Grease pencil edit extrude : odd behavior

Question Grease Pencil

I'm a latecomer to GP. Currently using 2.81a on very old laptop. Haven't had a chance to try 3.4 on another computer.

Usually when extruding a stroke in GP edit, I get a new segment ending with a semicircle. From time to time, a square or triangular end appears instead (often unstable and flickering). Am I missing something obvious? Thanks.

  • CCWieland replied

    Are you using the Arc tool in Draw mode?

  • techworker1 replied

    No, generally Pencil tool, sometimes Line tool.

    Maybe important: I was using additive drawing.

  • Omar Domenech replied

    Well I'm not sure, but I remember as the grease pencil was being developed that they fixed things like that along the way. Maybe you're just using an old one? Try downloading the latest version of Blender and see if it still does that, even if it's just for testing.

  • techworker1 replied

    On another computer, I tested with 3.4.0. Behavior is a lot better. If extrude is done at each keyframe, there seem to be no artifacts at all. If I interpolate a sequence between keyframes, there is a little bit of garbage/noise, but that is not surprising. And it is much better than 2.81a in any case. So I guess that is what I need to live with.

    A workaround in 2.81a (additive drawing) seems to be to add new strokes instead of extruding existing ones. This can get the job done, just not as precise or convenient.


  • Martin Bergwerf replied

    It's not supposed to happen, but you are using an old (early stage) GP on a very old laptop with (probably) also an old GPU, which might not have an updated driver....that's asking for trouble 😉

    I tested this on 2.80 and 2.82 (don't have a 2.81 lying around and don't think it's worth the trouble downloading it, just for this case), but could not reproduce the issue.

  • techworker1 replied

    Actually the issue seems to be different from what I thought. It still happens when I start from scratch in 3.4.0.

    • Turn on Additive Drawing
    • Draw a line at frame 1 - edit line to have only two points
    • Advance to frame 3
    • Extrude the line to have a third point (using E hotkey)
    • Repeat the process a few times to extend the line

    If I then step backward on the timeline, I always see junk at the end of the line. If I look carefully in edit mode, it seems that each extrusion actually produced 2 points at exactly the same location. If the duplicates are carefully deleted/dissolved (at each keyframe), then stepping looks clean. Mysterious.

    Basically I am trying to imitate something like a Build modifier, but on a stroke.

  • Martin Bergwerf replied

    Sorry, I don't think I understand what you are doing exactly. Extrusion doesn't appear to create double vertices when I try it.

    But I have not really used GP yet, so that's probably just me; I don't know what Additive Drawing is (I know it is a thing, just don't know what it is...I switched the Blend to Add...).

    How did you edit a line to have two points? (Dissolve the inner points, or draw a line with 0 Subdivisions, or....)

    You do know that GP already has a Build Modifier, right?

  • techworker1 replied

    (I'm not EXACTLY doing a Build - actually want to grow at front, shrink at rear)

    Maybe this isn't worth all the trouble... I made a crude video which I hope explains better. I hacked a small script which shows the duplicated spline points when I'm all done. Usually the artifacts are much worse than in the video.


  • CCWieland replied

    I don't think blender can do this, animate vertex to vertex in edit mode. I got the same artifacts as you did animating the line this way. I am using blender 3.4. I see no work around, but I am also not sure what you are doing.

  • techworker1 replied

    After the extra duplicate points have been dissolved, everything seems to work fine. Just an extra step required.

    Behavior (and workaround) are basically the same for 2.81a and 3.4.0. (Before workaround, 2.81a looks worse, probably due to older code and/or old GPU.)

    to project I was working on]

  • Martin Bergwerf replied

    Well, it looks to me that the lines are Z-fighting with the lines from Onion Skinning.

    Turning the Opacity of the Onion lines to 0 doesn't help with the Z=fighting, unfortunately. Setting the number of Keyframes in the Onion Skinning to 0 doesn't help either; it just 'hides' them.Even turning them off in the Overlays doesn't help.

    Also, the last drawn Vertex (in a certain Keyframe) is double, but the earlier ones are not; that has probably also to do with the Onion Skinning.

    I'm not being much of a help, I know. You should ask Paul Caggegi...

  • techworker1 replied

    Definitely seems to be Z-fighting, between duplicate stroke points at the same location. Independent of onion-skinning (and Additive Drawing, for that matter). I could post a better video.

    I can't explain why Extrude seems to actually create 2 new stroke points at the starting location, and then lets you move one.

    Maybe ppcaggegi has an explanation.

  • Paul Caggegi replied

    Hi techworker1 - this sounds like you need to toggle the line caps. Firstly, in later versions (I'm unsure which one exactly, but at least 3.3) you can toggle it via the tool shelf.

  • Paul Caggegi replied

    If you're using the pencil tool, any pressure sensitivity should override this, and is controlled by the "Radius" option. Toggling the Pressure sensitivity icon nest to it will enable/disable this.

  • Paul Caggegi replied

    You can further tweak your brush settings - Advanced, Stroke options - and in your brush tool window (N-Key, Tool Tabe) you can adjust the curve that will dictate how the pressure sensitivity should act. You also have post-processing and randomize settings to play with as well.