1 How about Graphics?

Graphics is one of the major strengths of the Amiga. Why don’t we have more answers here? :-(

1.1 What are chunky and planar displays?

Simply put, the terms chunky and planar (short for bitplanar) refer to different ways of storing graphics information in a computer’s memory. They are rather easy to understand, as far as things go, but incredibly difficult to explain:

Computer images are arranged as a grid of pixels, each of which can be thought of as a number representing the color number of the pixel, sort of like a paint-by-numbers scheme. For example, here’s a simplified example image, in four colors:

   00302132

The Amiga stores this image in a bitplane mode. That is, it is represented by several planes of bits (binary digits, 1s or 0s). This is a four-color image, so each color number could be represented by two bits. Therefore there are two bitplanes:

   00100110    Here's bitplane 0
   00101011    And here's bitplane 1
   --------    Now, let's add them up, binary style:
   00302132

Which is the final image. If the image was in two dimensions, it would truly be composed of bit planes. However, I’d need three dimensions to show multiple bitplanes overlayed, and therefore for simplicity we’re working in one dimension (which is all we need).

Now, there’s another way of storing this image. How about if we localize the bit data in little chunks?

   00 00 11 00 01 10 11 01 = 00302132

This is the principle of the chunky pixel mode.

Both methods of image storage are perfectly logical, and no one can say that one is better than the other. However, there are certain technical aspects which cause certain advantages and disadvantages.

First, if you’ve seen colored text scroll on your Amiga, you know there is a bit of "flicker" that arises. Specifically, what happens is that while the text is scrolling, its color temporarily changes to something completely different. What’s happening is that the computer’s moving several bitplanes of data while the raster (monitor electron gun) is sweeping across the screen. What that means is that, if the raster catches the data while it’s being moved, you can end up with some bitplanes being moved and some not. What if we filled bitplane 1 in the example above with 0s? Instantly all the 3s become 1s, and the 2s become 0s! This is what causes "flicker" when certain colors are scrolled. By contrast, if a chunky pixel display is caught while scrolling, all we see is a partially-scrolled image; the colors are preserved (since their units are the small ones).

That’s a disadvantage to planar pixels, but what about chunky pixels? Well, recall that a computer organizes information in terms of 8 bit bytes. These groups are static; you cannot decide to all of a sudden organize data in terms of three bytes or something! Therefore, when using chunky pixels, things get complicated if we decide to use a nonconvenient number of bits per pixel. In practice, the 8-bit (256-color) mode, and 24-bit (16 million color) modes are the most common candidates for chunky pixel displays.

Finally, certain effects can be accomplished with the different systems. Bitplanar mode is particularly useful for things like shadows (where an extra bitplane is set with 1s instead of 0s), and chunky mode is great for perspective and "mapping" (since the data for each pixel is localized in a single "chunk"). The latter advantage makes chunky pixel mode really great for games, and is what made Wolfenstein 3-D possible.

We all know that Amigas use the bitplane system for storing images. However, the Macintosh and PC(VGA) both use chunky pixel modes. While we can optimize our RAM usage with "bizarre" modes like 8- and 128-color, they gain the advantages of non-flicker scrolling, and the programming simplicity of just writing a byte where you want the pixel to go.

The difference between the two modes becomes problematic in things like emulation. EMPLANT has a "chunky to planar" routine which it uses to convert a Macintosh display into an Amiga one. "Chunky to planar" routines are also useful for getting chunky-inclined things to run on Amigas (see TMAPDemo, rotdemo). On a side note, there was some confusion as to what EMPLANT used the MMU for with regard to chunky to planar. The MMU itself is incapable of performing the algorithm for the conversion; rather, it is used to detect what portions of the display memory are updated from the Mac side, and therefore the processor is saved from having to perform the chunky to planar conversion for the entire display.

I sincerely hope that helped clear up most of the mystery concerning the terms "Chunky" and "Planar"!

(Joseph Luk, jluc@eis.calstate.edu)

1.2 What is doublebuffering?

Don’t be ashamed if you haven’t a clue as to what this is. It’s rather simple, really. Imagine you wanted to animate something by drawing out each frame. Now imagine you had only one piece of paper. Even if you drew pretty fast, it would be difficult to see what the animation looks like because you’d have to erase the frame you just drew, in order to draw the next one!

What if you had two pieces of paper? Why, then, you could see the difference between two adjacent frames. First you’d draw your first frame on the first piece of paper, then you’d draw the second frame on the other piece. Then you’d erase the picture on the first piece of paper, and draw in the third frame. Then you’d erase the picture on the second piece of paper, and draw in the fourth frame, and so forth.

This is the principle of doublebuffering. The computer shows you the picture it just drew, then turns around and draws the next one. It then swaps the picture in front of you with the one it just drew, and repeats the process. The result is a smooth animation, because you never need to see the computer draw; all you see is each finished product.

(Joseph Luk, jluc@eis.calstate.edu)

1.3 What monitors will work on my Amiga 1200/4000?

Monitors can be classified after the horizontal scan frequency they require. TVs, as well as C=’s 1084 monitor, need frequencies around 15 kHz. VGA/SVGA need approx. 30 kHz. Multisync monitors can take many frequencies.

