Getting false positives with SAT

Question

I've been trying to get proper collision detection with SAT in 3D. I started of with this post: How many and which axes to use for 3D OBB collision with SAT.

I've been trying to get the right axis to test, which I thought would be correct, but they are still giving me false positives. All actual collision seem to work.

What I try is the following:

• Get the model for the objects in my game.
• Get the corners for the objects
• Adjust these corners to my object's location
• Get the axis
• Check for overlap when projecting the corners on these axis

When positioning the object in this way:

Then I get a false positive. (Although these are axis aligned, they should be able to rotate)

I've been stuck on this for quit a while now, so I feel like I'm missing something I just can't find. Also if this approach is an overkill and there is a better way, please also let me know.

I hate to just go like here's my code, but breaking it up in pieces will probably make it more confusing, so.. here's my code:

#define NOMINMAX

#include "../../stdafx.h"
#include "CollisionSystem.h"
#include "../../Core/MovingGameObject.h"
#include "../Objects/StaticObjects/Skull.h"
#include "../Objects/StaticObjects/Primitives/Plane.h"
#include <limits>
#include <cmath>

using namespace DirectX;

namespace JurreGame {
    CollisionSystem::CollisionSystem()
    {
    }


    CollisionSystem::~CollisionSystem()
    {
    }

    void CollisionSystem::CheckCollisionBetween(GameObject* objectA, GameObject* objectB)
    {
        XMFLOAT4X4 modelA = objectA->GetModel();
        XMMATRIX modelAMatrix = XMLoadFloat4x4(&modelA);
        XMMATRIX invModel = XMMatrixInverse(&XMMatrixDeterminant(modelAMatrix), modelAMatrix);
        XMFLOAT4X4 invModel4x4;
        XMStoreFloat4x4(&invModel4x4, invModel);
        XMMATRIX modelBMatrix = XMLoadFloat4x4(&objectB->GetModel());
        XMMATRIX aAlignedObjectBModel = XMMatrixMultiply(invModel, modelBMatrix);


        /* Corners positions
            x y z
        0 = - - +
        1 = + - +
        2 = + + +
        3 = - + +
        4 = - - -
        5 = + - -
        6 = + + -
        7 = - + -

        axis for the planes are:
        X Axis => (3) - + + vs + + + (2)
        Y Axis => (3) - + + vs - - + (0)
        Z Axis => (3) - + + vs - + - (7)
        */

        // https://gamedev.stackexchange.com/questions/44500/how-many-and-which-axis-to-use-for-3d-obb-collision-with-sat

        // Get's the corners calculated for the extends.
        XMFLOAT3 objectACorners[8];
        objectA->bounds.GetCorners(objectACorners);
        XMFLOAT3 objectBCorners[8];
        objectB->bounds.GetCorners(objectBCorners);

        // translates them to world space
        for (int i = 0; i < 8; i++) {
            XMStoreFloat3(&objectACorners[i], XMVector3Transform(XMLoadFloat3(&objectACorners[i]), modelAMatrix));
            XMStoreFloat3(&objectBCorners[i], XMVector3Transform(XMLoadFloat3(&objectBCorners[i]), modelBMatrix));
        }

        XMVECTOR ObjectAaxis1 = XMVectorSubtract(XMLoadFloat3(&objectACorners[2]), XMLoadFloat3(&objectACorners[3]));
        XMVECTOR ObjectAaxis2 = XMVectorSubtract(XMLoadFloat3(&objectACorners[3]), XMLoadFloat3(&objectACorners[0]));
        XMVECTOR ObjectAaxis3 = XMVectorSubtract(XMLoadFloat3(&objectACorners[3]), XMLoadFloat3(&objectACorners[7]));

        XMVECTOR ObjectBaxis1 = XMVectorSubtract(XMLoadFloat3(&objectBCorners[2]), XMLoadFloat3(&objectBCorners[3]));
        XMVECTOR ObjectBaxis2 = XMVectorSubtract(XMLoadFloat3(&objectBCorners[3]), XMLoadFloat3(&objectBCorners[0]));
        XMVECTOR ObjectBaxis3 = XMVectorSubtract(XMLoadFloat3(&objectBCorners[3]), XMLoadFloat3(&objectBCorners[7]));

        XMVECTOR crossaxis1 = XMVector3Cross(ObjectAaxis1, ObjectBaxis1);
        XMVECTOR crossaxis2 = XMVector3Cross(ObjectAaxis1, ObjectBaxis2);
        XMVECTOR crossaxis3 = XMVector3Cross(ObjectAaxis1, ObjectBaxis3);
        XMVECTOR crossaxis4 = XMVector3Cross(ObjectAaxis2, ObjectBaxis1);
        XMVECTOR crossaxis5 = XMVector3Cross(ObjectAaxis2, ObjectBaxis2);
        XMVECTOR crossaxis6 = XMVector3Cross(ObjectAaxis2, ObjectBaxis3);
        XMVECTOR crossaxis7 = XMVector3Cross(ObjectAaxis3, ObjectBaxis1);
        XMVECTOR crossaxis8 = XMVector3Cross(ObjectAaxis3, ObjectBaxis2);
        XMVECTOR crossaxis9 = XMVector3Cross(ObjectAaxis3, ObjectBaxis3);

