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Editorial Team
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Asked: 2026-05-23T14:11:21+00:00

I have found something NOT funny with rectangles: Lets say, given are values of

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I have found something NOT funny with rectangles:

Lets say, given are values of left, top, right and bottom coordinates and all those coordinates are intended to be inclusive.

So, calculating the width goes like:

width = right - left + 1

So far, so logical. But!

A width of zero (which makes sense, sometimes) would have to be stored as:

right = left - 1

which makes problems, when it comes to the following operations:

  • Sorting the rectangle coordinates (to make it go left to right, top to bottom)
  • Looping

Ok, of course those things can be handled with extra code for the special case of Width == 0, but, seriously, is there no better solution, no standard pattern or best practice to handle this?

Edit:

For the time being I have abandoned the “sorting” of the coordinates in my code and replaced it with an assertion stating that the rectangle must be left -> right, up -> down, but seriously…

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1 Answer

  1. Editorial Team

    To address this problem, most graphics libraries will draw rectangles from the left coordinate up to but not including the right coordinate. So if left=10 and right=20, then the ten pixels 10 through 19 will be drawn.

    You can think of this as the pixel coordinate referring not to the lit-up portion, but the grid lines between pixels.

    +---+---+---+
|   |   |   |
+---+---+---+
|   |   |   |
+---+---+---+
^   ^   ^   ^
0   1   2   3
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