Simple 3d colored triangle

Dear guys
I m trying to display a simple 3d triangle using simple vertex color using:

        Node* node = m_scene->CreateChild("SimpleTriangle");
        Model* model = new Model(context_);
        StaticModel* staticModel = node->CreateComponent<StaticModel>();
        model->SetNumGeometries( 1 );
        //Urho3D::BoundingBox bb;
        Urho3D::SharedPtr<Urho3D::Geometry> newGeometry(new Urho3D::Geometry(context_));
        Urho3D::Vector<float> vertexData;
        Urho3D::Vector<unsigned short> indexData;
        vertexData.Push(0); vertexData.Push(0); vertexData.Push(0);  vertexData.Push(Color::RED.ToUInt());
        vertexData.Push(0); vertexData.Push(100); vertexData.Push(0); vertexData.Push(Color::RED.ToUInt());
        vertexData.Push(100); vertexData.Push(0); vertexData.Push(0); vertexData.Push(Color::RED.ToUInt());
        indexData.Push(0); indexData.Push(1); indexData.Push(2);
        Urho3D::SharedPtr<Urho3D::VertexBuffer> vertexBuffer(new Urho3D::VertexBuffer(context_));
        vertexBuffer->SetShadowed(true);
        vertexBuffer->SetSize( 3, Urho3D::MASK_POSITION|Urho3D::MASK_COLOR);
        vertexBuffer->SetData(&vertexData[0]);
        // create index buffer
        Urho3D::SharedPtr<Urho3D::IndexBuffer> indexBuffer(new Urho3D::IndexBuffer(context_));
        indexBuffer->SetShadowed(true);
        indexBuffer->SetSize(indexData.Size(), false );
        indexBuffer->SetData(&indexData[0]);
        // add buffers to geometry
        newGeometry->SetVertexBuffer(0, vertexBuffer); // , vertexDecl
        newGeometry->SetIndexBuffer(indexBuffer);
        newGeometry->SetDrawRange(Urho3D::TRIANGLE_LIST, 0, indexData.Size());

        model->SetGeometry(0, 0, newGeometry);
        model->SetNumGeometryLodLevels(0,1);

        staticModel->SetModel(model);

but the triangle is all dark/black/brown.

I have tried:

  • to add vertex normals
  • to manually create a material and to set it : material->SetTechnique(0, cache->GetResource(“Techniques/NoTextureNormal.xml”) );
  • to add a global scene light

Would anyone know how to simply display a colorful triangle using vertex colors in the vertex buffer ?
Cheers
Thanks
S.

Do you have a light? I know you have a “global scene light”, but is it actually illuminating your tri?

Thanks.
Yes there are even 2 lights:

        // Create a directional light without shadows
        Node* lightNode = m_scene->CreateChild("DirectionalLight");
        lightNode->SetDirection(Vector3(0.5f, -1.0f, 0.5f));
        lightNode->SetPosition(Vector3(0,100,0));
        Light* light = lightNode->CreateComponent<Light>();
        light->SetLightType(LIGHT_DIRECTIONAL);
        light->SetColor(Color(1.f, 1.f, 1.f));
        light->SetSpecularIntensity(100.0f);

        // add a light to the camera node as well
        {
            Light* light = m_camera_node->CreateComponent<Light>();
            light->SetLightType(LIGHT_POINT);
            light->SetRange(200);
            light->SetBrightness(200.0);
            light->SetColor(Color(1,1,1,1.0));
        }

but no impact, triangle still black/dark.
S.

[quote=“Sinoid”]You need to use a technique that includes “VERTEXCOLOR” as a preprocessor definition.

Thanks.
Here it is I have tried different techniques such way:

        Urho3D::SharedPtr<Urho3D::Material> material(new Urho3D::Material(context_));
        material->SetTechnique(0, cache->GetResource<Technique>("Techniques/DiffVCol.xml") ); // tried most DiffVCol .......
        staticModel->SetMaterial(material);

but no way, triangle still black.
WTH…

Try NoTextureUnlitVCol.xml

Tried but no way…
Thanks anyway.
S.

So wait, are you defining your own material or using an existing material? What happens if you turn off shadows? What happens if you reverse the winding order?

indexData.Push(0); indexData.Push(2); indexData.Push(1);

I think part of the problem is that you are pushing the color (Color::RED.ToUInt()) into a float Vector. This involves an implicit cast from unsigned int to float, which changes the bit representation of the value. Later, when this float value is re-interpreted as 4 separate unsigned char, the values are not the same.

Color::RED as an unsigned int (4 bytes combined from r,g,b,a) has the value of 4278190335 which, if re-interpreted as byte-sized color components, gives you r=255, g=0, b=0, a=255. However, casting to a float then interpreting that float as unsigned int gives you an unsigned value of 1333723137 which unpacks to r=79 g=127 b=0 a=1.

