Better Ellipse Drawing Algorithm
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parent
524ebebedb
commit
857e5ec098
64
ellipse.go
Normal file
64
ellipse.go
Normal file
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@ -0,0 +1,64 @@
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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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@ -98,3 +98,11 @@ func TrimBox(src, dst *Rect, p Point, S Rect, thickness int32) {
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dst.W = S.W - thickness
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}
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}
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// AbsInt32 returns the absolute value of an int32.
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func AbsInt32(v int32) int32 {
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if v < 0 {
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return -v
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}
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return v
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}
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107
shapes.go
107
shapes.go
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@ -2,8 +2,6 @@ package render
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import (
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"math"
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"git.kirsle.net/apps/doodle/pkg/log"
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)
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// IterLine is a generator that returns the X,Y coordinates to draw a line.
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@ -93,106 +91,15 @@ func IterRect(p1, p2 Point) chan Point {
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return generator
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}
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// IterEllipse is a generator that draws out the pixels of an ellipse.
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func IterEllipse(rx, ry, xc, yc float32) chan Point {
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generator := make(chan Point)
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mkPoint := func(x, y float32) Point {
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return NewPoint(int32(x), int32(y))
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}
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go func() {
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var (
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dx float32
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dy float32
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d1 float32
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d2 float32
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x float32
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y = ry
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)
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d1 = (ry * ry) - (rx * rx * ry) + (0.25 * rx * rx)
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dx = 2 * ry * ry * x
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dy = 2 * rx * rx * y
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// For region 1
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for dx < dy {
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// Yields points based on 4-way symmetry.
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for _, point := range []Point{
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mkPoint(x+xc, y+yc),
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mkPoint(-x+xc, y+yc),
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mkPoint(x+xc, -y+yc),
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mkPoint(-x+xc, -y+yc),
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} {
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generator <- point
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}
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if d1 < 0 {
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x++
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dx = dx + (2 * ry * ry)
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d1 = d1 + dx + (ry * ry)
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} else {
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x++
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y--
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dx = dx + (2 * ry * ry)
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dy = dy - (2 * rx * rx)
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d1 = d1 + dx - dy + (ry * ry)
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}
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}
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d2 = ((ry * ry) + ((x + 0.5) * (x + 0.5))) +
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((rx * rx) * ((y - 1) * (y - 1))) -
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(rx * rx * ry * ry)
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// Region 2
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for y >= 0 {
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// Yields points based on 4-way symmetry.
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for _, point := range []Point{
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mkPoint(x+xc, y+yc),
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mkPoint(-x+xc, y+yc),
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mkPoint(x+xc, -y+yc),
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mkPoint(-x+xc, -y+yc),
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} {
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generator <- point
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}
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if d2 > 0 {
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y--
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dy = dy - (2 * rx * rx)
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d2 = d2 + (rx * rx) - dy
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} else {
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y--
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x++
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dx = dx + (2 * ry * ry)
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dy = dy - (2 * rx * rx)
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d2 = d2 + dx - dy + (rx * rx)
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}
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}
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close(generator)
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}()
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return generator
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}
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// IterEllipse2 iterates an Ellipse using two Points as the top-left and
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// IterEllipse iterates an Ellipse using two Points as the top-left and
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// bottom-right corners of a rectangle that encompasses the ellipse.
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func IterEllipse2(A, B Point) chan Point {
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func IterEllipse(A, B Point) chan Point {
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var (
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// xc = float32(A.X+B.X) / 2
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// yc = float32(A.Y+B.Y) / 2
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xc = float32(B.X)
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yc = float32(B.Y)
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rx = float32(B.X - A.X)
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ry = float32(B.Y - A.Y)
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width = AbsInt32(B.X - A.X)
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height = AbsInt32(B.Y - A.Y)
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radius = NewPoint(width/2, height/2)
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center = NewPoint(AbsInt32(B.X-radius.X), AbsInt32(B.Y-radius.Y))
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)
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if rx < 0 {
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rx = -rx
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}
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if ry < 0 {
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ry = -ry
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}
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log.Info("Ellipse btwn=%s-%s radius=%f,%f at center %f,%f", A, B, rx, ry, xc, yc)
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return IterEllipse(rx, ry, xc, yc)
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return MidpointEllipse(center, radius)
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}
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