Better Collision Detection (Bouncy Jumps Up Hills)

* Add a debug view that draws the player bounding boxes.
* Improve the collision detection to add support for:
  * Doodads being "Grounded" so gravity need not apply.
  * Walking up hills, albeit a bit "bouncily"
  * Harder to clip out of bounds

doodads/doodads.go

@@ -1,6 +1,8 @@
 package doodads
 
 import (
+	"fmt"
+
 	"git.kirsle.net/apps/doodle/level"
 	"git.kirsle.net/apps/doodle/render"
 )
@@ -15,6 +17,8 @@ type Doodad interface {
 	Position() render.Point
 	Velocity() render.Point
 	Size() render.Rect
+	Grounded() bool
+	SetGrounded(bool)
 
 	// Movement commands.
 	MoveBy(render.Point) // Add {X,Y} to current Position.
@@ -26,89 +30,231 @@ type Doodad interface {
 
 // Collide describes how a collision occurred.
 type Collide struct {
-	X      int32
-	Y      int32
-	W      int32
-	H      int32
 	Top         bool
+	TopPoint    render.Point
 	Left        bool
+	LeftPoint   render.Point
 	Right       bool
+	RightPoint  render.Point
 	Bottom      bool
+	BottomPoint render.Point
+	MoveTo      render.Point
 }
 
+// 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
+}
+
+// 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.
-func CollidesWithGrid(d Doodad, grid *render.Grid) (Collide, bool) {
+func CollidesWithGrid(d Doodad, grid *render.Grid, target render.Point) (*Collide, bool) {
 	var (
 		P = d.Position()
 		S = d.Size()
-		topLeft  = P
+
-		topRight = render.Point{
+		result = &Collide{
-			X: P.X + S.W,
+			MoveTo: P,
-			Y: P.Y,
-		}
-		bottomLeft = render.Point{
-			X: P.X,
-			Y: P.Y + S.H,
-		}
-		bottomRight = render.Point{
-			X: bottomLeft.X + S.W,
-			Y: P.Y + S.H,
 		}
 	)
 
-	// Bottom edge.
+	// Test all of the bounding boxes for a collision with level geometry.
-	for point := range render.IterLine2(bottomLeft, bottomRight) {
+	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 {
+			P.Y++
+		}
+		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.
+		relPoint := P.Y + S.H
+		if result.Left && target.X < P.X {
+			relPoint -= result.LeftPoint.Y
+		} else {
+			relPoint -= result.RightPoint.Y
+		}
+		fmt.Printf("Touched a wall at %d pixels height (P=%s)\n", relPoint, P)
+		if S.H-relPoint > S.H-8 {
+			target.Y -= 12
+			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
+		}
+	}
+
+	// Trace a line from where we are to where we wanna go.
+	result.MoveTo = P
+	for point := range render.IterLine2(P, target) {
+		if ok := result.ScanBoundingBox(render.Rect{
+			X: point.X,
+			Y: point.Y,
+			W: S.W,
+			H: S.H,
+		}, grid); ok {
+			if d.Grounded() {
+				if !result.Bottom {
+					d.SetGrounded(false)
+				}
+			} else if result.Bottom {
+				d.SetGrounded(true)
+			}
+		}
+		result.MoveTo = point
+	}
+
+	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
+}
+
+// GetCollisionBox computes the full pairs of points for the collision box
+// around a doodad.
+func GetBoundingRect(d Doodad) render.Rect {
+	var (
+		P = d.Position()
+		S = d.Size()
+	)
+	return render.Rect{
+		X: P.X,
+		Y: P.Y,
+		W: S.W,
+		H: S.H,
+	}
+}
+
+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 + 1,
+			},
+			{
+				X: box.X,
+				Y: box.Y + box.H - 1,
+			},
+		},
+		Right: []render.Point{
+			{
+				X: box.X + box.W,
+				Y: box.Y + 1,
+			},
+			{
+				X: box.X + box.W,
+				Y: box.Y + box.H - 1,
+			},
+		},
+	}
+}
+
+// ScanBoundingBox scans all of the pixels in a bounding box on the grid and
+// returns if any of them intersect with level geometry.
+func (c *Collide) ScanBoundingBox(box render.Rect, grid *render.Grid) bool {
+	col := GetCollisionBox(box)
+
+	c.ScanGridLine(col.Top[0], col.Top[1], grid, Top)
+	c.ScanGridLine(col.Bottom[0], col.Bottom[1], grid, Bottom)
+	c.ScanGridLine(col.Left[0], col.Left[1], grid, Left)
+	c.ScanGridLine(col.Right[0], col.Right[1], grid, Right)
+	return c.IsColliding()
+}
+
+// ScanGridLine scans all of the pixels between p1 and p2 on the grid and tests
+// for any pixels to be set, implying a collision between level geometry and the
+// bounding boxes of the doodad.
+func (c *Collide) ScanGridLine(p1, p2 render.Point, grid *render.Grid, side Side) {
+	for point := range render.IterLine2(p1, p2) {
 		if grid.Exists(level.Pixel{
 			X: point.X,
 			Y: point.Y,
 		}) {
-			return Collide{
+			// A hit!
-				Bottom: true,
+			switch side {
-				X:      point.X,
+			case Top:
-				Y:      point.Y,
+				c.Top = true
-			}, true
+				c.TopPoint = point
+			case Bottom:
+				c.Bottom = true
+				c.BottomPoint = point
+			case Left:
+				c.Left = true
+				c.LeftPoint = point
+			case Right:
+				c.Right = true
+				c.RightPoint = point
 			}
 		}
-
-	// Top edge.
-	for point := range render.IterLine2(topLeft, topRight) {
-		if grid.Exists(level.Pixel{
-			X: point.X,
-			Y: point.Y,
-		}) {
-			return Collide{
-				Top: true,
-				X:   point.X,
-				Y:   point.Y,
-			}, true
 	}
 }
-
-	for point := range render.IterLine2(topLeft, bottomLeft) {
-		if grid.Exists(level.Pixel{
-			X: point.X,
-			Y: point.Y,
-		}) {
-			return Collide{
-				Left: true,
-				X:    point.X,
-				Y:    point.Y,
-			}, true
-		}
-	}
-
-	for point := range render.IterLine2(topRight, bottomRight) {
-		if grid.Exists(level.Pixel{
-			X: point.X,
-			Y: point.Y,
-		}) {
-			return Collide{
-				Right: true,
-				X:     point.X,
-				Y:     point.Y,
-			}, true
-		}
-	}
-
-	return Collide{}, false
-}

