Comet tail

[Paijan]

I'm writing a game in which moving objects leave tails behind themselves, like comets. Objects can be moved either by player input or mathematical function (e.g. on sinusoid).

I couldn't find a good way to perform this so I tried the simplest one - creating CircleShape in regular intervals in objects' positions. And it worked, because of simplicity, but later on it became a performance bottleneck. It's snappy and the tails sometimes break -pics.

How to do it properly? Thor particles?

[Jesper Juhl]

If you want the tail to be contiguous and stay behind you could simply draw a line between each of the points denoting the previous positions.
If the tail is supposed to "fade out" then something like Thor's particles may be better suited.
Or you could use a shader to draw the tail I guess.

[Paijan]

If you want the tail to be contiguous and stay behind you could simply draw a line between each of the points denoting the previous positions.

You mean storing coordinates each frame and appending it to VertexArray?

EDIT: Well, it really works fine, only now I can't alter line thickness

[kitteh-warrior]

can't alter line thickness

This shows how it is possible with a sf::VertexArray. If that doesn't work for you, the mathematical concepts behind it should help you.

[Nexus]

This is a really typical use case for particles. The more flexibility you add to a handcrafted solution, the closer it will get to a freely configurable particle system

In the Thor fireworks example, I've done exactly that -- tails for the firework explosions. You can have a look at it, even in case you don't end up using Thor.

[Paijan]

Thank you for your replies.

I decided using VertexArray and the tail works perfectly. I even tried fading it by iterating through all vertices and changing their alpha values calculated from quadratic function (to make it smooth). It looks nice.

Should I somehow dispose of faded vertices? Because they are faded, but they still exist in memory and are drawn each frame.

[Nexus]

Yes, definitely remove them. Maybe not every frame, because removing from the beginning of a vector is expensive, but once a second or so.