150 32 VDU 23,243,28,60,30,60,126,108,162,162 35 X%=600 37 VDU 5 38 GCOL 4,1 40 FOR Y%=120 TO 1023 STEP 10 50 PROCROCKET: REM draw the rocket 90 PROCROCKET: REM now delete it 120 NEXT Y% 130 END 1010 DEF PROCROCKET 1020 MOVE X%,Y% 1025 VDU 240 1030 VDU 10,8,241 1040 VDU 10,8,242 1050 IF Y% 1060 ENDPROC Notice that ‘integer’ variables (followed by a % sign) are used: these make the program run considerably faster than ‘real’ variables. The rocket is printed at line 50 by PROCROCKET . Line 90 prints the rocket again in its inverse colour (as specified in line 38 GCOL 4,1 ), and so deletes it.
As an alternative to this, the rocket could be deleted by replacing line 90 with PROCdelete , deleting line 38, and adding the new procedure 2000 DEF PROCdelete 2010 MOVE X%,Y% 2020 VDU 9,127 2030 VDU 10,9,127 2040 VDU 10,9,127 2050 VDU 10,9,127 2060 ENDPROC This just deletes the rocket with VDU 127 . We can get smoother movement if we just delete the bottom character every time. This removes most of the flicker and what remains becomes a good effect. The price is that the detail at the bottom of the rocket is lost, so this method only works if your character gets wider at the bottom! Delete line 90, and type this new procedure:
38 GCOL,1 40 FOR Y%=120 TO 1023 STEP 4 1010 DEF PROCROCKET 1020 MOVE X%,Y% 1025 VDU 240,10,8 1030 VDU 241,10,8