public void SetCellUV(BorderCell cell, float u1, float v1, float u2, float v2) {

            int cellIndex = (int)cell;



            // no choice but to lock/unlock each time here, locking only what we want to modify

            HardwareVertexBuffer buffer =

                renderOp2.vertexData.vertexBufferBinding.GetBuffer(TEXCOORDS);



            // can't use discard, or it will discard the whole buffer, wiping out the positions too

            IntPtr data = buffer.Lock(

                cellIndex * 8 * Marshal.SizeOf(typeof(float)), 

                Marshal.SizeOf(typeof(float)) * 8,

                BufferLocking.Normal);

            

            int index = 0;
            

            unsafe {

                float* texPtr = (float*)data.ToPointer();



                texPtr[index++] = u1; texPtr[index++] = v1;

                texPtr[index++] = u1; texPtr[index++] = v2; 

                texPtr[index++] = u2; texPtr[index++] = v1; 

                texPtr[index++] = u2; texPtr[index++] = v2; 

            }



            buffer.Unlock();

        }