From 94e3f8516ca45353f49af39c4349b12aa118f287 Mon Sep 17 00:00:00 2001
From: Matthew Kosarek <mattkae@protonmail.com>
Date: Wed, 30 Jun 2021 19:21:42 -0400
Subject: Small optimization for polygonal intersections

---
 2d/_collisions/polygon_polygon/dist/output.wasm | Bin 57631 -> 57769 bytes
 2d/_collisions/polygon_polygon/main.cpp         |  31 +++++++++++++++++-------
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/2d/_collisions/polygon_polygon/dist/output.wasm b/2d/_collisions/polygon_polygon/dist/output.wasm
index 5b2ba39..d865038 100755
Binary files a/2d/_collisions/polygon_polygon/dist/output.wasm and b/2d/_collisions/polygon_polygon/dist/output.wasm differ
diff --git a/2d/_collisions/polygon_polygon/main.cpp b/2d/_collisions/polygon_polygon/main.cpp
index 8648e94..ff01e52 100644
--- a/2d/_collisions/polygon_polygon/main.cpp
+++ b/2d/_collisions/polygon_polygon/main.cpp
@@ -115,8 +115,7 @@ struct ConvexPolygon {
 	Rigidbody previousBody;
 	Vector4 color;
 	int32 numVertices = 3;
-	float32 width = 0.f;
-	float32 height = 0.f;
+	float32 radius = 0.f;
 
     Vector2* originalVertices;
     Vector2* transformedVertices;
@@ -138,14 +137,14 @@ struct ConvexPolygon {
 			int32 indexPosition = vidx * 3;
 			
 			float32 firstAngle = angleIncrements * vidx;
-		    shaderVertices[indexPosition].position = {  cosf(firstAngle) * width, sinf(firstAngle) * height };
+		    shaderVertices[indexPosition].position = {  cosf(firstAngle) * radius, sinf(firstAngle) * radius };
 
             originalVertices[vidx] = shaderVertices[indexPosition].position;
 
 		    shaderVertices[indexPosition + 1].position = {  0.f, 0.f };
 
 			float32 secondAngle = angleIncrements * (vidx + 1);
-			shaderVertices[indexPosition + 2].position = {  cosf(secondAngle) * width, sinf(secondAngle) * height };
+			shaderVertices[indexPosition + 2].position = {  cosf(secondAngle) * radius, sinf(secondAngle) * radius };
 
 			// Apply some global stylings
 			for (int subIdx = 0; subIdx < 3; subIdx++) {
@@ -159,7 +158,7 @@ struct ConvexPolygon {
         edges = new Edge[numVertices]; // This will be filled in later when we are doing our SAT calculation.
 
         // Calculate moment of inertia
-        body.momentOfInertia = (PI * (width * height * body.mass)) / 4.f;
+        body.momentOfInertia = (PI * (radius * radius * body.mass)) / 4.f;
 	}
 
 	void update(float32 dtSeconds) {
@@ -167,7 +166,9 @@ struct ConvexPolygon {
 		
 		body.update(dtSeconds);
 		shape.model = Mat4x4().translateByVec2(body.position).rotate2D(body.rotation);
+	}
 
+    void calculateTransformedVertices() {
         // Populate the current position of our edges. Note that this might be slow depending
         // on how many edges your shaped have.
         for (int vidx = 0; vidx < numVertices; vidx++) {
@@ -177,7 +178,7 @@ struct ConvexPolygon {
             Vector2 end = shape.model * originalVertices[vidx == numVertices - 1 ? 0 : vidx + 1];
             edges[vidx] = { (end - start).getPerp(), start, end };
         }
-	}
+    }
 
     void restorePreviousBody() {
         body = previousBody;
@@ -244,8 +245,7 @@ void load() {
             polygons[index].body.mass = 8.f;
 		}
 
-        polygons[index].width = (polygons[index].body.mass / 2.f) * 20.f;
-		polygons[index].height = (polygons[index].body.mass / 2.f) * 20.f;
+        polygons[index].radius = (polygons[index].body.mass / 2.f) * 20.f;
 
 		polygons[index].numVertices = (index + 1) * 3;
 		polygons[index].color = Vector4 {
@@ -383,17 +383,30 @@ void resolveCollision(Rigidbody* first, Rigidbody* second, IntersectionResult* i
     second->rotationalVelocity = second->rotationalVelocity - secondPerp.dot(collisionNormal * impulseMagnitude) / second->momentOfInertia;
 }
 
+bool circleHitBoxesIntersect(ConvexPolygon* first, ConvexPolygon* second) {
+    return (first->body.position - second->body.position).length() <= (first->radius + second->radius);
+}
+
 void update(float32 deltaTimeSeconds, void* userData) {
 	// Update
 	for (int p = 0; p < 4; p++) {
 	    polygons[p].update(deltaTimeSeconds);
 	}
 
-	// Check collisions with other rectangles
+	// Collision detection
 	for (int i = 0; i < 4; i++) {
 	    ConvexPolygon* first = &polygons[i];
 		for (int j = i + 1; j < 4; j++) {
 		    ConvexPolygon* second = &polygons[j];
+
+            if (!circleHitBoxesIntersect(first, second)) {
+                continue;
+            }
+
+            printf("Might intersect\n");
+
+            first->calculateTransformedVertices();
+            second->calculateTransformedVertices();
 			
 			IntersectionResult ir = getIntersection(first, second);
 			if (!ir.intersect) {
-- 
cgit v1.2.1