Why set barRect.size.height = bottom - top to be negative?

[liuxuan30]

@danielgindi I was looking into some details about bar chart view today, and I found that the barRect height is negative after calculation, this surprised me a little. Could you explain some details here? Also, where you made the trick to handle the negative height? I don't see you manipulate the matrix.

var top = isInverted ? (y <= 0.0 ? CGFloat(y) : 0) : (y >= 0.0 ? CGFloat(y) : 0)
var bottom = isInverted ? (y >= 0.0 ? CGFloat(y) : 0) : (y <= 0.0 ? CGFloat(y) : 0)
...
barRect.origin.x = left
barRect.size.width = right - left
barRect.origin.y = top
barRect.size.height = bottom - top // supposed to be negative

[danielgindi]

It could be negative or positive, depending on the specific bar - but you don't have to do any "trick", as all rendering platforms (that I know of, including iOS and Android) take care of negative heights automatically.
It's simple for them because they do not consider width and height, but x1 = left, x2 = left + width, y1 = top, y2 = top + height

[liuxuan30]

@danielgindi but if I try to use barRect.size.height = abs(bottom - top), it actually broke the rendering. Any ideas?

[danielgindi]

Of course it did, you have change its direction. y2 = (10 + (-50)) = -40 vs y2 = (10 + abs(-50)) = 60

[liuxuan30]

Ah I see. Thanks for the lesson!

[danielgindi]

:-)