V3d_SpotLight setDirection doesn't work - Forum Open Cascade Technology

Daniel Duesentrieb
Fri, 03/28/2025 - 03:17

Forums:

Handle(Graphic3d_CLight) m_light =  new V3d_SpotLight(gp_Pnt(0.0, 0.0, 5000.0), V3d_XposYneg, Quantity_NOC_WHITE);
m_AISLightSource = new AIS_LightSource(m_light);

doesn't matter what I do, the spotlight always points down (z-). Also when I change with setDirection(gp_Dir(...));

the m_AISLightSource shows the cone in the correct given direction, but the light doesn't move at all. Position m_light is changing ok.

I have no problem with V3d_DirectionalLight

gkv311 n
Fri, 03/28/2025 - 09:07

Could you share some reproducible sample and screenshots? Which OCCT version you are using?

In Draw Harness spotlight could be defined via vlight command, and both vlight NAME -dir DX DY DZ and interactive vmanipulator work as expected for me:

pload MODELING VISUALIZATION
vclear
vinit View1
vlight -clear
vbackground -color GRAY
vrenderparams -shadingModel PHONG
vlight amblight -type AMBIENT -color WHITE -intensity 0.1
box b 0 0 0 30 30 30
vdisplay b -dispMode 1
vsetmaterial b Brass
vfit
vlight spot -type SPOTLIGHT -pos 15 -10 15 -dir 0 1 0 -color RED -display
vmanipulator m -attach spot -adjustPosition location

I've also tried samples/qt/OCCTOverview sample and changing spotlight direction in samples/OCCTOverview/code/Viewer3dSamples.cxxseems to be worked:

void Viewer3dSamples::SpotLight3dSample()
{
  // Spot light source creation
  Handle(V3d_SpotLight) aSpotLight = 
    new V3d_SpotLight(gp_Pnt(100.0, 0.0, 0.0), gp_Dir(-1.0, 0.0, 0.0), Quantity_NOC_RED);
  aSpotLight->SetIntensity(5000);
  myView->SetLightOn(aSpotLight);

  aSpotLight->SetDirection(gp_Dir(-1.0, 0.0, 0.25));

  Handle(AIS_LigthSource) aPrs = new AIS_LigthSource(aSpotLight);
  myContext->Display(aPrs, true);
}

Attachments:

spot.png

Daniel Duesentrieb
Fri, 03/28/2025 - 18:34

In your example I only see the cone but not the light and shadow. This is working here as well.

Spot1.png = setPosition(0,0,3000) setDirection(gp_Dir(1,0,-1)

Spot2.png = setPosition(0,0,3000) setDirection(gp_Dir(1,0,0)

Spot3.png = setPosition(1000,0,3000) setDirection(gp_Dir(1,0,0)

Shadow makes no sense. To me it looks like V3d_SpotLight is behaving like a V3d_PositionalLight

m_light->SetConcentration
m_light->SetSmoothRadius
m_light->SetAttenuation

Whatever (in range) values I put in, nothing changes.

Other problem:

Handle(Graphic3d_CLight ) m_light = new V3d_SpotLight(gp_Pnt(0.0, 0.0, 5000.0), V3d_XposYneg, Quantity_NOC_WHITE);
m_light->SetCastShadows(true); << crash here

Thanks!

PS: using 7.9.0

Attachments:

spot1.png

spot2.png

spot3.png

Daniel Duesentrieb
Fri, 03/28/2025 - 20:37

please see spot4.png. this is what your sample code is doing.

void Viewer3dSamples::SpotLight3dSample()
{
  // Spot light source creation
  Handle(V3d_SpotLight) aSpotLight = 
    new V3d_SpotLight(gp_Pnt(100.0, 0.0, 0.0), gp_Dir(-1.0, 0.0, 0.0), Quantity_NOC_RED);
  aSpotLight->SetIntensity(5000);
  myView->SetLightOn(aSpotLight);

  aSpotLight->SetDirection(gp_Dir(-1.0, 0.0, 0.25));

  Handle(AIS_LigthSource) aPrs = new AIS_LigthSource(aSpotLight);
  myContext->Display(aPrs, true);
}

Attachments:

spot4.png

gkv311 n
Fri, 03/28/2025 - 21:47

Shadow makes no sense. To me it looks like V3d_SpotLight is behaving like a V3d_PositionalLight

I see you are using Path Tracing in your screenshots. Indeed, Path-Tracing engine doesn't implement handling of Spot light sources - it treats them as positional sources (within OpenGl_View::updateRaytraceLightSources()). For that reason you'll not find such light sources in RayTracing, for example:

Daniel Duesentrieb
Fri, 03/28/2025 - 22:57

thank you

will this work in the near future?
and what is the point of having V3d_SpotLight if it doesn't work?

gkv311 n
Fri, 03/28/2025 - 23:56

and what is the point of having V3d_SpotLight if it doesn't work?

The list of light source types V3d_AmbientLight, V3d_PositionalLight, V3d_DirectionalLight, V3d_SpotLight originates from light sources that could be defined within legacy OpenGL API glLight(). And these types should still work within Phong and PBR shading models in OCCT viewer.

Path-Tracing engine has been added to OCCT Viewer later than light source API, and currently provides a mixture of properties, supported by legacy Phong (including non-physical properties like Graphic3d_CLight::LinearAttenuation()), by model PBR (like Graphic3d_CLight::Intensity()) and Path-Tracing engines (see Ray-Tracing / Path-Tracing light properties section within Graphic3d_CLight documentation).

I cannot say why Spot light source type hasn't been implemented within Path-Tracing engine - maybe developers haven't considered it useful enough, or postponed implementation for later and forgotten...

Daniel Duesentrieb
Sat, 03/29/2025 - 17:26

Thank you for taking the time to explain.
So there is still hope that this will come one day.

Daniel Duesentrieb
Fri, 03/28/2025 - 23:27

Found a workaround. Better then nothing:

Put a positional light into a cylinder and control the radius with adjusting the z of the light withing the cylinder. looks kind of ok.

Attachments:

spot5.png