(solved) Get the angle of the wall from the projectile

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(solved) Get the angle of the wall from the projectile

Postby Jekyll Grim Payne » Tue Jan 08, 2019 11:31 am

I want to spread some particle effects over the surface of the wall or plane that was hit by a projectile. How can I get the necessary information about the angles (ideally the slope too) and use it like that?

(Ideally I'd like to be able to do it from a puff of a hitscan attack as well, but let's start with projectiles.)
Last edited by Jekyll Grim Payne on Sat Jan 12, 2019 6:54 am, edited 1 time in total.
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby Matt » Tue Jan 08, 2019 1:52 pm

The Line class has 2 member classes, v1 and v2, that have a member vector2 called p that holds the coordinates of the vertex, e.g. you can grab a position with "vector2 linestart=myline.v1.p;"

Then something something arctangents and trying to figure out which side of the linedef you're coming in from, in order to get the correct relative angle.

If you can get a pointer for the line, whether by checking the actor's blockingline or with some other check like LineTrace (which I believe would also get you the side of the line hit), the rest is just trying to figure out the fastest way to do it without null pointer VM crashes.
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby Apeirogon » Tue Jan 08, 2019 3:07 pm

Sector struct have native "Sec(tor)Plane" struct, which contain "native Vector3 Normal;" variable, which is normal to the plane of a sector. You can find angle/slope/pitch of that sector from it, using some math.
How to do so here
https://en.wikipedia.org/wiki/Normal_(geometry)
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby ketmar » Tue Jan 08, 2019 3:36 pm

i believe that sector normals are only for floor/ceiling. as for walls, Matt is right: it is quite easy to get angles from line. something like this (quote from my engine):
Code: Select allExpand view
  TVec vec = v2-v1;
  double length = sqrt(vec.x*vec.x+vec.y*vec.y);
  if (!length) {
    angles.pitch = (vec.z > 0 ? 90 : 270);
    angles.yaw = 0;
  } else {
    angles.pitch = -RAD2DEG(atan2(vec.z, length));
    angles.yaw = RAD2DEG(atan2(vec.y, vec.x));
  }

this will give you angles for line direction. basically, `vec.z` will always be zero, so you can only use `yaw` part, and use simple arithmetics to get angle for normal, for example.

p.s.: as for determining the side, i believe that zscript has "PointOnLineSide()" API (or it can be easily exposed, as the engine has that function).
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby Matt » Tue Jan 08, 2019 4:36 pm

ZS also has a native length() function: double length=(v2.p-v1.p).length();

(Might also want to check of the two positions are identical before calculating the length, just to save the extra square root call, but I haven't checked for sure since ASMJIT was added whether that would still be faster)
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby ketmar » Tue Jan 08, 2019 4:53 pm

it is illegal to have zero-length lines on map. not that it is impossible, but any sane editor should warn and collapse that. the code was copypasted from my doom engine, therefore it has checks there. i mostly pasted it to save OP some effort on figuring out atan2 arguments. ;-)

p.s.: and i am pretty sure that you cannot hit zero-length lines anyway, so zero check can be safely omited.
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby Jekyll Grim Payne » Wed Jan 09, 2019 5:01 am

Matt wrote:The Line class has 2 member classes, v1 and v2, that have a member vector2 called p that holds the coordinates of the vertex, e.g. you can grab a position with "vector2 linestart=myline.v1.p;"


I'll be honest, I'm too new to this to fully understand that :( First of all, do I understand correctly that v1 and v2 represent the two vertices of the line? Second, in vector2 linestart=myline.v1.p I honestly really understand only "vector2". Linestrat and myline are implied to be my variables? Sorry for the basic questions.
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby Apeirogon » Wed Jan 09, 2019 11:29 am

Jekyll Grim Payne wrote: v1 and v2 represent the two vertices of the line

Yes

Jekyll Grim Payne wrote: vector2 linestart=myline.v1.p I honestly really understand only "vector2". Linestrat and myline are implied to be my variables

No, linestart "return" position, as vector 2, of the vertex with "number" v1 of a line "myline".
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby Jekyll Grim Payne » Thu Jan 10, 2019 2:48 am

Apeirogon wrote:
Jekyll Grim Payne wrote:
Jekyll Grim Payne wrote: vector2 linestart=myline.v1.p I honestly really understand only "vector2". Linestrat and myline are implied to be my variables

No, linestart "return" position, as vector 2, of the vertex with "number" v1 of a line "myline".


That... hasn't really made things clearer for me, sorry. How do I get "myline"? Will that be blockingline?
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby Apeirogon » Thu Jan 10, 2019 3:18 am

You store to variable "linestart", which can store vector2 type of data, position "p" of the vertex "v1" from line line "myline", where "myline" is a pointer to some line in map.
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby Matt » Thu Jan 10, 2019 8:08 pm

"myline" can be either the actor's BlockingLine after a CheckMove/TryMove check, or the hitline of the FLineTraceData of LineTrace.

EDIT: simpler to just learn LineTrace, really. Check the example at the bottom of that wiki page.
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Re: [ZScript] Get the angle of the wall from the puff/projec

Postby Jekyll Grim Payne » Sat Jan 12, 2019 6:54 am

Code: Select allExpand view
Angle = atan2(t.HitLine.delta.Y, t.HitLine.delta.X) - 90.;


That works.
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