Picodrive: cropping overscan crops too much!

mrmatteastwood · 3 March 2019 16:21

Hey guys, when I disable the “Show Overscan” option in PicoDrive, a bit of the image gets lost at the bottom.

Here’s Turrican with the “Show Overscan” option turned on:

Here it is, turned off (i.e., overscan gets cropped):

Is there a way to crop the overscan, but not part of the screen?

hunterk · 3 March 2019 16:40

Is that a consistent thing? That is, is it always the same overscan with every game?

Overscan varied from TV to TV, so programmers were aware that anywhere from 5% to 15% of their image was going to be lost to it and to avoid placing important information where it might get partially chopped off.

mrmatteastwood · 3 March 2019 19:25

Hey Hunterk, thanks for your quick response.

The other games I’ve tried are QuackShot (World), Sonic & Knuckles (World), ToeJam & Earl (World), Zero Tolerance (USA, Europe), Golden Axe (World), Golden Axe II (World), Golden Axe III (Japan) and Mickey Mouse - World of Illusion (Europe).

Seems like they’re all equally affected.

EDIT: The good news is that none of these have junk data in the overscan, as far as I can see.

hunterk · 3 March 2019 20:09

Looks like this is pertinent code:

github.com

libretro/picodrive/blob/master/platform/libretro/libretro.c#L533


PicoDrawSetOutBuf(vout_buf, vout_width);


if (ps2) {
   ps2->clearTexture = true;
}
#else
vout_width = is_32cols ? VOUT_32BIT_WIDTH : VOUT_MAX_WIDTH;
memset(vout_buf, 0, VOUT_MAX_WIDTH * VOUT_MAX_HEIGHT * 2);  
PicoDrawSetOutBuf(vout_buf, vout_width * 2);


   if (show_overscan == true) line_count += 16;
if (show_overscan == true) start_line -= 8;


vout_height = line_count;
vout_offset = vout_width * start_line;
#endif


// Update the geometry
retro_get_system_av_info(&av_info);
environ_cb(RETRO_ENVIRONMENT_SET_GEOMETRY, &av_info);
}

I suppose this could be turned into an option instead of a hardcoded value.

wertz · 4 March 2019 00:38

overscan has always been -8px, in some rare cases even 16 (aka sm3 on NES) so the cutoff should be expected (havent look at code and what it should look like with overscans shown)

mrmatteastwood · 6 March 2019 13:07

Hello, gentlemen! Yeah, it would be great if this could become customizable in the future, since it seems Picodrive at least crops parts off the game graphics consistently (based on the set of data I have).