RenderParticles' Direction can sometimes get a bit off

[rrTea]

In the following example, try to spawn a few models by clicking around the screen with left mouse button. Note how the particles are sprayed in the direction opposite of the red "head", and that they rotate following the model's rotation. After confirming this, trigger the launch by pressing the right mouse button... The direction of moving and the particles' direction will fall out of sync.

It's possible that it won't be very noticeable on the first try so maybe you'll need to try a few times, but in most cases it's pretty obvious (I'm attaching a gif where I marked two random examples), as if the particles' Direction continues to rotate a few frames after the model is "launched".

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<?xml version="1.0" encoding="iso-8859-1" ?>
<ZApplication Name="Prg" Caption="Particles test" ClearColor="0.502 0.502 1 1" Camera="cam_Front" FileVersion="2">
  <OnLoaded>
    <ZLibrary Comment="RndPol() Random polarity: 1 or -1">
      <Source>
<![CDATA[float RndPol()
{
float YinYang;
YinYang = (0-0.5)+rnd();
YinYang = YinYang/abs(YinYang);
return YinYang;
}]]>
      </Source>
    </ZLibrary>
    <Group Comment="Values">
      <Children>
        <Variable Name="ScreenRatio"/>
        <Variable Name="ScreenEdgeTop"/>
        <Variable Name="ScreenEdgeRight"/>
        <ZExpression Comment="Calculate">
          <Expression>
<![CDATA[ScreenRatio = (1f*Prg.ViewportWidth/Prg.ViewportHeight);

ScreenEdgeTop   = cam_Front.OrthoZoom*1f;
ScreenEdgeRight = cam_Front.OrthoZoom*ScreenRatio;]]>
          </Expression>
        </ZExpression>
        <Variable Name="PI2"/>
        <ZExpression Expression="PI2=PI*2;"/>
      </Children>
    </Group>
    <Camera Name="cam_Front" Kind="1" Position="0 0 10" OrthoZoom="12"/>
  </OnLoaded>
  <OnUpdate>
    <KeyPress Comment="Rockets spawn" Keys="{" RepeatDelay="0.2">
      <OnPressed>
        <ZExpression>
          <Expression>
<![CDATA[float RndX = rnd()*rndPol()*ScreenEdgeRight;
float RndY = rnd()*rndPol()*ScreenEdgeTop;

mod_RocketThick.Position = vector3(RndX,RndY,0);]]>
          </Expression>
        </ZExpression>
        <SpawnModel Model="mod_RocketThick"/>
      </OnPressed>
    </KeyPress>
    <KeyPress Comment="Rockets erase" Keys=" ">
      <OnPressed>
        <RemoveAllModels/>
      </OnPressed>
    </KeyPress>
  </OnUpdate>
  <Content>
    <Mesh Name="mesh_Rocket">
      <Producers>
        <MeshBox Scale="0.5 0.5 0.5"/>
        <MeshTransform Position="0 -0.5 -0.3" Rotation="0.1 0.1 0.065"/>
        <MeshExpression AutoNormals="0" VertexColors="255">
          <Expression>
<![CDATA[//V : current vertex
//N : current normal (turn off AutoNormals when modifying normals)
//C : current color (turn on VertexColors)
//TexCoord : current texture coordinate (turn on HasTexCoords)

C = vector4(1,0,0,1);]]>
          </Expression>
        </MeshExpression>
        <MeshBox Comment="Body" Scale="0.5 1 0.5" Grid2DOnly="255"/>
        <MeshExpression AutoNormals="0" VertexColors="255">
          <Expression>
<![CDATA[//V : current vertex
//N : current normal (turn off AutoNormals when modifying normals)
//C : current color (turn on VertexColors)
//TexCoord : current texture coordinate (turn on HasTexCoords)

C = vector4(1,1,1,1);
//colorWhiteOpaque;]]>
          </Expression>
        </MeshExpression>
        <MeshCombine/>
      </Producers>
    </Mesh>
    <Model Name="mod_RocketThick" Position="-1.9038 -7.2268 0" RotationVelocity="0 0 0.1" CollisionBounds="1 1 0 0">
      <States>
        <ModelState Name="mState_Preying">
          <OnUpdate>
            <KeyPress Keys="}">
              <OnPressed>
                <SetModelState State="mState_Flying"/>
              </OnPressed>
            </KeyPress>
          </OnUpdate>
        </ModelState>
        <ModelState Name="mState_Flying">
          <OnStart>
            <ZExpression Comment="Prepare rocket">
              <Expression>
<![CDATA[CurrentModel.RotationVelocity.Z = 0;

