[Interest] Qt/D3D integration through ANGLE PBuffer

Agocs Laszlo laszlo.agocs at theqtcompany.com
Fri Sep 25 10:16:22 CEST 2015


This should be set before constructing the QGuiApplication.

    EGLSurface pbuffer = eglCreatePbufferSurface(m_eglDisplay, m_eglConfig, attribs);

This should be eglCreatePbufferSurface(*m_eglDisplay, *m_eglConfig, attribs).

Note that you may be running into the problem of the implementation offering different configs for different purpose and rejecting the non-matching ones.
But try fixing the pbuffer creation first and see if that helps.


From: Thomas Sevaldrud <thomas at silentwings.no>
Sent: Friday, September 25, 2015 9:56 AM
To: Agocs Laszlo
Cc: Andrew Knight; Interest at qt-project.org
Subject: Re: [Interest] Qt/D3D integration through ANGLE PBuffer

Now I've tried a lot of other things, but I'm still not there...

I've tried using eglChooseConfig on the eglDisplay I got from the QPlatformNativeInterface (with different variations of the attribList below)

    const EGLint attribList[] =



        EGL_RED_SIZE, 8,

        EGL_GREEN_SIZE, 8,

        EGL_BLUE_SIZE, 8,

        EGL_ALPHA_SIZE, 8,

        EGL_DEPTH_SIZE, 16,

        EGL_STENCIL_SIZE, 8,



    EGLint iConfigs;

    EGLConfig eglConfig;

    eglChooseConfig(eglDisplay, attribList,

                     &eglConfig, 1, &iConfigs);

This returns no usable configs (iConfigs == 0).

I've also tried going all EGL:

    EGLDisplay eglDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY);
    eglInitialize(eglDisplay, NULL, NULL);

And used eglChooseConfig like above. This time I got the PBuffer and share handle, so this looks most promising. Now I could use an eglContext and QOpenGLContext->setNativeHandle() to get a context for use with Quick. However, when I try to create an eglContext I get EGL_BAD_CONFIG again...

    EGLContext eglContext = eglCreateContext(eglDisplay, eglConfig, NULL, NULL);

There must be something fundamental here that I have gotten wrong with regards to context and surface...

- Thomas

On Fri, Sep 25, 2015 at 12:03 AM, Thomas Sevaldrud <thomas at silentwings.no<mailto:thomas at silentwings.no>> wrote:
Ok, I've experimented a bit here now, but I am struggling to get a valid PBuffer (eglCreatePBufferSurface returns 0).

I have tried creating a new QOpenGLContext and pull the eglDisplay and eglConfig from that through the nativeResourceForContext.

If I have only the Context without any surface to begin with, I get EGL_NOT_INITIALIZED.

If I add an QOffscreenSurface and make the context current on this, I get EGL_BAD_CONFIG.

This is the relevant code, any idea what I'm doing wrong here?


    QSurfaceFormat format;


    m_glContext = new QOpenGLContext;



    QOffscreenSurface* surf = new QOffscreenSurface();




    QPlatformNativeInterface *nativeInterface = QGuiApplication::platformNativeInterface();

    EGLDisplay* m_eglDisplay = static_cast<EGLDisplay*>(nativeInterface->nativeResourceForContext("eglDisplay", m_glContext));

    EGLConfig* m_eglConfig = static_cast<EGLConfig*>(nativeInterface->nativeResourceForContext("eglConfig", m_glContext));

    EGLint attribs[] = {

        EGL_WIDTH, 1024,

        EGL_HEIGHT, 1024,





    EGLSurface pbuffer = eglCreatePbufferSurface(m_eglDisplay, m_eglConfig, attribs);

    int err = eglGetError(); // Returns EGL_BAD_CONFIG

On Thu, Sep 24, 2015 at 7:05 PM, Agocs Laszlo <laszlo.agocs at theqtcompany.com<mailto:laszlo.agocs at theqtcompany.com>> wrote:
Right. You can either use eglChooseConfig or pull it with nativeResourceForContext from the context you will use for the Qt Quick rendering.  The latter is probably the way to go since you also need the display, and eglGetCurrentDisplay() is not helpful at that stage due to the lack of a current context.


From: Thomas Sevaldrud [mailto:thomas at silentwings.no<mailto:thomas at silentwings.no>]
Sent: 24. september 2015 17:11
To: Agocs Laszlo <laszlo.agocs at theqtcompany.com<mailto:laszlo.agocs at theqtcompany.com>>
Cc: Andrew Knight <andrew.knight at intopalo.com<mailto:andrew.knight at intopalo.com>>; Interest at qt-project.org<mailto:Interest at qt-project.org>

Subject: Re: [Interest] Qt/D3D integration through ANGLE PBuffer

Ok, but I see that they use the existing context to get the eglDisplay and eglConfig parameters that are needed for the createPBufferSurface call:

    QPlatformNativeInterface *nativeInterface = QGuiApplication::platformNativeInterface();

    m_eglDisplay = static_cast<EGLDisplay*>(

                nativeInterface->nativeResourceForContext("eglDisplay", currentContext));

    m_eglConfig = static_cast<EGLConfig*>(

                nativeInterface->nativeResourceForContext("eglConfig", currentContext));

I suppose I can use eglGetDisplay and eglChooseConfig to get these, but how do I create a QOpenGLContext that matches the eglConfig? I need this for the QQuickRenderControl.

