How to make color of a section be different on a 3D object

Question

I have the following 3D object:

The material of my 3D object is coded like this with Qt3D:

void MyClass::addMaterial(Qt3DCore::QEntity *enti         


        

Answer 1

With the great help of @AdaRaider I managed to implement a custom effect with modifiable vertex shader and fragment shader. Custom effect can be used like this:

#include "customeffect.h"

static const QColor ambientColor("#576675");  // Shader input
static const QColor diffuseColor("#5F6E7D");  // Shader input
static const QColor SpecularColor("#61707F"); // Shader input
static const float shininess(0.0);            // Shader input

void MyClass::addMaterial(Qt3DCore::QEntity *entity)
{
    Qt3DRender::QMaterial * material = new Qt3DRender::QMaterial();
    material->setEffect(new CustomEffect());
    material->addParameter(new Qt3DRender::QParameter(QStringLiteral("ka"), ambientColor));
    material->addParameter(new Qt3DRender::QParameter(QStringLiteral("kd"), diffuseColor));
    material->addParameter(new Qt3DRender::QParameter(QStringLiteral("ks"), SpecularColor));
    material->addParameter(new Qt3DRender::QParameter(QStringLiteral("shininess"), shininess));
    entity->addComponent(material);
}

Custom effect header is:

#ifndef CUSTOMEFFECT_H
#define CUSTOMEFFECT_H

#include 

class CustomEffect : public Qt3DRender::QEffect
{
public:
    explicit CustomEffect(Qt3DCore::QNode *parent = nullptr);
};

#endif // CUSTOMEFFECT_H

The implementation of custom effect is with two versions of OpenGL in mind, OpenGL ES 2.0 and OpenGL 3.1:

#include "customeffect.h"

#include 
#include 
#include 

CustomEffect::CustomEffect(Qt3DCore::QNode *parent)
    : Qt3DRender::QEffect(parent)
{

    Qt3DRender::QTechnique *techniqueES20 = new Qt3DRender::QTechnique();
    techniqueES20->graphicsApiFilter()->setProfile(Qt3DRender::QGraphicsApiFilter::NoProfile);
    techniqueES20->graphicsApiFilter()->setApi(Qt3DRender::QGraphicsApiFilter::OpenGLES);
    techniqueES20->graphicsApiFilter()->setMajorVersion(2);
    techniqueES20->graphicsApiFilter()->setMinorVersion(0);

    Qt3DRender::QTechnique *techniqueGL31 = new Qt3DRender::QTechnique();
    techniqueGL31->graphicsApiFilter()->setProfile(Qt3DRender::QGraphicsApiFilter::CoreProfile);
    techniqueGL31->graphicsApiFilter()->setApi(Qt3DRender::QGraphicsApiFilter::OpenGL);
    techniqueGL31->graphicsApiFilter()->setMajorVersion(3);
    techniqueGL31->graphicsApiFilter()->setMinorVersion(1);

    Qt3DRender::QFilterKey *filterkey = new Qt3DRender::QFilterKey(this);
    filterkey->setName(QStringLiteral("renderingStyle"));
    filterkey->setValue(QStringLiteral("forward"));

    techniqueES20->addFilterKey(filterkey);
    techniqueGL31->addFilterKey(filterkey);

    Qt3DRender::QShaderProgram *shader2 = new Qt3DRender::QShaderProgram();
    shader2->setVertexShaderCode(Qt3DRender::QShaderProgram::loadSource(QUrl(QStringLiteral("qrc:/qt3deditorlib/shaders/es2/custom-shader.vert"))));
    shader2->setFragmentShaderCode(Qt3DRender::QShaderProgram::loadSource(QUrl(QStringLiteral("qrc:/qt3deditorlib/shaders/es2/custom-shader.frag"))));

    Qt3DRender::QShaderProgram *shader3 = new Qt3DRender::QShaderProgram();
    shader3->setVertexShaderCode(Qt3DRender::QShaderProgram::loadSource(QUrl(QStringLiteral("qrc:/qt3deditorlib/shaders/gl3/custom-shader.vert"))));
    shader3->setFragmentShaderCode(Qt3DRender::QShaderProgram::loadSource(QUrl(QStringLiteral("qrc:/qt3deditorlib/shaders/gl3/custom-shader.frag"))));

    Qt3DRender::QRenderPass *renderPass2 = new Qt3DRender::QRenderPass();
    renderPass2->setShaderProgram(shader2);

    Qt3DRender::QRenderPass *renderPass3 = new Qt3DRender::QRenderPass();
    renderPass3->setShaderProgram(shader3);

    techniqueES20->addRenderPass(renderPass2);
    techniqueGL31->addRenderPass(renderPass3);

    addTechnique(techniqueES20);
    addTechnique(techniqueGL31);
}

When I copy Phong shader default code inside my custom-shader.vert and custom-shader.frag files, it works exactly like Phong material, which shows the custom effect works fine.

---

Now that the above custom effect is implemented, its shaders can be modified by the methods described by @AdaRaider to produce any desired effect.