Add ability to draw normals

shaders/normal_frag.glsl

@@ -0,0 +1,7 @@
+#version 330 core
+
+out vec4 color;
+
+void main() {
+  color = vec4(1.0, 1.0, 0.0, 1.0);
+}

shaders/normal_geo.glsl

@@ -0,0 +1,34 @@
+#version 330 core
+
+#define MAGNITUDE 0.1
+
+layout (triangles) in;
+layout (line_strip, max_vertices = 6) out;
+
+uniform float time;
+
+in VS_OUT {
+  vec3 vert_normal;
+} gs_in[];
+
+layout (std140) uniform Common {
+  mat4 projection;
+  mat4 view;
+  vec3 camera_position;
+};
+
+void generate_line(int index) {
+  gl_Position = projection * gl_in[index].gl_Position;
+  EmitVertex();
+
+  gl_Position = projection * (gl_in[index].gl_Position + vec4(gs_in[index].vert_normal, 1.0) * MAGNITUDE);
+  EmitVertex();
+
+  EndPrimitive();
+}
+
+void main() {
+  for (int i = 0; i < 3; ++i) {
+    generate_line(i);
+  }
+}

shaders/normal_vert.glsl

@@ -0,0 +1,25 @@
+#version 330 core
+
+layout(location=0) in vec3 position;
+layout(location=1) in vec3 normal;
+layout(location=2) in vec2 uv;
+
+uniform mat3 normal_mat;
+uniform mat4 model;
+
+layout (std140) uniform Common {
+  mat4 projection;
+  mat4 view;
+  vec3 camera_position;
+};
+
+// interface block
+out VS_OUT {
+  vec3 vert_normal;
+} vs_out;
+
+void main() {
+  vs_out.vert_normal = normal_mat * normal;
+
+  gl_Position = view * model * vec4(position, 1.0);
+};