93 lines
1.6 KiB
Go
93 lines
1.6 KiB
Go
package engine
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import (
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"encoding/gob"
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"errors"
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"image"
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)
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// Ensure Actor satisfies interfaces.
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var _ Prepper = &Actor{}
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var errCollision = errors.New("collision detected")
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func init() {
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gob.Register(Actor{})
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}
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// Thorson-style movement:
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// https://maddythorson.medium.com/celeste-and-towerfall-physics-d24bd2ae0fc5
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// Actor handles basic movement.
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type Actor struct {
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CollisionDomain string
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Pos image.Point
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Size image.Point
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collisionDomain interface{}
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xRem, yRem float64
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}
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func (a *Actor) CollidesAt(p image.Point) bool {
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return nil != Walk(a.collisionDomain, func(c interface{}) error {
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coll, ok := c.(Collider)
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if !ok {
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return nil
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}
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if coll.CollidesWith(image.Rectangle{Min: p, Max: p.Add(a.Size)}) {
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return errCollision
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}
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return nil
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})
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}
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func (a *Actor) MoveX(dx float64, onCollide func()) {
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a.xRem += dx
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move := int(a.xRem + 0.5) // Note: math.Round can lead to vibration
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if move == 0 {
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return
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}
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a.xRem -= float64(move)
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sign := sign(move)
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for move != 0 {
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if a.CollidesAt(a.Pos.Add(image.Pt(sign, 0))) {
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if onCollide != nil {
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onCollide()
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}
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return
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}
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a.Pos.X += sign
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move -= sign
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}
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}
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func (a *Actor) MoveY(dy float64, onCollide func()) {
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a.yRem += dy
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move := int(a.yRem + 0.5)
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if move == 0 {
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return
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}
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a.yRem -= float64(move)
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sign := sign(move)
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for move != 0 {
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if a.CollidesAt(a.Pos.Add(image.Pt(0, sign))) {
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if onCollide != nil {
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onCollide()
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}
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return
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}
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a.Pos.Y += sign
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move -= sign
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}
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}
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func (a *Actor) Prepare(g *Game) {
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a.collisionDomain = g.Component(a.CollisionDomain)
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}
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func sign(m int) int {
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if m < 0 {
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return -1
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}
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return 1
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}
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