        /**

        if (HasOverlap(objectACorners, objectBCorners, ObjectAaxis1)) { OutputDebugString(L"Has overlap on ObjectAaxis1\n"); }
        if (HasOverlap(objectACorners, objectBCorners, ObjectAaxis2)) { OutputDebugString(L"Has overlap on ObjectAaxis2\n"); }
        if (HasOverlap(objectACorners, objectBCorners, ObjectAaxis3)) { OutputDebugString(L"Has overlap on ObjectAaxis3\n"); }
        if (HasOverlap(objectACorners, objectBCorners, ObjectBaxis1)) { OutputDebugString(L"Has overlap on ObjectBaxis1\n"); }
        if (HasOverlap(objectACorners, objectBCorners, ObjectBaxis2)) { OutputDebugString(L"Has overlap on ObjectBaxis2\n"); }
        if (HasOverlap(objectACorners, objectBCorners, ObjectBaxis3)) { OutputDebugString(L"Has overlap on ObjectBaxis3\n"); }
        if (HasOverlap(objectACorners, objectBCorners, crossaxis1))   { OutputDebugString(L"Has overlap on crossaxis1\n"); }
        if (HasOverlap(objectACorners, objectBCorners, crossaxis2))   { OutputDebugString(L"Has overlap on crossaxis2\n"); }
        if (HasOverlap(objectACorners, objectBCorners, crossaxis3))   { OutputDebugString(L"Has overlap on crossaxis3\n"); }
        if (HasOverlap(objectACorners, objectBCorners, crossaxis4))   { OutputDebugString(L"Has overlap on crossaxis4\n"); }
        if (HasOverlap(objectACorners, objectBCorners, crossaxis5))   { OutputDebugString(L"Has overlap on crossaxis5\n"); }
        if (HasOverlap(objectACorners, objectBCorners, crossaxis6))   { OutputDebugString(L"Has overlap on crossaxis6\n"); }
        if (HasOverlap(objectACorners, objectBCorners, crossaxis7))   { OutputDebugString(L"Has overlap on crossaxis7\n"); }
        if (HasOverlap(objectACorners, objectBCorners, crossaxis8))   { OutputDebugString(L"Has overlap on crossaxis8\n"); }
        if (HasOverlap(objectACorners, objectBCorners, crossaxis9))   { OutputDebugString(L"Has overlap on crossaxis9\n"); }

        */
        if (!HasOverlap(objectACorners, objectBCorners, ObjectAaxis1)) { OutputDebugString(L"No overlap on ObjectAaxis1\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, ObjectAaxis2)) { OutputDebugString(L"No overlap on ObjectAaxis2\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, ObjectAaxis3)) { OutputDebugString(L"No overlap on ObjectAaxis3\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, ObjectBaxis1)) { OutputDebugString(L"No overlap on ObjectBaxis1\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, ObjectBaxis2)) { OutputDebugString(L"No overlap on ObjectBaxis2\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, ObjectBaxis3)) { OutputDebugString(L"No overlap on ObjectBaxis3\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, crossaxis1))   { OutputDebugString(L"No overlap on crossaxis1\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, crossaxis2))   { OutputDebugString(L"No overlap on crossaxis2\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, crossaxis3))   { OutputDebugString(L"No overlap on crossaxis3\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, crossaxis4))   { OutputDebugString(L"No overlap on crossaxis4\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, crossaxis5))   { OutputDebugString(L"No overlap on crossaxis5\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, crossaxis6))   { OutputDebugString(L"No overlap on crossaxis6\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, crossaxis7))   { OutputDebugString(L"No overlap on crossaxis7\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, crossaxis8))   { OutputDebugString(L"No overlap on crossaxis8\n"); }
        else if (!HasOverlap(objectACorners, objectBCorners, crossaxis9))   { OutputDebugString(L"No overlap on crossaxis9\n"); }
        else {
            OutputDebugString(L"Has collision\n");
        }
    }

    bool CollisionSystem::HasOverlap(XMFLOAT3 objectACorners[], XMFLOAT3 objectBCorners[], XMVECTOR axis) {
        float minA = std::numeric_limits<float>::max(), maxA = std::numeric_limits<float>::lowest();
        float minB = std::numeric_limits<float>::max(), maxB = std::numeric_limits<float>::lowest();
        if (XMVectorGetX(XMVector3Length(axis)) == 0.0f) {
            return true;
        }

        for (int i = 0; i < 8; i++) {
            //XMVECTOR cornerA = ProjectPoint(XMLoadFloat3(&objectACorners[i]), axis);
            //float lengthA = XMVectorGetX(XMVector3Length(cornerA));
            XMVECTOR dotProductA = XMVector3Dot(XMLoadFloat3(&objectACorners[i]), axis);
            float lengthA = XMVectorGetX(XMVector3Length(dotProductA));

            minA = fmin(minA, lengthA);
            maxA = fmax(maxA, lengthA);

            // XMVECTOR cornerB = ProjectPoint(XMLoadFloat3(&objectBCorners[i]), axis);
            // float lengthB = XMVectorGetX(XMVector3Length(cornerB));
            XMVECTOR dotProductB = XMVector3Dot(XMLoadFloat3(&objectBCorners[i]), axis);
            float lengthB = XMVectorGetX(XMVector3Length(dotProductB));

            minB = fmin(minB, lengthB);
            maxB = fmax(maxB, lengthB);

        }
        float longSpan = fmax(maxA, maxB) - fmin(minA, minB);
        float sumSpan = maxA - minA + maxB - minB;
        return longSpan < sumSpan;

        //return minB <= maxA && maxB >= minA;
    }

    XMVECTOR CollisionSystem::ProjectPoint(XMVECTOR point, XMVECTOR axis)
    {
        return (XMVector3Dot(point, axis) / XMVector3Dot(axis, axis)) * axis;
    }
}