[Interest] QSGMaterial & QSGMaterialShader on iOS

[Nuno Santos]

Hi,

I’m working on a small example on how to use QSGMaterial & QSGMaterialShader based on the following stackoverflow answer:

https://stackoverflow.com/questions/28125425/how-to-smooth-the-painting-of-a-custom-qml-element/28126383#28126383

The example works on desktop, but when it gets iOS, all I see is black.

Might this be related with the fact that Qt 5.15 is now using Metal to render graphics and the shaders are not compatible? The implementation of QSGSmoothColorMaterial is below. 

Any ideas?

Thanks!

Nuno


#ifndef SMOOTHCOLORMATERIAL_H
#define SMOOTHCOLORMATERIAL_H

#include <QSGMaterial>
#include <QSGMaterialShader>

class QSGSmoothColorMaterial : public QSGMaterial
{
public:
    QSGSmoothColorMaterial();
    int compare(const QSGMaterial *other) const;
protected:
    virtual QSGMaterialType *type() const;
    virtual QSGMaterialShader *createShader() const;
};

class QSGSmoothColorMaterialShader : public QSGMaterialShader
{
public:
    QSGSmoothColorMaterialShader();
    virtual void updateState(const RenderState &state, QSGMaterial *newEffect, QSGMaterial *oldEffect);
    virtual char const *const *attributeNames() const;
private:
    void initialize();
    int m_matrixLoc;
    int m_opacityLoc;
    int m_pixelSizeLoc;
};

#endif // SMOOTHCOLORMATERIAL_H


#include <smoothcolormaterial.h>

QSGSmoothColorMaterial::QSGSmoothColorMaterial()
{
    setFlag(RequiresFullMatrixExceptTranslate, true);
    setFlag(Blending, true);
}

int QSGSmoothColorMaterial::compare(const QSGMaterial *other) const
{
    Q_UNUSED(other)

    return 0;
}

QSGMaterialType *QSGSmoothColorMaterial::type() const
{
    static QSGMaterialType type;

    return &type;
}

QSGMaterialShader *QSGSmoothColorMaterial::createShader() const
{
    return new QSGSmoothColorMaterialShader();
}

QSGSmoothColorMaterialShader::QSGSmoothColorMaterialShader()
    : QSGMaterialShader()
{
    setShaderSourceFile(QOpenGLShader::Vertex, QStringLiteral(":/shaders/smoothcolor.vert"));
    setShaderSourceFile(QOpenGLShader::Fragment, QStringLiteral(":/shaders/smoothcolor.frag"));
}

void QSGSmoothColorMaterialShader::updateState(const QSGMaterialShader::RenderState &state, QSGMaterial *newEffect, QSGMaterial *oldEffect)
{
    Q_UNUSED(newEffect)

    if (state.isOpacityDirty())
        program()->setUniformValue(m_opacityLoc, state.opacity());

    if (state.isMatrixDirty())
        program()->setUniformValue(m_matrixLoc, state.combinedMatrix());

    if (oldEffect == 0) {
        // The viewport is constant, so set the pixel size uniform only once.
        QRect r = state.viewportRect();
        program()->setUniformValue(m_pixelSizeLoc, 2.0f / r.width(), 2.0f / r.height());
    }
}

const char * const *QSGSmoothColorMaterialShader::attributeNames() const
{
    static char const *const attributes[] = {
        "vertex",
        "vertexColor",
        "vertexOffset",
        0
    };

    return attributes;
}

void QSGSmoothColorMaterialShader::initialize()
{
    m_matrixLoc = program()->uniformLocation("matrix");
    m_opacityLoc = program()->uniformLocation("opacity");
    m_pixelSizeLoc = program()->uniformLocation("pixelSize");
}




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