Re: Coordinates of Pixels
Re: Coordinates of Pixels
- Subject: Re: Coordinates of Pixels
- From: Greg Titus <email@hidden>
- Date: Wed, 18 Jul 2007 13:21:00 -0700
On Jul 18, 2007, at 1:06 PM, Richard Somers wrote:
This may be elementary computer graphics but I can't seem to find
the answer.
Consider a rectangular matrix of pixels in device space with the
origin at the lower left corner. Is the pixel at the lower left
corner pixel 0, 0 or pixel 1, 1?
The pixel at the lower left corner is the rectangle with origin 0,0
and size 1,1.
When mapping from user space to device space (userSpaceScaleFactor
= 1.0) are pixels considered located at even integer boundaries or
half way in-between?
Half way in between. It helps me to think of the coordinates as a
grid between the pixels, and the pixels as the little boxes made by
the grid lines.
The Cocoa Drawing Guide example Listing 3-1 for pixel-exact drawing
adjusts the origin of the drawn rectangle by 0.5 in x and y. This
would lead you to the conclusion that the center of the pixels fall
on 0.5 increment boundaries when overlaid with a floating point
coordinate system from user space. Is this a correct conclusion?
Exactly.
Hope this helps,
- Greg
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