Routines
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69E8: Update Streamer
Moves a streamer 08 pixels at a time in the direction it was fired. The streamer alternates between two sprites as it travels, and is removed if it hits a bug (see CheckWeaponHit) or reaches the edge of the play area.
Input
IX Streamer object
UpdateStreamer 69E8 CALL StoreEntity Remember the position and state using StoreEntity.
69EB LD A,(IX+$05) Jump to RemoveStreamer to remove the streamer if it has hit a bug.
69EE AND A
69EF JR NZ,RemoveStreamer
69F1 LD A,$08 A=08 (the distance to move).
69F3 BIT 6,(IX+$00) Jump to UpdateStreamer_Move if the streamer is moving right (bit 6 is not set).
69F7 JR Z,UpdateStreamer_Move
69F9 NEG Negate the distance (move left).
UpdateStreamer_Move 69FB ADD A,(IX+$01) Add the X position of the streamer.
69FE CP $18 Jump to RemoveStreamer to remove the streamer if it is past the left edge.
6A00 JR C,RemoveStreamer
6A02 CP $E0 Jump to RemoveStreamer to remove the streamer if it is past the right edge.
6A04 JR NC,RemoveStreamer
6A06 LD (IX+$01),A Write the new X position.
Choose the sprite for the new position, using bit 3 of the X position.
6A09 AND $08 Jump to UpdateStreamer_SecondSprite if bit 3 of the X position is not set.
6A0B JR Z,UpdateStreamer_SecondSprite
6A0D LD DE,$7991 DE=Sprite_Streamer_1 (the first sprite).
UpdateStreamer_Draw 6A10 CALL SetUpSprite_Address Set up the new sprite using SetUpSprite_Address.
6A13 EXX Switch to the shadow registers.
Choose the sprite for the previous position in the same way.
6A14 LD A,($5E0B) A=the previous X position from Actor.
6A17 AND $08 Jump to UpdateStreamer_PreviousSecondSprite if bit 3 of the previous X position is not set.
6A19 JR Z,UpdateStreamer_PreviousSecondSprite
6A1B LD DE,$7991 DE=Sprite_Streamer_1 (the first sprite).
UpdateStreamer_Previous 6A1E CALL SetUpPreviousSprite_Address Set up the previous sprite using SetUpPreviousSprite_Address.
6A21 CALL DisplayEntity_Compare Erase the previous sprite and draw the new one using DisplayEntity_Compare.
6A24 JP ColouriseSprite Jump to ColouriseSprite to colour the sprite.
UpdateStreamer_SecondSprite 6A27 LD DE,$79A2 DE=Sprite_Streamer_2 (the second sprite).
6A2A JR UpdateStreamer_Draw Jump to UpdateStreamer_Draw.
UpdateStreamer_PreviousSecondSprite 6A2C LD DE,$79A2 DE=Sprite_Streamer_2 (the second sprite).
6A2F JR UpdateStreamer_Previous Jump to UpdateStreamer_Previous.
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