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lairworks / nas2d-core

NAS2D is an open source, object oriented 2D game development framework written in portable C++.
http://nas2d.lairworks.com
zlib License
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Fix box alignment #1087

Closed DanRStevens closed 1 year ago

DanRStevens commented 1 year ago

Fix alignment so drawBox and drawBoxFilled line up as expected.

Avoid drawing zero and negative area boxes.

Related: #1086

cugone commented 1 year ago

Small nitpick. A rectangle with a width or height of zero is a line, a rectangle with a width and height of zero is a point; both should still be drawable. A negative width or height can be handled by swapping the offending points which decays to a normal rectangle again.

DanRStevens commented 1 year ago

In the current code base, rectangles are generally treated as endpoint exclusive. I wanted the graphics code to match the existing convention. That makes it easier to place rectangles next to each other with no gaps and no overlap. In such a scheme, a rectangle with a dimension of 1 would be a line. A dimension of 0 would effectively have no interior, and so would not have any area to draw. It also means that when a rectangle is drawn, it's size in pixels exactly matches the size of the rectangle. There is no plus 1 to the size to draw the bottom and right edges.

I suppose we are being a bit loose with terminology though. We have functions to draw points and lines, which technically, in the true mathematical sense, are not directly drawable as they have no area. Pixels have area, not points.

The negative dimension case may or may not make sense depending on context. I figure if drawing code has a calculation that results in negative dimensions, it's probably because something was out of bounds and needs to be clipped, hence the guard to not draw such rectangles.