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Routines |
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Used by the routine at DrawObject.
Called by DrawObject for an object that can be an entity. Checks that the object is in view and, if it is of kind 02 03 or 04 makes an entity for it in the pool of four entities at B670. The entity is of type 0C for kind 02 and type 10 for the other two. Any object that is in view is also recorded with RecordObject.
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Check that the object is not off the left or right edge of the view.
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| AddObjectEntity | BE01 | BIT 7,H | Jump to AddObjectEntity_RightEdge if bit 7 of the high byte of the screen column is set. | |||||||
| BE03 | JR NZ,AddObjectEntity_RightEdge | |||||||||
| BE05 | LD BC,$0028 | BC is 28 the margin on the left of the view. | ||||||||
| BE08 | ADD HL,BC | Add the margin to the screen column. | ||||||||
| BE09 | RL H | Rotate bit 7 of the high byte into the carry flag. | ||||||||
| BE0B | RET NC | Return if the object is off the left edge of the view. | ||||||||
| BE0C | JR AddObjectEntity_Position | Jump to AddObjectEntity_Position. | ||||||||
| AddObjectEntity_RightEdge | BE0E | LD BC,$80E0 | BC is 80E0 the right edge of the view. | |||||||
| BE11 | SBC HL,BC | Subtract it from the screen column. | ||||||||
| BE13 | RET NC | Return if the object is off the right edge of the view. | ||||||||
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Work out the coordinates of the object. The x coordinate is the column of the cell and the upper four bits of the first byte of the object. The y coordinate is the row of the cell and the lower four bits, multiplied by sixteen. They are kept on the stack for the entity.
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| AddObjectEntity_Position | BE14 | LD A,($5CBA) | Fetch the row of the cell and keep it in D. | |||||||
| BE17 | LD D,A | |||||||||
| BE18 | LD A,(IX+$00) | Fetch the first byte of the object. | ||||||||
| BE1B | ADD A,A | Multiply it by sixteen, to move the lower four bits to the top... | ||||||||
| BE1C | ADD A,A | |||||||||
| BE1D | ADD A,A | |||||||||
| BE1E | ADD A,A | |||||||||
| BE1F | LD E,A | ...and keep the result in E, as the low byte of the y coordinate. | ||||||||
| BE20 | LD HL,($5CB8) | Fetch the column of the cell into H. | ||||||||
| BE23 | LD A,(IX+$00) | Fetch the first byte of the object. | ||||||||
| BE26 | AND %11110000 | Keep the upper four bits. | ||||||||
| BE28 | LD L,A | Keep them in L, as the low byte of the x coordinate. | ||||||||
| BE29 | PUSH DE | Save the y coordinate. | ||||||||
| BE2A | PUSH HL | Save the x coordinate. | ||||||||
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Work out the screen row of the object. This is half of the difference between its x and y coordinates, plus the offset to the view, less the height of the object.
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| BE2B | SRL D | Halve the y coordinate. | ||||||||
| BE2D | RR E | |||||||||
| BE2F | SRL H | Halve the x coordinate. | ||||||||
| BE31 | RR L | |||||||||
| BE33 | SBC HL,DE | Subtract half of the y coordinate from half of the x coordinate. | ||||||||
| BE35 | LD DE,($C061) | Fetch the offset to the view from the drawing code. | ||||||||
| BE39 | ADD HL,DE | Add the offset. | ||||||||
| BE3A | LD A,(IX+$01) | Fetch the second byte of the object. | ||||||||
| BE3D | AND %01110000 | Keep the height in bits 4-6. | ||||||||
| BE3F | LD E,A | Keep it in E. | ||||||||
| BE40 | LD A,(IX+$02) | Fetch the third byte of the object. | ||||||||
| BE43 | ADD A,A | Move bit 6, the top bit of the height, to bit 7... | ||||||||
| BE44 | AND %10000000 | ...and keep it. | ||||||||
| BE46 | ADD A,E | Add the other bits of the height to find the height of the object. | ||||||||
| BE47 | LD E,A | Keep the low byte of the height in E. | ||||||||
| BE48 | LD D,$00 | Clear D. | ||||||||
| BE4A | SBC HL,DE | Subtract the height from the screen row. | ||||||||
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Check that the object is not above or below the view.
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| BE4C | BIT 7,H | Jump to AddObjectEntity_TopMargin if bit 7 of the high byte of the screen row is not set. | ||||||||
| BE4E | JR Z,AddObjectEntity_TopMargin | |||||||||
| BE50 | LD DE,$80A4 | DE is 80A4 the bottom of the view. | ||||||||
| BE53 | SBC HL,DE | Subtract it from the screen row. | ||||||||
| BE55 | POP BC | Restore the x coordinate. | ||||||||
| BE56 | POP DE | Restore the y coordinate. | ||||||||
| BE57 | RET NC | Return if the object is below the view. | ||||||||
| BE58 | JR AddObjectEntity_Pool | Jump to AddObjectEntity_Pool. | ||||||||
| AddObjectEntity_TopMargin | BE5A | LD DE,$0028 | DE is 28 the margin at the top of the view. | |||||||
| BE5D | ADD HL,DE | Add the margin to the screen row. | ||||||||
| BE5E | RL H | Rotate bit 7 of the high byte into the carry flag. | ||||||||
| BE60 | POP BC | Restore the x coordinate. | ||||||||
| BE61 | POP DE | Restore the y coordinate. | ||||||||
| BE62 | RET NC | Return if the object is above the view. | ||||||||
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Only objects of kind 02 03 and 04 that are not hidden have an entity. Record all of the others.
