From 89f88b0918aa5e972f83b9ceadfcaff629ce09d3 Mon Sep 17 00:00:00 2001
From: dpethes <dejvu@email.cz>
Date: Mon, 6 Jul 2015 18:35:34 +0200
Subject: [PATCH] terrain viewer: simple lighting with per-face normals

---
 terrain_viewer/terrain_mesh.pas   | 32 ++++++++++++++++++++++++++++++-
 terrain_viewer/terrain_viewer.pas | 12 +++++++++++-
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/terrain_viewer/terrain_mesh.pas b/terrain_viewer/terrain_mesh.pas
index 495681f..9a72375 100644
--- a/terrain_viewer/terrain_mesh.pas
+++ b/terrain_viewer/terrain_mesh.pas
@@ -136,15 +136,45 @@ begin
       GenTexture(i);
 end;
 
+
+//cross product + normalize
+function GetNormalv(const v0, v1, v2: TVertex3f): TVertex3f;
+var
+  a, b: TVertex3f;
+  len: single;
+begin
+  a.x := v0.x - v1.x;
+  a.y := v0.y - v1.y;
+  a.z := v0.z - v1.z;
+
+  b.x := v1.x - v2.x;
+  b.y := v1.y - v2.y;
+  b.z := v1.z - v2.z;
+
+  result.x := (a.y * b.z) - (a.z * b.y);
+  result.y := (a.z * b.x) - (a.x * b.z);
+  result.z := (a.x * b.y) - (a.y * b.x);
+
+  len := sqrt( sqr(result.x) + sqr(result.y) + sqr(result.z) );
+  if len = 0 then len := 1;
+
+  result.x /= len;
+  result.y /= len;
+  result.z /= len;
+end;
+
+
 //draw vertices from each block
 procedure TTerrainMesh.DrawGL(opts: TRenderOpts);
 
   procedure RenderBlock(var blk: TTerrainBlock);
     procedure RenderTri(i0, i1, i2:integer);
     var
-      v: TVertex3f;
+      v, n: TVertex3f;
     begin
+      n := GetNormalv(blk.vertices[i0], blk.vertices[i1], blk.vertices[i2]);
       v := blk.vertices[i0];
+      glNormal3f(n.x, n.y, n.z);
       glTexCoord2f(v.u, v.v);
       glVertex3fv(@v);
       v := blk.vertices[i1];
diff --git a/terrain_viewer/terrain_viewer.pas b/terrain_viewer/terrain_viewer.pas
index 76c02a2..b644667 100644
--- a/terrain_viewer/terrain_viewer.pas
+++ b/terrain_viewer/terrain_viewer.pas
@@ -78,6 +78,10 @@ end;
 
 // initial parameters
 procedure InitGL;
+const
+  LightAmbient: array[0..3] of single = (0.5, 0.5, 0.5, 1);
+  LightDiffuse: array[0..3] of single = (1, 1, 1, 1);
+  LightPosition: array[0..3] of single = (1, 1, 0, 1);
 var
   ogl_info: string;
 begin
@@ -86,7 +90,7 @@ begin
   ogl_info := 'version: ' + glGetString(GL_VERSION);
   writeln(ogl_info);
 
-  //glShadeModel( GL_SMOOTH );                  // Enable smooth shading
+  glShadeModel( GL_SMOOTH );                  // Enable smooth shading
   glClearColor( 0.0, 0.0, 0.0, 0.0 );
   glClearDepth( 1.0 );                        // Depth buffer setup
   glEnable( GL_DEPTH_TEST );                  // Enables Depth Testing
@@ -97,6 +101,12 @@ begin
   //glCullFace( GL_BACK );
 
   glEnable(GL_TEXTURE_2D);
+
+  glEnable(GL_LIGHTING);
+  glEnable(GL_LIGHT0);
+  glLightfv(GL_LIGHT0, GL_AMBIENT, LightAmbient);
+  glLightfv(GL_LIGHT0, GL_DIFFUSE, LightDiffuse);
+  glLightfv(GL_LIGHT0, GL_POSITION,LightPosition);
 end;