Question to the King of Ti 99 / 4a Hi-res Graphics Tursi

[MueThor]

Dear Tursi,

 

Do you know, if non-moving sprites could also be implemented into TI 99 bitmap mode images and used as additional colored pixels?

 

 

Regards

Edited July 18, 2017 by MueThor

[MueThor]

Addendum

 

Hi Tursi,

 

It is me again. I just found out that your conversion program Convert9918 doesn't include dual bitmap flicker mode, or? Have you experimented with the aforementioned mode? Is the CPU and/or the VDP of the TI 99 too slow for such a mode? If so, how is about reducing the edge lengths of the two flickered bitmaps?

 

 

Regards

Edited July 18, 2017 by MueThor

[Tursi]

I think that title is likely to irritate people...

 

Yes, sprites can be used in bitmap mode to have additional colors. No, I will not create software to automate it.

 

No, I don't do any double bitmap screen flicker modes, because my goal was to create graphical modes that don't require any CPU->VDP uploads /and/ operates in full screen. So far as I've determined so far, only the bitmap+multicolor flicker pulls off both of those.

[MueThor]

Hello folks and Tursi,

 

For this thread a somewhat unadequate title had been chosen by me. Of course all other guys are invited to post their thoughts and proposals into this thread here. Therefore I include a message referring to the topic of this thread I received from the member Airshack:

 

The E/A manual, Section 21, covers bitmap mode or "Graphics II."

This mode includes Sprites w/o Auto-Motion, if that's what you were asking Tursi? Yes!

BitMap mode simply adds more color data to the 32col * 34row (768 tiled) Screen Image Table.

This mode divides the screen into three 256 tiled sections, each with its own pattern descriptor table and color table, instead of just one of each for the entire screen.

- James

 

@Tursi: After having done some investigation on this topic, I have discovered that a dual bitmap flicker mode had already been realised with the BMPTO105 tool for MSX1 standard computers. Thus I have following request to you (of course only, if you have the spare time and motivation): Please implement the code into your Convert9918 tool, with modifications where needed.

 

 

Regards

Edited July 22, 2017 by MueThor

[Asmusr]

But the dual bitmap flicker mode only works for half screen images, e.g. 128x192, right? Tursi only wants to add full screen modes to his tool.

[Tursi]

@Tursi: After having done some investigation on this topic, I have discovered that a dual bitmap flicker mode had already been realised with the BMPTO105 tool for MSX1 standard computers. Thus I have following request to you (of course only, if you have the spare time and motivation): Please implement the code into your Convert9918 tool, with modifications where needed.

I was aware of that tool before I developed the multicolor/bitmap flicker, and I prefer my results as it's fullscreen. There's not that much difference between the results -- my mode also has 105 flicker colors. Or more, you can select how much flicker you can tolerate. The worst case is a little more fringe.

 

A lot of the codepaths in Convert9918 are hard coded, particularly the screen size. It's very non-trivial to change things like that.

[artrag]

This 105 color mode does not involve any cpu-vram transfer and allows images up to 256x128 pixels

[artrag]

Each picture is 2x256x8x2 bytes of patters shapes and 2x256x8 bytes of color definitions

[MueThor]

Hello guys,

 

 

But the dual bitmap flicker mode only works for half screen images, e.g. 128x192, right? Tursi only wants to add full screen modes to his tool.

It had been overseen by me that the BMPTO105 tool for MSX1 standard computers works only for half screen images, because two half screen bitmaps are flickered, one consisting of the even, the other of the odd rows. I had thought about a mode with two full screen bitmaps flickered. In this case the color of each pixel of the resulting image would arise from the mixing of the colors from each pair of overlaying pixels of the flickering two full screen bitmaps. Therefore I asked Tursi, if the CPU and/or the VDP of the TI 99 is too slow for such a mode. Is that right, Tursi?

 

 

Regards

 

 

P.S.: Probably the idea of creating full screen images with two flickered full screen bitmaps works only on CRT TVs, or?

Edited July 25, 2017 by MueThor

[Tursi]

A full bitmap screen takes 12k of VRAM plus a little more for the screen table. So you can't fit two of them in VDP at a time. The TI can only push about 1.5k of data to the VDP in a single frame, so you can't just do a full-screen bitmap flicker by brute force.

 

Flicker works on non-CRTs, but you see it a lot more.

[MueThor]

Dear Tursi,

 

Okay, thank you for your explanations. A last question: You surely also have tried to create full screen images by a bitmap (Mode 2)+"half bitmap" (Mode 1) flicker, or? It should be possible to create such full screen images... Furthermore, in both Modes 32 non-moving Sprites with edge lenghts of 16 pixels and 2 of 16 colors for each Sprite can additionally be generated. Thus the maximum graphic capabilities of TI for displaying one Hi-res image on the screen have not been exhausted up to this day by writing sophisticated code?

 

 

Regards

Edited July 31, 2017 by MueThor

[Tursi]

Do the math.

