Routines
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51842: Place Player At Door
Used by the routine at BuildRoom.
Moves the player to the doorway on the opposite side of a room to the one that it left the last room by. When the player goes through a door, TestDoorPassage sets the x or y position of the player to 0 or 255 to show which wall it went through. In the new room, the player is put in front of the door in the opposite wall, in the doorway, with the edge of the player nearest the centre of the room two units inside the wall. Nothing is done when the player is not at one of the edges, which is how a game starts.
Input
IX Address of the player
Fetch the wall distances, then see which way the player came.
PlacePlayerAtDoor 51842 LD A,(42781) Fetch RoomSizeX.
51845 SUB 2 Subtract 2.
51847 LD L,A Copy it to L.
Fetch the distance to the walls along y and take off two.
51848 LD A,(42782) Fetch RoomSizeY.
51851 SUB 2 Subtract 2.
51853 LD H,A Copy it to H.
51854 LD A,(IX+1) Fetch the x position of the player.
51857 AND A Jump to PlacePlayerAtDoor_EndOfX if the player went through the wall at the start of x.
51858 JR Z,PlacePlayerAtDoor_EndOfX
51860 INC A Jump to PlacePlayerAtDoor_StartOfX if it went through the wall at the end of x, which is 255.
51861 JR Z,PlacePlayerAtDoor_StartOfX
51863 LD A,(IX+2) Fetch the y position of the player.
51866 AND A Jump to PlacePlayerAtDoor_EndOfY if the player went through the wall at the start of y.
51867 JR Z,PlacePlayerAtDoor_EndOfY
51869 INC A Jump to PlacePlayerAtDoor_StartOfY if it went through the wall at the end of y, which is 255.
51870 JR Z,PlacePlayerAtDoor_StartOfY
51872 RET Return.
The player came from the north.
PlacePlayerAtDoor_StartOfY 51873 LD C,3 Set the wall to look for a door in, which is at the start of y.
51875 CALL FindDoor Call FindDoor to find the door and put the player in front of it.
51878 LD A,128 Set the position of the wall at the start of y, which is the centre of the room.
51880 SUB H Subtract the distance to the walls less two...
51881 SUB (IX+5) ...and the half size of the player along y, which puts the edge of the player nearest the centre of the room two units inside the wall.
PlacePlayerAtDoor_SetPlayerY 51884 LD (IX+2),A Store it as the y position of the player.
Mark the player to be drawn.
PlacePlayerAtDoor_MarkPlayerForDrawing 51887 SET 4,(IX+7) Set bit 4 of the flags.
51891 SET 4,(IX+39) Set bit 4 of the flags of the top half.
Copy the x position of the player to the body.
51895 LD A,(IX+1) Fetch the x position of the player.
51898 LD (IX+33),A Set the x position of the top half.
Copy the y position of the player to the body.
51901 LD A,(IX+2) Fetch the y position of the player.
51904 LD (IX+34),A Set the y position of the top half.
51907 RET Return.
The player came from the south.
PlacePlayerAtDoor_EndOfY 51908 LD C,2 Set the wall to look for a door in, which is at the end of y.
51910 CALL FindDoor Call FindDoor to find the door and put the player in front of it.
51913 LD A,H Fetch the distance to the walls less two.
51914 ADD A,128 Add the position of the centre of the room...
51916 ADD A,(IX+5) ...and the half size of the player along y.
51919 JR PlacePlayerAtDoor_SetPlayerY Jump to PlacePlayerAtDoor_SetPlayerY to store it.
The player came from the east.
PlacePlayerAtDoor_StartOfX 51921 LD C,1 Set the wall to look for a door in, which is at the start of x.
51923 CALL FindDoor Call FindDoor to find the door and put the player in front of it.
51926 LD A,128 Set the position of the wall at the start of x, which is the centre of the room.
51928 SUB L Subtract the distance to the walls less two...
51929 SUB (IX+4) ...and the half size of the player along x, which puts the edge of the player nearest the centre of the room two units inside the wall.
PlacePlayerAtDoor_SetPlayerX 51932 LD (IX+1),A Store it as the x position of the player.
51935 JR PlacePlayerAtDoor_MarkPlayerForDrawing Jump to PlacePlayerAtDoor_MarkPlayerForDrawing to finish.
The player came from the west.
PlacePlayerAtDoor_EndOfX 51937 LD C,0 Set the wall to look for a door in, which is at the end of x.
51939 CALL FindDoor Call FindDoor to find the door and put the player in front of it.
51942 LD A,L Fetch the distance to the walls less two.
51943 ADD A,128 Add the position of the centre of the room...
51945 ADD A,(IX+4) ...and the half size of the player along x.
51948 JR PlacePlayerAtDoor_SetPlayerX Jump to PlacePlayerAtDoor_SetPlayerX to store it.
View the equivalent code in;
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