The PreviewLandscape subroutine - The Sentinel on the BBC Micro

       Name: PreviewLandscape                                        [Show more]
       Type: Subroutine
   Category: Landscape
    Summary: Draw an aerial preview of the landscape
  Deep dive: Program flow of the main title loop
             Adding enemies and trees to the landscape
             Drawing the landscape preview
             Drawing the title screens
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * JumpToPreview calls PreviewLandscape


.PreviewLandscape

 JSR SpawnEnemies       \ Calculate the number of enemies for this landscape,
                        \ add them to the landscape and set the palette
                        \ accordingly

 LDX #3                 \ Set X = 3 to pass to DrawTitleView so the background
                        \ of the landscape preview is black with stars

 LDY #0                 \ Set Y = 0 to pass to DrawTitleView so it draws the
                        \ screen with the correct perspective for the landscape
                        \ preview

 LDA #&80               \ Set A = &80 so the call to DrawTitleView does not draw
                        \ a 3D object as part of the landscape preview

 JSR DrawTitleView      \ Draw the landscape preview

 LDX #4                 \ Print text token 4: Background colour black, print
 JSR PrintTextToken     \ "PRESS ANY KEY" at (192, 64), print "LANDSCAPE" two
                        \ characters right of (64, 768), move cursor right

 JSR PrintLandscapeNum  \ Print the four-digit landscape number (0000 to 9999)

 JSR SpawnPlayer        \ Add the player and trees to the landscape, and then
                        \ generate and check the landscape secret code (the
                        \ SpawnPlayer routine falls through into SpawnTrees,
                        \ which falls through into CheckSecretCode)
                        \
                        \ If the entered secret entry code in the keyboard input
                        \ buffer does not match the generated secret code for
                        \ this landscape, then the call to CheckSecretCode will
                        \ return here so we can display an error with the jump
                        \ to SecretCodeError below
                        \
                        \ If the codes match then the CheckSecretCode routine
                        \ will jump to the PlayGame routine to play the game, so
                        \ we will not return here

 JMP SecretCodeError    \ The entered secret entry in the keyboard input buffer
                        \ does not match the generated secret code for this
                        \ landscape, so jump to SecretCodeError to display the
                        \ "WRONG SECRET CODE" error, wait for a key press and
                        \ rejoin the main title loop

[X]

Subroutine DrawTitleView (category: Title screen)

Draw the main title screen, the secret code screen or the landscape preview

[X]

Subroutine PrintLandscapeNum (category: Text)

Print the four-digit landscape number (0000 to 9999)

[X]

Subroutine PrintTextToken (category: Text)

Print a recursive text token

[X]

Subroutine SecretCodeError (category: Main title loop)

Display the "WRONG SECRET CODE" error, wait for a key press and rejoin the main title loop

[X]

Subroutine SpawnEnemies (category: Landscape)

Calculate the number of enemies for this landscape, add them to the landscape and set the palette accordingly

[X]

Subroutine SpawnPlayer (category: Landscape)

Add the player object to the landscape, ideally placing it below all the enemies and in the bottom half of the landscape

Landscape: PreviewLandscape