MSX 2's higher resolution modes and 15-Khz emulation

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By NYYRIKKI

Enlighted (5745)

NYYRIKKI's picture

14-08-2014, 22:56

@Milsancho Ok, It seems that I didn't take your quest of getting this right in quite enough serious level. I apologize that. I can also see that there are pretty strong feelings involved. I also know that propabbly none of us is expert with your case, but we know MSX pretty well, so let's try to be professional and help each other.

Because I've fighted with many other display device problems, I suggest that you try out my monitor test program. (for MSX2 and up) Although the examples don't cover your case exactly I think the problems may be pretty similar. Please read the attached documentation. You can download the test software from here.

First how ever I must say that unfortunately you can't get it absolutely right with any of the emulators since AFAIK there are none that for example would use different screen mode for "interlaced" and "progressive" screen modes. With Interlaced mode I mean that the number of lines is doubled by displaying every odd frame 1/2 lines lower position.

How ever let's look at the "not interlaced" modes as they are the most interesting for gaming purposes:
As I respect Grauw as an expert in this issue I trust that his calculations of 284.75 x 262/313 are correct. In the 60Hz NTSC mode (262 lines) the pixels are at least quite a close to square. In 50Hz PAL (313 lines) the pixels are quite a flat. To get the MSX screen 0(width 80), 6 & 7 display correctly you need to double the vertical resolution to 569,5 but as you can't output half pixels from ATI I think you need to scale it to 1139x262/313

The problem with emulators is anyway that I'm afraid they dont't try to keep the 2^x pixel width but they try to scale picture to the given resolution. This means that they will anyway show scaling in pixels and wrong amount of border. I very much hope that I'm wrong, but I don't know... The 50/60Hz sync may be also problematic, but I don't go there at this point because I don't know that ATI driver well enough.

By Grauw

Ascended (9817)

Grauw's picture

14-08-2014, 23:04

Oh, I’m really not an expert on this electronics cathode ray tube driving stuff. It could very well be that I’m overlooking some details Smile. There are a lot of people who would be more informed, e.g. maxis or wouterv or KdL. But these are the numbers that I’m aware of and my understanding of them.

By ~mk~

Champion (296)

~mk~'s picture

14-08-2014, 23:20

The numbers are correct but they are theoretical.
15750 / 60 = 262.5
15750 / 50 = 315

From my experience, you can't go above 240 lines with single scan.
Horizontal resolution is not a problem, only vertical.

To check if the emulator switches resolutions you can use the SCREEN basic command.
To check if the emulator switches refresh rate try VDP(10)=0 to switch to 60Hz and VDP(10)=2 to switch to 50Hz (only on MSX2 VDP I think).

By NYYRIKKI

Enlighted (5745)

NYYRIKKI's picture

14-08-2014, 23:45

~mk~ wrote:

The numbers are correct but they are theoretical.
15750 / 60 = 262.5
15750 / 50 = 315

Actually theory goes like:
15750 / 60 = 262.5
15625 / 50 = 312.5

How ever I remember reading from Portar: (No idea if correct)
Horizontal Timing Scanline Rate : 15716.99 Hz
50Hz Vertical Frame Height: 313 scanlines, Actual Frame Rate : 50.214 Hz
60Hz Vertical Frame Height: 262 scanlines, Actual Frame Rate : 59.9885 Hz

By Grauw

Ascended (9817)

Grauw's picture

15-08-2014, 00:13

~mk~ wrote:

The numbers are correct but they are theoretical.
15750 / 60 = 262.5
15750 / 50 = 315

I quoted these numbers from the V9938 application manual, see r#9 *NT flag.

Quite easy to confirm I suppose, enable overscan, put some nice picture on screen, fiddle with your monitor’s vertical adjust pots and count the lines.

By Milsancho

Resident (63)

Milsancho's picture

15-08-2014, 02:26

The point is which are both, the horizontal and the vertical values for the particular case of MSX 2's physical resolution, in all its video modes. Given that we've settled that the system always uses a "windowed" format, the active area's resolution per se is not enough for accurate graphic emulation (nor proper documentation). In fact, I'd hardly believe that the borders currently being rendered by Blue MSX are a guess (was it 272 x 240?); they must have used them for some factual reason, so maybe the author can answer that.

