Move on rails (path)

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rrTea
Posts: 323
Joined: Sat Feb 15, 2014 9:54 am

Move on rails (path)

Post by rrTea » Mon May 07, 2018 6:33 am

I'm working on some models that are supposed to follow a 2d path (and Z-rotate accordingly) with varying speeds (for example if it were a horizontally elongated ellipse the models should move slower on the left and right extremes etc). I already implemented some simple paths but now I'd like to test something slightly more complicated, like this:
剪貼簿圖片.png
剪貼簿圖片.png (5.62 KiB) Viewed 636 times
Is there a simple way to go about it?

User avatar
Kjell
Posts: 1650
Joined: Sat Feb 23, 2008 11:15 pm

Re: Move on rails (path)

Post by Kjell » Tue May 08, 2018 1:51 pm

Hi rrTea,
rrTea wrote:Is there a simple way to go about it?
I'd probably go with a quadratic or cubic spline, but curves are generally a personal preference kind-of-deal ( some people might prefer a B-Spline for instance ) :wink: Anyway, here's a simple quadratic example:

Code: Select all

<?xml version="1.0" encoding="iso-8859-1" ?>
<ZApplication Name="App" Caption="ZGameEditor application" CameraPosition="2 2 4" FileVersion="2">
  <OnLoaded>
    <ZExternalLibrary ModuleName="opengl32">
      <Source>
<![CDATA[//

void glBegin(int mode){}
void glEnd(){}
void glVertex2f(float x, float y){}]]>
      </Source>
    </ZExternalLibrary>
    <ZLibrary>
      <Source>
<![CDATA[//

float quadratic(float v1, float v2, float v3, float t)
{
  float k = 1-t;
  return k*k*v1+2*k*t*v2+t*t*v3;
}

vec2 quadraticSpline(vec4[] spline, float t)
{
  int p = spline.SizeDim1-1;
  float s = p*frac(t);
  float f = frac(s);
  int i = s;

  vec4 p1, p2;

  p1 = spline[i];
  p2 = spline[i+1];

  return vector2(quadratic(p1.x, p1.z, p2.x, f),
                 quadratic(p1.y, p1.w, p2.y, f));
}]]>
      </Source>
    </ZLibrary>
    <ZExpression>
      <Expression>
<![CDATA[//

Points[0] = vector4(2, 2, 0, 3);
Points[1] = vector4(0, 2, 0, 1);
Points[2] = vector4(2, 2, 4, 3);
Points[3] = vector4(4, 2, 4, 1);
Points[4] = vector4(2, 2, 0, 0);

//

createModel(Box);]]>
      </Expression>
    </ZExpression>
  </OnLoaded>
  <OnRender>
    <ZExpression>
      <Expression>
<![CDATA[// This is just for debugging purposes, never do this in a actual game ;-P

glBegin(0);

for(int i=0; i<128; i++)
{
  float t = i/128f;
  vec2 p = quadraticSpline(Points, t);
  glVertex2f(p.x, p.y);
}

glEnd();]]>
      </Expression>
    </ZExpression>
  </OnRender>
  <Content>
    <Model Name="Box" Scale="0.25 0.25 0.25">
      <OnUpdate>
        <ZExpression>
          <Expression>
<![CDATA[//

float t = frac(App.Time*0.25);

//

vec2 p = quadraticSpline(Points, t);

//

Box.Position.X = p.x;
Box.Position.Y = p.y;

//

float d, t1, t2;

d = (Points.SizeDim1-1)*0.01;

t1 = frac(t-d);
t2 = frac(t+d);

vec2 p1 = quadraticSpline(Points, t1);
vec2 p2 = quadraticSpline(Points, t2);

Box.Rotation.Z = atan2(p2.y-p1.y, p2.x-p1.x)/PI/2;]]>
          </Expression>
        </ZExpression>
      </OnUpdate>
      <OnRender>
        <RenderNet RenderVertexExpression="//"/>
      </OnRender>
    </Model>
    <Array Name="Points" Type="8" SizeDim1="5"/>
  </Content>
</ZApplication>
K

User avatar
rrTea
Posts: 323
Joined: Sat Feb 15, 2014 9:54 am

Re: Move on rails (path)

Post by rrTea » Thu May 10, 2018 10:39 am

At one point I was thinking of doing something similar to this Following Waypoints from an Array but I'll try to implement this example first (previous post) and see what happens.

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