This is definitely part of it, but I'm pretty sure the main reason for the jaggedness for the yellow line (from what I remember) has to do with using the paint bucket/pencil tools to change the color of whatever you have drawn on that particular layer without locking the transparency for that layer first. (Something that took a little whole for me to realize when I was first using GIMP way back in the day.) If you remember to lock the transparency first, then it won't look nearly as pixelated when changing the colors around as a result.it's because you are working in a raster program on a raster template. the jaggedness is just individual pixels. the more pixels in a template, the less noticeable it is. For example, a 2048x2048 template will look better than a 1024x1024 template. there is no fix
what do you mean by "lock the transparency"This is definitely part of it, but I'm pretty sure the main reason for the jaggedness for the yellow line (from what I remember) has to do with using the paint bucket/pencil tools to change the color of whatever you have drawn on that particular layer without locking the transparency for that layer first. (Something that took a little whole for me to realize when I was first using GIMP way back in the day.) If you remember to lock the transparency first, then it won't look nearly as pixelated when changing the colors around as a result.