 

Bitmap mode requires 12k for the color and pattern tables, plus 768 bytes for a pattern table. In a standard mode 1, or 'half bitmap', you need 768 bytes again for a pattern table and 8 bytes for every character pattern you want to use (16 in half bitmap). So we're up to 13.5k, leaving 2.5k for patterns in the second screen, which is plenty of room for standard mode 1. For mode 2 half bitmap, you'd have to get the CPU involved to overwrite tables as the location of the color and pattern tables are fixed in bitmap mode, whether full or "half". So it might be possible to layout and flicker a bitmap mode against a standard mode 1 screen without any video RAM updates - the problem is that my converter, which is intended as a brute force search of the bitmap screen - would never be able to calculate that mode 1 screen.

 

But to answer your question, absolutely it's possible to create more sophisticated screens than Convert9918A produces. Utilizing flicker, sprites, and VRAM updates you can still push the system. Scanline techniques could be used to increase the number of sprites onscreen, too (thanks Rasmus for convincing me it can work! ). But none of these things are the direction my tools are aimed at... I wanted a way to get still backdrops for gaming and title pages.

 

I do have a flicker mode, because I'd always wanted to see one on the TI, but once I got it working I determined that there's no future in flicker code. Modern televisions don't blend the flicker correctly, more and more they upscale and deinterlace it... it doesn't look as good as it should. I don't intend to research that direction any further -- but that doesn't stop anyone else from doing it.

[MueThor]

Dear Tursi and all other guys,

 

Thank you for answering my questions and your patience.

Be also clear in your mind that I have only programmed in TI Basic and Extended Basic in earlier years, but never in Assembly language. For this reason I am asking you questions.

 

Scanline techniques could be used to increase the number of sprites onscreen, too (thanks Rasmus for convincing me it can work! ).

Not knowing, what scanline techniques are, I assume that it is not flicker? If so, would it be possible to create on screen real bitmap images of 256 pixels x 192 pixels size and 1 of 16 colors for each pixel of this image? If the latter can be realized, would you be so nice to also implement this into your Convert9918 tool?

 

I do have a flicker mode, because I'd always wanted to see one on the TI, but once I got it working I determined that there's no future in flicker code. Modern televisions don't blend the flicker correctly, more and more they upscale and deinterlace it... it doesn't look as good as it should. I don't intend to research that direction any further -- but that doesn't stop anyone else from doing it.

Please heed that the motivation for my reinvolvement with the TI is not limited to retro gaming and following: Way back in my youth time it was very early clear to me that the full capabilities of the TI would never be exhausted without 32k RAM, RS232 and a printer. Additionally, as you know the CRT TV or Monitor was the standard by that time. Therefore my reinvolvement with the TI today is always connected with following question: What would have been possible, if I had the money to buy the 32k RAM, RS232 and a printer?

BTW, would you be so nice to agree to release the code for this aforementioned special flicker mode in this thread? In case that you have already released the corresponding code somewhere in this forum: Please specify the link to this code.

 

@Asmusr (now the same questions and requests to you, only in connection with your code for the scanline techniques to increase the number of sprites on the screen ): Would you be so nice to agree to release the code in this thread? In case that you have already released the corresponding code somewhere in this forum: Please specify the link to this code.

 

 

Regards

Edited August 3, 2017 by MueThor

[Asmusr]

@Asmusr (now the same questions and requests to you, only in connection with your code for the scanline techniques to increase the number of sprites on the screen ): Would you be so nice to agree to release the code in this thread? In case that you have already released the corresponding code somewhere in this forum: Please specify the link to this code.

 

The code is here:

http://atariage.com/forums/topic/231597-vdp-scanline-tricks/page-2?do=findComment&comment=3113792

But there is still limitation of 4 sprites per line, so even with a good algorithm for where to place the sprites this trick could only be used to add a little more color to a bitmap image.

[MueThor]

Dear Asmusr,

 

There is a question that I would also have asked you:

Not knowing, what scanline techniques are, I assume that it is not flicker?

 

 

Regards

[Tursi]

Not knowing, what scanline techniques are, I assume that it is not flicker?

If so, would it be possible to create on screen real bitmap images of 256 pixels x 192 pixels size and 1 of 16 colors for each pixel of this image?

If the latter can be realized, would you be so nice to also implement this into your Convert9918 tool?

By scanline techniques I'm talking about racing the beam - changing the video registers while the VDP is actively drawing the screen. Rasmus covered the part two of your question, and no, Convert9918A will never incorporate additional features like sprites. I don't even know where to start with such a concept, and Convert9918 was an experiment in brute force. It's not intelligent enough to figure out where to put sprites and what to make them look like.

 

What would have been possible, if I had the money to buy the 32k RAM, RS232 and a printer?

That's why many of us are here, including me, but there are limits to free time that mean no one person can investigate every possibility!

 

BTW, would you be so nice to agree to release the code for this aforementioned special flicker mode in this thread?

The display code and a discussion about how it works is included with the Convert9918 download. The readme.txt contains the technical discussion of how it works and how to lay it out (scroll down to 'Half-multicolor Mode VDP Layout'), and the examples.zip includes source code for displaying all of the supported files.

 

You can also look at my slideshow program which incorporates display of all these modes except the pure multicolor ones:

http://atariage.com/forums/topic/257630-slideshow99