As for MESS, I indeed believe it's far from provinding decent-enough accuracy and compatibility, but thanks for the reply, MK. The thing is, I don't think it'd be that hard to get Blue MSX, which seems very accurate and developed, behaving for full-screen 512 x 212 much like it does for 256 x 212 (or 272 x 240), which is pretty much perfect for 15-kHz low-res set-ups, and that would never go against current usability for average [sic] users. It's just another extra feature which indeed would go in favour of actual emulation. That's why I thought it was worth asking (until Mars 2000's latest post, that is). Many other emu authors listened to this petition, indeed.

The truth is that 640 x 480 may be a solution in the end. Some 15-kHz Trinitrons (and some Loewes, maybe others too) have de-interlace features. That is, they repeat the second scan on the first scan's lines, so a "480i" picture turns into a "240p" one. If the original picture was simply line-doubled (not scaled), you get pretty much what I'm looking for (borders would a bit too big though, I'm afraid). I said may, though, because I can't get Blue MSX to display anything bigger than 256 active pixels as the horizontal resolution (testing it with Xak 1, for those wondering) no matter the resolution I select in its menu (admittedly, I can't select 640 x 480, most likely due to the emulator's listing limitations, since I have many modes, but who knows; I'm trying with 512 x 480, Blue MSX v. 282).

So let me ask you another thing before going any further: have you ever taken a snapshot (internally) of exactly 512 x 212 (+ borders) (1 : 1)? If you haven't, could any of you please try? Maybe we can get something out of this, in the end.

--

Edited. Sorry.

By Milsancho

Resident (63)

Milsancho's picture

15-08-2014, 02:27

Quote:

The numbers are correct but they are theoretical.
15750 / 60 = 262.5
15750 / 50 = 315

From my experience, you can't go above 240 lines with single scan.
Horizontal resolution is not a problem, only vertical.

I misunderstood you here by thinking that you were not talking about the MSX 2 in particular, I believe, so sorry for that. I've now read it all.

I tried changing to Screen 7 and then to Screen 5 (apparently I did, at least) with no effect in the emulation whatsoever. So again I'm asking: Does Blue MSX emulate Screen 7 properly (does it render the whole horizontal res. without subscaling it to 256 px)?

Thanks.

By mars2000you

Enlighted (5885)

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15-08-2014, 04:09

Quote:

admittedly, I can't select 640 x 480, most likely due to the emulator's listing limitations, since I have many modes, but who knows; I'm trying with 512 x 480, Blue MSX v. 282

The blueMSX listing is not limited by the emulator, but by your own system. On my laptop, blueMSX gives a long listing of options, including 640x 480. These options correspond to all options that are compatible with the used PC/videocard.

By ~mk~

Champion (296)

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15-08-2014, 04:56

Yes I was talking about 15khz monitors in general.
You are probably reaching the limit with a 256 lines video mode.
If I were you I would try if the current version of MESS changes video modes on the fly.
I know it didn't in the past, but many things have improved lately, even on the MSX front.
In my opinion, MESS with the proper software database, has very good compatibility and you get for free all MESS features.
For hard disk support, development, etc. I recommend openMSX.
And another emulator I love for its simplicity and cool features, is Meisei (but only has MSX1 support)

By NYYRIKKI

Enlighted (5745)

NYYRIKKI's picture

15-08-2014, 08:53

Taking hires screenshots on BlueMSX is not any problem. If I go to take a look at screenshot directory then I will find 544x480 pictures where MSX picture size is 512x424. Only way I can get low resolution screenshot is when I specifically select Small window (LAlt + F10) even then the pixels are scaled down properly, so the hires pictures look just blurry. If I get screen captures with normal window size (LAlt+F11) I get 640x480 screenshots where MSX screen size depends of selected video effects. (I think the stretch settings might be the thing you should look carefully) Full screen screen shot sizes depend of selected resolution.

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