From 9014eb92e6a5cb3235cbcd598e45ba5391a8738a Mon Sep 17 00:00:00 2001
From: "sigonasr2, Sig, Sigo" <sigonasr2@gmail.com>
Date: Mon, 1 Nov 2021 13:06:20 +0000
Subject: [PATCH] The Hello World of 3D Rendering.

Co-authored-by: sigonasr2 <sigonasr2@gmail.com>
---
 src/sig/Panel.java       | 20 ++++++++++++++++-
 src/sig/SigRenderer.java | 11 ++++++----
 src/sig/Triangle.java    | 46 +++++++++++++++++++++++++++++++++++++++-
 3 files changed, 71 insertions(+), 6 deletions(-)

diff --git a/src/sig/Panel.java b/src/sig/Panel.java
index eb49f29..e7ee5f0 100644
--- a/src/sig/Panel.java
+++ b/src/sig/Panel.java
@@ -1,9 +1,27 @@
 package sig;
 import javax.swing.JPanel;
+import javax.vecmath.Vector3d;
+
 import java.awt.Graphics;
+import java.awt.Color;
 
 public class Panel extends JPanel{
     public void paintComponent(Graphics g) {
-
+        Vector3d origin = new Vector3d(0,0,10);
+        for (int x=0;x<SigRenderer.SCREEN_WIDTH;x++) {
+            for (int y=0;y<SigRenderer.SCREEN_HEIGHT;y++) {
+                Vector3d dir = new Vector3d((-SigRenderer.SCREEN_WIDTH/2d+x),(-SigRenderer.SCREEN_HEIGHT/2d+y),SigRenderer.SCREEN_WIDTH);
+                if (SigRenderer.tri.rayTriangleIntersect(origin, dir)) {
+                    g.setColor(Color.BLACK);
+                    g.fillRect(SigRenderer.SCREEN_WIDTH-x,SigRenderer.SCREEN_HEIGHT-y,1,1);
+                    //System.out.println("Intersects at "+origin+"/"+dir);
+                }
+                if (SigRenderer.tri2.rayTriangleIntersect(origin, dir)) {
+                    g.setColor(Color.BLUE);
+                    g.fillRect(SigRenderer.SCREEN_WIDTH-x,SigRenderer.SCREEN_HEIGHT-y,1,1);
+                    //System.out.println("Intersects at "+origin+"/"+dir);
+                }
+            }
+        }
     }
 }
diff --git a/src/sig/SigRenderer.java b/src/sig/SigRenderer.java
index e0273ac..c6298f5 100644
--- a/src/sig/SigRenderer.java
+++ b/src/sig/SigRenderer.java
@@ -6,20 +6,23 @@ import java.awt.event.MouseListener;
 import java.awt.event.MouseMotionListener; 
 
 public class SigRenderer implements MouseListener,MouseMotionListener{
-    Triangle tri;
+    public static Triangle tri;
+    public static Triangle tri2;
     public final static int SCREEN_WIDTH=1280;
     public final static int SCREEN_HEIGHT=720;
     public final static long TIMEPERTICK = 16666667l;
     public static double DRAWTIME=0;
 
+    Vector3d origin = new Vector3d(0,0,-10);
+    Vector3d dir = new Vector3d(0,0,1);
+
     public void runGameLoop() {
 
     }
 
     SigRenderer(JFrame f) {
-        tri = new Triangle(new Vector3d(-1,-1,0),new Vector3d(1,0,0),new Vector3d(0,2,0));
-        System.out.println(tri);   
-        System.out.println(tri.getNormal()); 
+        tri = new Triangle(new Vector3d(-1,-1,0),new Vector3d(1,-1,0),new Vector3d(0,2,0));
+        tri2 = new Triangle(new Vector3d(-1,-1,120),new Vector3d(1,-1,120),new Vector3d(0,2,120));
 
         Panel p = new Panel();
 
diff --git a/src/sig/Triangle.java b/src/sig/Triangle.java
index d2af587..46ae22d 100644
--- a/src/sig/Triangle.java
+++ b/src/sig/Triangle.java
@@ -20,7 +20,51 @@ public class Triangle {
         BC.sub(C);
         Vector3d crossP = new Vector3d();
         crossP.cross(AB,BC);
-        crossP.normalize();
+        //crossP.normalize();
         return crossP;
     }
+    public double distanceFromOrigin() {
+        return getNormal().dot(A);
+    }
+
+    public boolean rayTriangleIntersect(Vector3d origin,Vector3d dir) {
+        Vector3d N = getNormal();
+
+        double NrayDir = N.dot(dir);
+        if (NrayDir<=0.001) { //Very small, so it's parallel.
+            return false;
+        }
+
+        double d = distanceFromOrigin();
+
+        double T=(getNormal().dot(origin)+d)/(NrayDir);
+
+        if (T<0) {return false;} //Triangle is behind the ray.
+
+        //System.out.println("Not behind.");
+
+        Vector3d scaleMult = (Vector3d)dir.clone();
+        scaleMult.scale(T);
+        Vector3d P = (Vector3d)origin.clone();
+        P.add(scaleMult);
+
+        Vector3d C;
+
+        Vector3d edge0 = (Vector3d)B.clone(); edge0.sub(A);
+        Vector3d vp0 = (Vector3d)P.clone(); vp0.sub(A);
+        C = new Vector3d(); C.cross(edge0,vp0);
+        if (N.dot(C)<0) {return false;}
+
+        Vector3d edge1 = (Vector3d)this.C.clone(); edge1.sub(B);
+        Vector3d vp1 = (Vector3d)P.clone(); vp1.sub(B);
+        C = new Vector3d(); C.cross(edge1,vp1);
+        if (N.dot(C)<0) {return false;}
+
+        Vector3d edge2 = (Vector3d)A.clone(); edge2.sub(this.C);
+        Vector3d vp2 = (Vector3d)P.clone(); vp2.sub(this.C);
+        C = new Vector3d(); C.cross(edge2,vp2);
+        if (N.dot(C)<0) {return false;}
+
+        return true;
+    }
 }