Routines
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25770: Level Object Placement And Special Terrain Generation
Used by the routine at InitialiseLevel.
Search the level buffer for special terrain markers (50) and replace with objects/ terrain.
ObjectPlacement_SpecialTerrain 25770 LD HL,40448 Load HL with LevelBuffer.
25773 LD BC,2560 Set the length of the level buffer in BC (2560 bytes).
ObjectPlacement_SpecialTerrain_Loop 25776 LD A,50 Search for the next 50 marker in the level buffer.
25778 CPIR
25780 LD A,B Return if no more markers were found.
25781 OR C
25782 RET Z
A marker was found.
25783 PUSH HL Stash the level buffer position and buffer counter on the stack.
25784 PUSH BC
25785 XOR A Clear A.
25786 NOP No operation.
25787 NOP
25788 LD B,4 Set a counter in B for 4 bytes to process.
25790 LD E,A E=A.
25791 DEC L Decrease L by one.
Determine what to place based on a random number.
25792 CALL GetRandomNumber Call GetRandomNumber.
25795 AND %00000111 A=random number between 0 and 7.
25797 CP E Jump to PlaceSimpleTerrain_Loop if A is lower than E.
25798 JR C,PlaceSimpleTerrain_Loop
Generate terrain/ object from the data table.
This part of the routine takes a random number between 0-7 and uses it to fetch terrain data:
Random Number Calculation Address
0 108 Data_Terrain_01
1 114 Data_Terrain_02
2 120 Data_Terrain_03
3 126 Data_Terrain_04
4 132 Data_Terrain_05
5 138 Data_Terrain_06
6 144 Data_Terrain_07
7 150 Data_Terrain_08
25800 CALL ContextualRandomNumber Call ContextualRandomNumber.
25803 AND %00000111 Ensure the random number is between 0-7.
Calculate the low-byte of the object data table address.
25805 ADD A,A E=(A*6)+108.
25806 LD E,A
25807 ADD A,A
25808 ADD A,E
25809 ADD A,108
25811 LD E,A
25812 LD D,180 Set the high-byte in D to 180.
Copy a byte of the 4 bytes of object data into the level buffer.
PlaceObjectData 25814 LD A,(DE) Fetch an object data byte.
25815 LD (HL),A Write the object data byte into the level buffer.
25816 INC E Move to the next object data byte.
25817 INC L Move to the next position in the level buffer.
25818 DJNZ PlaceObjectData Decrease the byte counter by one and loop back to PlaceObjectData until all the object data bytes have been written into the level buffer.
Check if the object has a vertical component.
25820 LD A,(DE) Jump to ObjectPlacement_SpecialTerrain_Next if the current data byte is zero (no vertical component).
25821 AND A
25822 JR Z,ObjectPlacement_SpecialTerrain_Next
Place the vertical component of the object.
25824 DEC L Decrease L by three.
25825 DEC L
25826 DEC L
25827 INC H Increment H by one.
25828 LD B,2 B=2.
PlaceVerticalComponent 25830 LD A,(HL) A=*HL.
25831 AND A Set flags.
25832 LD A,(DE) A=*DE.
25833 JR Z,PlaceVerticalByte Jump to PlaceVerticalByte if *HL is zero.
25835 INC A Increment A by two.
25836 INC A
PlaceVerticalByte 25837 LD (HL),A Write A to *HL.
25838 INC L Increment L by one.
25839 INC E Increment E by one.
25840 DJNZ PlaceVerticalComponent Decrease counter by one and loop back to PlaceVerticalComponent until counter is zero.
25842 JR ObjectPlacement_SpecialTerrain_Next Jump to ObjectPlacement_SpecialTerrain_Next.
Place a simple terrain block (block type: 1).
PlaceSimpleTerrain_Loop 25844 LD (HL),1 Write block type 1 to the level buffer pointer.
25846 INC L Move to the next buffer position.
25847 DJNZ PlaceSimpleTerrain_Loop Decrease the byte counter by one and loop back to PlaceSimpleTerrain_Loop until all bytes have been written into the buffer.
Continue searching for the next terrain markers.
ObjectPlacement_SpecialTerrain_Next 25849 POP BC Restore the buffer counter and level buffer position from the stack.
25850 POP HL
25851 JR ObjectPlacement_SpecialTerrain_Loop Jump to ObjectPlacement_SpecialTerrain_Loop.
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