code: func (f *Fpdf) ClipRect(x, y, w, h float64, outline bool) {
  	f.clipNest++
  	f.outf("q %.2f %.2f %.2f %.2f re W %s", x*f.k, (f.h-y)*f.k, w*f.k, -h*f.k, strIf(outline, "S", "n"))
  }
docs: // ClipRect begins a rectangular clipping operation. The rectangle is of width
  // w and height h. Its upper left corner is positioned at point (x, y). outline
  // is true to draw a border with the current draw color and line width centered
  // on the rectangle's perimeter. Only the outer half of the border will be
  // shown. After calling this method, all rendering operations (for example,
  // Image(), LinearGradient(), etc) will be clipped by the specified rectangle.
  // Call ClipEnd() to restore unclipped operations.
  //
  // This ClipText() example demonstrates this method.