Main loop: LoseLife

       Name: LoseLife                                                [Show more]
       Type: Subroutine
   Category: Main loop
    Summary: Display a crash animation when we lose a life and end the game if
             this is our last life
  Deep dive: The main game loop
             Collisions and bullets
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * LandOnLaunchpad calls LoseLife
             * MoveAndDrawPlayer (Part 3 of 5) calls LoseLife


.LoseLife

 MOV     R0, #0                     \ Set playingGame = 0 to flag that the game
 STR     R0, [R11, #playingGame]    \ is no longer being played and that this is
                                    \ the crash animation

 MOV     R0, #30                    \ Set crashLoopCount = 30 to act as a loop
 STR     R0, [R11, #crashLoopCount] \ the crash animation below

 MOV     R8, #81                    \ Set R8 = 81 to use as the size of the
                                    \ explosion in AddExplosionToBuffer

 ADD     R0, R11, #xPlayer          \ Set (R0, R1, R2) to the coordinate in
 LDMIA   R0, {R0-R2}                \ xPlayer

 SUB     R1, R1, #CRASH_CLOUD_Y     \ Subtract CRASH_CLOUD_Y from the ship's
                                    \ y-coordinate so the explosion occurs just
                                    \ above the player's ship (5/16 tile sizes
                                    \ above the ship, to be precise)

 BL      AddExplosionToBuffer       \ Draw a large explosion in place of the
                                    \ player's ship

.lose1

                                    \ We now run a cut-down version of the main
                                    \ loop to display the crash animation (this
                                    \ is like the main loop but without the
                                    \ calls to drop rocks from the sky, draw the
                                    \ player's ship or update the fuel level)

                                    \ We now set up the rotation matrix for the
                                    \ rocks, using the main loop counter to
                                    \ generate rotation angles that change along
                                    \ with the main loop (so the rocks spin at a
                                    \ nice steady speed)

 LDR     R0, [R11, #mainLoopCount]  \ Set R0 = mainLoopCount << 24
 MOV     R0, R0, LSL #24

 MOV     R1, R0, LSL #1             \ Set R1 = mainLoopCount << 25

 BL      CalculateRotationMatrix    \ Calculate the rotation matrix from the
                                    \ "angles" given in R0 and R1, which we can
                                    \ apply to any rocks we draw in the
                                    \ MoveAndDrawParticles routine (as rocks are
                                    \ only rotating 3D objects apart from the
                                    \ player, and the player calculates its own
                                    \ rotation matrix)

 BL      MoveAndDrawParticles       \ Move and draw all the particles, such as
                                    \ smoke clouds and bullets, into the
                                    \ graphics buffers

 BL      DrawObjects                \ Draw all the objects, such as trees and
                                    \ buildings, into the graphics buffers

 BL      AddTerminatorsToBuffers    \ Add terminators to the ends of the
                                    \ graphics buffers so we know when to stop
                                    \ drawing

 BL      DrawLandscapeAndBuffers    \ Draw the landscape and the contents of the
                                    \ graphics buffers

 BL      PrintCurrentScore          \ Print the number of remaining bullets at
                                    \ the left end of the score bar

 BL      SwitchScreenBank           \ Switch screen banks and clear the newly
                                    \ hidden screen bank to black

 LDR     R0, [R11, #mainLoopCount]  \ Increment the main loop counter
 ADD     R0, R0, #1
 STR     R0, [R11, #mainLoopCount]

 LDR     R0, [R11, #crashLoopCount] \ Decrement the loop counter for the crash
 SUBS    R0, R0, #1                 \ animation above
 STR     R0, [R11, #crashLoopCount]

 BPL     lose1                      \ Loop back to keep running the crash
                                    \ animation until the loop counter runs down

 LDR     R0, [R11, #remainingLives] \ Decrement the number of remaining lives
 SUBS    R0, R0, #1                 \ and set the flags accordingly
 STR     R0, [R11, #remainingLives] \ 

 ADD     R13, R13, #4               \ Increment the stack pointer by one word so
                                    \ we discard the return address from the top
                                    \ of the stack, so we rejoin the main loop
                                    \ without keeping the return address of the
                                    \ subroutine we were in before we jumped
                                    \ here (i.e. MoveAndDrawPlayer or
                                    \ LandOnLaunchpad)

 BNE     PlacePlayerOnLaunchpad     \ If we still have one or more lives left,
                                    \ jump to PlacePlayerOnLaunchpad to play the
                                    \ next life