Zooming, Bezier Paths and Affine Transforms
Zooming, Bezier Paths and Affine Transforms
- Subject: Zooming, Bezier Paths and Affine Transforms
- From: Greg <email@hidden>
- Date: Mon, 27 Dec 2004 17:49:31 +1000
Hi,
I am creating a graph view that allows the user to be able to zoom an
area of the x-axis only. This is because a plot can contain up to
around 10,000 samples, so to make it easier in viewing areas of the
graph I need to be able to zoom areas of it. I am having some trouble
trying to display the graph correctly. I can get the correct range of
samples to display from the user drawing a box on the graph to zoom it,
but when it comes to display it correctly, is where my problems occur.
The steps I am using are to translate to the start of the graph area as
there is a margin for axis values and labels. I then translate the x
axis to the start of the zoomed samples, (_durationStart). I then scale
the X axis by the width and number of zoomed samples
(NSWidth(graphBounds) / (_durationEnd - _durationStart)) and the height
by the number of values in the Y axis. I then translate the graph by
the Y axis minimum value as this might not be set at 0.
I seem to have problems when I use affine transforms as my
understanding of them is very limited. I would appreciate it if someone
could recommend a book or resource on the net to help me better
understand what is happening to the co-ordinate space when I do
translations, scales and rotations. Does anyone know what I am doing
wrong fundamentally?
Thanks,
Greg
if (_flags.showHeartRate)
{
NSAffineTransform *scale = [NSAffineTransform transform];
NSBezierPath *p = [cur objectForKey:HeartRateKey];
NSRect pathRect = [p bounds];
[scale translateXBy:NSMinX(graphBounds) yBy:NSMinY(graphBounds)];
[scale translateXBy:-_durationStart yBy:0];
[scale scaleXBy:NSWidth(graphBounds) / (_durationEnd -
_durationStart)
yBy:NSHeight(graphBounds)/(_heartRateMax - _heartRateMin)];
[scale translateXBy:0 yBy: - _heartRateMin];
[scale concat];
[[_heartRateColor colorWithAlphaComponent:1.0 - (i / (c * 1.0))]
set];
[p setLineWidth:_heartRateStroke];
[p stroke];
[scale invert];
[scale concat];
}
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