Blackmagic Forum

What's the best way to flip (vertically, for example) my video source?

Specifically, in the CapturePreviewCSharp project, I'd like to flip the video feed that's rendered to the PreviewWindow. It wasn't immediately obvious where I can apply this transform. I tried applying the transform to the m_d3DDevice using the below, but it never made an impact:

Inside PreviewWindow.cs: Render()

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m_d3DDevice.SetTransform(Direct3D.TransformType.Projection, Matrix.RotationX(180));

or

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m_d3DDevice.Transform.World.RotateX(180);

Neither throw an error, but neither flip the image either.

I also looked at flipping the incoming IDeckLinkVideoFrame inside IDeckLinkScreenPreviewCallback.DrawFrame, but it wasn't clear how to flip a video frame.

Any guidance is greatly appreciated!

Hi Scott,

The IDeckLinkDX9ScreenPreviewHelper has it's own transform function implemented, so it will override attempt to call SetTransform externally. However, it is possible to rotate the preview by 180 degrees (in case camera is mounted up-side-down), by swapping left/right and top/bottom coordinates of the viewport rectangle.

For flipping, the solution will be to either:
1) Iterate through frame lines and manually swap lines (CPU intensive).
2) Implement own DirectX or OpenGL helper to perform own custom transforms.

Regards
Cameron

Thanks very much! For anyone facing the same issue, here's the code that worked for me:

in PreviewWindow.cs:

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public bool Flip;

void Render()
        {


            try
            {
                m_d3DDevice.BeginScene();

                tagRECT rect;
                if(Flip)
                {
                    rect.top = m_d3DDevice.Viewport.Y;
                    rect.left = m_d3DDevice.Viewport.X;
                    rect.bottom = m_d3DDevice.Viewport.Y + m_d3DDevice.Viewport.Height;
                    rect.right = m_d3DDevice.Viewport.X + m_d3DDevice.Viewport.Width;
                }
                else
                {
                    rect.bottom = m_d3DDevice.Viewport.Y;
                    rect.right = m_d3DDevice.Viewport.X;
                    rect.top = m_d3DDevice.Viewport.Y + m_d3DDevice.Viewport.Height;
                    rect.left = m_d3DDevice.Viewport.X + m_d3DDevice.Viewport.Width;
                }
               
....//the rest of the method