150 lines
3.6 KiB
Go
150 lines
3.6 KiB
Go
package engine
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import (
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"image"
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"math"
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"drjosh.dev/gurgle/geom"
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"github.com/hajimehoshi/ebiten/v2"
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)
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const commonDrawerComparisons = true
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var _ Drawer = tombstone{}
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type tombstone struct{}
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func (tombstone) Draw(*ebiten.Image, *ebiten.DrawImageOptions) {}
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func (tombstone) DrawAfter(x Drawer) bool { return x != tombstone{} }
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func (tombstone) DrawBefore(Drawer) bool { return false }
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func (tombstone) String() string { return "tombstone" }
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type drawList struct {
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list []Drawer
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rev map[Drawer]int
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}
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func (d drawList) Less(i, j int) bool {
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// Deal with tombstones first, in case anything else thinks it
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// needs to go last.
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if d.list[i] == (tombstone{}) {
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return false
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}
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if d.list[j] == (tombstone{}) {
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return true
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}
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if commonDrawerComparisons {
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// Common logic for known interfaces (BoundingBoxer, ZPositioner), to
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// simplify Draw{Before,After} implementations.
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switch x := d.list[i].(type) {
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case BoundingBoxer:
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xb := x.BoundingBox()
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switch y := d.list[j].(type) {
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case BoundingBoxer:
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yb := y.BoundingBox()
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if xb.Min.Z >= yb.Max.Z { // x is in front of y
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return false
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}
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if xb.Max.Z <= yb.Min.Z { // x is behind y
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return true
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}
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if xb.Max.Y <= yb.Min.Y { // x is above y
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return false
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}
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if xb.Min.Y >= yb.Max.Y { // x is below y
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return true
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}
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case ZPositioner:
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return xb.Max.Z < y.ZPos() // x is before y
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}
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case ZPositioner:
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switch y := d.list[j].(type) {
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case BoundingBoxer:
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return x.ZPos() < y.BoundingBox().Min.Z
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case ZPositioner:
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return x.ZPos() < y.ZPos()
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}
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}
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}
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// Fallback case: ask the components themselves
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return d.list[i].DrawBefore(d.list[j]) || d.list[j].DrawAfter(d.list[i])
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}
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func (d drawList) Len() int { return len(d.list) }
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func (d drawList) Swap(i, j int) {
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d.rev[d.list[i]], d.rev[d.list[j]] = j, i
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d.list[i], d.list[j] = d.list[j], d.list[i]
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}
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// Slow topological sort. Uses a projection π to flatten bounding boxes for
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// overlap tests, in order to reduce edge count.
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func (d *drawList) topsort(π geom.Projector) {
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// Produce edge lists and count indegrees - O(|V|^2)
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// TODO: optimise this
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edges := make([][]int, len(d.list))
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indegree := make([]int, len(d.list))
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for i, u := range d.list {
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if u == (tombstone{}) {
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// Prevents processing this vertex later on
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indegree[i] = -1
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continue
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}
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// If we can't get a more specific bounding rect, assume entire plane.
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ub := image.Rect(math.MinInt, math.MinInt, math.MaxInt, math.MaxInt)
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if x, ok := u.(BoundingBoxer); ok {
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ub = x.BoundingBox().BoundingRect(π)
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}
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// For each possible neighbor...
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for j, v := range d.list {
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if i == j || v == (tombstone{}) {
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continue
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}
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// Does it have a bounding rect? Do overlap test.
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if y, ok := v.(BoundingBoxer); ok {
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if vb := y.BoundingBox().BoundingRect(π); !ub.Overlaps(vb) {
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continue
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}
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}
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// If the edge goes u->v, add it.
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if d.Less(i, j) {
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edges[i] = append(edges[i], j)
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indegree[j]++
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}
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}
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}
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// Initialise queue with all the zero-indegree vertices
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var queue []int
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for i, n := range indegree {
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if n == 0 {
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queue = append(queue, i)
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}
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}
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// Process into new list. O(|V| + |E|)
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list := make([]Drawer, 0, len(d.list))
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for len(queue) > 0 {
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// Get front of queue.
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i := queue[0]
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queue = queue[1:]
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// Add to output list.
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d.rev[d.list[i]] = len(list)
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list = append(list, d.list[i])
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// Reduce indegree for all outgoing edges, enqueue if indegree now 0.
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for _, j := range edges[i] {
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indegree[j]--
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if indegree[j] == 0 {
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queue = append(queue, j)
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}
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}
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}
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// Job done!
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d.list = list
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}
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