CurrentModel.Velocity.X = 0+sin(CurrentModel.Rotation.Z*PI2)*2f;
CurrentModel.Velocity.Y = 0-cos(CurrentModel.Rotation.Z*PI2)*2f;]]>
              </Expression>
            </ZExpression>
          </OnStart>
        </ModelState>
      </States>
      <OnSpawn>
        <SetModelState State="mState_Preying"/>
      </OnSpawn>
      <OnUpdate>
        <Condition Comment="Out of screen?">
          <Expression>
<![CDATA[return (
abs(CurrentModel.Position.X) > CurrentModel.Scale.X*4 + ScreenEdgeRight ||
abs(CurrentModel.Position.Y) > CurrentModel.Scale.X*4 + ScreenEdgeTop
);]]>
          </Expression>
          <OnTrue>
            <RemoveModel/>
          </OnTrue>
        </Condition>
      </OnUpdate>
      <OnRender>
        <UseMaterial Material="mat_ColorMondrian"/>
        <RenderMesh Mesh="mesh_Rocket"/>
        <UseMaterial Material="mat_Dotted"/>
        <RenderParticles ParticlesPerSecond="10" Spread="0.2" ParticleWidth="2" ParticleHeight="2" Speed="3" SpeedRange="0.2" ParticleLifetime="1" AnimateSize="-2" FollowModel="0">
          <OnEmitExpression>
<![CDATA[//Emit particle.
//PColor : particle color, PAngle : particle angle

PColor = vector3(0.5,0.25,0);

//PAngle = CurrentModel.Rotation.Z;]]>
          </OnEmitExpression>
        </RenderParticles>
      </OnRender>
    </Model>
    <Bitmap Name="bmp_Dot" Filter="1">
      <Producers>
        <BitmapExpression UseBlankSource="255">
          <Expression>
<![CDATA[// Local variables

float X1, Y1, B, S;

// Distance from center ( per axis )

X1 = 0.5-x;
Y1 = 0.5-y;

B = 64/2f    ; // 64 = BitMapsize | 2 = Anti-Aliasing bias ( in pixels )

pixel.A = B*0.5-sqrt(X1*X1+Y1*Y1)*B;

// Set RGB to white

pixel.R = 1;
pixel.G = 1;
pixel.B = 1;]]>
          </Expression>
        </BitmapExpression>
      </Producers>
    </Bitmap>
    <Material Name="mat_ColorMondrian" Shading="1" Light="0"/>
    <Material Name="mat_Dotted" Light="0" Blend="2">
      <Textures>
        <MaterialTexture Texture="bmp_Dot" TextureWrapMode="2" TexCoords="1"/>
      </Textures>
    </Material>
  </Content>
</ZApplication>

Edit: Removed the gif as it was distracting

[VilleK]

I can see it happening but I don't have an immediate idea of why. Kjell, do you have time to check it out?

[Kjell]

Hmm,

I can see it happening but I don't have an immediate idea of why. Kjell, do you have time to check it out?

At the very least there's something strange going on when rotating a model that contains a RenderParticles component ( with FollowModel turned off ).



As you can see in the GIF, when re-positioning the model all particles continue independently from the model ( as you'd expect ), but when you rotate the model their position gets affected by the rotation.

K

[rrTea]

I would expect that unticking "FollowModel" would mean that, once it is launched, the particle goes off independently of the model - in other words, a model's position matters only for starting coordinates of a particle. So in Kjell's example I'd expect particles to not rotate when the model's Rotation.Z / RotationVelocity.Z are changed.

Related to this - is it by design that RenderParticles' Direction has to be multiplied by 2PI to direct it in a specific angle, unlike any other angles like rotations of models etc? This always confuses me, I usually write

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particles_Rocket.Direction = 0.5+CurrentModel.Rotation.Z;

and then (after discovering it doesn't work) have to fix it to

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particles_Rocket.Direction = (0.5+CurrentModel.Rotation.Z)*Pi2;

[Rado1]

I completely agree with rrTea: unchecking the FollowModel property should cause independent moving of particles on model transformation after its spawning and Direction and Spread properties should be expressed in interval <0,1> as rotations of models. BTW also RenderText.CharRotate uses radians, it should be unified with other rotations as well.