Mesh(BitmapData bitmapData, int vertexCount, int triangleCount)

Create a new Mesh with vertexCount vertices and triangleCount triangles.

Source 

Mesh(this.bitmapData, int vertexCount, int triangleCount)
    : indexCount = triangleCount * 3,
      triangleCount = triangleCount,
      vertexCount = vertexCount,
      ixList = new Int16List(triangleCount * 3),
      vxList = new Float32List(vertexCount * 4);