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Routines |
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Used by the routine at MainLoop.
Called every frame while the robot is alive. It tries to start a new enemy at a random position in the sector that the robot is in, and tries to start a new destroyer in the sector that is under attack. A new enemy starts as the sprites that show it materialising. The enemy is only started if there is a free entity, and if the cell that is chosen at random is empty.
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| SpawnEnemies | 42809 | LD A,(38544) | Fetch the type of the robot. | |
| 42812 | CP 16 | Return if it is below 16. | ||
| 42814 | RET C | |||
| 42815 | CP 48 | Return if it is 48 or above, as the robot is not in a walking state. | ||
| 42817 | RET NC | |||
| 42818 | LD HL,38608 | Point HL at the first of the six entities that are used for enemies. | ||
| 42821 | LD DE,16 | Each entity is 16 bytes long. | ||
| 42824 | LD B,6 | There are six entities to check. | ||
| SpawnEnemies_Find | 42826 | LD A,(HL) | Fetch the type of the entity. | |
| 42827 | AND A | Jump if it is not in use. | ||
| 42828 | JR Z,SpawnEnemies_UseFirstEntity | |||
| 42830 | ADD HL,DE | Move on to the next entity. | ||
| 42831 | DJNZ SpawnEnemies_Find | Loop back until all of them have been tried. | ||
| 42833 | JR SpawnEnemies_Destroyer | Jump to try to start a destroyer. | ||
| SpawnEnemies_UseFirstEntity | 42835 | PUSH HL | Copy the address of the entity into IX... | |
| 42836 | POP IX | Pop it into IX. | ||
| 42838 | LD B,16 | There are 16 bytes to clear. | ||
| SpawnEnemies_Clear | 42840 | LD (HL),0 | Clear a byte of the entity. | |
| 42842 | INC HL | Move on to the next byte. | ||
| 42843 | DJNZ SpawnEnemies_Clear | Loop back until the entity has been cleared. | ||
| 42845 | LD A,(38546) | Fetch the X cell of the camera... | ||
| 42848 | AND 48 | ...and keep the sector (a multiple of 16). | ||
| 42850 | LD E,A | Keep the sector column of the camera. | ||
| 42851 | LD A,(38423) | Fetch the random number... | ||
| 42854 | AND 15 | ...limited to 0-15... | ||
| 42856 | OR E | ...and combine it with the sector to choose the X cell. | ||
| 42857 | CP 47 | Jump if it is outside the map, which is 48 cells wide. | ||
| 42859 | JR NC,SpawnEnemies_Destroyer | |||
| 42861 | LD D,A | Keep the X cell... | ||
| 42862 | LD E,0 | ...and use zero for the fraction. | ||
| 42864 | LD A,(38548) | Fetch the Y cell of the camera... | ||
| 42867 | AND 48 | ...and keep the sector. | ||
| 42869 | LD L,A | Keep the sector row of the camera. | ||
| 42870 | LD A,(38421) | Fetch the frame counter... | ||
| 42873 | AND 15 | ...limited to 0-15... | ||
| 42875 | OR L | ...and combine it with the sector to choose the Y cell. | ||
| 42876 | CP 47 | Jump if it is outside the map, which is 48 cells high. | ||
| 42878 | JR NC,SpawnEnemies_Destroyer | |||
| 42880 | LD H,A | Keep the Y cell... | ||
| 42881 | LD L,0 | ...and use zero for the fraction. | ||
| 42883 | CALL FindMapCell | Find the cell using FindMapCell. | ||
| 42886 | JR NZ,SpawnEnemies_Destroyer | Jump if it is not empty. | ||
| 42888 | LD (IX+0),64 | Start the enemy with the first sprite of the sequence that shows it materialising. | ||
| 42892 | CALL SetPosition | Store its position. | ||
| 42895 | CALL CheckEnemyOverlap | Check whether another enemy is in the way using CheckEnemyOverlap. | ||
| 42898 | JR NC,SpawnEnemies_Random | Jump if there is not. | ||
| 42900 | LD (IX+0),0 | Otherwise cancel the new enemy... | ||
| 42904 | JR SpawnEnemies_Destroyer | ...and jump to try to start a destroyer. | ||
| SpawnEnemies_Random | 42906 | LD A,R | Fetch a number from the memory refresh register... | |
| 42908 | AND 243 | ...limit it to a time and a direction... | ||
| 42910 | LD (IX+7),A | ...and store it. | ||
| 42913 | LD A,(38488) | Fetch the number of sectors that have been activated. | ||
| 42916 | AND A | Test whether there are any. | ||
| 42917 | LD A,(38423) | Fetch the random number. | ||
| 42920 | JR NZ,SpawnEnemies_AnyKind | Jump if some sectors have been activated, to use any of the kinds of enemy. | ||
| 42922 | AND 5 | Otherwise limit the choice to the first two kinds of enemy... | ||
| SpawnEnemies_AnyKind | 42924 | AND 7 | ...and limit the choice to the eight entries of the table. | |
| 42926 | LD L,A | Use it as an index... | ||
| 42927 | LD H,0 | |||
| 42929 | LD BC,43038 | Point BC at EnemyTypes. | ||
| 42932 | ADD HL,BC | Add the index. | ||
| 42933 | LD A,(HL) | Fetch the type that the enemy is going to have... | ||
| 42934 | LD (IX+5),A | ...and store it. | ||
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Now try to start a destroyer. Destroyers are only started while a sector is under attack.
