in qt3D can not use custom QMaterial on QEntity, why?

[BAIY]

i use a customs QMaterial move to an entity，but Show blank. when i use QPhongMaterial, it worked。this is my codes：
Qt3DCore：：QEntity* createTorusWithGradient（Qt3DCore：：QEntity* rootEntity）
{
Qt3DCore：：QEntity* torusEntity = new Qt3DCore：：QEntity（rootEntity）;
// 圆环网格
Qt3DExtras::QTorusMesh* torusMesh = new Qt3DExtras::QTorusMesh(torusEntity);
torusMesh->setRadius(5.0f);
torusMesh->setMinorRadius(1.0f);
torusMesh->setRings(100);
torusMesh->setSlices(20);
torusEntity->addComponent(torusMesh);

// 变换组件（可选）
Qt3DCore::QTransform* transform = new Qt3DCore::QTransform(torusEntity);
transform->setScale3D(QVector3D(1.5, 1.5, 01.5));
transform->setRotation(QQuaternion::fromAxisAndAngle(QVector3D(1, 0, 0), 60.0f));
torusEntity->addComponent(transform);

Qt3DExtras::QPhongMaterial* torusMaterial = new Qt3DExtras::QPhongMaterial();
torusMaterial->setDiffuse(QColor(QRgb(0x000000)));

QMaterial* material1 = new QMaterial(torusEntity);
QMaterial* material2 = new QMaterial(torusEntity);

// Create effect, technique, render pass and shader
QEffect* effect1 = new QEffect();
QTechnique* gl3Technique = new QTechnique();
QRenderPass* gl3Pass = new QRenderPass();
QShaderProgram* glShader = new QShaderProgram();

// Set the shader on the render pass
gl3Pass->setShaderProgram(glShader);

// Add the pass to the technique
gl3Technique->addRenderPass(gl3Pass);

// Set the targeted GL version for the technique
gl3Technique->graphicsApiFilter()->setApi(QGraphicsApiFilter::OpenGL);
gl3Technique->graphicsApiFilter()->setMajorVersion(3);
gl3Technique->graphicsApiFilter()->setMinorVersion(3);
gl3Technique->graphicsApiFilter()->setProfile(QGraphicsApiFilter::CoreProfile);

// Add the technique to the effect
effect1->addTechnique(gl3Technique);

// Set the effect on the materials
material1->setEffect(effect1);
material2->setEffect(effect1);

// Set different parameters on the materials
const QString parameterName = QStringLiteral("color");
material1->addParameter(new QParameter(parameterName, QColor::fromRgbF(0.0f, 1.0f, 0.0f, 1.0f)));
material2->addParameter(new QParameter(parameterName, QColor::fromRgbF(1.0f, 0.0f, 1.0f, 1.0f)));
// 添加组件到实体
torusEntity->addComponent(material1);

// 监听编译状态
QObject::connect(shaderProgram, &Qt3DRender::QShaderProgram::statusChanged,
[=](Qt3DRender::QShaderProgram::Status status) {
if (status == Qt3DRender::QShaderProgram::Error) {
qDebug() << "Shader Error:" << shaderProgram->log();
}
});

return torusEntity;
}
when i use custom QMaterial it can run successfully, but Show blank：
when i use QPhongMaterial, it worked ：
why ? any help please!

[BAIY]

by the way, qt5.14.2, windows11

[JoeCFD]

You can ask deepseek or grok first. 5.14.2 is old. Better to use the latest Qt and this module has been changed a lot.

QMaterial (custom material) setup is incomplete because you haven’t provided shader code to the QShaderProgram object (glShader). When you use QPhongMaterial, it works because it’s a pre-built material with its own shaders and properties handled internally by Qt 3D. For a custom material like QMaterial, you need to explicitly define and load the vertex and fragment shaders to tell the renderer how to draw the entity. Without shaders, the material has no instructions, and the entity renders blank.

[JoeCFD]

@JoeCFD Try the following

Qt3DCore::QEntity* createTorusWithGradient(Qt3DCore::QEntity* rootEntity)
{
    Qt3DCore::QEntity* torusEntity = new Qt3DCore::QEntity(rootEntity);

    // Torus mesh
    Qt3DExtras::QTorusMesh* torusMesh = new Qt3DExtras::QTorusMesh(torusEntity);
    torusMesh->setRadius(5.0f);
    torusMesh->setMinorRadius(1.0f);
    torusMesh->setRings(100);
    torusMesh->setSlices(20);
    torusEntity->addComponent(torusMesh);

    // Transform
    Qt3DCore::QTransform* transform = new Qt3DCore::QTransform(torusEntity);
    transform->setScale3D(QVector3D(1.5f, 1.5f, 1.5f)); // Fixed typo
    transform->setRotation(QQuaternion::fromAxisAndAngle(QVector3D(1, 0, 0), 60.0f));
    torusEntity->addComponent(transform);

    // Custom material setup
    Qt3DRender::QMaterial* material = new Qt3DRender::QMaterial(torusEntity);

