OpenGl/TF: Help with results i can't explain and centering geometry

Hello,

Still wet behind the ears in OpenGL land. As a first exercise i've decided to convert a patch from cpu to gpu but i'm running into an issue i can't explain and need some help with.

I'm not using the velocity-buffer here so i thought it was a good idea to use the x-component to store the lifetime of a particle (0.-1.) and .yz-components as a spawnlocation.

The issue here lies with the if-statement, there are some things going on i can't explain. After enabling jit.gl.tf for example i immediately see a steady stream of particles spawn from 0.5 0.5. Why is that? Even if i bang the jit.matrix instead of the jit.noise i still get particles spawn from that location from the start? I don't expect to see any particles come from that location for the first 10000 frames if i'm correct?
I've added some comments in the jxs as well.

How do you center geometry and still keep everything on the math-side between 0.-1.? On the cpu i would just keep all calculations between 0. and 1. and have a jit.gen on the end of the chain where i would do [(in1*2)-1] to center everything around 0. I fixed that with the camera in this patch but is there a good solution for this? I guess the desire for this comes from the convenience of using mod() to wrap the particles around so if anyone has a good aproach to that i'd love to hear it.

Thanks a bunch!

Save the shader as MeshTff.jxs or adjust the jit.gl.shader to your chosen filename

<jittershader name="TFFlowfield">
    <description>Basic Transform Feedback Locomotion</description>
    <param name="position" type="vec3" state="POSITION" />
    <param name="velocity" type="vec3" state="NORMAL" />
    <param name="speed" type="float" default="0.005" />
    <param name="theta" type="float" default="0.0" />
    
    <param name="randomTex" type="int" default="0" />
    
    <language name="glsl" version="1.5">
        <bind param="position" program="vp" />
        <bind param="velocity" program="vp" />
        <bind param="speed" program="vp" />
        <bind param="theta" program="vp" />
        
        <bind param="randomTex" program="vp" />
        
        <program name="vp" type="vertex">
<![CDATA[
#version 330 core
uniform float speed;
uniform float theta;
in vec3 position;
in vec3 velocity;

out vec3 Position1;
out vec3 Velocity1;

const float PI = 3.1415926535897932384626433832795;

uniform sampler2DRect randomTex;

void main() {
    
    vec2 texLookup = vec2(position.x * 99.0, position.y * 99.0);
    float theta = texture(randomTex, texLookup).x;
    
    Position1.x = mod(1.0 + (position.x + (cos(theta * (PI * 2)) * speed)), 1.0);
    Position1.y = mod(1.0 + (position.y + (sin(theta * (PI * 2)) * speed)), 1.0);
    Position1.z = 0.0;
    
    Velocity1.x += 0.00001;
    Velocity1.y = velocity.y;
    Velocity1.z = velocity.z;
    
    if(Velocity1.x > 1.0) 
        {
            Position1 = vec3(0.5, 0.5, 0.0);

            //Position1 = vec3(velocity.y, velocity.z, 0.0); // Why doesn't this line work but line 48 does?
                
            
            //Position1.x = velocity.y; //And why doesn't this work when it does on line 38?
            //Position1.y = velocity.z;
            //Position1.z = 0.0;
            
            Velocity1.x = 0.0;
        }
    
}

]]>
        </program>
        <program name="fp" type="fragment"  >
        <![CDATA[
#version 330 core
void main() 
{
}
        ]]>
        </program>
    </language>
</jittershader>