In short: You can use any monitor you want with an A1200. BUT:

• - If you use a regular VGA/SVGA monitor, you can only use a few display modes (like DblPAL, DblNTSC and/or Productivity). I.e. (320|640) x (256|512|1024) for DblPAL. This is great for Workbench and all "serious" utilities (DTP etc), but don’t expect any games to work... they don’t use your preferences, just take over the machine and assume a 15 kHz monitor. Also, you cannot utilize the "Early Startup Control" screen (you know, disable cache, and that stuff), which also requires a 15 kHz monitor. Furthermore, VGA monitors don’t have speakers. And the VGA-type modes don’t support Genlocks. But for a lot of "serious" work, a VGA monitor is quite adequate.
• - You already know what happens with a 15 kHz monitor; the flickering in Interlace mode. A small tip: Try to use NTSC instead of PAL. This increases the refresh rate from 25 Hz to 30 Hz, at the expense of lower vertical resolution (482 lines maximum). The NTSC and PAL modes aren’t as bad as many people think. If your monitor has a lot of phosphorous (long afterglow), PAL Laced can be quite OK, and it gives you a resolution of 1448x566 in SuperHiRes. That’s the highest resolution currently supported on AGA Amigas, in _any_ display mode.
• - A Multisync gives you the best of both worlds. The 1940 and 1942 monitors from C= are quite OK, although rather cumbersome to use... The h/v size and offset must be set manually each time you switch display mode. (1) The 1960 monitor doesn’t have this problem, but it’s a bit more expensive.

For a VGA/SVGA or Multisync monitor, you’d need a little shiny box which gives you the standard 15-pin "D" connector. It costs around $15.

There are other alternatives... like the "AmiVGA" box ($50 or so), which I think is a cheapo version of the Flicker Fixer. (But it’s really a shame to use this on an AGA Amiga.)

Also, you can get a VGA monitor, and hook up your TV to the composite or RF port on the Amiga - one monitor for games, one for serious stuff.

(Per Espen Hagen, per.e.hagen@ffi.no)

1.4 How do I switch between PAL and NTSC?

PAL and NTSC are two different video standards, the former being European, and the latter being American. PAL has a slightly taller screen (256 lines non-interlaced, non-overscanned) as opposed to NTSC (200 lines), so if you see the bottom portion of a program’s screen getting cut off on your American machine, chances are the program was written for PAL, and is running on your shorter NTSC screen. PAL and NTSC differences are somewhat less important to European users; since their machines default to PAL, running an NTSC program is no more than a minor annoyance having the screen only appear in the top portion of the display.

Therefore, for us NTSC folks, switching into PAL mode becomes important to avoid loss of some picture on Euro Demos, etc.

First, the most common misconception about switching between PAL and NTSC is that you need a Multiscan or special monitor for such a purpose. Not so! Just about any monitor can handle the minor signal difference between PAL and NTSC (50Hz vertical refresh versus 60Hz). The 108x, 19xx, and 20xx series, and even most TVs, can display both PAL and NTSC. Sometimes it is necessary to perform minor tweaking of vertical hold and/or v. size on your monitor to achieve full display, though this is trivial.

What IS needed to switch between PAL and NTSC in software, is a "Fatter" (1MB) Agnus or better. If your system has more than 512K of CHIP RAM (use the avail command to find out) you have this chip. If you do not, ou can still construct a hardware switch (see below).

The following directions assume you’re an NTSC user who wants to switch into PAL mode, but the procedure for going from PAL to NTSC is much the same.

The most common use of switching into PAL is for self-booting games, demos, etc. The best way to accomplish this on pre-3.0 systems is to use Chris Hames’ Degrader program (most recent version: 1.30). Once you have procured this program, the switch is as simple as selecting "50Hz", and "50Hz System", then installing the program’s ROMTag (little program that runs at boot-time) by pressing the "Survive Reset(s)" button.

AmigaDOS 3.0 added a PAL/NTSC switch feature to its Boot Menu, and all you need to do in order to access this is hold down both mouse buttons as the computer boots. Select Display Options, Display Mode/PAL, and then Boot. If the program still fails to go into PAL mode (Zool is one I’ve found), you may wish to get Degrader anyway and try that.

Software PAL/NTSC switching is easy and painless. Some people have gone even further by installing hardware PAL/NTSC switches. This results in a system which even the most nasty hardware-banging programs can’t bring to its original configuration (if it has been switched). The procedure is simple – most Amigas have jumpers already – but beyond the scope of this document.

Therefore, if your screen is too short or cut off, seek the different screen mode. You’ll "see new horizons", literally!

(Joseph Luk, jluc@eis.calstate.edu)

(2)

Footnotes

(1)

A patch is available on Aminet for Kickstart 3.0 to do this without manual actions in the file ‘os30/util/Monitor30Patch.lha’.

(2)

PAL/NTSC switching with a MultiSync monitor is possible on 2.0+ and easily accomplished by moving the PAL monitor type to (or NTSC, as applicable, I have them both in) the Devs/Monitors drawer (from the Storage/Monitors drawer), reboot, then go into the Prefs drawer and select the ScreenMode program. You will see at least two PAL modes available (PAL and PAL Interlaced). Simply select one of the (usually non-interlaced for demos) and select "Use". All windows on the Workbench will close, the video mode will change, and then the windows will reopen – that simple!

Allen J. Newton, anewton@alturia.abq.nm.us

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