The Absolute Beginners Guide to OPL

Part 8 - Splashing around...

---

Several people have emailed me to comment how strange it is to have a program which initially just shows a blank screen, with no prompt as to what to do next. Quite right, so let's fix it now.

The first (and quickest) thing we can do is add a brief flashed message in a screen corner. After the WHILE 1 line, add

gIPRINT "Press the Menu key to proceed"

Translate and run and you'll see it flash up. All well and good, but it's gone after a couple of seconds, leaving the blank screen as before. There's nothing wrong with our application being 'menu-driven' but we ought at least to put something up on screen to show that the program hasn't broken! Although most professional programs have one or more main screens of information which form the core of what the user sees, our "MiLo" program is simple enough that we haven't got sufficient information to even partially fill a screen in any kind of relevant way. So we'll fall back on another common technique, the idea of a 'splash' screen.

A Splash screen is a picture or block of information which

1. gives the user something to look at while waiting for the program to finish launching itself
2. can act as a little bit of self-advertising (getting across your logo etc)
3. provides a pretty screen backdrop for those occasions (like today) when the programmer can't think what else to fill the screen with!

The first step is to create a suitable picture/logo etc. This will obviously vary according to whether you're on a Series 5 or Series 3, but essentially you want to create an "EPOC picture" or ".PIC" file of appropriate size (say, 480 by 160 pixels, a size which will work on both machines) and store it in a suitable folder (e.g. the root directory of the default disk).

You'll see my rather half-hearted splash screen attempt above (I'm no artist!), created in my case in SKETCH on a Series 5 and exported as an EPOC picture to "front.mbm" in the root directory. Series 3 users can use DRAW, saving the resulting bitmap in .PIC format in the same place.

If you're unsure about graphics files and their formats, check out Phil Spencer's and Lieuwe de Vries' excellent web sites, each of which cover (amongst other things) these issues.

Time to load the graphic into our program. In the list of LOCAL variables at the top of the program, add another, image%.

LOCAL i%,j%,image% rem etc.

Psion's OPL graphics system works on the principle of 'drawables'. Essentially, every loaded image or graphics window is assigned a number which acts as a name and can be used to reference the graphic later on. As a special case, the main screen is drawable no.1, and we're here defining a new drawable as number image%. Note that we never need to know what number is actually stored inside image% as OPL handles all that. We just use the image% variable name.

As you'll imagine we need to insert a few lines of code to make the picture display. The sequence of events is:

1. Load the picture into memory (by the way, this automatically sets it as the 'current' drawable)
2. Switch the 'current' drawable back to '1', the main screen
3. Set the drawing position to 0,0 (the top-left of the screen)
4. Copy across 480 by 160 pixels' worth of graphic information from the in-memory picture
5. Close the picture file (just to be tidy!)

Translated into code to be placed just after the DEFAULTWIN line, this becomes:

image%=gLOADBIT("\front.mbm")
gUSE 1
gAT 0,0
gCOPY image%,0,0,480,160,0
gCLOSE image%

If you're an OPL/16 (Series 3) user, you'll need to use "front.pic" instead, of course! A few other quick notes:

• I've used a single "\" before the picture filename to indicate the root directory (on the default disk), but of course you may wish to put any directory path you want in here instead.
• The gUSE 1 sets the 'current' drawable back to the main screen. This line of code is essential but often forgotten. Without it, any drawing commands would end up taking effect (if possible) on the picture file drawable instead.
• The parameters given for gCOPY are fairly obvious (see the manual), but note the zero at the end, indicating the graphics 'mode' in which the picture is to be overlaid on the screen, in this case 'Set' (i.e. pixels will be set black if needed and all other pixels left unchanged). If the screen wasn't already known to be blank, I'd be tempted to use mode 3, which says that all pixels (black and white) should replace the current screen contents.
• Never forget to close each drawable as it's finished with. If you don't do this you'll eventually run out of available 'drawables' and the program will crash.
• (Series 3 users only) Note that I'm assuming you haven't used the 'grey' colour when creating your picture. 3-colour images on a Series 3 are decidedly tricky to manipulate and so we'll stick to black and white for now! 8-)

... which, once translated and run, gives:

One last thing: you need to add a new line to the top of the proc setup: procedure:

gCLS rem Clear the screen

Without this screen-clearing line, the picture will persist on screen, leading to a rather ugly effect!

Make sure you understand the lines of graphics code above, as a basic knowledge of OPL's graphics commands will let you display almost anything in your programs. Pictures, animations, special effects are all within your grasp. It's also worth finding a painting program you're happy with, too and learning how to get the most out of it to create images of a particular size as smoothly as possible. Series 5 users currently have a choice of SKETCH or Photo5, Series 3 users a whole multitude (including Draw, Palmtop Picasso, Perfect Paint, S3aDraw and others).

That about wraps things up for now; why not pop back next week?