From 6d1cbd928ed2f84445d9390efdfcb992e0beb493 Mon Sep 17 00:00:00 2001
From: William Moberg <william.moberg@live.se>
Date: Wed, 16 Dec 2015 16:34:27 +0100
Subject: [PATCH] Improved collision logic, still not perfect since it updates
 before PlayerSystem.

---
 include/Engine/Collision/Collision.h     |  3 +++
 src/Engine/Collision/Collision.cpp       | 34 ++++++++++++++++++++++++
 src/Engine/Collision/CollisionSystem.cpp | 17 ++++++------
 3 files changed, 46 insertions(+), 8 deletions(-)

diff --git a/include/Engine/Collision/Collision.h b/include/Engine/Collision/Collision.h
index 1fcb910e..64bf2d2c 100644
--- a/include/Engine/Collision/Collision.h
+++ b/include/Engine/Collision/Collision.h
@@ -41,6 +41,9 @@ bool RayVsModel(const Ray& ray,
 
 //Return true if the boxes are intersecting.
 bool AABBVsAABB(const AABB& a, const AABB& b);
+//Return true if the boxes are intersecting.
+//Also outputs the minimum translation that box [a] would need in order to resolve collision.
+bool AABBVsAABB(const AABB& a, const AABB& b, glm::vec3& minimumTranslation);
 bool IsSameBoxProbably(const AABB& first, const AABB& second, const float epsilon = 0.0001f);
 
 //Returns true if the entity has a boundingbox. Outputs the aabb in [outBox].
diff --git a/src/Engine/Collision/Collision.cpp b/src/Engine/Collision/Collision.cpp
index 500d59bc..d9cf8a0e 100644
--- a/src/Engine/Collision/Collision.cpp
+++ b/src/Engine/Collision/Collision.cpp
@@ -81,6 +81,40 @@ namespace Collision
         return (abs(aCenter[1] - bCenter[1]) <= (aHSize[1] + bHSize[1]));
     }
 
+    bool AABBVsAABB(const AABB& a, const AABB& b, glm::vec3& minimumTranslation)
+    {
+        minimumTranslation = glm::vec3(0, 0, 0);
+        const glm::vec3& aMax = a.MaxCorner();
+        const glm::vec3& bMax = b.MaxCorner();
+        const glm::vec3& aMin = a.MinCorner();
+        const glm::vec3& bMin = b.MinCorner();
+        const glm::vec3& bSize = b.Size();
+        const glm::vec3& aSize = a.Size();
+        float minOffset = INFINITY;
+        float off;
+        auto axisesIntersecting = glm::tvec3<bool, glm::highp>(false, false, false);
+        for (int i = 0; i < 3; ++i) {
+            off = bMax[i] - aMin[i];
+            if (off > 0 && off < bSize[i] + aSize[i]) {
+                if (off < minOffset) {
+                    minimumTranslation = glm::vec3();
+                    minimumTranslation[i] = minOffset = off;
+                }
+                axisesIntersecting[i] = true;
+            }
+            off = aMax[i] - bMin[i];
+            if (off > 0 && off < bSize[i] + aSize[i]) {
+                if (off < minOffset) {
+                    minOffset = off;
+                    minimumTranslation = glm::vec3();
+                    minimumTranslation[i] = -off;
+                }
+                axisesIntersecting[i] = true;
+            }
+        }
+        return glm::all(axisesIntersecting);
+    }
+
     bool RayVsModel(const Ray& ray,
         const std::vector<RawModel::Vertex>& modelVertices,
         const std::vector<unsigned int>& modelIndices)
diff --git a/src/Engine/Collision/CollisionSystem.cpp b/src/Engine/Collision/CollisionSystem.cpp
index ee5d4d29..dec33a20 100644
--- a/src/Engine/Collision/CollisionSystem.cpp
+++ b/src/Engine/Collision/CollisionSystem.cpp
@@ -4,15 +4,18 @@
 
 void CollisionSystem::UpdateComponent(World * world, ComponentWrapper & cAABB, double dt)
 {
-    //cAABB is any entity that should be collideable.
+    //TODO: Update CollisionSystem system after PlayerSystem.
+
+    //Right now, cAABB is a component attached to any entity that should be collideable.
     AABB thisBox;
     if (!Collision::GetEntityBox(world, cAABB, thisBox)) {
         return;
     }
-    //Here c should be an object that moves, currently only players.
+    //Press 'Z' to enable/disable collision.
     if (zPress) {
         return;
     }
+    //Here, mover should be an object that moves, currently only players.
     for (auto& mover : *world->GetComponents("Player")) {
         if (cAABB.EntityID == mover.EntityID) {
             continue;
@@ -21,13 +24,11 @@ void CollisionSystem::UpdateComponent(World * world, ComponentWrapper & cAABB, d
         if (!Collision::GetEntityBox(world, mover.EntityID, otherBox)) {
             continue;
         }
-        if (Collision::AABBVsAABB(thisBox, otherBox)) {
+        glm::vec3 resolveTranslation;
+        if (Collision::AABBVsAABB(otherBox, thisBox, resolveTranslation)) {
             ComponentWrapper& trans = world->GetComponent(mover.EntityID, "Transform");
-            //TODO: Move entity to correct position on collision instead of this. Special treatment if both are movers.
-            glm::vec3 newPos = trans["Position"];
-            float moveSpeed = 0.12f;
-            newPos += moveSpeed * glm::normalize(newPos - thisBox.Center());
-            trans["Position"] = newPos;
+            //TODO: Special treatment if both are movers.
+            trans["Position"] = (glm::vec3)trans["Position"] + resolveTranslation;
         }
     }
 }