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Elite on the BBC Micro

Version analysis of nWq

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

Name: nWq Type: Subroutine Category: Stardust Summary: Create a random cloud of stardust
Create a random cloud of stardust containing the correct number of dust particles, i.e. NOSTM of them, which is 3 in witchspace and 18 (#NOST) in normal space. Also clears the scanner and initialises the LSO block. This is called by the DEATH routine when it displays our untimely demise.
.nWq

Code variation 1 of 3Related to the screen mode

This variation is blank in the Cassette, Disc (flight), 6502 Second Processor and Electron versions.

Master

LDA #DUST \ Switch to stripe 3-2-3-2, which is cyan/red in the STA COL \ space view

Code variation 2 of 3Related to the Electron version

The Electron version has no witchspace, so the number of stardust particles shown is always the same, so the value is hard-coded rather than needing to use a location (which the other versions need so they can vary the number of particles when in witchspace).

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, 6502SP, Master

Electron

LDY NOSTM \ Set Y to the current number of stardust particles, so \ we can use it as a counter through all the stardust
LDY #NOST \ Set Y to the number of stardust particles, so we can \ use it as a counter through all the stardust
.SAL4

 JSR DORND              \ Set A and X to random numbers

 ORA #8                 \ Set A so that it's at least 8

 STA SZ,Y               \ Store A in the Y-th particle's z_hi coordinate at
                        \ SZ+Y, so the particle appears in front of us

 STA ZZ                 \ Set ZZ to the particle's z_hi coordinate

 JSR DORND              \ Set A and X to random numbers

 STA SX,Y               \ Store A in the Y-th particle's x_hi coordinate at
                        \ SX+Y, so the particle appears in front of us

 STA X1                 \ Set X1 to the particle's x_hi coordinate

 JSR DORND              \ Set A and X to random numbers

 STA SY,Y               \ Store A in the Y-th particle's y_hi coordinate at
                        \ SY+Y, so the particle appears in front of us

 STA Y1                 \ Set Y1 to the particle's y_hi coordinate

 JSR PIXEL2             \ Draw a stardust particle at (X1,Y1) with distance ZZ

 DEY                    \ Decrement the counter to point to the next particle of
                        \ stardust

 BNE SAL4               \ Loop back to SAL4 until we have randomised all the
                        \ stardust particles

Code variation 3 of 3Related to Elite's use of the Tube

This variation is blank in the Cassette, Disc (flight), Master and Electron versions.

6502SP

JSR PBFL \ Call PBFL to send the contents of the pixel buffer to \ the I/O processor for plotting on-screen
                        \ Fall through into WPSHPS to clear the scanner and
                        \ reset the LSO block

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