casio/pv1000.cpp: Three tiny changes

[lidnariq]

• ioFF has a toggle that just draws border color instead of tiles, so that the CPU runs faster.
• The pixel clock is slow, so the pixel aspect is noticeably wide - about 4:3
• ioFF supports drawing tile data from all eight 8KiB windows out of the 64KiB address space; add support for the easy bottom four

[rb6502]

I don't think the aspect part of this can be right. The real PV-1000 was used on 4:3 NTSC TVs, so the final output image should be 4:3 and you shouldn't care about the individual pixel shape. We don't for extreme cases like 640x240 on the PlayStation and it works out fine.

[lidnariq]

What's the desired behavior for things that are extremely overscanned?

The PV-1000 uses a pixel clock that is NTSC x 5/4, 4.47MHz. Per rec.701 for digitizing SDTV, that works out to an exact PAR of 48:35. The PV-1000 generates a raw image that is 224 pixels by 244 scanlines, which when scaled by that 48:35 works out to roughly 307 x 244 square pixels. The TV then crops that down to somewhere around 290 x 215 square pixels: video of real hardware show the left-most and right-most tiles in the tilemap are often partially lost to overscan.

For comparison, a real NTSC NES generates a 284 x 242 image, much of which is also border. Early emulators pretended it's 256x240, but real TVs show somewhere around 250 x 215 ish.

[cuavas]

I think all you can do is set the default position/scaling so that it will be cropped the way it would be on a TV – see screen_device::set_default_position.

[lidnariq]

is this now ok?