Overscan setting

[pvmm]

An overscan setting would allow OpenMSX to cut out pixels on both edges of the screen. On a CRT TV, a few pixels on each side of the screen were usually invisible to the player. Because of this, some games often have glitches on the edges of the screen – this is normal and caused by the game itself. Setting a value of 8 or so on each side of the screen would hide most glitches. Some emulators like Mesen use this trick to improve emulation of NES games like a CRT TV would.

[mrparn]

This would be great to approximate the experience of using a real MSX on a real CRT TV. Since OpenMSX apparently renders its graphics on a 320x240 virtual window and the maximum horizontal_stretch is 256, currently it would be impossible to simulate the horizontal overscan without overstretching the pixels and ruining the pixel aspect ratio. It would be nice if there was an option to render the screen on a picture aspect ratio of 4:3 but with a smaller target resolution, like 240x206 pixels (I calculated this considering an 8:7 pixel aspect ratio), so 14 pixels of vertical underscan in 192 pixels vertical resolution modes and 6 pixels of vertical overscan in 212 pixels vertical resolution modes.