Re: Pixel Drawing Program 2
Re: Pixel Drawing Program 2
- Subject: Re: Pixel Drawing Program 2
- From: Shawn Erickson <email@hidden>
- Date: Sat, 15 Feb 2003 09:38:44 -0800
On Friday, February 14, 2003, at 07:16 PM, Sebastian Gomez Papiol
wrote:
Wow, it's true! Where you find this information? very thanks... this
is OK for simple lines, but drawing curves or ovals of 1 pixel seems
more difficult. Perhaps I can change the (0,0) origin to (0.5, 0.5)
origin with some method or perform some trick?
Quartz 2D closely follows PDF and postscript drawing environments, I
think I picked up on the fact that pixel are centered by reading
comments on this list a year or two back. Anyway...
Drawing curved paths or any path not aligned (and centered) with x or y
axis will result in the true mathematical path falling between pixels
and hence an attempt must be made to approximate the path. If
anti-aliasing is turned on then the path will be approximated by partly
"turning" on pixels to various degrees based on how close they are to
the mathematical path. If anti-aliasing is turned off then pixels near
the mathematical line will be fully turned on and you will get a more
gagged line.
This is the reality when rendering paths on a fixed pixel system
(screen, printer, etc.).
Basically saying the the path is 1 point wide does not mean one pixel
wide on screen but 1 point wide in the paths mathematical form. Don't
forget the same path you draw to the screen a 72 DPI can be drawn at,
for example, 300 DPI just by switching graphics contexts. In the 300
DPI case the line is still 1 point wide in mathematical form but many
pixels wide when rendered because more pixels are available at the
higher resolution in the same coordinate grid.
-Shawn
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