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Elite on the BBC Micro

Main loop: Main game loop (Part 5 of 6) [Electron version]

Name: Main game loop (Part 5 of 6) [Show more] Type: Subroutine Category: Main loop Summary: Cool down lasers, make calls to update the dashboard Deep dive: Program flow of the main game loop The dashboard indicators
Context: See this subroutine in context in the source code Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * Main game loop (Part 2 of 6) calls entry point MLOOP * Main game loop (Part 3 of 6) calls entry point MLOOP * Main game loop (Part 4 of 6) calls entry point MLOOP * Main game loop (Part 6 of 6) calls entry point MLOOP

This is the first half of the minimal game loop, which we iterate when we are docked. This section covers the following: * Cool down lasers * Make calls to update the dashboard Other entry points: MLOOP The entry point for the main game loop. This entry point comes after the call to the main flight loop and spawning routines, so it marks the start of the main game loop for when we are docked (as we don't need to call the main flight loop or spawning routines if we aren't in space)
.MLOOP LDA LASCT \ Set A to the value of LASCT, the laser pulse count SBC #4 \ Decrement the value of LASCT by 4 BCS P%+4 \ If we just reduced LASCT below 0, set it to 0 LDA #0 STA LASCT \ Store the decremented value of X in LASCT, so LASCT \ gets reduced by 4, but not into negative territory LDX #&FF \ Set the stack pointer to &01FF, which is the standard TXS \ location for the 6502 stack, so this instruction \ effectively resets the stack INX \ Set KEYB = 0 to indicate we are not currently reading STX KEYB \ the keyboard using an OS command LDX GNTMP \ If the laser temperature in GNTMP is non-zero, BEQ EE20 \ decrement it (i.e. cool it down a bit) DEC GNTMP .EE20 JSR DIALS \ Call DIALS to update the dashboard LDA QQ11 \ If this is a space view, skip the following four BEQ P%+11 \ instructions (i.e. jump to JSR TT17 below) AND PATG \ If PATG = &FF (author names are shown on start-up) LSR A \ and bit 0 of QQ11 is 1 (the current view is type 1), BCS P%+5 \ then skip the following instruction JSR DELAY-5 \ Delay for 1 delay loop, to slow the main loop down a \ bit JSR TT17 \ Scan the keyboard for the cursor keys, returning the \ cursor's delta values in X and Y and the key pressed \ in A