BGFX & Qt integration (multiple windows/context)

[vloppin]

Hello,

I'm working on BGFX interoperability with Qt. Especially QOpenGLWidget.
In our project, we need to handle several windows/widgets.
So, we let (as we don't have choice) Qt provide OpenGL contexts.

First BGFX is initialized by providing a Qt Context (through init() function)
In the widget code, framebuffers are created in initializeGL() & resizeGL() Qt methods to ensure the correct context is set up.

With this setup, we can properly render our scene from several windows / widgets, but since we have to change contexts for every window, we need to disable VAOs and query timers in BGFX to avoid crashes or errors (as container and query objects cannot be shared between contexts)
https://www.khronos.org/opengl/wiki/OpenGL_Object#Object_Sharing

So my question is how to use or modify BGFX properly to allow full function usage ?

I see that BGFX doesn't allow to change context after init, so it seems difficult to associate container object to a context.

Thanks !

To illustrate:

void BGFX_QOpenGLWidget::initializeGL()
{
	QOpenGLContext * lCxt = context();
	QWGLNativeContext native = lCxt->nativeHandle().value<QWGLNativeContext>();
    void * lNativeCxt = (void*)native.context();
	
	static bool sInit = false;
    if (!sInit)
    {
        bgfx::Init lInitBGFX;
        lInitBGFX.type = bgfx::RendererType::OpenGL;
        lInitBGFX.platformData.context = lNativeCxt;

        bgfx::renderFrame(); // single thread

        bgfx::init(lInitBGFX);

        sInit = true;
    }
	
    const uint64_t lFlags = 0 | BGFX_TEXTURE_NONE | BGFX_SAMPLER_NONE | BGFX_TEXTURE_RT /*| BGFX_TEXTURE_RT_MSAA_X16 */;
    backBufferTexture = bgfx::createTexture2D(width(), height(), false, 1, bgfx::TextureFormat::RGBA8, lFlags);
    backBufferDepthTexture = bgfx::createTexture2D(width(), height(), false, 1, bgfx::TextureFormat::D24S8, lFlags);

    bgfx::Attachment attachments[2];
    attachments[0].init(backBufferTexture, bgfx::Access::Write, 0, 1, 0, BGFX_RESOLVE_AUTO_GEN_MIPS);
    attachments[1].init(backBufferDepthTexture, bgfx::Access::Write, 0, 1, 0, BGFX_RESOLVE_NONE);

    fbo = bgfx::createFrameBuffer(sizeof(attachments) / sizeof(attachments[0]), attachments);
    bgfx::frame();  // force creation
}


void BGFX_QOpenGLWidget::resizeGL(int w, int h)
{
    if (bgfx::isValid(fbo))
    {
        bgfx::destroy(fbo);
    }

    if (bgfx::isValid(backBufferTexture))
    {
        bgfx::destroy(backBufferTexture);
    }

    if (bgfx::isValid(backBufferDepthTexture))
    {
        bgfx::destroy(backBufferDepthTexture);
    }

    const uint64_t lFlags = 0 | BGFX_TEXTURE_NONE | BGFX_SAMPLER_NONE | BGFX_TEXTURE_RT /*| BGFX_TEXTURE_RT_MSAA_X16 */;
    backBufferTexture = bgfx::createTexture2D(width(), height(), false, 1, bgfx::TextureFormat::RGBA8, lFlags);
    backBufferDepthTexture = bgfx::createTexture2D(width(), height(), false, 1, bgfx::TextureFormat::D24S8, lFlags);

    bgfx::Attachment attachments[2];
    attachments[0].init(backBufferTexture, bgfx::Access::Write, 0, 1, 0, BGFX_RESOLVE_AUTO_GEN_MIPS);
    attachments[1].init(backBufferDepthTexture, bgfx::Access::Write, 0, 1, 0, BGFX_RESOLVE_NONE);

    fbo = bgfx::createFrameBuffer(sizeof(attachments) / sizeof(attachments[0]), attachments);
    bgfx::frame();  // force creation

    mIsValidFBO = false;
}


void BGFX_QOpenGLWidget::paintGL()
{
    GLuint lQtFBO = defaultFramebufferObject();
    if (lQtFBO == 0)
        return;

    uint16_t lWidth = width(), lHeight = height();

    uint32_t lClearColor = 0x000000FF;
    if (idx == 0)
    {
        lClearColor = 0xFF0000FF;
    }
    else
    {
        lClearColor = 0x00FF00ff;
    }
    // Set view 0 clear state.
    bgfx::setDebug(BGFX_DEBUG_STATS); //BGFX_DEBUG_TEXT 
    bgfx::setViewFrameBuffer(0, fbo);
    bgfx::setViewClear(0, BGFX_CLEAR_COLOR | BGFX_CLEAR_DEPTH, lClearColor.ucolor, 1.0f, 0);
    bgfx::setViewRect(0, 0, 0, lWidth, lHeight);
    bgfx::touch(0);
    bgfx::frame();

    // Blit FBO throught Qt opengl functions QOpenGLContext::currentContext()->extraFunctions();
	// ...
}