1 files changed, 49 insertions, 4 deletions
diff --git a/stl.go b/stl.go
index 35e69eb..60ada3e 100644
--- a/stl.go
+++ b/stl.go
@@ -20,6 +20,8 @@ type StlModel struct {
 	surface Surface
 }
 
+type Vector3 [3]float32
+
 // read and parse a given binary STL file
 func ReadBinaryStlFile(filePath string) (StlModel, error) {
 
@@ -75,9 +77,12 @@ func ParseBinaryStlTriangle(data []byte) *Triangle {  // FIXME: This function sh
 	return triangle
 }
 
-func (stl StlModel) toVertices() []float32 {
+func (stl StlModel) toVertices() (vertex_position []float32, vertex_normal []float32) {
+
+	vertex_position = make([]float32, stl.numberOfTriangles * 9)
+	vertex_normal = make([]float32, stl.numberOfTriangles * 9)
 
-	retval := make([]float32, stl.numberOfTriangles * 9)
+	var point0,point1,point2,edge0,edge1,normal Vector3;
 
 	for triangleIndex,triangle := range(stl.surface.triangles) {
 
@@ -85,13 +90,53 @@ func (stl StlModel) toVertices() []float32 {
 
 			for scalarIndex,scalar := range(point.scalars) {
 
-				retval[triangleIndex*9+pointIndex*3+scalarIndex] = scalar
+				vertex_position[triangleIndex*9+pointIndex*3+scalarIndex] = scalar
 
 			}
 
 		}
 
+		// calculate normal
+		point0 = Vector3{triangle.points[0].scalars[0], triangle.points[0].scalars[1], triangle.points[0].scalars[2]}
+		point1 = Vector3{triangle.points[1].scalars[0], triangle.points[1].scalars[1], triangle.points[1].scalars[2]}
+		point2 = Vector3{triangle.points[2].scalars[0], triangle.points[2].scalars[1], triangle.points[2].scalars[2]}
+		edge0 = point1.subtract(point0)
+		edge1 = point2.subtract(point1)
+		normal = edge0.crossProduct(edge1)
+		normal.divideScalar(2.0)  // length of normal vector corresponds to triangle area
+
+		// save normal to each vertex of the triangle
+		for i := 0; i<3; i++ {
+			vertex_normal[triangleIndex*9+i*3+0] = normal[0]
+			vertex_normal[triangleIndex*9+i*3+1] = normal[1]
+			vertex_normal[triangleIndex*9+i*3+2] = normal[2]
+		}
+
 	}
 
-	return retval
+	return vertex_position, vertex_normal
+}
+
+func (vector *Vector3) divideScalar(scalar float32) {
+	vector[0] = vector[0] / scalar
+	vector[1] = vector[1] / scalar
+	vector[2] = vector[2] / scalar
+}
+
+func (vectorA Vector3) subtract(vectorB Vector3) (vectorC Vector3) {
+
+	vectorC[0] = vectorA[0] - vectorB[0]
+	vectorC[1] = vectorA[1] - vectorB[1]
+	vectorC[2] = vectorA[2] - vectorB[2]
+
+	return vectorC
+}
+
+func (vectorA Vector3) crossProduct(vectorB Vector3) (vectorC Vector3) {
+
+	vectorC[0] = vectorA[1] * vectorB[2] - vectorA[2] * vectorB[1]
+	vectorC[1] = vectorA[2] * vectorB[0] - vectorA[0] * vectorB[2]
+	vectorC[2] = vectorA[0] * vectorB[1] - vectorA[1] * vectorB[0]
+
+	return vectorC
 }