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Elite on the BBC Micro

Encyclopedia: ships_ag [Elite-A, Parasite]

Name: ships_ag [Show more] Type: Subroutine Category: Encyclopedia Summary: Show the Ships A-G or Ships K-W menu and display the chosen ship card Deep dive: The Encyclopedia Galactica
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * encyclopedia calls ships_ag * encyclopedia calls entry point ships_kw

Agruments: A The menu to show: * 1 = Show the Ships A-G menu * 2 = Show the Ships K-W menu C flag Set if this is the second menu (Ships K-W) Other entry points: ships_kw Does exactly the same as a call to ships_kw
.ships_ag .ships_kw PHA \ Store the menu number on the stack TAX \ Call menu with X = A to show the correct menu, so A JSR menu \ is now set to the type of ship card we need to show, \ depending on which ships menu we just displayed: \ \ * 1 for Adder to 14 for Ghavial \ * 1 for Iguana to 14 for Worm SBC #0 \ Decrement A so it is now in the range 0 to 13 (as menu \ clears the C flag when the number entered is within \ range), so we now have: \ \ * 0 for Adder to 13 for Ghavial \ * 0 for Iguana to 13 for Worm PLP \ Pull the menu number from the stack into the processor \ flags, which will set the C flag to bit 0 of the value \ on the stack (so if we called the routine with A = 1, \ the C flag will be set, and if we called it with A = 2 \ it will be clear) BCS ship_over \ If the C flag is set, then we called the routine with \ A = 1, so jump to ship_over as the choice number is \ already correct (i.e. 0 for Adder to 13 for Ghavial) ADC menu_entry+1 \ We just showed the the second menu, so the choice \ number is currently: \ \ * 0 for Iguana to 13 for Worm \ \ which is not right - we want the range to follow on \ from the end of the first menu. To fix this, we need \ to add the number of entries in the first menu to A \ to get the correct choice number. The menu_entry table \ contains the menu sizes, and menu_entry+1 contains the \ size of menu 1 (the Ships A-G menu), so this adds the \ number of entries in the first menu to give the \ correct choice range, as follows: \ \ * 14 for Iguana to 27 for Worm .ship_over STA TYPE \ A contains the ship that we just chose from the Ships \ menu, so store it in TYPE, so TYPE is now: \ \ * 0 for Adder to 27 for Worm CLC \ Store type + 7 on the stack, to give the token number ADC #7 \ of the title to show for the relevant ship card, from PHA \ Adder (token 7) to Worm (token 34) LDA #32 \ Clear the top part of the screen, draw a white border, JSR TT66 \ and set the current view type in QQ11 to 32 JSR MT1 \ Switch to ALL CAPS when printing extended tokens LDX TYPE \ Set X to the number of this ship type within the LDA ship_posn,X \ ship_list table, so we can pass it to the install_ship TAX \ routine LDY #0 \ Install this ship into blueprint position 0 so we can JSR install_ship \ show it on the ship card LDX TYPE \ Set A to the cards's title x-coordinate (fetched from LDA ship_centre,X \ the ship_centre table) STA XC \ Move the text cursor to the correct column for the \ title PLA \ Pull the token number for the title from the stack JSR write_msg3 \ (type + 7) and print it JSR NLIN4 \ Draw a horizontal line at pixel row 19 to box in the \ title JSR ZINF \ Call ZINF to reset the INWK ship workspace, so we can \ spawn a rotating ship to display in the centre of the \ ship card LDA #&60 \ Set byte #14 (nosev_z_hi) to 1 (&60), so the ship will STA INWK+14 \ be pointing away from us LDA #176 \ Set z_hi = 176 (very far away) STA INWK+7 LDX #127 \ Set roll counter = 127, so don't dampen the roll STX INWK+29 STX INWK+30 \ Set pitch counter = 127, so don't dampen the pitch INX \ Set X = 128 STA QQ17 \ Set QQ17 = %10110000, which has bit 7 set, to \ switch standard tokens to Sentence Case LDA TYPE \ Call write_card to display the ship card for the ship JSR write_card \ type in TYPE LDA #0 \ Add a new ship of type 0 to the local bubble (or, in JSR NWSHP \ this case, the encyclopedia ship card), which will \ spawn the correct shop for this ship card, as we \ installed the correct blueprint into position 0 with \ the call to install_ship above JSR l_release \ Call l_release so if a key is currently being pressed, \ we wait until it is released before continuing .l_395a LDX TYPE \ Set A to the closest distance that we want to show the LDA ship_dist,X \ ship (fetched from the ship_dist table) CMP INWK+7 \ If z_hi (the ship's distance) is equal to A, skip the BEQ P%+4 \ following decrement, as the ship is already close \ enough DEC INWK+7 \ Decrement the ship's distance, to bring the ship \ a bit closer to us JSR MVEIT \ Move the ship in space according to the orientation \ vectors and the new value in z_hi LDA #128 \ Set z_lo = 128, so the closest the ship gets to us is STA INWK+6 \ z_hi * 256 + 128 (where z_hi is the value in the \ ship_dist table) ASL A \ Set A = 0 STA INWK \ Set x_lo = 0, so the ship remains in the screen centre STA INWK+3 \ Set y_lo = 0, so the ship remains in the screen centre JSR LL9 \ Call LL9 to display the ship DEC MCNT \ Decrement the main loop counter JSR check_keys \ Call check_keys to wait until a key is pressed, \ quitting the game if the game if COPY (pause) and \ ESCAPE are pressed CPX #0 \ If check_keys returns with X = 0, then we paused the BEQ l_395a \ game with COPY and then unpaused it with DELETE, in \ which case loop back to l_395a to keep rotating the \ ship JMP BAY \ Otherwise a key was pressed, so jump to BAY to go to \ the docking bay (i.e. show the Encyclopedia screen)
Table containing the number of entries in each menu