Yoomp! Tunnel is on my TFT not "round"

[Tigerduck]

Hi!

 

I have the effect on my TFT that the tunnels are oval (height larger than width, see picture).

Normally the TFT works without distortion (see circle picture)

On a CRT TV it works ok, too.

 

Anyone with the same "effect" or any idea what's the reason for this?

 

Best regards

 

Tigerduck

 

[Bryan]

I've got an NTSC system (I don't know where you're located) and the tube is somewhat tall on my system too. My guess is that the graphics probably look more normal on PAL systems.

[Tigerduck]

It is a PAL System, I'm from germany.

So NTSC or PAL should make no difference...

[MaPa]

Probably it's because of your TFT has screen ratio 5:4 instead of 4:3 like TV or CRT so the tunnel is taller. Your example with circle.. you are not drawing circle if you have different radius in X axis and Y axis.. If you would draw circle and have Y axis multiplied by 50 too then it would be taller "circle" like tunnel.

[eru]

Correct, if you draw a circle, make sure it's a circle - perhaps show us the program

 

Yoomp! draws a perfect circle, doesn't do anything special.

[Bryan]

It looks the same on my system. It doesn't bother me at all.

 

The game is probably drawing a circle that is the same number of pixels vertically and horizontally, which will appear slightly tall on the Atari since the pixels aren't square (which is why an 8x8 cursor is a rectangle instead of a square).

Edited July 18, 2008 by Bryan

[Gunstar]

I have a Commodore 1084S monitor, and it has a horizontal size adjust to correct it. I think most other Commodore montiors have this pot too, like the 1702(?) I think it was I used to own. Atari ST montiors can also be adjusted the same way, which I use when using a 50Hz PAL game. Both Atari and Commodore monitors, at least those for the 16-bit systems, were able to accept either 50/60Hz. The oval is definately the result of a PAL game screen being looking stretched on an NTSC screen due to fewer horizontal scan lines. The extra PAL lines are also clipped at the top and bottom. This is noticable in many of the European demos where scrolling text at the top or bottom of the screen is often cut off in the overscan areas. The text can also be seen again when the horizontal size adjust is made on my 1084S or Atari ST monitors.

Edited July 19, 2008 by Gunstar

[_The Doctor__]

Your TFT should have a horizontal height adjustment in one of it's menus. take a circular object that has no weight or rough edges place it over the computer generated circle and adjust the height so it evenly surrounds the object.

[Rybags]

That monitor is displaying a nice amount of horizontal overscan area that you wouldn't necessarily see on most older TVs.

 

Vertically it looks the same.

 

So, I'd say cut down the H-size in preference to altering the V-size if you can.

[Fröhn]

It looks the same on my system. It doesn't bother me at all.

 

The game is probably drawing a circle that is the same number of pixels vertically and horizontally, which will appear slightly tall on the Atari since the pixels aren't square (which is why an 8x8 cursor is a rectangle instead of a square).

PAL square pixels need 14.75 MHz pixel clock. Because A8 doesn't display interlace, that means: 7.375 MHz to compare to A8.

 

A8 has 7.094 MHz pixel clock -> 4% wider pixels than 7.375 MHz. So it shouldn't be taller than wide but other way round.

[Bryan]

It looks the same on my system. It doesn't bother me at all.

 

The game is probably drawing a circle that is the same number of pixels vertically and horizontally, which will appear slightly tall on the Atari since the pixels aren't square (which is why an 8x8 cursor is a rectangle instead of a square).

PAL square pixels need 14.75 MHz pixel clock. Because A8 doesn't display interlace, that means: 7.375 MHz to compare to A8.

 

A8 has 7.094 MHz pixel clock -> 4% wider pixels than 7.375 MHz. So it shouldn't be taller than wide but other way round.

 

I don't have time to look up the numbers right now but something isn't right with those figures.

 

Look at the photo of the circle drawn in BASIC above. It uses a 45/50 correction ratio to make the circle round. Why? Because the cursor at the bottom of the screen isn't square even though it's 8x8 pixels. Atari pixels are always a little taller than they are wide. If the Yoomp tunnel is same number of pixels across as down, then it should be tall.

[Fröhn]

PAL square pixels need 14.75 MHz pixel clock. Because A8 doesn't display interlace, that means: 7.375 MHz to compare to A8.

 

A8 has 7.094 MHz pixel clock -> 4% wider pixels than 7.375 MHz. So it shouldn't be taller than wide but other way round.

I don't have time to look up the numbers right now but something isn't right with those figures.

 

Look at the photo of the circle drawn in BASIC above. It uses a 45/50 correction ratio to make the circle round. Why? Because the cursor at the bottom of the screen isn't square even though it's 8x8 pixels. Atari pixels are always a little taller than they are wide. If the Yoomp tunnel is same number of pixels across as down, then it should be tall.

Your photo is from an NTSC system. Ofcourse numbers from a PAL system do not apply there.

 

NTSC square pixels: 12.27 MHz, without interlace: 6.136 MHz

 

NTSC A8 pixel clock: 7.159 MHz

 

In that case taller-than-wide pixels are ofcourse correct. In fact they should be even 17% taller than wide.

Edited November 27, 2008 by Fröhn

[Bryan]

Your photo is from an NTSC system. Ofcourse numbers from a PAL system do not apply there.

 

It's someone else's photo.

 

NTSC square pixels: 12.27 MHz, without interlace: 6.136 MHz

 

NTSC A8 pixel clock: 7.159 MHz

 

In that case taller-than-wide pixels are ofcourse correct. In fact they should be even 17% taller than wide.

So, on PAL Ataris the cursor is fatter than wide?

[Rybags]

PAL pixels are fatter horizontally.

 

Colour clocks aren't exactly relevant - PAL non-interlaced display is a full 60 lines extra, packed into the same space.

[Bryan]

Update...

 

I got my PAL 800XL working tonight and I'm using a JVC multi-system professional monitor.

 

One the PAL system, the tunnel is round. This means pixels are square (or nearly so) on PAL Atari's. On my NTSC systems, the tunnel is still a little tall.

[Allas]

Here are some screenshot captures from a NTSC tv

 

[Bryan]

Well, there are 50 more lines in a PAL field, so it guess it makes sense that they're a little closer together.