diff --git a/draw/ellipse.go b/draw/ellipse.go index 116cf1b..ba44624 100644 --- a/draw/ellipse.go +++ b/draw/ellipse.go @@ -3,6 +3,7 @@ package draw import ( "image" "image/color" + "math" ) // ellipse defines the struct components required to apply the ellipse's formula. @@ -40,7 +41,15 @@ func (e *ellipse) At(x, y int) color.Color { eqn := p1 + p2 if eqn <= 1 { - return color.Alpha{255} + rMin := math.Min(float64(e.rx), float64(e.ry)) + rMax := math.Max(float64(e.rx), float64(e.ry)) + + grad := &NewRadialGradient(float64(x), float64(y), rMin*0.7, float64(x), float64(y), rMax-(rMin/4)) + grad.AddColorStop(0, color.RGBA{255, 255, 255, 255}) + grad.AddColorStop(0.6, color.RGBA{127, 127, 127, 127}) + grad.AddColorStop(1, color.RGBA{0, 0, 0, 0}) + + return grad.ColorAt(e.cx, e.cy) } return color.Alpha{0} } diff --git a/draw/gradient.go b/draw/gradient.go new file mode 100644 index 0000000..5a16880 --- /dev/null +++ b/draw/gradient.go @@ -0,0 +1,139 @@ +package draw + +import ( + "image/color" + "math" + "sort" +) + +type Gradient interface { + AddColorStop(offset float64, color color.Color) + ColorAt(x, y int) color.Color +} + +type stop struct { + pos float64 + color color.Color +} + +type stops []stop + +// Len satisfies the Sort interface. +func (s stops) Len() int { return len(s) } +func (s stops) Less(i, j int) bool { return s[i].pos < s[j].pos } +func (s stops) Swap(i, j int) { s[i], s[j] = s[j], s[i] } + +type circle struct { + x, y, r float64 +} + +type radialGradient struct { + c0, c1, cd circle + a, inva float64 + mindr float64 + stops stops +} + +func dot3(x0, y0, z0, x1, y1, z1 float64) float64 { + return x0*x1 + y0*y1 + z0*z1 +} + +func (g *radialGradient) ColorAt(x, y int) color.Color { + if len(g.stops) == 0 { + return color.Transparent + } + + // copy from pixman's pixman-radial-gradient.c + dx, dy := float64(x)+0.5-g.c0.x, float64(y)+0.5-g.c0.y + b := dot3(dx, dy, g.c0.r, g.cd.x, g.cd.y, g.cd.r) + c := dot3(dx, dy, -g.c0.r, dx, dy, g.c0.r) + + if g.a == 0 { + if b == 0 { + return color.Transparent + } + t := 0.5 * c / b + if t*g.cd.r >= g.mindr { + return getColor(t, g.stops) + } + return color.Transparent + } + + discr := dot3(b, g.a, 0, b, -c, 0) + if discr >= 0 { + sqrtdiscr := math.Sqrt(discr) + t0 := (b + sqrtdiscr) * g.inva + t1 := (b - sqrtdiscr) * g.inva + + if t0*g.cd.r >= g.mindr { + return getColor(t0, g.stops) + } else if t1*g.cd.r >= g.mindr { + return getColor(t1, g.stops) + } + } + + return color.Transparent +} + +func (g *radialGradient) AddColorStop(offset float64, color color.Color) { + g.stops = append(g.stops, stop{pos: offset, color: color}) + sort.Sort(g.stops) +} + +func NewRadialGradient(x0, y0, r0, x1, y1, r1 float64) Gradient { + c0 := circle{x0, y0, r0} + c1 := circle{x1, y1, r1} + cd := circle{x1 - x0, y1 - y0, r1 - r0} + a := dot3(cd.x, cd.y, -cd.r, cd.x, cd.y, cd.r) + var inva float64 + if a != 0 { + inva = 1.0 / a + } + mindr := -c0.r + g := &radialGradient{ + c0: c0, + c1: c1, + cd: cd, + a: a, + inva: inva, + mindr: mindr, + } + return g +} + +func getColor(pos float64, stops stops) color.Color { + if pos <= 0.0 || len(stops) == 1 { + return stops[0].color + } + + last := stops[len(stops)-1] + + if pos >= last.pos { + return last.color + } + + for i, stop := range stops[1:] { + if pos < stop.pos { + pos = (pos - stops[i].pos) / (stop.pos - stops[i].pos) + return colorLerp(stops[i].color, stop.color, pos) + } + } + + return last.color +} + +func colorLerp(c0, c1 color.Color, t float64) color.Color { + r0, g0, b0, a0 := c0.RGBA() + r1, g1, b1, a1 := c1.RGBA() + + return color.RGBA{ + lerp(r0, r1, t), + lerp(g0, g1, t), + lerp(b0, b1, t), + lerp(a0, a1, t), + } +} + +func lerp(a, b uint32, t float64) uint8 { + return uint8(int32(float64(a)*(1.0-t)+float64(b)*t) >> 8) +}