CathodeRetro::ScanlineType

            enum class ScanlineType
            {
              Odd,
              Even,

              Progressive = Odd,
            }

The type of mask to use for the CRT emulation.

To emulate an interlaced mode, the caller of CathodeRetro::Render should alternate between Odd and Even every other scanline.

For progressive modes, the caller should keep the same value. For this purpose, a Progressive entry is also there - it's just an alias for Odd but it can make it clearer at the call site that it is intentionally not alternating for interlacing purposes.

Index

Values

Odd

This frame is an "odd" frame, which means the input image contains the (1-based) odd scanlines of a frame (that is, the first scanline of the input image is the first scanline of the output, second input scanline is third output scanline, third input is fifth output, etc).

Even

This frame is an "even" frame, which means the input image contains the (1-based) even scanlines of a frame (that is, the first scanline of the input image is the second scanline of the output, second input scanline is fourth output scanline, third input is sixth output, etc).

Progressive

This is just an alias for Odd, to make it clearer at call sites when using a progressive (non-interlaced) output.

Rather than alternate every other frame between Even and Odd, non-interlaced drawing should keep a consistent one - and it seems that most consoles that ran interlaced at 240p used odd rather than even scanlines.