The usual method for building a vertex stream like this is to pack it into an unsigned char buffer rather than a float buffer. See the dynamic geometry sample ( github.com/urho3d/Urho3D/blob/m … y.cpp#L111 ) for what this can look like. (In the sample, you are locking an existing vertex stream as an unsigned buffer, but the process of creating a stream is similar.)

I haven’t tried your code to see if this is the actual issue or not, but perhaps it will help.

[quote=“thebluefish”]So wait, are you defining your own material or using an existing material? What happens if you turn off shadows? What happens if you reverse the winding order?
[/quote]

Hi

  • I m creating a new Material on purpose:
    Urho3D::SharedPtrUrho3D::Material material(new Urho3D::Material(context_));
    and then setting the technique material->SetTechnique(0, cache->GetResource(“Techniques/XXXXXXXXX.xml”) );
  • I have tried staticModel->SetCastShadows(false); but no effect
  • I have tried reverse winding : the triangle is ofcourse now visible from the back but still all black
    Let me try JTippetts advice.
    Thanks.
    S.

Here it is I have tried to play with a unsigned int vertex buffer but nothing does appear at all probably because the model expects 4bytes per vertex position and 1 byte for the color. I could not load box.mdl because the mesh I am generating does contain variable number fo vertexes.
Now JTippet is probably right, the direct cast from uint to float is dirty, modifying the value of the color.
Here is what I have tried to avoid any corruption to the UINT color:

        Node* node = m_scene->CreateChild("SimpleTriangle");
        Model* model = new Model(context_);
        StaticModel* staticModel = node->CreateComponent<StaticModel>();
        model->SetNumGeometries( 1 );
        Urho3D::BoundingBox bb;
        Urho3D::SharedPtr<Urho3D::Geometry> newGeometry(new Urho3D::Geometry(context_));
        Urho3D::Vector<float> vertexData;
        std::cout << "sizeof(unsigned char)" << sizeof(unsigned char) <<  std::endl; // usually 1 byte
        std::cout << "sizeof(float)" << sizeof(float) <<  std::endl; // usually 4 bytes
        Urho3D::Vector<unsigned short> indexData;
        unsigned int r = Color::RED.ToUInt();
        float colorFloat = 0;
        memcpy(&colorFloat, &r, sizeof(float));

        #define ADD_VERTEX(V, C) bb.Merge(V); vertexData.Push(V.x_); vertexData.Push(V.y_); vertexData.Push(V.z_); vertexData.Push(0); vertexData.Push(100); vertexData.Push(0); vertexData.Push(C);

        Urho3D::Vector3 v1(0,0,0); ADD_VERTEX(v1, colorFloat);
        Urho3D::Vector3 v2(100,0,0); ADD_VERTEX(v2, colorFloat);
        Urho3D::Vector3 v3(0,0,100); ADD_VERTEX(v3, colorFloat);
        indexData.Push(0); indexData.Push(2); indexData.Push(1);

        Urho3D::SharedPtr<Urho3D::VertexBuffer> vertexBuffer(new Urho3D::VertexBuffer(context_));
        vertexBuffer->SetShadowed(true);
        vertexBuffer->SetSize( 3, Urho3D::MASK_POSITION|Urho3D::MASK_NORMAL|Urho3D::MASK_COLOR);
        vertexBuffer->SetData(&vertexData[0]);
        // create index buffer
        Urho3D::SharedPtr<Urho3D::IndexBuffer> indexBuffer(new Urho3D::IndexBuffer(context_));
        indexBuffer->SetShadowed(true);
        indexBuffer->SetSize(indexData.Size(), false);
        indexBuffer->SetData(&indexData[0]);
        // add buffers to geometry
        newGeometry->SetVertexBuffer(0, vertexBuffer); // chek me: add vertexDecl ?
        newGeometry->SetIndexBuffer(indexBuffer);
        // TRIANGLE_LIST = 0, LINE_LIST, POINT_LIST, TRIANGLE_STRIP, LINE_STRIP, TRIANGLE_FAN
        newGeometry->SetDrawRange(Urho3D::TRIANGLE_LIST, 0, indexData.Size());

        model->SetGeometry(0, 0, newGeometry);
        model->SetNumGeometryLodLevels(0,1);
        model->SetBoundingBox(bb);

        ResourceCache* cache = GetSubsystem<ResourceCache>();

        Urho3D::SharedPtr<Urho3D::Material> material(new Urho3D::Material(context_));
        material->SetTechnique(0, cache->GetResource<Technique>("Techniques/NoTextureVCol.xml") );
        staticModel->SetMaterial(material);
        staticModel->SetCastShadows(false);

        staticModel->SetModel(model);

but the triangle is still not red: playing with the normal, it is either black when null normal or grey with upward normal.
Damned…
Thanks
S.