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I don't have a problem programing to that corner, but I want to know the reason behind this choice.

skystar7
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  • See also [*Historic reasons for Left-Handed Coordinate System*](http://stackoverflow.com/questions/6698817/historic-reasons-for-left-handed-coordinate-system). – trashgod Feb 06 '12 at 03:58

3 Answers3

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It’s an accident of history.

So you’re asking why the pixels on a monitor are indexed in left-to-right rows arranged from top to bottom, making the +y axis downward rather than upward as in the Cartesian system. Long story short, CRTs display scanlines in this order, so by arranging video memory in the same way, the video driver can just scan forward through a contiguous chunk of memory, sending scanlines to the monitor as it goes. The choice is essentially arbitrary, just as it is with Cartesian coordinates where +y points upward; that arrangement is more convenient for graphs on paper in left-to-right languages, because it readily serves as a mnemonic for progress over time and so on.

Likewise, on a CRT, the choice was probably made to follow the reading order of the creators. On a character-based display, if you display characters in the same order they’re read, then characters that have been added to the screen since the last update will be displayed as early as possible, reducing visual lag.

Jon Purdy
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This is probably a historical thing, due most probably to the way the scan lines are ordered in a television raster (left to right, top to bottom).

Sergey Kalinichenko
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  • historical you wrote on the paper from LEFT_TOP

  • technical CRT starting from LEFT_TOP

mKorbel
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