Filling correction for Fillbetweenitem

[BousquetSophie]

Detail the reasoning behind the code change. If there is an associated issue that this PR will resolve add

Fixes #1698 When we have 2 intersecting polygons, there's no more fill at the intersection.

So, we've extracted the intersection points and used them to create a new polygon to fill the empty space.

Other Tasks

Bump Dependency Versions

• ubuntu 22.04

• python 3.10.12

• Pyqtgraph 0.13.4.dev0

Files that need updates

Confirm the following files have been either updated or there has been a determination that no update is needed.

• README.md
• setup.py
• tox.ini
• .github/workflows/main.yml and associated requirements.txt and conda environemt.yml files
• pyproject.toml
• binder/requirements.txt

Pre-Release Checklist

Pre Release Checklist

• Update version info in __init__.py
• Update CHANGELOG primarily using contents from automated changelog generation in GitHub release page
• Have git tag in the format of pyqtgraph-

Post-Release Checklist

Steps To Complete

• Append .dev0 to __version__ in __init__.py
• Announce on mail list
• Announce on Twitter

[j9ac9k]

Thanks for the PR @BousquetSophie ! FillBetweenItem doesn't get as much attention as it should.

The only comment I had is regarding the use of lineTo; I won't let that be a deal breaker, but if you could implement a fix without having moveTo/lineTo that would be preferred.

[j9ac9k]

Thanks for the PR @BousquetSophie Merging!

[jmakovicka]

Hi, this started causing problems for us when filling between two non-convex curves that are not closed (basically, an area chart) . The intersected() function closes the curves and creates an additional undesired area.

[jmakovicka]

Would it be sufficient to restrict this logic to closed polygons?

diff --git a/pyqtgraph/graphicsItems/FillBetweenItem.py b/pyqtgraph/graphicsItems/FillBetweenItem.py
index 30be3092..a702bab2 100644
--- a/pyqtgraph/graphicsItems/FillBetweenItem.py
+++ b/pyqtgraph/graphicsItems/FillBetweenItem.py
@@ -78,8 +78,9 @@ class FillBetweenItem(QtWidgets.QGraphicsPathItem):
             return
         
         for p1, p2 in zip(ps1, ps2):
-            intersection = p1.intersected(p2)
-            if not intersection.isEmpty():
-                path.addPolygon(intersection)
+            if not p1.isEmpty() and not p2.isEmpty() and p1[0] == p1[-1] and p2[0] == p2[-1]:
+                intersection = p1.intersected(p2)
+                if not intersection.isEmpty():
+                    path.addPolygon(intersection)
             path.addPolygon(p1 + p2)       
         self.setPath(path)

[j9ac9k]

Hi, this started causing problems for us when filling between two non-convex curves that are not closed (basically, an area chart) . The intersected() function closes the curves and creates an additional undesired area.

Sorry about that! I think restricting to closed polygons would indeed be a sufficient solution.

[j9ac9k]

Would it be sufficient to restrict this logic to closed polygons?

diff --git a/pyqtgraph/graphicsItems/FillBetweenItem.py b/pyqtgraph/graphicsItems/FillBetweenItem.py
index 30be3092..a702bab2 100644
--- a/pyqtgraph/graphicsItems/FillBetweenItem.py
+++ b/pyqtgraph/graphicsItems/FillBetweenItem.py
@@ -78,8 +78,9 @@ class FillBetweenItem(QtWidgets.QGraphicsPathItem):
             return
         
         for p1, p2 in zip(ps1, ps2):
-            intersection = p1.intersected(p2)
-            if not intersection.isEmpty():
-                path.addPolygon(intersection)
+            if not p1.isEmpty() and not p2.isEmpty() and p1[0] == p1[-1] and p2[0] == p2[-1]:
+                intersection = p1.intersected(p2)
+                if not intersection.isEmpty():
+                    path.addPolygon(intersection)
             path.addPolygon(p1 + p2)       
         self.setPath(path)

Can you verify that #3006 fixes your issue?

[jmakovicka]

Can you verify that #3006 fixes your issue?

Sure, that one works too.

[j9ac9k]

Can you verify that #3006 fixes your issue?

Sure, that one works too.

Hey, sorry to ask you again, would you mind trying that branch again? I just made another update to it (that will better satisfy #1698) but it may have some downstream consequences.

If FillBetweenItem is working as expected, I'll likely do another release with the FillBetweenItem regression fix.

[jmakovicka]

This one breaks it again for us, this time producing a stray line crossing the whole chart.

[j9ac9k]

This one breaks it again for us, this time producing a stray line crossing the whole chart.

Really appreciate you checking, if you have an example I can run (doesn't have to be a minimum reproducible example), I'll gladly check that while trying to come up w/ a solution to #1698 so I don't have to bug you each time I try something new 😆

[jmakovicka]

Sure, I believe this one illustrates the problems well

import numpy as np

import pyqtgraph as pg
from pyqtgraph.Qt import QtCore

win = pg.plot()
win.setWindowTitle('pyqtgraph example: FillBetweenItem')
win.setXRange(-1, 6)
win.setYRange(-1, 6)

x = np.linspace(0, 5, 5)

y1 = [2,3,5,2,1]
y2 = [1,2,4,1,0]

d1 = pg.PlotDataItem(x, y1)
d2 = pg.PlotDataItem(x, y2)

fb = pg.FillBetweenItem(d1, d2, brush='w')

win.addItem(fb)

if __name__ == '__main__':
    pg.exec()

[j9ac9k]

I just got this image when running this example code, I'm not seeing a stray line, maybe this is platform dependent?

[jmakovicka]

The simplified example looks different, but the expected output is definitely this:

[jmakovicka]

In the original, the "stray line" is in fact the two triangles at the bottom, just stretched.

[j9ac9k]

ahh god it, I'm being daft.. my apologies. Alright, I'm getting to work 👍🏻

[j9ac9k]

@jmakovicka Released 0.13.7, which includes a fix to the regression I shipped. Also added a fillRule optional arg and updated the docstrings (can you really say they were an update if there were hardly any to begin with?).

Thanks for your prompt report on the breakage.