easymesh: fix vertex lerp function prototypes.

src/easymesh/easymesh.cpp

@@ -1211,7 +1211,7 @@ void EasyMesh::AddLerpVertex(int i, int j, float alpha)
 
 }
 //-----------------------------------------------------------------------------
-void EasyMesh::AddLerpVertex(VertexData &vi, VertexData &vj, float alpha)
+void EasyMesh::AddLerpVertex(VertexData const &vi, VertexData const &vj, float alpha)
 {
     m_vert.Push(GetLerpVertex(vi, vj, alpha));
     m_state = MeshRender::NeedConvert;
@@ -1224,7 +1224,7 @@ VertexData EasyMesh::GetLerpVertex(int i, int j, float alpha)
 }
 
 //-----------------------------------------------------------------------------
-VertexData EasyMesh::GetLerpVertex(VertexData &vi, VertexData &vj, float alpha)
+VertexData EasyMesh::GetLerpVertex(VertexData const &vi, VertexData const &vj, float alpha)
 {
     return VertexData(
         lol::lerp(vi.m_coord,    vj.m_coord,      alpha),

src/easymesh/easymesh.h

@@ -718,9 +718,9 @@ private:
     void AddVertex(vec3 const &coord);
     void AddDuplicateVertex(int i);
     void AddLerpVertex(int i, int j, float alpha);
-    void AddLerpVertex(VertexData &vi, VertexData &vj, float alpha);
+    void AddLerpVertex(VertexData const &vi, VertexData const &vj, float alpha);
     VertexData GetLerpVertex(int i, int j, float alpha);
-    VertexData GetLerpVertex(VertexData &vi,VertexData &vj, float alpha);
+    VertexData GetLerpVertex(VertexData const &vi, VertexData const &vj, float alpha);
     void AppendQuad(int i1, int i2, int i3, int i4, int base);
     void AppendQuadDuplicateVerts(int i1, int i2, int i3, int i4, int base);
     void AppendTriangle(int i1, int i2, int i3, int base);