QRhi rendering question

divide

Hi, I managed to have a perfectly working rendering code with QRhi (offline rendering), fully functional with Metal, DX11 and OpenGL, but unfortunately I can't use it in debug mode because it turns out I'm doing something forbidden, a cb->resourceUpdate() during a cb->beginPass() and cb->endPass() in the SpectralChannel::render() method below.

Do you know how I can fix my code to move or remove that unwanted resourceUpdate() and still get all the proper resources refresh ? Here's how it goes (simplified):

void SpectralChannel::paintEvent(QPaintEvent *event)
{
    QRhiCommandBuffer *cb;
    m_rhi->beginOffscreenFrame(&cb);

    render(cb);

    m_rhi->endOffscreenFrame();

    QImage image(reinterpret_cast<const uchar *>(readbackResult.data.constData()),
                 readbackResult.pixelSize.width(),
                 readbackResult.pixelSize.height(),
                 QImage::Format_RGBA8888_Premultiplied);
    if (m_rhi->isYUpInFramebuffer())
        image = image.mirrored();
    image.setDevicePixelRatio(devicePixelRatio());

    QPainter painter(this);
    painter.drawImage(0,0,image);
}
QRhiResourceUpdateBatch* SpectralChannel::updateFrameBuffer()
{
    QRhiResourceUpdateBatch* updateBatch = resourceUpdateBatch(true);
    updateBatch->readBackTexture({ texTarget.get() }, &readbackResult);
    return updateBatch;
}

QRhiResourceUpdateBatch* SpectralChannel::resourceUpdateBatch(bool renewBatch)
{
    if(!m_resourceUpdateBatch)
        m_resourceUpdateBatch=rhi()->nextResourceUpdateBatch();

    if(renewBatch)
    {
        QRhiResourceUpdateBatch* currentBatch=m_resourceUpdateBatch;
        m_resourceUpdateBatch=rhi()->nextResourceUpdateBatch();
        return currentBatch;
    } else
        return m_resourceUpdateBatch;
}
void SpectralChannel::render(QRhiCommandBuffer *cb)
{
    updateTextures(); //bunch of textures update/creation (several textures are destroyed and rebuilt due to changing sizes)

    resourceUpdateBatch()->updateDynamicBuffer(uniformCommonBuf.get(),0,sizeof(float)*4*4,scaledDisplayMatrix.constData());

    //start drawing commands
    cb->beginPass(renderTarget(), Qt::black, { 1.0f, 0 }, resourceUpdateBatch(true));
    cb->setViewport({ 0, 0, float(width()*devicePixelRatio()), float(height()*devicePixelRatio()) });

    for(QHash<LayerPtr, SpectralTextureMeta2>::iterator tex = textureList.begin(); tex != textureList.end(); tex++)
    {
        cb->setGraphicsPipeline(tex.value().spectralPipeline.get());

        resourceUpdateBatch()->updateDynamicBuffer(...);
        ...
        resourceUpdateBatch()->updateDynamicBuffer(...);

        cb->resourceUpdate(resourceUpdateBatch(true)); //this resourceUpdate is forbidden in debug mode !

        cb->setShaderResources();

        const QRhiCommandBuffer::VertexInput vbufBinding(...);
        cb->setVertexInput(0, 1, &vbufBinding);
        cb->draw(4);
    }

    cb->endPass(updateFrameBuffer());
}

divide

FWIW, the fixed code (thanks to github copilot)

void SpectralChannel::render(QRhiCommandBuffer *cb)
{
    //update resources first
    updateTextures();

    Area scaledDisplayArea=convert.toScaled(displayArea);
    scaledDisplayArea.moveLeft(0.);
    QMatrix4x4 scaledDisplayMatrix=scaledDisplayArea.toMatrix();

    resourceUpdateBatch()->updateDynamicBuffer(...);

    for(QHash<LayerPtr, SpectralTextureMeta2>::iterator tex = textureList.begin(); tex != textureList.end(); tex++)
    {
            resourceUpdateBatch()->updateDynamicBuffer(...);
...
    }

    cb->resourceUpdate(resourceUpdateBatch(true));

    //start drawing commands
    cb->beginPass(renderTarget(), Qt::black, { 1.0f, 0 }, resourceUpdateBatch(true));
    cb->setViewport({ 0, 0, float(width()*devicePixelRatio()), float(height()*devicePixelRatio()) });

    for(QHash<LayerPtr, SpectralTextureMeta2>::iterator tex = textureList.begin(); tex != textureList.end(); tex++)
    {
            cb->setGraphicsPipeline(tex.value().spectralPipeline.get());
            const QRhiCommandBuffer::VertexInput vbufBinding(tex.value().vertexBuf.get(), 0);
            cb->setVertexInput(0, 1, &vbufBinding);
            cb->setShaderResources();
            cb->draw(4);
    }

    cb->endPass(updateFrameBuffer());
}