[reportlab-users] Rotated paragraph/document with ReportLab (vertical text)

[Tim Roberts]

Jesus Sanchez-Palencia wrote:

> Is there any documentation about what happens to the coordinates after

> we canvas.rotate(90) everything?


This is all part of PostScript, and it's all from a mathematical point
of view.  A standard canvas has its origin at the bottom left, with X
increasing to the right, and Y increasing as you go up.  For a 250 x 80
document:

    +Y
  (0,80)      (250,80)
     +-----------+
     |           |
     |  canvas   |
     |           |
     o-----------+   +X
   (0,0)      (250,0)
    
Positive rotation is counter-clockwise about the origin, so rotating by
90 degrees changes things so that Y increases to the left, and X
increases going up.  The origin remains the same, so after this
rotation, all of the Y coordinates in the canvas will be negative. 
That's why you often use a translation when you do a rotation:

          +X
        (250,0)   (250,-80)
   . - - - +-------+
   :       |       |
   :       |       |
   :       |canvas |
   :       |       |
   :       |       |
   :       |       |
+Y . - - - o-------+
         (0,0)     (0,-80)

-- 
Tim Roberts, timr at probo.com
Providenza & Boekelheide, Inc.