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march.go
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march.go
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package cm
import "github.com/setanarut/vec"
// This is a user defined function that gets passed in to the Marching process
// the user establishes a PolyLineSet, passes a pointer to their function, and they
// populate it. In most cases you want to use PolyLineCollectSegment instead of defining your own
type MarchSegmentFunc func(v0 vec.Vec2, v1 vec.Vec2, segmentData *PolyLineSet)
// This is a user defined function that gets passed every single point from the bounding
// box the user passes into the March process - you can use this to sample an image and
// check for alpha values or really any 2d matrix you define like a tile map.
// NOTE: I could not determine a use case for the sampleData pointer from the original code
// so I removed it here - open to adding it back in if there is a reason.
type MarchSampleFunc func(point vec.Vec2) float64
type MarchCellFunc func(t, a, b, c, d, x0, x1, y0, y1 float64, marchSegment MarchSegmentFunc, segmentData *PolyLineSet)
// The looping and sample caching code is shared between MarchHard() and MarchSoft().
func MarchCells(bb BB, xSamples int64, ySamples int64, t float64, marchSegment MarchSegmentFunc, marchSample MarchSampleFunc, marchCell MarchCellFunc) *PolyLineSet {
var xDenom, yDenom float64
xDenom = 1.0 / float64(xSamples-1)
yDenom = 1.0 / float64(ySamples-1)
buffer := make([]float64, xSamples)
var i, j int64
for i = 0; i < xSamples; i++ {
buffer[i] = marchSample(vec.Vec2{lerp(bb.L, bb.R, float64(i)*xDenom), bb.B})
}
segmentData := &PolyLineSet{}
for j = 0; j < ySamples-1; j++ {
y0 := lerp(bb.B, bb.T, float64(j+0)*yDenom)
y1 := lerp(bb.B, bb.T, float64(j+1)*yDenom)
// a := buffer[0] // unused variable ?
b := buffer[0]
c := marchSample(vec.Vec2{bb.L, y1})
d := c
buffer[0] = d
for i = 0; i < xSamples-1; i++ {
x0 := lerp(bb.L, bb.R, float64(i+0)*xDenom)
x1 := lerp(bb.L, bb.R, float64(i+1)*xDenom)
a := b // = -> :=
b = buffer[i+1]
c = d
d = marchSample(vec.Vec2{x1, y1})
buffer[i+1] = d
marchCell(t, a, b, c, d, x0, x1, y0, y1, marchSegment, segmentData)
}
}
return segmentData
}
func seg(v0 vec.Vec2, v1 vec.Vec2, marchSegment MarchSegmentFunc, segmentData *PolyLineSet) {
if !v0.Equal(v1) {
marchSegment(v1, v0, segmentData)
}
}
func midlerp(x0, x1, s0, s1, t float64) float64 {
return lerp(x0, x1, (t-s0)/(s1-s0))
}
func MarchCellSoft(t, a, b, c, d, x0, x1, y0, y1 float64, marchSegment MarchSegmentFunc, segmentData *PolyLineSet) {
at := 0
bt := 0
ct := 0
dt := 0
if a > t {
at = 1
}
if b > t {
bt = 1
}
if c > t {
ct = 1
}
if d > t {
dt = 1
}
switch (at)<<0 | (bt)<<1 | (ct)<<2 | (dt)<<3 {
case 0x1:
seg(vec.Vec2{x0, midlerp(y0, y1, a, c, t)}, vec.Vec2{midlerp(x0, x1, a, b, t), y0}, marchSegment, segmentData)
case 0x2:
seg(vec.Vec2{midlerp(x0, x1, a, b, t), y0}, vec.Vec2{x1, midlerp(y0, y1, b, d, t)}, marchSegment, segmentData)
case 0x3:
seg(vec.Vec2{x0, midlerp(y0, y1, a, c, t)}, vec.Vec2{x1, midlerp(y0, y1, b, d, t)}, marchSegment, segmentData)
case 0x4:
seg(vec.Vec2{midlerp(x0, x1, c, d, t), y1}, vec.Vec2{x0, midlerp(y0, y1, a, c, t)}, marchSegment, segmentData)
case 0x5:
seg(vec.Vec2{midlerp(x0, x1, c, d, t), y1}, vec.Vec2{midlerp(x0, x1, a, b, t), y0}, marchSegment, segmentData)
case 0x6:
seg(vec.Vec2{midlerp(x0, x1, a, b, t), y0}, vec.Vec2{x1, midlerp(y0, y1, b, d, t)}, marchSegment, segmentData)
seg(vec.Vec2{midlerp(x0, x1, c, d, t), y1}, vec.Vec2{x0, midlerp(y0, y1, a, c, t)}, marchSegment, segmentData)
case 0x7:
seg(vec.Vec2{midlerp(x0, x1, c, d, t), y1}, vec.Vec2{x1, midlerp(y0, y1, b, d, t)}, marchSegment, segmentData)
case 0x8:
seg(vec.Vec2{x1, midlerp(y0, y1, b, d, t)}, vec.Vec2{midlerp(x0, x1, c, d, t), y1}, marchSegment, segmentData)
case 0x9:
seg(vec.Vec2{x0, midlerp(y0, y1, a, c, t)}, vec.Vec2{midlerp(x0, x1, a, b, t), y0}, marchSegment, segmentData)
seg(vec.Vec2{x1, midlerp(y0, y1, b, d, t)}, vec.Vec2{midlerp(x0, x1, c, d, t), y1}, marchSegment, segmentData)
case 0xA:
seg(vec.Vec2{midlerp(x0, x1, a, b, t), y0}, vec.Vec2{midlerp(x0, x1, c, d, t), y1}, marchSegment, segmentData)
case 0xB:
seg(vec.Vec2{x0, midlerp(y0, y1, a, c, t)}, vec.Vec2{midlerp(x0, x1, c, d, t), y1}, marchSegment, segmentData)
case 0xC:
seg(vec.Vec2{x1, midlerp(y0, y1, b, d, t)}, vec.Vec2{x0, midlerp(y0, y1, a, c, t)}, marchSegment, segmentData)
case 0xD:
seg(vec.Vec2{x1, midlerp(y0, y1, b, d, t)}, vec.Vec2{midlerp(x0, x1, a, b, t), y0}, marchSegment, segmentData)
case 0xE:
seg(vec.Vec2{midlerp(x0, x1, a, b, t), y0}, vec.Vec2{x0, midlerp(y0, y1, a, c, t)}, marchSegment, segmentData)
}
}
// Trace an anti-aliased contour of an image along a particular threshold.
