attempt to fix collision

animationMario.go

@@ -60,45 +60,96 @@ func (a *Animation) updateMarioPosition() {
 	centerX := a.ctx.Width() / 2
 	centerY := a.ctx.Height() / 2
 
+	// Determine sprite size (use current updown image if available)
+	var sprite image.Image
+	if img, ok := a.mario.images[a.mario.updown]; ok && img != nil {
+		sprite = img
+	} else {
+		for _, im := range a.mario.images {
+			sprite = im
+			break
+		}
+	}
+
+	// default half sizes if sprite missing
+	halfW, halfH := 8, 8
+	if sprite != nil {
+		halfW = sprite.Bounds().Dx() / 2
+		halfH = sprite.Bounds().Dy() / 2
+	}
+
+	// allowable center range so the sprite stays fully on the panel
+	minCenterX := halfW
+	maxCenterX := a.ctx.Width() - 1 - halfW
+	minCenterY := halfH
+	maxCenterY := a.ctx.Height() - 1 - halfH
+
+	// parametric angle before any reflection
 	t := a.mario.angle
-	marioX := int(math.Round(float64(a.mario.a * math.Cos(t))))
-	marioY := int(math.Round(float64(a.mario.b * math.Sin(t))))
 
-	// Adjust position relative to the center of the panel
+	// compute candidate center position on the ellipse
-	marioX += centerX
+	marioX := int(math.Round(a.mario.a*math.Cos(t))) + centerX
-	marioY += centerY
+	marioY := int(math.Round(a.mario.b*math.Sin(t))) + centerY
+
+	// detect collisions against allowed center ranges
+	collidedX := marioX < minCenterX || marioX > maxCenterX
+	collidedY := marioY < minCenterY || marioY > maxCenterY
 
-	// Check for edge collision and change direction if necessary
+	// Reflect the parametric angle correctly:
-	if marioX < 0 {
+	// - For horizontal collision we want cos(t_new) = -cos(t) => t_new = Pi - t
-		a.mario.angle = -a.mario.angle + math.Pi // Reflect horizontally and adjust angle
+	// - For vertical collision we want sin(t_new) = -sin(t)   => t_new = -t
-	} else if marioX >= a.ctx.Width() {
+	if collidedX {
-		a.mario.angle = -a.mario.angle + math.Pi // Reflect horizontally and adjust angle
+		t = math.Pi - t
 	}
+	if collidedY {
+		t = -t
+	}
+
+	// normalize angle into [0, 2π)
+	for t < 0 {
+		t += 2 * math.Pi
+	}
+	for t >= 2*math.Pi {
+		t -= 2 * math.Pi
+	}
+	a.mario.angle = t
 
-	if marioY < 0 {
+	// recompute position from possibly-updated angle so sprite is inside bounds
-		a.mario.angle = math.Pi - a.mario.angle // Flip vertically and adjust angle
+	marioX = int(math.Round(a.mario.a*math.Cos(t))) + centerX
-	} else if marioY >= a.ctx.Height() {
+	marioY = int(math.Round(a.mario.b*math.Sin(t))) + centerY
-		a.mario.angle = math.Pi - a.mario.angle // Flip vertically and adjust angle
+
+	// clamp as a safety net
+	if marioX < minCenterX {
+		marioX = minCenterX
+	}
+	if marioX > maxCenterX {
+		marioX = maxCenterX
+	}
+	if marioY < minCenterY {
+		marioY = minCenterY
+	}
+	if marioY > maxCenterY {
+		marioY = maxCenterY
 	}
 
 	a.mario.position.X = marioX
 	a.mario.position.Y = marioY
 
-	// Update angle to move along the ellipse (slower by half)
+	// advance angle for next frame
-	a.mario.angle += 0.05 // Slow down Mario's movement by half
+	a.mario.angle += 0.05
 	if a.mario.angle >= 2*math.Pi {
 		a.mario.angle -= 2 * math.Pi
 	}
 
-	// Direction logic for up and down movement
+	// Direction logic (based on param t used for the current frame)
 	if math.Sin(t) > 0 {
-		a.mario.dir.X = -1 // Moving left
+		a.mario.dir.X = -1 // moving left
 	} else {
-		a.mario.dir.X = 1 // Moving right
+		a.mario.dir.X = 1 // moving right
 	}
 	if math.Cos(t) > 0 {
-		a.mario.updown = "marioDown" // Moving downward
+		a.mario.updown = "marioDown" // moving downward
 	} else {
-		a.mario.updown = "marioUp" // Moving upward
+		a.mario.updown = "marioUp" // moving upward
 	}
 }