Re: [Matplotlib-users] fill_over behaves weird

[John H. <jdh...@ac...>]

>>>>> "Stephen" == Stephen Walton <ste...@cs...> writes:

    Stephen> It looks to me, when running your code, that fill_over is
    Stephen> doing the right thing: filling everything between 0.5 and
    Stephen> your plotted line with a color.  It is just that with
    Stephen> your coarse spacing, you don't have points at every
    Stephen> multiple of pi/2.  However, this is with the current CVS
    Stephen> version, so you may have a problem with 0.60.2.

Probably what Philipp is looking for is for fill_over to do some
linear interpolation between his data points, which I think gives the
least surprising results.  The attached code probably comes closer to
what he's looking for.  It's probably a useful function to include in
the library - see if it meets your needs

from matplotlib.matlab import *

def fill_over(ax, x, y, val, color, over=True):
    """
    Plot filled x,y for all y over val

    If over = False, fill under
    """
    x = asarray(x).astype(nx.Float32)
    y = asarray(y).astype(nx.Float32)
    ybase = asarray(y)-val
    crossings = nonzero(less(ybase[:-1] * ybase[1:],0))
    
    on = not over
    indLast = 0
    for ind in crossings:        
        if not on:
	   on = not on
	   indLast = ind
	   continue
	thisX = array(x[indLast:ind+2]) 
	thisY = array(y[indLast:ind+2]) 
	#find the x point between x[0] and x[1] on the line
	#connecting them such that f(x) = 0.5
	#if len(thisX)<3: continue
	m = (thisY[1]-thisY[0])/(thisX[1]-thisX[0])
	x0 = (val-thisY[0])/m+thisX[0]

	thisX[0] = x0
	thisY[0] = val

	# now get the last point on the interpolated line
	m = (thisY[-1]-thisY[-2])/(thisX[-1]-thisX[-2])
	xend = (val-thisY[-2])/m+thisX[-2]

	thisX[-1] = xend
	thisY[-1] = val
	on = not on
	ax.fill(thisX, thisY, color)
	indLast = ind


x=arange(0.0, 20.0, 1.0)
y = sin(x)

plot(x,y, 'ro-')
fill_over(gca(), x, y, 0.5, '#0000FF', over=True)

show()