doodads/player.go

@@ -12,6 +12,7 @@ type Player struct {
 	point    render.Point
 	velocity render.Point
 	size     render.Rect
+	grounded bool
 }
 
 // NewPlayer creates the special Player Character doodad.
@@ -22,8 +23,8 @@ func NewPlayer() *Player {
 			Y: 100,
 		},
 		size: render.Rect{
-			W: 16,
+			W: 32,
-			H: 16,
+			H: 32,
 		},
 	}
 }
@@ -59,9 +60,19 @@ func (p *Player) Size() render.Rect {
 	return p.size
 }
 
+// Grounded returns if the player is grounded.
+func (p *Player) Grounded() bool {
+	return p.grounded
+}
+
+// SetGrounded sets if the player is grounded.
+func (p *Player) SetGrounded(v bool) {
+	p.grounded = v
+}
+
 // Draw the player sprite.
 func (p *Player) Draw(e render.Engine) {
-	e.DrawRect(render.Magenta, render.Rect{
+	e.DrawBox(render.Color{255, 255, 153, 255}, render.Rect{
 		X: p.point.X,
 		Y: p.point.Y,
 		W: p.size.W,

fps.go

@@ -3,6 +3,7 @@ package doodle
 import (
 	"fmt"
 
+	"git.kirsle.net/apps/doodle/doodads"
 	"git.kirsle.net/apps/doodle/render"
 )
 
@@ -49,6 +50,19 @@ func (d *Doodle) DrawDebugOverlay() {
 	}
 }
 
+// DrawCollisionBox draws the collision box around a Doodad.
+func (d *Doodle) DrawCollisionBox(actor doodads.Doodad) {
+	var (
+		rect = doodads.GetBoundingRect(actor)
+		box  = doodads.GetCollisionBox(rect)
+	)
+
+	d.Engine.DrawLine(render.DarkGreen, box.Top[0], box.Top[1])
+	d.Engine.DrawLine(render.DarkBlue, box.Bottom[0], box.Bottom[1])
+	d.Engine.DrawLine(render.DarkYellow, box.Left[0], box.Left[1])
+	d.Engine.DrawLine(render.Red, box.Right[0], box.Right[1])
+}
+
 // TrackFPS shows the current FPS once per second.
 func (d *Doodle) TrackFPS(skipped uint32) {
 	fpsFrames++

play_scene.go

@@ -82,6 +82,9 @@ func (s *PlayScene) Draw(d *Doodle) error {
 	// Draw our hero.
 	s.player.Draw(d.Engine)
 
