Force Alpha value for an element.

  • Hello,
    I am using custom render control where I am drawing some "raw" OpenGL elements and then the QML Scene into FBO to be ultimately painted over my OpenGL components.
    I wanted to have some Rectangle elements in the QML tree with the color set to RGBA=(255,255,255,0) which would set the alpha value of the FBO area alpha channel to zero.
    This would allow me to combine the QML Scene with the underlying OpenGL elements using alpha blending, - the rectangles with alpha value=0 acting as "transparency windows" showing the OpenGL elements underneath.
    Unfortunately I am not able to influence the alpha channel of the FBO anyhow. No matter which color and opacity I set for the rectangle element, the alpha channel of the FBO where the scene is rendered to is always (255 / 1.0) that is fully opaque.
    Is there a way to force the alpha value to zero for particular elements in QML scene?

    Any hints appreciated.

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