Why the rendering effect of samples/SampleOpenGL.py is flipped vertically.

[TurtleZhong]

Describe the bug
In samples/SampleOpenGL.py, the rendering effect of OpenGL is flipped vertically. here is the origin video in tests/test.mp4

and below is the render results of OpenGL

python3 SampleOpenGL.py -g 0 -e /PATH/VideoProcessingFramework/tests/test.mp4

To Reproduce
Steps to reproduce the behavior:

1. Before I use this command line, I need fix some bugs in SampleOpenGL.py, Line 346 and Line 347 need to be exchanged.
2. Go to the samples folder and run

python3 SampleOpenGL.py -g 0 -e /PATH/VideoProcessingFramework/tests/test.mp4

3. Then we can get the above result.
4. See error->the rendering result is flipped vertically.

Screenshots

vpf-opengl-2023-11-14_10.26.42.mp4

Desktop (please complete the following information):

• OS: [Linux, ubuntu 20.04]
• Nvidia driver version[535.129.03]
• CUDA Version [11.4]
• Python Version [3.8]
• Video Codec SDK Version [latest]

[wld22145]

Hi, I faced the same problem and here is my solution:

Add one line of code in the vertex shader of the compile_shader() function to vertically flip the uv coordinates:

vertex_shader_source = """
        #version 450 core
        out vec2 uv;
        void main( void)
        {
            // Declare a hard-coded array of positions
            const vec2 vertices[4] = vec2[4](vec2(-0.5,  0.5),
                                                 vec2( 0.5,  0.5),
                                                 vec2( 0.5, -0.5),
                                                 vec2(-0.5, -0.5));
            // Index into our array using gl_VertexID
            uv=vertices[gl_VertexID]+vec2(0.5,0.5);
            uv.y = 1.0 - uv.y; // Flip the texture vertically
            gl_Position = vec4(2*vertices[gl_VertexID],1.0,1.0);
            }
        """

Hopefully, this will also work for you.