewPoint(center.X-pos.X, center.Y+pos.Y)
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yield <- NewPoint(center.X-pos.X, center.Y-pos.Y)
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pos.Y++
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if err < 0 {
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delta.Y += 2 * radius.X * radius.X
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err += delta.Y + radius.X*radius.X
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} else {
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pos.X--
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delta.Y += 2 * radius.X * radius.X
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delta.X -= 2 * radius.Y * radius.Y
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err += delta.Y - delta.X + radius.X*radius.X
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}
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}
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err = radius.X*radius.X*(pos.Y*pos.Y+pos.Y) +
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radius.Y*radius.Y*(pos.X-1)*(pos.X-1) -
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radius.Y*radius.Y*radius.X*radius.X
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for pos.X >= 0 {
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yield <- NewPoint(center.X+pos.X, center.Y+pos.Y)
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yield <- NewPoint(center.X+pos.X, center.Y-pos.Y)
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yield <- NewPoint(center.X-pos.X, center.Y+pos.Y)
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yield <- NewPoint(center.X-pos.X, center.Y-pos.Y)
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pos.X--
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if err > 0 {
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delta.X -= 2 * radius.Y * radius.Y
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err += radius.Y*radius.Y - delta.X
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} else {
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pos.Y++
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delta.Y += 2 * radius.X * radius.X
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delta.X -= 2 * radius.Y * radius.Y
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err += delta.Y - delta.X + radius.Y*radius.Y
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}
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}
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close(yield)
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}()
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return yield
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}
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