220 PLOT 131,91: DRAW OVER 1;sx,sy:
    REM rub out old hand
230 t1=t: GO TO 120

The real time clock that this method uses should be accurate to about .001% regardless if the computer is just running its program, or about 1 second per day; unlike the PEEK method shown above where the computer (and the counter) stops temporarily whenever you do BEEP, or a storage device operation, or use the printer or any of the other extra pieces of equipment you can use with the computer. All these would make it lose time however using the RTC which runs independently bypasses this issue.

If you have chosen to run your ZX Spectrum Next in 60Hz mode then for any program that uses PAUSE you must replace 50 by 60 where appropriate.

INKEY$

The function INKEY$ (which has no argument) reads the keyboard. If you are pressing exactly one key (or a SHIFT key and just one other key) then the result is the character that that key gives in L mode; otherwise the result is the empty string.

Try this program, which works like a typewriter:

10 IF INKEY$ <>"" THEN GO TO 10
20 IF INKEY$ = "" THEN GO TO 20
30 PRINT INKEY$;
40 GO TO 10

Here line 10 waits for you to lift your finger off the keyboard and line 20 waits for you to press a new key.

Remember that unlike INPUT, INKEY$ doesn't wait for you. So you don't type ENTER, but on the other hand if you don't type anything at all then you've missed your chance.

INKEY$ is very useful for a control loop where you can set objects on the screen to move according to which key you're pressing (for example the cursor keys). As you will also see from Chapter 20, one more option for you is to use the NEXT #...TO keyword that works in a very similar manner. Finally it's also possible to query the keyboard hardware directly as well as the optional mouse as you will see in Chapter 22.

Animation: a quick primer

Animation is defined as any process with which static objects or pictures are manipulated to appear as moving. The word itself comes from the Latin anima which means life. In essence, it is to convey the appearance of life and movement to otherwise static constructs.

In computers, this is achievable using the rapid succession of images faster than the eye can perceive. On the ZX Spectrum Next specifically, there are basically five methods of animation; one using mass storage frame playback, the other using memory based frame playback, the third using sprites, the fourth using scrolling and the fifth is to use a combination of all the above. Let's examine them in turn.

Mass Storage Frame Playback

This technique deals with restoring partial or complete frames of screens stored on your SD card to or RAMdisk to the screen memory in rapid succession at the maximum possible speed. Consider this example using the RAMdisk:

10 INK 5: PAPER 0: BORDER 0: CLS
20 FOR f=1 TO 10
30 CIRCLE f*20,150,f
40 SAVE "m:ball"+ STR$ (f) CODE
   16384,2048