Dragging on touch starts too late (ontouchend) – with video

[wahlatlas]

Dragging/Panning the map on a current iPad pro running iOS 16.5.1 I experience the following – even without WMS background layer:

• the map only moves after I am ending the drag with a touch end

Will post a video of the observed behaviour versus the expected one.

[wahlatlas]

Have a look at this 19sec video that demonstrates the issue
https://wahlatlas.net/experimente/testcases/gridviz_drag_touch_issue98.mp4

[wahlatlas]

Here's a reduced testcase:
https://wahlatlas.net/experimente/testcases/gridviz_issue98.html

The above described unexpected behaviour should be able to be reproduced on an iPad.

However, if I first touch until the tooltip shows and than touch again the same – now highlighted – cell, the drag works as expected

[wahlatlas]

The WebGLStyle doesn’t exhibit the described issue, dragging on touch is instant as it should, see
https://wahlatlas.net/experimente/testcases/gridviz_issue98WGLStyle.html

[joewdavies]

For some reason...

CanvasRenderingContext2D.drawImage()

...updates the canvas during desktop pan events, but not on mobile.

gridviz/src/GeoCanvas.js

Line 218 in 4fed315

this.ctx.drawImage(this.canvasSave.c, this.canvasSave.dx, this.canvasSave.dy)

I've tried to fix it but no luck so far.

I will keep investigating!

[joewdavies]

For some reason this issue doesnt happen for me (on android) when the viewport meta tag is omitted from the HTML document head:
<meta name="viewport" content="width=device-width, initial-scale=1" />

On mobile:

This works: https://eurostat.github.io/gridviz/examples/styles/joyplot_shading.html (without tag)
This doesnt: https://eurostat.github.io/gridviz/examples/styles/joyplot.html (with tag)

Of course by removing the meta tag, the zoom buttons and placenames are not scaled correctly so this is not a solution.

Im not yet sure why this affects the panning and zooming. And why it works well with webgl but not with 2D canvas.
The investigation continues!

[joewdavies]

This issue appears to be solved as of v3.0.17. (tested on android)
@wahlatlas please let us know if you still encounter the issue