Issues Rendering Textures in WebGL

Hello!

I've been attempting to render a texture via WebGL using the latest OCCT release (7.4.1 beta), but I can't quite get it to work. Ultimately the end result is a black surface and a browser warning: "RENDER WARNING: there is no texture bound to the unit 0".

I'm compiling via Emscripten, and have already compiled the opencascade library with the third party FreeType and FreeImage libraries.

This occurs in a pretty minimal arrangement using the existing WebGL sample. I've tweaked the file upload bit to load an image file into a pixmap to be used as a texture. Although I've tried several different approaches, the "simplest" approach of rendering an AIS_SHAPE with a texture configuration as described in its header file produces the previously mentioned result. My code for this follows
(This is in the onFileDataRead function in the WebGL sample, everything else is mostly the same, in some cases there were some issues I had to resolve in the default WasmOcctView.cpp file)
 

  const char* aName = theOpaque != NULL ? (const char* )theOpaque : "";

  Standard_ArrayStreamBuffer aStreamBuffer ((const char* )theBuffer, theDataLen);
  std::istream aStream (&aStreamBuffer);
  
  Message::DefaultMessenger()->Send (OSD_MemInfo::PrintInfo(), Message_Trace);

  Handle(Image_AlienPixMap) pixmap = new Image_AlienPixMap();
  pixmap->Load((Standard_Byte*)theBuffer, theDataLen, aName);
    
  double w = (double)(pixmap->Width()); 
  double h = (double)(pixmap->Height());

  Handle(AIS_Shape) aPrs = new AIS_Shape(BRepBuilderAPI_MakeFace(gp_Pln(), -w, 0, -h, 0));
  aPrs->Attributes()->SetupOwnShadingAspect();
  aPrs->Attributes()->ShadingAspect()->Aspect()->SetTextureMapOn();
  aPrs->Attributes()->ShadingAspect()->Aspect()->SetTextureMap (new Graphic3d_Texture2Dmanual (pixmap));
  aViewer.Context()->Display(aPrs, 1, -1, true);
  aViewer.View()->Redraw();
  aViewer.Context()->UpdateCurrentViewer();

Since I was wrestling with this for a bit I also tried an alternate approach to try have a little more control of the details of what was being set by "manually" creating an array of primitives to display the texture as follows
 

  const char* aName = theOpaque != NULL ? (const char* )theOpaque : "";

  Standard_ArrayStreamBuffer aStreamBuffer ((const char* )theBuffer, theDataLen);
  std::istream aStream (&aStreamBuffer);
  
  Message::DefaultMessenger()->Send (OSD_MemInfo::PrintInfo(), Message_Trace);
  Handle(Image_AlienPixMap) pixmap = new Image_AlienPixMap();
  pixmap->Load((Standard_Byte*)theBuffer, theDataLen, aName);

  Handle(Graphic3d_AspectFillArea3d) aspect = new Graphic3d_AspectFillArea3d();
  Handle(Graphic3d_Texture2Dmanual) texture_map = new Graphic3d_Texture2Dmanual(pixmap);
  // Due to limited non-power-of-two sized texture support in WebGL, disable related items
  // as described https://www.khronos.org/webgl/wiki/WebGL_and_OpenGL_Differences#Non-Power_of_Two_Texture_Support
  // That said, it doesn't work when using a power-of-two sized texture either so this is more in theory
  texture_map->SetMipMaps(false);
  texture_map->DisableRepeat();
  texture_map->DisableSmooth();
  Handle(Graphic3d_TextureSet) texture_set = new Graphic3d_TextureSet(texture_map);
  aspect->SetTextureSet(texture_set);
  aspect->SetTextureMapOn();
  aspect->SetInteriorStyle(Aspect_IS_SOLID);
  aspect->SetShadingModel(Graphic3d_TOSM_UNLIT);
  
  Handle(Graphic3d_ArrayOfTriangleStrips) aTriangles = new Graphic3d_ArrayOfTriangleStrips (4, 0, false, false, false, true);
  double w = (double)(pixmap->Width()); 
  double h = (double)(pixmap->Height());
  aTriangles->AddVertex (gp_Pnt(-w/2., -h/2., 0.0), gp_Pnt2d(0, 0));
  aTriangles->AddVertex (gp_Pnt(-w/2.,  h/2., 0.0), gp_Pnt2d(0, 1));
  aTriangles->AddVertex (gp_Pnt(w/2., -h/2., 0.0), gp_Pnt2d(1, 0));
  aTriangles->AddVertex (gp_Pnt(w/2.,  h/2., 0.0), gp_Pnt2d(1, 1));

  Handle(Graphic3d_Structure) img_struct = new Graphic3d_Structure(aViewer.View()->Viewer()->StructureManager());
  img_struct->SetVisual(Graphic3d_TOS_ALL);
  img_struct->Display();
  Handle(Graphic3d_Group) graphic_group = img_struct->CurrentGroup();

  graphic_group->SetPrimitivesAspect(aspect);
  graphic_group->AddPrimitiveArray(aTriangles);
  // graphic_group->SetGroupPrimitivesAspect (aspect);
  // graphic_group->SynchronizeAspects();

  aViewer.View()->Redraw();
  aViewer.Context()->UpdateCurrentViewer();

but again, no luck, same result.

Going by the warning it seems like it's related to the texture not getting bound, but going through the source so far there it appears that everything necessary for texture binding is appropriately configured. So I'm at a bit of a loss. I tried these arrangements (and many more, with different tweaks to the texture configurations, using different texture map classes like Graphic3d_2dplane, etc.) with a few different newer commit versions of OCCT just in case but nothing seems to resolve the issue.

I also checked the pixel values of the pixmap just in case, and they looked valid (along with the dimensions of the image used in the code snippets), so it would appear that FreeImage is working normally.

Is there something I'm missing here? How can I render image textures when compiling to use WebGL?

Thanks for any help or suggestions!