// The given number of samples will be taken and spread across the bounding box area using the sampling function and context.
// The segment function will be called for each segment detected that lies along the density contour for @c threshold.
func MarchSoft(bb BB, xSamples, ySamples int64, t float64, marchSegment MarchSegmentFunc, marchSample MarchSampleFunc) *PolyLineSet {
return MarchCells(bb, xSamples, ySamples, t, marchSegment, marchSample, MarchCellSoft)
}
func segs(a, b, c vec.Vec2, marchSegment MarchSegmentFunc, segmentData *PolyLineSet) {
seg(b, c, marchSegment, segmentData)
seg(a, b, marchSegment, segmentData)
}
func MarchCellHard(t, a, b, c, d, x0, x1, y0, y1 float64, marchSegment MarchSegmentFunc, segmentData *PolyLineSet) {
xm := lerp(x0, x1, 0.5)
ym := lerp(y0, y1, 0.5)
at := 0
bt := 0
ct := 0
dt := 0
if a > t {
at = 1
}
if b > t {
bt = 1
}
if c > t {
ct = 1
}
if d > t {
dt = 1
}
switch (at)<<0 | (bt)<<1 | (ct)<<2 | (dt)<<3 {
case 0x1:
segs(vec.Vec2{x0, ym}, vec.Vec2{xm, ym}, vec.Vec2{xm, y0}, marchSegment, segmentData)
case 0x2:
segs(vec.Vec2{xm, y0}, vec.Vec2{xm, ym}, vec.Vec2{x1, ym}, marchSegment, segmentData)
case 0x3:
seg(vec.Vec2{x0, ym}, vec.Vec2{x1, ym}, marchSegment, segmentData)
case 0x4:
segs(vec.Vec2{xm, y1}, vec.Vec2{xm, ym}, vec.Vec2{x0, ym}, marchSegment, segmentData)
case 0x5:
seg(vec.Vec2{xm, y1}, vec.Vec2{xm, y0}, marchSegment, segmentData)
case 0x6:
segs(vec.Vec2{xm, y0}, vec.Vec2{xm, ym}, vec.Vec2{x0, ym}, marchSegment, segmentData)
segs(vec.Vec2{xm, y1}, vec.Vec2{xm, ym}, vec.Vec2{x1, ym}, marchSegment, segmentData)
case 0x7:
segs(vec.Vec2{xm, y1}, vec.Vec2{xm, ym}, vec.Vec2{x1, ym}, marchSegment, segmentData)
case 0x8:
segs(vec.Vec2{x1, ym}, vec.Vec2{xm, ym}, vec.Vec2{xm, y1}, marchSegment, segmentData)
case 0x9:
segs(vec.Vec2{x1, ym}, vec.Vec2{xm, ym}, vec.Vec2{xm, y0}, marchSegment, segmentData)
segs(vec.Vec2{x0, ym}, vec.Vec2{xm, ym}, vec.Vec2{xm, y1}, marchSegment, segmentData)
case 0xA:
seg(vec.Vec2{xm, y0}, vec.Vec2{xm, y1}, marchSegment, segmentData)
case 0xB:
segs(vec.Vec2{x0, ym}, vec.Vec2{xm, ym}, vec.Vec2{xm, y1}, marchSegment, segmentData)
case 0xC:
seg(vec.Vec2{x1, ym}, vec.Vec2{x0, ym}, marchSegment, segmentData)
case 0xD:
segs(vec.Vec2{x1, ym}, vec.Vec2{xm, ym}, vec.Vec2{xm, y0}, marchSegment, segmentData)
case 0xE:
segs(vec.Vec2{xm, y0}, vec.Vec2{xm, ym}, vec.Vec2{x0, ym}, marchSegment, segmentData)
}
}
// Trace an aliased curve of an image along a particular threshold.
// The given number of samples will be taken and spread across the bounding box area using the sampling function and context.
// The segment function will be called for each segment detected that lies along the density contour for @c threshold.
func MarchHard(bb BB, xSamples, ySamples int64, t float64, marchSegment MarchSegmentFunc, marchSample MarchSampleFunc) *PolyLineSet {
return MarchCells(bb, xSamples, ySamples, t, marchSegment, marchSample, MarchCellHard)
}