Expanding circle without extending x and y

[Roberto]

OK so I'm trying to do a sort of "wave" effect of an expanding circle but for the life of me I can't seem to figure out how to do it without using image_xscale and image_yscale. The stretching I get with this method is fairly undesirable.

If anyone knows a better way It would be greatly appreciated if you could share it.
The closest visual example I could give for what I'm aiming for would be the various "wave" attacks of the recently released Furi, those are pretty close to what I'm aiming for.

Thank you: Rob DC

 

[Robert]

I mean stretching a sprite always has the same results, there is only one way, that I know of, to stretch a sprite.

If the problem is that stretching something larger than its native size will cause it to look blurry since it has to interpret all the new pixels, so basically never stretch something larger than its native size (unless you know what your doing).

So with that in mind I would make the circle sprite at its largest size and then SCALE IT DOWN for its regular state, so this way when you stretch it back up you are just stretching it to its normal size.

If you don't need a sprite though you could maybe get away with just drawing basic shapes.

 

[TDSrock]

Why are you not using draw_circle?

There you could simply modify the the radius of the circle in the functions parameter.

 

[Roberto]

I thought about it but I need it to be able to check for collision. I haven't been able to find any explanations on how to do that. If you know a way please say.

 

[jo-thijs]

You can use collision_circle to check for collisions with circles.
You won't be able to use collision events with that though,
so you'll have to check for collisions yourself in the (end) step event.

 

[Strawbry_jam]

You could even just draw a circle in the draw event and use a sprite mask for standard collision events.

 

[jo-thijs]

That won't remain a nice circle though when scaling, not even if you choose for an ellipse collision mask.

 

[Roberto]

Bit late to this. Took a brief vacation. Is there any way to give the circle a thickness?

 

[Jaqueta]

Yes (click me).

 

[jo-thijs]

I'd like to give a code alternative without using extensions (though using the extension isn't the worst idea, as it might be more optimized and easy to use, though it might lack adaptability and compatibility):

draw_set_color(...);
draw_set_alpha(...);

var X = // x coordinate of center of circle
var Y = // y coordinate of centre of circle
var r1 = // lower radius bound
var r2 = // upper radius bound
var precision = 24;
draw_primitive_begin(pr_trianglefan);
for(var d = 0; d < 360; d += precision) {
    draw_vertex(X + lengthdir_x(r1, d), Y + lengthdir_y(r1, d));
    draw_vertex(X + lengthdir_x(r2, d), Y + lengthdir_y(r2, d));
}
draw_vertex(X + r1, Y);
draw_vertex(X + r2, Y);
draw_primitive_end();

I haven't tested the code yet, but this should do.

 

[flyingsaucerinvasion]

I don't think a triangle fan is the correct primitive type there.

 

[Jaqueta]

Yep, that would be triangle strip.

 

[jo-thijs]

I sure did mean to use pr_trianglestrip...
Well, my mistake, thanks for correcting it!

 

[Roberto]

Thanks for all the help guys.