From 5cb3ff9fbdcf950fa129f5a94c906ac532761176 Mon Sep 17 00:00:00 2001
From: Colin McMillen <colin@semicolin.games>
Date: Sun, 2 Feb 2020 08:57:49 -0500
Subject: [PATCH] first pass at implementing line-of-sight algorithm

partial solution for #29

GitOrigin-RevId: bb5f5dc057ba5947573f9b9c8eb30cc20f635bb0
---
 Shared/Player.cs | 94 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 91 insertions(+), 3 deletions(-)

diff --git a/Shared/Player.cs b/Shared/Player.cs
index 12e156d..1ce9b1d 100644
--- a/Shared/Player.cs
+++ b/Shared/Player.cs
@@ -31,6 +31,8 @@ namespace SemiColinGames {
     // centered at that point and extending out by halfSize.X and halfSize.Y.
     private Point position = new Point(64, 16 * 13);
     private Vector2 halfSize = new Vector2(11, 24);
+    private Vector2 eyeOffsetStanding = new Vector2(7, -14);
+    private Vector2 eyeOffsetWalking = new Vector2(15, -7);
 
     private int jumps = 0;
     private Facing facing = Facing.Right;
@@ -70,7 +72,7 @@ namespace SemiColinGames {
         new Vector2(halfSize.X + Math.Abs(movement.X) + 1, halfSize.Y + Math.Abs(movement.Y) + 1));
       foreach (var box in collisionTargets) {
         if (box.Intersect(largeBox) != null) {
-          Debug.AddRect(box, Color.Green);
+          // Debug.AddRect(box, Color.Green);
           candidates.Add(box);
         }
       }
@@ -121,10 +123,10 @@ namespace SemiColinGames {
       if (standingOnGround) {
         jumps = 1;
         ySpeed = -0.0001f;
-        Debug.AddRect(Box(position), Color.Cyan);
+        // Debug.AddRect(Box(position), Color.Cyan);
       } else {
         jumps = 0;
-        Debug.AddRect(Box(position), Color.Orange);
+        // Debug.AddRect(Box(position), Color.Orange);
       }
 
       if (movement.X > 0) {
@@ -145,6 +147,92 @@ namespace SemiColinGames {
       } else {
         pose = Pose.Standing;
       }
+
+      DrawSightLines(collisionTargets);
+    }
+
+    Vector2 Rotate(Vector2 point, float angle) {
+      float cos = FMath.Cos(angle);
+      float sin = FMath.Sin(angle);
+      return new Vector2(
+        point.X * cos - point.Y * sin,
+        point.Y * cos + point.X * sin);
+    }
+
+    bool PointInCone(
+        float visionRangeSq, float fovCos, Vector2 eyePos, Vector2 direction, Vector2 test) {
+      Vector2 delta = Vector2.Subtract(test, eyePos);
+      if (delta.LengthSquared() > visionRangeSq) {
+        return false;
+      }
+      float dot = Vector2.Dot(Vector2.Normalize(direction), Vector2.Normalize(delta));
+      return dot > fovCos;
+    }
+
+    void DrawSightLines(AABB[] collisionTargets) {
+      float fov = FMath.DegToRad(45);
+      float fovCos = FMath.Cos(fov);
+      Color color = Color.LightYellow;
+
+      Vector2 eyeOffset = pose == Pose.Walking ? eyeOffsetWalking : eyeOffsetStanding;
+      Vector2 eyePos = Vector2.Add(
+        Position.ToVector2(), new Vector2(eyeOffset.X * (int) facing, eyeOffset.Y));
+
+      float visionRange = 150;
+      float visionRangeSq = visionRange * visionRange;
+      Vector2 ray = new Vector2(visionRange * (int) facing, 0);
+      Vector2 coneBottom = Rotate(ray, fov);
+      Vector2 coneTop = Rotate(ray, -fov);
+
+      List<Vector2> points = new List<Vector2>();
+      List<AABB> boxes = new List<AABB>();
+      points.Add(Vector2.Add(eyePos, coneBottom));
+      points.Add(Vector2.Add(eyePos, coneTop));
+      foreach (AABB box in collisionTargets) {
+        int hitCount = points.Count;
+        if (PointInCone(visionRangeSq, fovCos, eyePos, ray, box.TopLeft)) {
+          points.Add(box.TopLeft);
+        }
+        if (PointInCone(visionRangeSq, fovCos, eyePos, ray, box.TopRight)) {
+          points.Add(box.TopRight);
+        }
+        if (PointInCone(visionRangeSq, fovCos, eyePos, ray, box.BottomLeft)) {
+          points.Add(box.BottomLeft);
+        }
+        if (PointInCone(visionRangeSq, fovCos, eyePos, ray, box.BottomRight)) {
+          points.Add(box.BottomRight);
+        }
+        if (points.Count > hitCount) {
+          boxes.Add(box);
+        }
+      }
+
+      HashSet<AABB> boxesSeen = new HashSet<AABB>();
+      foreach (Vector2 hit in points) {
+        float minTime = 1;
+        AABB? closestBox = null;
+        Vector2 delta = Vector2.Subtract(hit, eyePos);
+        foreach (AABB box in boxes) {
+          Hit? maybeHit = box.IntersectSegment(eyePos, delta);
+          if (maybeHit != null && maybeHit.Value.Time < minTime) {
+            minTime = maybeHit.Value.Time;
+            closestBox = box;
+          }
+        }
+        if (closestBox != null) {
+          Vector2 target = Vector2.Add(eyePos, Vector2.Multiply(delta, minTime));
+          Debug.AddLine(eyePos, target, color);
+          boxesSeen.Add(closestBox.Value);
+        }
+      }
+
+      foreach (AABB box in boxesSeen) {
+        Debug.AddRect(box, color);
+      }
+
+      Debug.AddLine(eyePos, Vector2.Add(eyePos, ray), Color.Red);
+      Debug.AddLine(eyePos, Vector2.Add(eyePos, coneTop), Color.Red);
+      Debug.AddLine(eyePos, Vector2.Add(eyePos, coneBottom), Color.Red);
     }
 
     // Returns the desired (dx, dy) for the player to move this frame.