GCodeViewer -> Pass vertex normal to shaders for toolpaths

resources/shaders/toolpaths.vs

@@ -0,0 +1,21 @@
+#version 110
+
+varying vec3 eye_position;
+varying vec3 eye_normal;
+
+vec3 world_normal()
+{
+    // the world normal is always parallel to the world XY plane
+    // the x component is stored into gl_Vertex.w
+    float x = gl_Vertex.w;
+    float y = sqrt(1.0 - x * x);
+    return vec3(x, y, 0.0);
+}
+
+void main()
+{
+    vec4 world_position = vec4(gl_Vertex.xyz, 1.0);
+    gl_Position = gl_ModelViewProjectionMatrix * world_position;
+    eye_position = (gl_ModelViewMatrix * world_position).xyz;
+    eye_normal = gl_NormalMatrix * world_normal();    
+}