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Elite on the BBC Micro

Dashboard: DIALS (Part 3 of 4) (Master version)

Name: DIALS (Part 3 of 4) [View in context] Type: Subroutine [Compare versions] Category: Dashboard Summary: Update the dashboard: four energy banks Deep dive: The dashboard indicators
LDY #0 \ Set Y = 0, for use in various places below JSR PZW \ Call PZW to set A to the colour for dangerous values \ and X to the colour for safe values STX K \ Set K (the colour we should show for high values) to X \ (the colour to use for safe values) STA K+1 \ Set K+1 (the colour we should show for low values) to \ A (the colour to use for dangerous values) \ The above sets the following indicators to show red \ for low values and yellow/white for high values, which \ we use not only for the energy banks, but also for the \ shield levels and current fuel LDX #3 \ Set up a counter in X so we can zero the four bytes at \ XX15, so we can then calculate each of the four energy \ banks' values before drawing them later STX T1 \ Set T1 to 3, the threshold at which we change the \ indicator's colour .DLL23 STY XX15,X \ Set the X-th byte of XX15 to 0 DEX \ Decrement the counter BPL DLL23 \ Loop back for the next byte until the four bytes at \ XX12 are all zeroed LDX #3 \ Set up a counter in X to loop through the 4 energy \ bank indicators, so we can calculate each of the four \ energy banks' values and store them in XX12 LDA ENERGY \ Set A = Q = ENERGY / 4, so they are both now in the LSR A \ range 0-63 (so that's a maximum of 16 in each of the LSR A \ banks, and a maximum of 15 in the top bank) STA Q \ Set Q to A, so we can use Q to hold the remaining \ energy as we work our way through each bank, from the \ full ones at the bottom to the empty ones at the top .DLL24 SEC \ Set A = A - 16 to reduce the energy count by a full SBC #16 \ bank BCC DLL26 \ If the C flag is clear then A < 16, so this bank is \ not full to the brim, and is therefore the last one \ with any energy in it, so jump to DLL26 STA Q \ This bank is full, so update Q with the energy of the \ remaining banks LDA #16 \ Store this bank's level in XX15 as 16, as it is full, STA XX15,X \ with XX15+3 for the bottom bank and XX15+0 for the top LDA Q \ Set A to the remaining energy level again DEX \ Decrement X to point to the next bank, i.e. the one \ above the bank we just processed BPL DLL24 \ Loop back to DLL24 until we have either processed all \ four banks, or jumped out early to DLL26 if the top \ banks have no charge BMI DLL9 \ Jump to DLL9 as we have processed all four banks (this \ BMI is effectively a JMP as A will never be positive) .DLL26 LDA Q \ If we get here then the bank we just checked is not STA XX15,X \ fully charged, so store its value in XX15 (using Q, \ which contains the energy of the remaining banks - \ i.e. this one) \ Now that we have the four energy bank values in XX12, \ we can draw them, starting with the top bank in XX12 \ and looping down to the bottom bank in XX12+3, using Y \ as a loop counter, which was set to 0 above .DLL9 LDA XX15,Y \ Fetch the value of the Y-th indicator, starting from \ the top STY P \ Store the indicator number in P for retrieval later JSR DIL \ Draw the energy bank using a range of 0-15, and \ increment SC to point to the next indicator (the \ next energy bank down) LDY P \ Restore the indicator number into Y INY \ Increment the indicator number CPY #4 \ Check to see if we have drawn the last energy bank BNE DLL9 \ Loop back to DLL9 if we have more banks to draw, \ otherwise we are done