+	// Draw out bounding boxes.
+	d.DrawCollisionBox(s.player)
+
 	return nil
 }
 
@@ -105,20 +108,20 @@ func (s *PlayScene) movePlayer(ev *events.State) {
 	}
 
 	// Apply gravity.
+	// var onFloor bool
+
+	info, ok := doodads.CollidesWithGrid(s.player, &s.canvas, delta)
+	if ok {
+		// Collision happened with world.
+	}
+	delta = info.MoveTo
+
+	// Apply gravity if not grounded.
+	if !s.player.Grounded() {
 		delta.Y += gravity
-
-	// Draw a ray and check for collision.
-	var lastOk = s.player.Position()
-	for point := range render.IterLine2(s.player.Position(), delta) {
-		s.player.MoveTo(point)
-		if _, ok := doodads.CollidesWithGrid(s.player, &s.canvas); ok {
-			s.player.MoveTo(lastOk)
-		} else {
-			lastOk = s.player.Position()
-		}
 	}
 
-	s.player.MoveTo(lastOk)
+	s.player.MoveTo(delta)
 }
 
 // LoadLevel loads a level from disk.

render/interface.go

@@ -45,6 +45,16 @@ type Color struct {
 	Alpha uint8
 }
 
+// RGBA creates a new Color.
+func RGBA(r, g, b, a uint8) Color {
+	return Color{
+		Red:   r,
+		Green: g,
+		Blue:  b,
+		Alpha: a,
+	}
+}
+
 func (c Color) String() string {
 	return fmt.Sprintf(
 		"Color<#%02x%02x%02x>",
@@ -92,17 +102,23 @@ func (t Text) String() string {
 // Common color names.
 var (
 	Invisible  = Color{}
-	White     = Color{255, 255, 255, 255}
+	White      = RGBA(255, 255, 255, 255)
-	Grey      = Color{153, 153, 153, 255}
+	Grey       = RGBA(153, 153, 153, 255)
-	Black     = Color{0, 0, 0, 255}
+	Black      = RGBA(0, 0, 0, 255)
-	SkyBlue   = Color{0, 153, 255, 255}
+	SkyBlue    = RGBA(0, 153, 255, 255)
-	Blue      = Color{0, 0, 255, 255}
+	Blue       = RGBA(0, 0, 255, 255)
-	Red       = Color{255, 0, 0, 255}
+	DarkBlue   = RGBA(0, 0, 153, 255)
-	Green     = Color{0, 255, 0, 255}
+	Red        = RGBA(255, 0, 0, 255)
-	Cyan      = Color{0, 255, 255, 255}
+	DarkRed    = RGBA(153, 0, 0, 255)
-	Yellow    = Color{255, 255, 0, 255}
+	Green      = RGBA(0, 255, 0, 255)
-	Magenta   = Color{255, 0, 255, 255}
+	DarkGreen  = RGBA(0, 153, 0, 255)
-	Pink      = Color{255, 153, 255, 255}
+	Cyan       = RGBA(0, 255, 255, 255)
+	DarkCyan   = RGBA(0, 153, 153, 255)
+	Yellow     = RGBA(255, 255, 0, 255)
+	DarkYellow = RGBA(153, 153, 0, 255)
+	Magenta    = RGBA(255, 0, 255, 255)
+	Purple     = RGBA(153, 0, 153, 255)
+	Pink       = RGBA(255, 153, 255, 255)
 )
 
 // IterLine is a generator that returns the X,Y coordinates to draw a line.

render/sdl/canvas.go

@@ -25,7 +25,7 @@ func (r *Renderer) DrawPoint(color render.Color, point render.Point) {
 // DrawLine draws a line between two points.
 func (r *Renderer) DrawLine(color render.Color, a, b render.Point) {
 	if color != r.lastColor {
-		r.renderer.SetDrawColor(color.Red, color.Blue, color.Green, color.Alpha)
+		r.renderer.SetDrawColor(color.Red, color.Green, color.Blue, color.Alpha)
 	}
 	r.renderer.DrawLine(a.X, a.Y, b.X, b.Y)
 }