The Ray Tracer Challenge: Cylinder test #7 (p185) - failed corner cases

Community PragProg Customers
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Hi,

I’m stuck on the test for #7 “Intersecting the caps of a closed cylinder”.
Tests 3 & 5 are failing as the intersections count is equal to one (one the cap intersection is detected).

After staring at the code for some time, any help is appreciated!

override internal func shapeSpecificIntersection(transformedRay:Ray<T>) -> Array<Intersection<T>> {
    var result = Array<Intersection<T>>()
    
    let a = transformedRay.direction.x * transformedRay.direction.x + transformedRay.direction.z * transformedRay.direction.z
    let b = 2 * transformedRay.origin.x * transformedRay.direction.x +
            2 * transformedRay.origin.z * transformedRay.direction.z
    if (a.magnitude < Self.defaultEpsilon || b.magnitude < Self.defaultEpsilon) {
        return intersectCaps(ray: transformedRay)
    }

    let c = transformedRay.origin.x * transformedRay.origin.x + transformedRay.origin.z * transformedRay.origin.z - 1

    
    let disc = b * b - 4 * a * c
    
    if (disc < 0) {
        return intersectCaps(ray: transformedRay)
    }
    
    var t0 = (-b - sqrt(disc)) / (2 * a)
    var t1 = (-b + sqrt(disc)) / (2 * a)

    if t0 > t1 {
        let tmp = t1
        t1 = t0
        t0 = tmp
    }

    let y0 = transformedRay.origin.y + t0 * transformedRay.direction.y
    if minimum < y0 && y0 < maximum {
        result.append(Intersection<T>(shape: self, t: t0))
    }
    
    let y1 = transformedRay.origin.y + t1 * transformedRay.direction.y
    if minimum < y1 && y1 < maximum {
        result.append(Intersection<T>(shape: self, t: t1))
    }
    
    result.append(contentsOf: intersectCaps(ray: transformedRay))
    
    return result
}

func checkCap(ray: Ray<T>, t: T) -> Bool {
    let x = ray.origin.x + t * ray.direction.x
    let z = ray.origin.z + t * ray.direction.z
    
    return (x * x) + (z * z) <= 1
}

func intersectCaps(ray: Ray<T>) -> Array<Intersection<T>> {
    var result = Array<Intersection<T>>()
    
    if !closed {
        return result
    }
        
    var t = (minimum - ray.origin.y) / ray.direction.y
    if (checkCap(ray: ray, t: t)) {
        result.append(Intersection<T>(shape: self, t: t))
    }
        
    t = (maximum - ray.origin.y) / ray.direction.y
    if (checkCap(ray:ray, t: t)) {
        result.append(Intersection<T>(shape: self, t: t))
    }
    
    return result
}

Best regards & happy coding! doja