    // Effect, technique, render pass, and shader
    Qt3DRender::QEffect* effect = new Qt3DRender::QEffect();
    Qt3DRender::QTechnique* gl3Technique = new Qt3DRender::QTechnique();
    Qt3DRender::QRenderPass* gl3Pass = new Qt3DRender::QRenderPass();
    Qt3DRender::QShaderProgram* glShader = new Qt3DRender::QShaderProgram();

    // Simple vertex shader
    const QByteArray vertexShaderCode = R"(
        #version 330 core
        in vec3 vertexPosition;
        in vec3 vertexNormal;
        uniform mat4 modelViewProjection;
        out vec3 fragPosition;
        void main() {
            fragPosition = vertexPosition;
            gl_Position = modelViewProjection * vec4(vertexPosition, 1.0);
        }
    )";

    // Simple fragment shader with color parameter
    const QByteArray fragmentShaderCode = R"(
        #version 330 core
        in vec3 fragPosition;
        out vec4 fragColor;
        uniform vec4 color;
        void main() {
            fragColor = color; // Use the color parameter directly
        }
    )";

    // Set shader code
    glShader->setVertexShaderCode(vertexShaderCode);
    glShader->setFragmentShaderCode(fragmentShaderCode);

    // Connect shader program to render pass
    gl3Pass->setShaderProgram(glShader);
    gl3Technique->addRenderPass(gl3Pass);

    // Set OpenGL 3.3 Core profile
    gl3Technique->graphicsApiFilter()->setApi(Qt3DRender::QGraphicsApiFilter::OpenGL);
    gl3Technique->graphicsApiFilter()->setMajorVersion(3);
    gl3Technique->graphicsApiFilter()->setMinorVersion(3);
    gl3Technique->graphicsApiFilter()->setProfile(Qt3DRender::QGraphicsApiFilter::CoreProfile);

    // Add technique to effect
    effect->addTechnique(gl3Technique);
    material->setEffect(effect);

    // Add a color parameter
    material->addParameter(new Qt3DRender::QParameter("color", QColor::fromRgbF(0.0f, 1.0f, 0.0f, 1.0f)));

    // Add material to entity
    torusEntity->addComponent(material);

    // Debug shader compilation errors
    QObject::connect(glShader, &Qt3DRender::QShaderProgram::statusChanged,
                     [=](Qt3DRender::QShaderProgram::Status status) {
                         if (status == Qt3DRender::QShaderProgram::Error) {
                             qDebug() << "Shader Error:" << glShader->log();
                         }
                     });

    return torusEntity;
}

[BAIY]

@JoeCFD
i have asked the deepseek, and it give me the similar code as yours, but it still shown blank

[BAIY]

@JoeCFD said in in qt3D can not use custom QMaterial on QEntity, why?:

// Custom material setup
Qt3DRender::QMaterial* material = new Qt3DRender::QMaterial(torusEntity);

// Effect, technique, render pass, and shader
Qt3DRender::QEffect* effect = new Qt3DRender::QEffect();
Qt3DRender::QTechnique* gl3Technique = new Qt3DRender::QTechnique();
Qt3DRender::QRenderPass* gl3Pass = new Qt3DRender::QRenderPass();
Qt3DRender::QShaderProgram* glShader = new Qt3DRender::QShaderProgram();

// Simple vertex shader
const QByteArray vertexShaderCode = R"(
    #version 330 core
    in vec3 vertexPosition;
    in vec3 vertexNormal;
    uniform mat4 modelViewProjection;
    out vec3 fragPosition;
    void main() {
        fragPosition = vertexPosition;
        gl_Position = modelViewProjection * vec4(vertexPosition, 1.0);
    }
)";

// Simple fragment shader with color parameter
const QByteArray fragmentShaderCode = R"(
    #version 330 core
    in vec3 fragPosition;
    out vec4 fragColor;
    uniform vec4 color;
    void main() {
        fragColor = color; // Use the color parameter directly
    }
)";

// Set shader code
glShader->setVertexShaderCode(vertexShaderCode);
glShader->setFragmentShaderCode(fragmentShaderCode);

// Connect shader program to render pass
gl3Pass->setShaderProgram(glShader);
gl3Technique->addRenderPass(gl3Pass);

// Set OpenGL 3.3 Core profile
gl3Technique->graphicsApiFilter()->setApi(Qt3DRender::QGraphicsApiFilter::OpenGL);
gl3Technique->graphicsApiFilter()->setMajorVersion(3);
gl3Technique->graphicsApiFilter()->setMinorVersion(3);
gl3Technique->graphicsApiFilter()->setProfile(Qt3DRender::QGraphicsApiFilter::CoreProfile);

// Add technique to effect
effect->addTechnique(gl3Technique);
material->setEffect(effect);

// Add a color parameter
material->addParameter(new Qt3DRender::QParameter("color", QColor::fromRgbF(0.0f, 1.0f, 0.0f, 1.0f)));

// Add material to entity
torusEntity->addComponent(material);

i used your code in qt6.5.3，it still shown blank

[BAIY]

@JoeCFD
and this is debug information:
17:52:58: Starting E:\C++\test_3d\build\Desktop_Qt_6_5_3_MinGW_64_bit-Debug\debug\test_3d.exe...
Qt3D.Renderer.RHI.Backend: Initializing RHI with OpenGL backend