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Old 06 May 2017, 12:14   #18
Registered User
Join Date: Dec 2015
Location: Poland
Posts: 164
Hello Evryone

Thanx for so much input but i have to clear some confusion here.

If someone would ask me which slideshow i know from Amiga, I would go for only one choice:
[ Show youtube player ]
Combination of great music and 35 digitised 16colour low resolution pictures combined on 2 floppy discs are doing tits job quite nicelly even today.
I believe if someone wants to make a good slideshow need to combine 3 things:
1. Great music
2. Nice pictures
3. MAximum 2 floppy disc.
There are many productions which do not have even one of those points and are not remebered lost in cyberspace.
I know only one slideshow which uses Hires pictures, but IMHO its not entertaining
[ Show youtube player ]

It is true 1985 computer could display 640x512 with 16colours and even change them dynamically, but it is connected with serious limitations.
1. Memory - 163840Bytes in Chip memory are needed for Frame Buffer
2. Speed - In rastertime of Display area CPU,Blitter,Copper have no access to memory. All is monopolled by Display DMA. The only time when CPU can do something is in offscreen area. Just imagine CPU is working at 20% of its normal speed to understand how hard is to se it.
3. Disk space - High resolution usually requies more space, but Amiga has only 880kB floppy

Lets just examine Khph_re idea from practical side.
1. He has chosen 720x566 resolution which requie 203760bytes frame buffer. His copper lists about 20kB, Music lets assume 100kB. We have left with 180kBytes of Chip and 0.5Mbytes of slow Ram. Chip memory is too low for another frame buffer so we would have to make our music smaller (probably worse quality) or blank the display to load another picture.
2. 720x566 blocks sprites and allows to change only 4 colours in each line by copper and the CPU would work at 10% of original speed. During that time we could play music but what about loading another picture, what about decompressing it? And how to make scroll on it?
3. If he uses 120kB for each picture in compressed form then he could place only 6 pictures on disk. Certainly not enough for good slideshow

In general khph_re idea is purelly theorethical and because he used more than 4 changes in line probably not able to display on standard OCS machine. If he would lower the resolution a bit this could be done, but he would still have not enough pictures, because his pictures compresses to 120kB vs mine 50kB). Of course my fellow amiga friend if you can make me wrong I would be more than happy

I think i must explain why my idea is uniqe and complete.
1. I opted for 640x480 which uses only 153600Bytes. Adding to that 100kb for music and 50kB for code would leave 700kB for compressed pictures, so we could load them directly into memory and decompress directly into the same frame buffer during black pauses between pictures.
2. 640x480 still uses a lot of CPU, but it is still some left for music and scroll on sprite layer. Decompression would requie more power but this is possible when we will black the screen
3. Disk space is ok as long as we keep the compression high. PNG i have are just plain chunky pixels packed with optimised deflate algorythm. Their decompression would probably be too long but i have an idea how to pack bitplane IFF to comparable sizes.

As you could see my approach is doneable and would be something unique noone has done before because you just cant do it without good compression. Thats a start and i did it. If someone can help me to finisz this idea he is most welcome.

Last edited by Trachu; 06 May 2017 at 13:14.
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