Polyline texture coordinate chunkiness

[emackey]

Polylines have texture coordinates that indicate to the shader where a given pixel is along the width of the line, and along the length of the line. The width positioning seems quite stable, but the length position somehow is quantized into chunks, or rounded in some way. It appears to update only at intervals, even when the line grows every frame.

I've made a demo that shows how this affects the arrow material, but I also have cases where this affects other materials too. I think it's an issue with the way the texture coordinates are calculated.

What we're supposed to see in this demo is some growing arrow lines, with circled arrow heads (the circles come from large point outlines). You can see that the circles (points) travel smoothly, as expected, and the polyline grows smoothly, but the arrowheads are not smooth.

[emackey]

Here's a modified demo that uses the hexadecimal digits (0123456789abcdef) as an image texture, so that texture placement is more visually apparent. The last letter and a half (ef) of the texture get repeatedly squished and expanded in this demo.

[emackey]

Also this happens at both ends.

I would expect this demo to look more like an aircraft smoothly pulling an advertisement banner across the sky. Parts of the banner should not be repeatedly crushed in the process.