- Thomas

On Thu, Sep 24, 2015 at 5:02 PM, Agocs Laszlo <laszlo.agocs at theqtcompany.com<mailto:laszlo.agocs at theqtcompany.com>> wrote:
That’s most likely used only for the texture handle that gets generated in that function. Neither that nor the EGL_TEXTURE_* parameters are relevant in your case.


From: interest-bounces+laszlo.agocs=theqtcompany.com at qt-project.org<mailto:theqtcompany.com at qt-project.org> [mailto:interest-bounces+laszlo.agocs<mailto:interest-bounces%2Blaszlo.agocs>=theqtcompany.com at qt-project.org<mailto:theqtcompany.com at qt-project.org>] On Behalf Of Thomas Sevaldrud
Sent: 24. september 2015 16:46
To: Andrew Knight <andrew.knight at intopalo.com<mailto:andrew.knight at intopalo.com>>
Cc: Interest at qt-project.org<mailto:Interest at qt-project.org>
Subject: Re: [Interest] Qt/D3D integration through ANGLE PBuffer

Ah, excellent, so I just set up a QQuickWindow with the RenderControl as parent, right?

Just one more question:

In the QtMultimedia D3D9 example they set up a QOpenGLContext with an invisble QWindow as current context before creating the EGL Pbuffer. I suppose this is in order to get the correct EGL Config and surface parameters? I suppose I could just as well use a QOffscreenSurface as the hidden QWindow? Is this the best way to do it? It just seems a little backwards to create an offscreen surface first in order to create the offscreen surface I actually want... Or maybe I'm not thinking straight here :-)

- Thomas

On Thu, Sep 24, 2015 at 4:30 PM, Andrew Knight <andrew.knight at intopalo.com<mailto:andrew.knight at intopalo.com>> wrote:

On 09/24/2015 05:15 PM, Thomas Sevaldrud wrote:
This is great, thanks for very useful info!

I'm not sure I understood Andew's part about rendering the Quick Scene graph, or I may have been a bit unclear when describing the problem. Basically I want to render a Qt Quick scene graph and some custom OpenGL graphics into a Direct3D control (D3DImage in WPF). What Andew suggests would be the other way around I think? I.e use a D3D texture in the scene graph? Or did I misunderstand?

Yes, that's what I was referring to. Sorry for the misunderstanding.
As Laszlo suggests I'll try using QQuickRenderControl to render my scene into the PBuffer/D3D texture, but I must admit I am a bit confused as to how this works too. For instance I'm not sure I understand how to set up the QML Engine so that it is associated with the QQuickRenderControl. In the QuickRenderControl example from Qt 5.5 it appears that they set up the QML Engine in a QQuickWindow with an FBO as render target. In my case I need the EGL PBuffer as render target. How would I go about doing that?

You don't need the QOpenGLFramebufferObject in this case. As Laszlo said, simply bind the pbuffer and it will become the current render target. The scene graph will render to the pbuffer and you can use that in your D3D scene as a normal texture.
- Thomas

On Thu, Sep 24, 2015 at 2:48 PM, Andrew Knight <andrew.knight at intopalo.com<mailto:andrew.knight at intopalo.com> <mailto:andrew.knight at intopalo.com<mailto:andrew.knight at intopalo.com>>> wrote:

    Hi Thomas,

    On 09/24/2015 03:11 PM, Thomas Sevaldrud wrote:


        I have earlier made an implementation of Qt/D3D integration by
        hacking into the ANGLE D3D SwapChain and extracting the
        D3DSurface directly there.

        However, this is a bit flakey, and I have had to change this
        code several times when new versions of Qt and ANGLE are released.

        So, now I want to do this the supported way through the
        EGL_ANGLE_surface_d3d_texture_2d_share_handle extension. If I
        understand this correctly I can set up a PBuffer-based render
        target which I can query for a D3D texture sharing handle
        using the eglQuerySurfacePointerANGLE extension.

    Yes, this is possible.

        Now, before I start coding, I wonder if anyone has an example
        of using this extension for rendering to a D3D Texture?
        Someone mentioned on the list earlier that there should be an
        example of this in QtMultimedia, but I haven't been able to
        find it.

    The two places this extension is used are at:

    This one creates a shared texture using D3D and shares it with
    ANGLE. This texture is updated when a video player or camera
    queues a frame. It is bound to the pipeline with a QOpenGLTexture
    object and eglBindTexImage().


    This one first creates a pbuffer using EGL, gets the shared
    texture handle from it, and then opens up the texture in D3D.

    Both cases are therefore covered, as well as both major D3D versions.

        Also, for the PBuffer implementation, should I create a
        PBuffer directly through EGL, or can I use QOffsceenSurface?
        If I understand correctly, QOffscreenSurface will be
        implemented with a PBuffer on Windows?
        To complicate matters even more I want to include a Quick
        scene graph in this as well, but I suppose I can use the new
        QQuickRenderControl class for this when I have the PBuffer
        render target sorted out?

    I would just render to your D3D texture (by creating it via one of
    the ways described above) and use it in the scene graph by binding
    its content to the currently bound QOpenGLTexture object with
    eglBindTexImage(). You can create a QSGTexture from a
    QOpenGLTexture by passing the texture id to

        Best regards,

        Interest mailing list
        Interest at qt-project.org<mailto:Interest at qt-project.org> <mailto:Interest at qt-project.org<mailto:Interest at qt-project.org>>

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