From c9bcb0ace535d241e32d9dade9db4e82f9697f45 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miloslav=20=C4=8C=C3=AD=C5=BE?= <tastyfish@seznam.cz>
Date: Thu, 6 Jun 2019 01:08:29 +0200
Subject: [PATCH] Compute normals

---
 programs/testSDL.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++
 small3dlib.h       | 16 ++++++++-----
 2 files changed, 66 insertions(+), 6 deletions(-)

diff --git a/programs/testSDL.c b/programs/testSDL.c
index 8569827..3366c7a 100644
--- a/programs/testSDL.c
+++ b/programs/testSDL.c
@@ -134,6 +134,62 @@ int previousTriangle = 255;
 
 void drawPixel(S3L_PixelInfo *p)
 {
+
+S3L_Vec4 a,b,c,n,V;
+
+int tmpI = scene.models[p->modelIndex].triangles[p->triangleIndex * 3] * 3;
+
+a.x = scene.models[p->modelIndex].vertices[tmpI];
+tmpI++;
+a.y = scene.models[p->modelIndex].vertices[tmpI];
+tmpI++;
+a.z = scene.models[p->modelIndex].vertices[tmpI];
+
+tmpI = scene.models[p->modelIndex].triangles[p->triangleIndex * 3 + 1] * 3;
+
+b.x = scene.models[p->modelIndex].vertices[tmpI];
+tmpI++;
+b.y = scene.models[p->modelIndex].vertices[tmpI];
+tmpI++;
+b.z = scene.models[p->modelIndex].vertices[tmpI];
+
+tmpI = scene.models[p->modelIndex].triangles[p->triangleIndex * 3 + 2] * 3;
+
+c.x = scene.models[p->modelIndex].vertices[tmpI];
+tmpI++;
+c.y = scene.models[p->modelIndex].vertices[tmpI];
+tmpI++;
+c.z = scene.models[p->modelIndex].vertices[tmpI];
+
+S3L_triangleNormal(a,b,c,&n);
+/*
+printf("--------\n");
+S3L_logVec4(a);
+S3L_logVec4(b);
+S3L_logVec4(c);
+S3L_logVec4(n);
+*/
+V.x = 10; 
+V.y = 10;
+V.z = 10;
+
+S3L_normalizeVec3(&V);
+
+int16_t l = S3L_clamp(S3L_dotProductVec3(V,n) / 2,0,255);
+
+l &= 192;
+
+/*
+setPixel(p->x,p->y,
+ S3L_clamp(128 + n.x / 4,0,255),
+ S3L_clamp(128 + n.y / 4,0,255),
+ S3L_clamp(128 + n.z / 4,0,255));
+*/
+
+setPixel(p->x,p->y,l,l,l);
+
+return;
+
   if (p->triangleIndex != previousTriangle)
   {
     l0 = houseVertexLighting[houseTriangleIndices[p->triangleIndex * 3]];
diff --git a/small3dlib.h b/small3dlib.h
index ea7af70..e5cb308 100644
--- a/small3dlib.h
+++ b/small3dlib.h
@@ -774,13 +774,17 @@ void S3L_crossProduct(S3L_Vec4 a, S3L_Vec4 b, S3L_Vec4 *result)
 void S3L_triangleNormal(S3L_Vec4 t0, S3L_Vec4 t1, S3L_Vec4 t2,
   S3L_Vec4 *n)
 {
-  t1.x = t1.x - t0.x;
-  t1.y = t1.y - t0.y;
-  t1.z = t1.z - t0.z;
+  #define antiOverflow 32
 
-  t2.x = t2.x - t0.x;
-  t2.y = t2.y - t0.y;
-  t2.z = t2.z - t0.z;
+  t1.x = (t1.x - t0.x) / antiOverflow;
+  t1.y = (t1.y - t0.y) / antiOverflow;
+  t1.z = (t1.z - t0.z) / antiOverflow;
+
+  t2.x = (t2.x - t0.x) / antiOverflow;
+  t2.y = (t2.y - t0.y) / antiOverflow;
+  t2.z = (t2.z - t0.z) / antiOverflow;
+
+  #undef antiOverflow
 
   S3L_crossProduct(t1,t2,n);
   S3L_normalizeVec3(n);