PIL ImageDraw line not long enough

nikie n.estner at gmx.de
Fri Mar 31 01:18:48 CEST 2006

Bob Greschke wrote

> I've resorted to actually drawing all of the characters of the alphabet on a
> graph to avoid having to drag around font files.  It's mostly just uppercase
> characters, so it's not too bad.
> But I noticed that some of the line segments have to be extended one pixel
> longer than they should be in order for the last pixel to show up.
> The character cells are 6 pixels wide by 8 pixels high.  An "L" is drawn
> with
>    Graph.line((x,y, x,y+7, x+5,y+7), Color)
> where the starting x and y are supplied to the function.  An L works OK, but
> to get a "T" to look right I have to do
>    Graph.line((x+1,y, x+5,y), Color)
>    Graph.line((x+3,y, x+3,y+8), Color)
> I have to extend the vertical line to y+8, instead of y+7 to get the line
> segment to be drawn long enough.  This is on Linux, Solaris, 2.x versions of
> Python, 1.1.5 version of PIL, and on Windows with the latest of everything.
> Am I missing a setting somewhere?

Some drawing APIs (e.g. Windows GDI) draw lines including the starting
point but excluding the end point: I think the reason is that this way,
if you draw a series of connected lines (like in your "L" case), no
pixel gets drawn twice (this is important if you use colors with alpha
channels, or line patterns).

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