[Interest] Creating Custom QSGTexture

[Benjamin B (BBenj)]

Hi
I also had some troubles figuring that out. Might not be the best way but it works:
I derive QSGTexture and create/update a QRhiTexture in commitTextureOperations.
I update the texture data and call commitTextureOperations in my QSGMaterial instance (in QSGMaterial::updateTextures, called from QSGMaterialShader::updateSampledImage).

class RgbTexture : public QSGTexture ...
std::unique_ptr<QRhiTexture> m_rhiTexture;
void RgbTexture::commitTextureOperations(QRhi* rhi, QRhiResourceUpdateBatch* resourceUpdates) override
    {
        if ( ! m_data || m_size <= 0) // raw RGBA data
            return;

        if ( ! m_rhiTexture) {
            m_rhiTexture.reset(rhi->newTexture(QRhiTexture::RGBA8, textureSize(), 1, {}) );
            bool const created = m_rhiTexture->create();
            Q_ASSERT("Failed to create texture" && created);
        }

        QRhiTextureSubresourceUploadDescription subresDesc(m_data, m_size);
        subresDesc.setSourceSize(textureSize());
        subresDesc.setDestinationTopLeft(QPoint(0,0));
        QRhiTextureUploadEntry entry(0,0, subresDesc);
        QRhiTextureUploadDescription desc(entry);

        resourceUpdates->uploadTexture(m_rhiTexture.get(), desc);
    }

void RgbMaterial::updateTextures(QRhi* rhi, QRhiResourceUpdateBatch* resourceUpdates)
{
    //std::unique_ptr<RgbTexture> m_texture;
    m_texture->setData(...);
    m_texture->commitTextureOperations(rhi, resourceUpdates);
}

-Benjamin

> Le 11 sept. 2025 à 15:11, Mike Krus via Interest <interest at qt-project.org> a écrit :
> 
> Thanks, think I may have explained it wrong though.
> 
> I don’t have a native texture to use. I have some data I want to use in a shader via a texture.
> I need to create a QSGTexture type object but there doesn’t seem to be any existing API to
> do that beyond createTextureFromImage().
> 
> I presume I’d need to derive and use RHI itself to create an RHI texture but was hoping to 
> find an example which that in the context of the scene graph, especially when it comes to
> the creation of the RHI texture and the uploading/updating of the data.
> 
> Mike
> 
> 
>> On 11 Sep 2025, at 13:44, Allan Sandfeld Jensen <kde at carewolf.com> wrote:
>> 
>> On Thursday, 11 September 2025 12:28:52 Central European Summer Time Mike Krus 
>> via Interest wrote:
>>> Hi
>>> 
>>> I’m porting a project from Qt5/OpenGL SceneGraph code to new Qt6/RHI
>>> 
>>> I have a custom item with a scene graph which creates a custom shader and a
>>> custom texture from some application data (not an image).
>>> 
>>> In Qt5, I have Texture class derived from QSGTexture which create the
>>> underlying OpenGL buffers for the textures and handles to data, binding,
>>> etc.
>>> 
>>> In Qt6, the same classes exists but the custom Texture class needs to create
>>> RHI based texture objects, with the appropriate format, copy the data into
>>> it, etc. But I have not been able to find some relevant code to do that.
>>> All the code I found in QtDeclarative itself either use
>>> QQuickWindow::createTextureFromImage() or a QSGTextureProvider.
>>> 
>>> There some example which create custom RHI textures, but not in the context
>>> of the scene graph (using RHI directly in QQuickRHIItem for example).
>>> 
>>> Any ideas how this can be done?
>>> 
>> The way we do in Qt WebEngine now, is using QNativeInterface. For instance 
>> from OpenGL texture
>> QNativeInterface::QSGOpenGLTexture::fromNative(texture, win, size, texOpts);
>> or from Metal texture
>>  QNativeInterface::QSGMetalTexture::fromNative(texture, win, size, texOpts);
>> or from Vulkan texture
>> QNativeInterface::QSGVulkanTexture::fromNative(importedImage,
>> importedImageCreateInfo.initialLayout, win, size, texOpts);
>> 
>> Best regards
>> Allan
> 
> 
> —
> Mike Krus | mike.krus at kdab.com <mailto:mike.krus at kdab.com> | Senior Software Engineer & Teamlead
> KDAB (UK) Ltd., a KDAB Group company
> Tel: UK Office +44 1625 809908   Mobile +44 7833 491941
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