doodle/pkg/doodads/collision.go

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package doodads
import (
"git.kirsle.net/apps/doodle/lib/render"
"git.kirsle.net/apps/doodle/pkg/level"
)
// Collide describes how a collision occurred.
type Collide struct {
Top bool
TopPoint render.Point
TopPixel *level.Swatch
Left bool
LeftPoint render.Point
LeftPixel *level.Swatch
Right bool
RightPoint render.Point
RightPixel *level.Swatch
Bottom bool
BottomPoint render.Point
BottomPixel *level.Swatch
MoveTo render.Point
}
// Reset a Collide struct flipping all the bools off, but keeping MoveTo.
func (c *Collide) Reset() {
c.Top = false
c.Left = false
c.Right = false
c.Bottom = false
}
// CollisionBox holds all of the coordinate pairs to draw the collision box
// around a doodad.
type CollisionBox struct {
Top []render.Point
Bottom []render.Point
Left []render.Point
Right []render.Point
}
// GetCollisionBox returns a CollisionBox with the four coordinates.
func GetCollisionBox(box render.Rect) CollisionBox {
return CollisionBox{
Top: []render.Point{
{
X: box.X,
Y: box.Y,
},
{
X: box.X + box.W,
Y: box.Y,
},
},
Bottom: []render.Point{
{
X: box.X,
Y: box.Y + box.H,
},
{
X: box.X + box.W,
Y: box.Y + box.H,
},
},
Left: []render.Point{
{
X: box.X,
Y: box.Y + box.H - 1,
},
{
X: box.X,
Y: box.Y + 1,
},
},
Right: []render.Point{
{
X: box.X + box.W,
Y: box.Y + box.H - 1,
},
{
X: box.X + box.W,
Y: box.Y + 1,
},
},
}
}
// Side of the collision box (top, bottom, left, right)
type Side uint8
// Options for the Side type.
const (
Top Side = iota
Bottom
Left
Right
)
/*
CollidesWithGrid checks if a Doodad collides with level geometry.
The `target` is the point the actor wants to move to on this tick.
*/
func CollidesWithGrid(d Actor, grid *level.Chunker, target render.Point) (*Collide, bool) {
var (
P = d.Position()
S = d.Size()
result = &Collide{
MoveTo: P,
}
ceiling bool // Has hit a ceiling?
capHeight int32 // Stop vertical movement thru a ceiling
capLeft int32 // Stop movement thru a wall
capRight int32
capFloor int32 // Stop movement thru the floor
hitLeft bool // Has hit an obstacle on the left
hitRight bool // or right
hitFloor bool
)
// Test all of the bounding boxes for a collision with level geometry.
if ok := result.ScanBoundingBox(GetBoundingRect(d), grid); ok {
// We've already collided! Try to wiggle free.
if result.Bottom {
if !d.Grounded() {
d.SetGrounded(true)
} else {
// result.Bottom = false
}
} else {
d.SetGrounded(false)
}
if result.Top {
// Never seen it touch the top.
}
if result.Left {
P.X++
}
if result.Right {
P.X--
}
}
// If grounded, cap our Y position.
if d.Grounded() {
if !result.Bottom {
// We've fallen off a ledge.
d.SetGrounded(false)
} else if target.Y < P.Y {
// We're moving upward.
d.SetGrounded(false)
} else {
// Cap our downward motion to our current position.
target.Y = P.Y
}
}
// Cap our horizontal movement if we're touching walls.
if (result.Left && target.X < P.X) || (result.Right && target.X > P.X) {
// If the step is short enough, try and jump up.
height := P.Y + S.H
if result.Left && target.X < P.X {
height -= result.LeftPoint.Y
} else {
height -= result.RightPoint.Y
}
if height <= 8 {
target.Y -= height
if target.X < P.X {
target.X-- // push along to the left
} else if target.X > P.X {
target.X++ // push along to the right
}
} else {
target.X = P.X
}
}
// Cap our vertical movement if we're touching ceilings.
if ceiling {
// The existing box intersects a ceiling, this will almost never
// happen because gravity will always pull you away at the last frame.
// But if we do somehow get here, may as well cap it where it's at.
capHeight = P.Y
}
// Trace a line from where we are to where we wanna go.
result.Reset()
result.MoveTo = P
for point := range render.IterLine2(P, target) {
if has := result.ScanBoundingBox(render.Rect{
X: point.X,
Y: point.Y,
W: S.W,
H: S.H,
}, grid); has {
if result.Bottom {
if !hitFloor {
hitFloor = true
capFloor = result.BottomPoint.Y - S.H
}
d.SetGrounded(true)
}
if result.Top && !ceiling {
// This is a newly discovered ceiling.
ceiling = true
capHeight = result.TopPoint.Y
}
if result.Left && !hitLeft {
hitLeft = true
capLeft = result.LeftPoint.X
}
if result.Right && !hitRight {
hitRight = true
capRight = result.RightPoint.X - S.W
}
}
// So far so good, keep following the MoveTo to
// the last good point before a collision.
result.MoveTo = point
}
// If they hit the roof, cap them to the roof.
if ceiling && result.MoveTo.Y < capHeight {
result.Top = true
result.MoveTo.Y = capHeight
}
if hitFloor && result.MoveTo.Y > capFloor {
result.Bottom = true
result.MoveTo.Y = capFloor
}
if hitLeft {
result.Left = true
result.MoveTo.X = capLeft
}
if hitRight {
result.Right = true
result.MoveTo.X = capRight
}
return result, result.IsColliding()
}
// IsColliding returns whether any sort of collision has occurred.
func (c *Collide) IsColliding() bool {
return c.Top || c.Bottom || c.Left || c.Right
}