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| AddObjectEntity_Pool | BE63 | LD IY,$B670 | Point IY at the pool of four entities for objects. | |||||||
| BE67 | LD A,(IX+$02) | Fetch the third byte of the object. | ||||||||
| BE6A | BIT 7,A | Jump to RecordObject to record the object if it has one. | ||||||||
| BE6C | JP NZ,RecordObject | |||||||||
| BE6F | AND %00011111 | Keep the kind of the object. | ||||||||
| BE71 | CP $03 | Jump to AddObjectEntity_Search if it is kind 03. | ||||||||
| BE73 | JR Z,AddObjectEntity_Search | |||||||||
| BE75 | CP $04 | Jump to AddObjectEntity_Search if it is kind 04. | ||||||||
| BE77 | JR Z,AddObjectEntity_Search | |||||||||
| BE79 | CP $02 | Jump to RecordObject to record the object if it is not kind 02. | ||||||||
| BE7B | JP NZ,RecordObject | |||||||||
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Search the pool for an entity that is not in use.
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| AddObjectEntity_Search | BE7E | LD A,$04 | Set the number of entities left to try to 04. | |||||||
| BE80 | EX DE,HL | Put the y coordinate into HL. | ||||||||
| BE81 | LD DE,$0026 | Set the size of an entity, 26. | ||||||||
| AddObjectEntity_Next | BE84 | EX AF,AF' | Save the number of entities left. | |||||||
| BE85 | LD A,(IY+$00) | Fetch the type of the entity. | ||||||||
| BE88 | AND A | Test it. | ||||||||
| BE89 | JP NZ,AddObjectEntity_NextEntity | Jump to AddObjectEntity_NextEntity if the entity is in use. | ||||||||
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Make the entity. It starts as type 0C which is kind 02.
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| BE8C | LD (IY+$02),B | Store the high byte of the x coordinate in field 02 of the entity. | ||||||||
| BE8F | LD (IY+$03),C | Store the low byte of the x coordinate in field 03. | ||||||||
| BE92 | LD (IY+$05),H | Store the high byte of the y coordinate in field 05. | ||||||||
| BE95 | LD A,L | Fetch the low byte of the y coordinate. | ||||||||
| BE96 | ADD A,$04 | Add 04 to put the entity in the middle of the cell. | ||||||||
| BE98 | LD L,A | Keep it in L. | ||||||||
| BE99 | LD (IY+$06),L | Store it in field 06. | ||||||||
| BE9C | LD (IY+$1C),$00 | Set the animation counter in field 1C to 00. | ||||||||
| BEA0 | LD (IY+$1D),$20 | Set the first and last frames in field 1D to 20. | ||||||||
| BEA4 | LD (IY+$00),$0C | Set the type of the entity to 0C. | ||||||||
| BEA8 | LD (IY+$0B),$0C | Set the size in field 0B to 0C. | ||||||||
| BEAC | LD (IY+$0C),$0C | Set the size in field 0C to 0C. | ||||||||
| BEB0 | LD (IY+$0D),$01 | Set field 0D to 01. | ||||||||
| BEB4 | LD A,(IX+$02) | Fetch the third byte of the object. | ||||||||
| BEB7 | AND %00011111 | Keep the kind of the object. | ||||||||
| BEB9 | CP $02 | Jump to AddObjectEntity_Fields if it is kind 02. | ||||||||
| BEBB | JR Z,AddObjectEntity_Fields | |||||||||
| BEBD | LD (IY+$00),$10 | Change the type of the entity to 10. | ||||||||
| BEC1 | LD (IY+$1D),$00 | Set the first and last frames in field 1D to 00. | ||||||||
| BEC5 | LD (IY+$0D),$0A | Set field 0D to 0A. | ||||||||
| BEC9 | CP $03 | Jump to AddObjectEntity_Fields if it is kind 03. | ||||||||
| BECB | JR Z,AddObjectEntity_Fields | |||||||||
| BECD | LD (IY+$1D),$11 | Set the first and last frames in field 1D to 11 for kind 04. | ||||||||
| BED1 | LD (IY+$0D),$10 | Set field 0D to 10. | ||||||||
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Work out the z coordinate of the entity from the height of the object, less one.
