private void MeasureCell(TreePath path, GridViewColumn col)
{
int w, h, x, y, x_offset, y_offset;
TreeIter i;
bool header = path.Indices[0] < c_span;
Rectangle rect = new Rectangle();
CellRenderer renderer = header && col.HeaderRenderer != null ?
col.HeaderRenderer : col.FieldRenderer;
model.GetIter(out i, path);
col.CellSetCellData(model, i, header);
renderer.GetSize(this, ref rect, out x_offset, out y_offset,
out w, out h);
TranslateCoords(path, col, out x, out y);
widths[x] = Math.Max((int)widths[x], w + 20);
heights[y] = Math.Max((int)heights[y], h + 4);
}