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| SpawnEnemies_Destroyer | 42937 | LD HL,38704 | Point HL at the first of the four entities that are used for destroyers. | |
| 42940 | LD DE,16 | Each entity is 16 bytes long. | ||
| 42943 | LD B,4 | There are four entities to check. | ||
| SpawnEnemies_FindDestroyer | 42945 | LD A,(HL) | Fetch the type of the entity. | |
| 42946 | AND A | Jump if it is not in use. | ||
| 42947 | JR Z,SpawnEnemies_UseSecondEntity | |||
| 42949 | ADD HL,DE | Move on to the next entity. | ||
| 42950 | DJNZ SpawnEnemies_FindDestroyer | Loop back until all of them have been tried. | ||
| 42952 | RET | Return. | ||
| SpawnEnemies_UseSecondEntity | 42953 | PUSH HL | Copy the address of the entity into IX... | |
| 42954 | POP IX | Pop it into IX. | ||
| 42956 | LD B,16 | There are 16 bytes to clear. | ||
| SpawnEnemies_ClearDestroyer | 42958 | LD (HL),0 | Clear a byte of the entity. | |
| 42960 | INC HL | Move on to the next byte. | ||
| 42961 | DJNZ SpawnEnemies_ClearDestroyer | Loop back until the entity has been cleared. | ||
| 42963 | LD A,(38471) | Fetch the code of the sector that is under attack... | ||
| 42966 | LD C,A | ...and keep it in C. | ||
| 42967 | RRA | Move the bits for the row into place... | ||
| 42968 | RRA | Shift the row one more place. | ||
| 42969 | AND 48 | ...and keep them. | ||
| 42971 | CP 48 | Return if there is no sector under attack. | ||
| 42973 | RET Z | |||
| 42974 | XOR 48 | Turn the row upside down... | ||
| 42976 | SUB 16 | ...and use it to find the Y cell of the sector. | ||
| 42978 | LD H,A | Keep the Y cell. | ||
| 42979 | LD A,(38423) | Fetch the random number... | ||
| 42982 | AND 15 | ...limited to 0-15... | ||
| 42984 | OR H | ...and combine it with the sector to choose the Y cell... | ||
| 42985 | LD H,A | ...and keep it in H. | ||
| 42986 | LD A,C | Fetch the code of the sector again. | ||
| 42987 | RLA | Move the bits for the column into place... | ||
| 42988 | RLA | |||
| 42989 | RLA | |||
| 42990 | AND 48 | ...and keep them. | ||
| 42992 | CP 48 | Return if there is no sector under attack. | ||
| 42994 | RET Z | |||
| 42995 | LD D,A | Keep the sector. | ||
| 42996 | LD A,R | Fetch a number from the memory refresh register... | ||
| 42998 | AND 15 | ...limited to 0-15... | ||
| 43000 | OR D | ...combine it with the sector to choose the X cell... | ||
| 43001 | LD D,A | ...and keep it in D. | ||
| 43002 | LD L,0 | Use zero for the fraction of the Y position... | ||
| 43004 | LD E,L | ...and of the X position. | ||
| 43005 | CALL FindMapCell | Find the cell using FindMapCell. | ||
| 43008 | RET NZ | Return if it is not empty. | ||
| 43009 | LD (IX+0),64 | Start the destroyer with the first sprite of the sequence that shows it materialising. | ||
| 43013 | CALL SetPosition | Store its position. | ||
| 43016 | CALL CheckEnemyOverlap | Check whether another enemy is in the way using CheckEnemyOverlap. | ||
| 43019 | JR NC,SpawnEnemies_SetType | Jump if there is not. | ||
| 43021 | LD (IX+0),0 | Otherwise cancel the new destroyer... | ||
| 43025 | RET | ...and return. | ||
| SpawnEnemies_SetType | 43026 | LD (IX+5),100 | Set the type that the destroyer will have when it has materialised. | |
| 43030 | LD A,R | Choose a random direction and time... | ||
| 43032 | AND 243 | |||
| 43034 | LD (IX+7),A | ...and store it. | ||
| 43037 | RET | Return. | ||
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