Demos: Implement basic Lambertian lighting for the GLTeapot

The teapot now looks more realistic

Userland/Demos/GLTeapot/Mesh.cpp

@@ -7,7 +7,8 @@
 
 #include <LibGL/GL/gl.h>
 #include <LibGfx/Color.h>
-#include <stdlib.h>
+#include <LibGfx/Vector3.h>
+#include <LibGfx/Vector4.h>
 
 #include "Mesh.h"
 
@@ -15,10 +16,10 @@ const Color colors[] {
     Color::Red,
     Color::Green,
     Color::Blue,
-    Color::Blue,
     Color::Magenta,
-    Color::White,
     Color::Yellow,
+    Color::Cyan,
+    Color::White
 };
 
 Mesh::Mesh(Vector<Vertex> vertices, Vector<Triangle> triangles)
@@ -29,35 +30,62 @@ Mesh::Mesh(Vector<Vertex> vertices, Vector<Triangle> triangles)
 
 void Mesh::draw()
 {
-    u32 color_index = 0;
-    Color cur_color;
+    // Light direction
+    const FloatVector3 light_direction(1.f, 1.f, 1.f);
 
-    for (const auto& triangle : m_triangle_list) {
-        cur_color = colors[color_index];
+    // Mesh color
+    const FloatVector4 mesh_ambient_color(0.2f, 0.2f, 0.2f, 1.f);
+    const FloatVector4 mesh_diffuse_color(0.6f, 0.6f, 0.6f, 1.f);
 
-        glBegin(GL_TRIANGLES);
-        glColor4ub(cur_color.red(), cur_color.green(), cur_color.blue(), 255);
+    for (u32 i = 0; i < m_triangle_list.size(); i++) {
+        const auto& triangle = m_triangle_list[i];
 
-        // Vertex 1
-        glVertex3f(
+        const FloatVector3 vertex_a(
             m_vertex_list.at(triangle.a).x,
             m_vertex_list.at(triangle.a).y,
             m_vertex_list.at(triangle.a).z);
 
-        // Vertex 2
-        glVertex3f(
+        const FloatVector3 vertex_b(
             m_vertex_list.at(triangle.b).x,
             m_vertex_list.at(triangle.b).y,
             m_vertex_list.at(triangle.b).z);
 
-        // Vertex 3
-        glVertex3f(
+        const FloatVector3 vertex_c(
             m_vertex_list.at(triangle.c).x,
             m_vertex_list.at(triangle.c).y,
             m_vertex_list.at(triangle.c).z);
 
-        glEnd();
+        // Compute the triangle normal
+        const FloatVector3 vec_ab = vertex_b - vertex_a;
+        const FloatVector3 vec_ac = vertex_c - vertex_a;
+        const FloatVector3 normal = vec_ab.cross(vec_ac).normalized();
 
-        color_index = ((color_index + 1) % 7);
+        // Compute lighting with a Lambertian color model
+        const auto light_intensity = max(light_direction.dot(normal), 0.f);
+        const FloatVector4 color = mesh_ambient_color
+            + mesh_diffuse_color * light_intensity;
+
+        glBegin(GL_TRIANGLES);
+        glColor4f(color.x(), color.y(), color.z(), color.w());
+
+        // Vertex 1
+        glVertex3f(
+            m_vertex_list.at(m_triangle_list[i].a).x,
+            m_vertex_list.at(m_triangle_list[i].a).y,
+            m_vertex_list.at(m_triangle_list[i].a).z);
+
+        // Vertex 2
+        glVertex3f(
+            m_vertex_list.at(m_triangle_list[i].b).x,
+            m_vertex_list.at(m_triangle_list[i].b).y,
+            m_vertex_list.at(m_triangle_list[i].b).z);
+
+        // Vertex 3
+        glVertex3f(
+            m_vertex_list.at(m_triangle_list[i].c).x,
+            m_vertex_list.at(m_triangle_list[i].c).y,
+            m_vertex_list.at(m_triangle_list[i].c).z);
+
+        glEnd();
     }
 }