Noah Petherbridge
6af60f1128
* Improve the collision detection algorithm so that Actor OnCollide
scripts get called more often WHILE an actor is moving, to prevent a
fast-moving actor from zipping right through the "solid" hitbox and
not giving the subject actor time to protest the movement.
* It's implemented by adding a `Settled` boolean to the OnCollide event
object. When the game is testing out movement, Settled=false to give
the actor a chance to say "I'm solid!" and have the moving party be
stopped early.
* After all this is done, for any pair of actors still with overlapping
hitboxes, OnCollide is called one last time with Settled=true. This is
when the actor should run its actions (like publishing messages to
other actors, changing state as in a trapdoor, etc.)
* The new collision detection algorithm works as follows:
* Stage 1 is the same as before, all mobile actors are moved and
tested against level geometry. They record their Original and New
position during this phase.
* Stage 2 is where we re-run that movement but ping actors being
intersected each step of the way. We trace the steps between
Original and New position, test OnCollide handler, and if it returns
false we move the mobile actor to the Last Good Position along the
trace.
* Stage 3 we run the final OnCollide(Settled=true) to let actors run
actions they wanted to for their collide handler, WITHOUT spamming
those actions during Stage 2.
* This should now allow for tweaking of gravity speed and player speed
without breaking all actor collision checking.
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/apps/doodle/lib/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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