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| AddObjectEntity_Fields | BED5 | LD A,(IX+$01) | Fetch the second byte of the object. | |||||||
| BED8 | AND %01110000 | Keep the height in bits 4-6. | ||||||||
| BEDA | LD E,A | Keep it in E. | ||||||||
| BEDB | LD (IY+$08),$01 | Set the high byte of the z coordinate in field 08 to 01. | ||||||||
| BEDF | LD A,(IX+$02) | Fetch the third byte of the object. | ||||||||
| BEE2 | ADD A,A | Move bit 6, the top bit of the height, to bit 7... | ||||||||
| BEE3 | AND %10000000 | ...and keep it. | ||||||||
| BEE5 | ADD A,E | Add the other bits of the height. | ||||||||
| BEE6 | SUB $01 | Take away one. | ||||||||
| BEE8 | LD (IY+$09),A | Store it in field 09 as the low byte of the z coordinate. | ||||||||
| BEEB | JR NC,AddObjectEntity_SetFrame | Jump to AddObjectEntity_SetFrame if it did not go below zero. | ||||||||
| BEED | DEC (IY+$08) | Decrease the high byte of the z coordinate by one. | ||||||||
| AddObjectEntity_SetFrame | BEF0 | LD A,(IY+$1D) | Fetch the first frame of the entity from field 1D. | |||||||
| BEF3 | AND %00001111 | Keep the frame. | ||||||||
| BEF5 | OR %10000000 | Set bit 7 to hide the entity until it is known to be in view. | ||||||||
| BEF7 | LD (IY+$01),A | Store it as the frame of the entity in field 01. | ||||||||
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Remember the address of the object in fields 1A and 1B of the entity.
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| BEFA | PUSH IX | Put the address of the object into DE, via the stack. | ||||||||
| BEFC | POP DE | |||||||||
| BEFD | LD (IY+$1A),D | Store the high byte in field 1A. | ||||||||
| BF00 | LD (IY+$1B),E | Store the low byte in field 1B. | ||||||||
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Check that the new entity is in view, and free it again if it is not.
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| BF03 | EXX | Switch to the alternate registers, to keep the coordinates. | ||||||||
| BF04 | PUSH IX | Save the address of the object. | ||||||||
| BF06 | PUSH IY | Put the address of the new entity into IX, via the stack. | ||||||||
| BF08 | POP IX | |||||||||
| BF0A | LD (IX+$16),$00 | Set the width of the sprite in field 16 to 00. | ||||||||
| BF0E | LD (IX+$17),$18 | Set the height of the sprite in field 17 to 18. | ||||||||
| BF12 | LD BC,$0010 | Set the margin to 10. | ||||||||
| BF15 | CALL TestEntityVisible | Test whether the entity is in view. | ||||||||
| BF18 | JR NZ,AddObjectEntity_Visible | Jump to AddObjectEntity_Visible if it is. | ||||||||
| BF1A | LD (IX+$00),$00 | Set the type of the entity to 00 to free it. | ||||||||
| BF1E | LD (IX+$01),$80 | Set the frame of the entity to 80 so that it is hidden. | ||||||||
| BF22 | POP IX | Restore the address of the object. | ||||||||
| BF24 | JR AddObjectEntity_Done | Jump to AddObjectEntity_Done. | ||||||||
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The entity is in view. Work out where it is on the screen and which sprite it has, and mark the object as having an entity so that it is not made again.
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| AddObjectEntity_Visible | BF26 | CALL ProjectEntity | Work out the screen position of the entity. | |||||||
| BF29 | CALL SetEntitySize | Fetch the sprite of the entity. | ||||||||
| BF2C | POP IX | Restore the address of the object. | ||||||||
| BF2E | POP HL | Take the return address off the stack. | ||||||||
| BF2F | POP DE | Take the screen column of the object off the stack. | ||||||||
| BF30 | POP BC | Take the second and third bytes of the object off the stack. | ||||||||
| BF31 | SET 7,B | Set bit 7 of the third byte, to show that the object has an entity. | ||||||||
| BF33 | PUSH BC | Put the bytes of the object back on the stack... | ||||||||
| BF34 | PUSH DE | ...then the screen column... | ||||||||
| BF35 | PUSH HL | ...and then the return address. | ||||||||
| AddObjectEntity_Done | BF36 | EXX | Switch back to the main registers. | |||||||
| BF37 | JR AddObjectEntity_Record | Jump to AddObjectEntity_Record to record the object. | ||||||||
| AddObjectEntity_NextEntity | BF39 | ADD IY,DE | Move on to the next entity of the pool. | |||||||
| BF3B | EX AF,AF' | Restore the number of entities left. | ||||||||
| BF3C | DEC A | Decrease the number of entities left. | ||||||||
| BF3D | JP NZ,AddObjectEntity_Next | Jump back to AddObjectEntity_Next until all four have been tried. | ||||||||
| AddObjectEntity_Record | BF40 | EX DE,HL | Put the y coordinate back into DE, and carry on into RecordObject to record the object. | |||||||
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Continue on to RecordObject.
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| Prev: BDBB | Up: Map | Next: BF41 |