128 lines
2.9 KiB
Go
128 lines
2.9 KiB
Go
package collision
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import (
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"errors"
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"math"
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"git.kirsle.net/go/render"
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)
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// BoxCollision holds the result of a collision BetweenBoxes.
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type BoxCollision struct {
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// A and B are the indexes of the boxes sent to BetweenBoxes.
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A int
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B int
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// Overlap is the rect of how the boxes overlap.
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Overlap render.Rect
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}
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// IndexTuple holds two integers used as array indexes.
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type IndexTuple [2]int
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// BetweenBoxes checks if there is a collision between any
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// two bounding rectangles.
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//
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// This returns a generator that spits out indexes of the
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// intersecting boxes.
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func BetweenBoxes(boxes []render.Rect) chan BoxCollision {
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generator := make(chan BoxCollision)
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go func() {
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// Outer loop: test each box for intersection with the others.
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for i, box := range boxes {
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for j, other := range boxes {
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if i == j {
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continue
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}
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collision, err := CompareBoxes(box, other)
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if err == nil {
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collision.A = i
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collision.B = j
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generator <- collision
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}
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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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// CompareBoxes checks if two boxes overlaps and returns information about
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// the overlap. The boxes are bounding rectangles like those given to
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// BetweenBoxes().
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func CompareBoxes(box, other render.Rect) (BoxCollision, error) {
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if box.Intersects(other) {
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var (
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overlap = OverlapRelative(box, other)
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topLeft = overlap.TopLeft()
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bottomRight = overlap.BottomRight()
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)
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return BoxCollision{
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Overlap: render.Rect{
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X: topLeft.X,
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Y: topLeft.Y,
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W: bottomRight.X,
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H: bottomRight.Y,
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},
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}, nil
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}
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return BoxCollision{}, errors.New("boxes do not intersect")
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}
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/*
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OverlapRelative returns the Overlap box using coordinates relative
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to the source rect instead of absolute coordinates.
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*/
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func OverlapRelative(source, other render.Rect) CollisionBox {
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var (
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// Move the source rect to 0,0 and record the distance we need
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// to go to get there, so we can move the other rect the same.
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deltaX = 0 - source.X
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deltaY = 0 - source.Y
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)
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source.X = 0
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source.Y = 0
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other.X += deltaX
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other.Y += deltaY
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return Overlap(source, other)
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}
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/*
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Overlap returns the overlap rectangle between two boxes.
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The two rects given have an X,Y coordinate and their W,H are their
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width and heights.
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The returned CollisionBox uses absolute coordinates in the same space
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as the passed-in rects.
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*/
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func Overlap(a, b render.Rect) CollisionBox {
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max := func(x, y int32) int32 {
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return int32(math.Max(float64(x), float64(y)))
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}
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min := func(x, y int32) int32 {
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return int32(math.Min(float64(x), float64(y)))
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}
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var (
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A = GetCollisionBox(a)
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B = GetCollisionBox(b)
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ATL = A.TopLeft()
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ABR = A.BottomRight()
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BTL = B.TopLeft()
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BBR = B.BottomRight()
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// Coordinates of the intersection box.
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X1, Y1 = max(ATL.X, BTL.X), max(ATL.Y, BTL.Y)
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X2, Y2 = min(ABR.X, BBR.X), min(ABR.Y, BBR.Y)
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)
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return NewBox(render.NewPoint(X1, Y1), render.NewPoint(X2, Y2))
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}
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