Author Topic: Vectors display slightly wobbly and flickery  (Read 308 times)

hcmffm

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Vectors display slightly wobbly and flickery
« on: November 13, 2016, 06:11:35 PM »
My Vectrex friend had the Vectrex32 cartridge for some time. He tried the Vectrex32 out and did some programming. His feelings were so-so. Apart from the somewhat cumbersome way of developing programs (no real debugging, no hot-code replacement, ...) the way the vectors are displayed made him frown. He said that the vectors would slightly flicker and wobble.
We tried the Vectrex32 on two of my Vectrexes and right: The vectors are displayed a bit wobbly and a bit flickery. This can be seen in the menu (text) of the Vectrex32 and in Moon Lander: All lines wobble and slightly vary their positions plus the whole display slightly flickers. Other games like Minestorm run on those Vectrex consoles display the vectors 100 flicker-free and without any wobble.

Is there a reason why graphics generated by the Vectrex32 slightly wobble and flicker? Could something be done about this?
« Last Edit: November 13, 2016, 06:58:53 PM by hcmffm »

Vectrex32

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Re: Vectors display wobbly and flickery
« Reply #1 on: November 13, 2016, 06:24:29 PM »
The wobbling might be the "pen drift" problem which is discussed in the Vectrex32 manual, section 6.5. If you're drawing a lot of objects, try putting ReturnToOrigin sprites in between some of them.

Flickering can sometimes be improved by changing the frame rate, using the SetFrameRate function. The default is 30; try increasing it to 50 or 60.

Vectrex32 uses the Vectrex BIOS' line-drawing routines so in theory, wobbling and flickering should be no worse with Vectrex32 than with Vectrex. But programmers have always had to be careful about how many lines they draw and how often they reset the pen to the origin.

I'd be interested in any suggestions you have about debugging. It's true there's no hot-code replacement; you'd need BASIC line numbers or a built-in text editor for that. But as for "no real debugging": there's breakpoints, tracing, single-stepping, and the ability to examine and modify variables. What else would you want for "real debugging"?

- Bob

Vectrex32

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Re: Vectors display slightly wobbly and flickery
« Reply #2 on: November 13, 2016, 06:40:54 PM »
I just did an experiment jacking the frame rate up to 120 and it made a big difference with wobble and flickering.

- Bob

hcmffm

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Re: Vectors display slightly wobbly and flickery
« Reply #3 on: November 14, 2016, 05:27:50 PM »
I just did an experiment jacking the frame rate up to 120 and it made a big difference with wobble and flickering.
Sounds good. Is there a reason why the Vectrex32 main menu and Moonlander use 30 frames/s and not a higher framerate?

Vectrex32

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Re: Vectors display slightly wobbly and flickery
« Reply #4 on: November 14, 2016, 05:30:25 PM »
Is there a reason why the Vectrex32 main menu and Moonlander use 30 frames/s and not a higher framerate?

No good reason; I just didn't think to experiment with different frame rates at the time. Since they're written in BASIC, it's easy for anyone to change them.

- Bob