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Docs clarification: What's a hairline line?
Chris Katko
Member #1,881
January 2002
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https://www.allegro.cc/manual/5/al_draw_line

thickness - Thickness of the line, pass <= 0 to draw hairline lines

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jmasterx
Member #11,410
October 2009

It's a line that recedes with time :'(.

SiegeLord
Member #7,827
October 2006
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It basically means that it's thickness is infinitesimal. You still see it, but e.g. if you zoom in with a transformation, it won't get thicker. At the same time, it won't disappear if you zoom out either. It's in some sense the smallest thing the device can draw to represent the mathematical line segment.

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Elias
Member #358
May 2000

As a side effect, hairlines are undefined to as in which pixels are lit up. If you specify a thickness, the GPU guarantees that each pixel whose center lies inside of the line is lit. If you draw a hairline, the GPU is pretty much free to do whatever it wants.

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SiegeLord
Member #7,827
October 2006
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Elias said:

As a side effect, hairlines are undefined to as in which pixels are lit up.

That's mostly because OpenGL neglected to specify this, they could have easily came up with a definition (like the one A4 uses, which is just nearest pixel to the line).

"For in much wisdom is much grief: and he that increases knowledge increases sorrow."-Ecclesiastes 1:18
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amarillion
Member #940
January 2001
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jmasterx said:

It's a line that recedes with time :'(.

;D ;D ;D

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