How to avoid polygon distortion when zooming? - echarts

Question

Here is a full jsfiddle example
I use a custom series and draw a polygon:
data = [
[80.9251933067, 207.9047427038],
[52.8853803102, 337.7443022089],
[25.9926385814, 120.3586150136]
];
I use echarts.graphi.clipPointsByRect() (like in this echarts-example) to make sure, the polygon is not drawn outside of the grid.
echarts.graphic.clipPointsByRect(points, {
x: params.coordSys.x,
y: params.coordSys.y,
width: params.coordSys.width,
height: params.coordSys.height
})
Initially the polygon is drawn correctly, like this:
But when I zoom in, the polygon is distorted: e.g. you can click the zoom part buttom below the chart to zoom from 40 to 60 - in this case I'd expect to see the part of the shape (like highlighted in yellow in the image above) - but instead I see this distorted image:
Maybe this function is not meant for this use-case, or is this a bug?
Is there another function for this use-case or does anyone know a workaround?

Answer 1

Update
Version 4.4.x contains a new clip feature. This makes it easy to avoid the distortion:
in the render function we don't need to clip our shapes: i.e. no need to call clipPointsByRect()
instead we just activate clip on the custom series:
New series definition with clip: 'true':
series: [{
type: 'custom',
clip: 'true',
renderItem: renderItem,
data: data
}]
Here is an updated jsfiddle expample
Original Version
it seems that the function is really not working as expected - see echarts-source code comment:
export function clipPointsByRect(points, rect) {
// FIXME: this way migth be incorrect when grpahic clipped by a corner.
// and when element have border.
I've created an issue #10222 for the e-charts project
A workaround for now is to use a custom clipping function
e.g. lineclip supports the Sutherland-Hodgman algorithm for polygon clipping
Here is the updated jsfiddle-example that shows the correct result when you zoom in: