The biggest problem to realize such effects is:
The emulated systems have a screen resolution of 320x240 (or so) so it's easy to resize this screen to a triple size.
There you can add easily new rendered dots, lines etc...
But the CPC uses at least 768x272 pixels.
There it's much harder to add additional pixels.
I am doing the same method as its used in DosBox.
I also use just 384x272 pixels, and stretch them to double (768x544)
So I can re-render each pixel to a new 2x2 dot.
{R}{G}
{B}{L}
This demonstrates a single CPC dot in MODE 1.
I split this pixel into R,G, B and also L (RGB as its by default)
Thus, a MODE 2 screen looks more weird of course.I also can't use any hardware accelerators (jogl, or similar) to improve the speed, so really just some tricky algorithms can do the effects I made in JavaCPC.
WinApe for example:
I am sure, the PAL effect is done with usage of Direct-X accelerated routines...