Pentagram: Routine at B58A

Used by the routine at DrawChangedObjects.

Draws the objects in the list at DrawList so that the objects at the back are drawn before the objects in front of them. It takes the first object in the list that has not been drawn yet and compares it with each of the other objects that are waiting. If another object has to be drawn first, that object takes the place of the first object and is compared with the others in its turn. This carries on until an object is found that does not have to wait for any other object, and that one is drawn. This is repeated until the list is empty. The objects drawn are counted in DrawingWorkCount.

Used by the routine at DrawChangedObjects. Draws the objects in the list at DrawList so that the objects at the back are drawn before the objects in front of them. It takes the first object in the list that has not been drawn yet and compares it with each of the other objects that are waiting. If another object has to be drawn first, that object takes the place of the first object and is compared with the others in its turn. This carries on until an object is found that does not have to wait for any other object, and that one is drawn. This is repeated until the list is empty. The objects drawn are counted in DrawingWorkCount.
Clear the count and find the first object that is still waiting.
DrawObjectsInOrder	B58A	XOR A	Write 00 to DrawingWorkCount.
	B58B	LD ($A714),A	Write 00 to DrawingWorkCount.
	B58E	PUSH IX	Stash IX and IY on the stack.
	B590	PUSH IY	Stash IX and IY on the stack.
This entry point is used by the routine at ResolveObjectOrder. Find the first object in the list that has not been drawn.
DrawObjectsInOrder_Restart	B592	LD DE,$B55A	Point DE at DrawList.
Skip entries that have already been drawn.
DrawObjectsInOrder_NextCandidate	B595	LD A,(DE)	Fetch an index from the list.
	B596	INC DE	Move on to the next entry.
	B597	CP $FF	Jump to ResolveObjectOrder_Done if the end of the list has been reached, as every object has been drawn.
	B599	JP Z,ResolveObjectOrder_Done
	B59C	BIT 7,A	Jump to DrawObjectsInOrder_NextCandidate if the object has already been drawn.
	B59E	JR NZ,DrawObjectsInOrder_NextCandidate
	B5A0	CALL FindObjectAddress	Call FindObjectAddress to get the address of the object.
	B5A3	LD ($A719),DE	Remember the place in the list.
	B5A7	PUSH HL	Copy the address of the object to IX (using the stack).
	B5A8	POP IX	Copy the address of the object to IX (using the stack).
This entry point is used by the routine at ResolveObjectOrder. Compare it with each later object that is still waiting.
DrawObjectsInOrder_NextOther	B5AA	LD A,(DE)	Fetch an index from the list.
	B5AB	INC DE	Move on to the next entry.
	B5AC	CP $FF	Jump to ResolveObjectOrder_Draw if the end of the list has been reached, as nothing has to be drawn before the object considered.
	B5AE	JP Z,ResolveObjectOrder_Draw
	B5B1	BIT 7,A	Jump to DrawObjectsInOrder_NextOther if the object has already been drawn.
	B5B3	JR NZ,DrawObjectsInOrder_NextOther
	B5B5	CALL FindObjectAddress	Call FindObjectAddress to get the address of the object.
	B5B8	LD ($A71B),DE	Remember the place in the list.
	B5BC	PUSH HL	Copy the address of the object to IY (using the stack).
	B5BD	POP IY	Copy the address of the object to IY (using the stack).
	B5BF	PUSH IX	Copy IX to BC (using the stack).
	B5C1	POP BC	Copy IX to BC (using the stack).
	B5C2	AND A	Jump to DrawObjectsInOrder_NextOther if the other object is the object considered, as an object is not compared with itself.
	B5C3	SBC HL,BC
	B5C5	JR Z,DrawObjectsInOrder_NextOther
Each of the three directions gives a number. The number along z is 00 if the first object is above the other, 01 if the objects overlap along z and 02 if the first object is below. The number along y is 00 if the first object is to the north of the other, 03 if the objects overlap along y and 06 if the first object is to the south. The number along x is 00 if the first object is to the east of the other, 09 if the objects overlap along x and 12 if the first object is to the west. The three numbers are added together in C.
	B5C7	LD C,$00	Set the number to 00.
Compare the heights. The code is 0 if the object considered is above the other and so in front, 1 if they overlap and 2 if it is below the other.
	B5C9	LD A,(IY+$03)	Fetch the height of the top of the other object.
	B5CC	ADD A,(IY+$06)
	B5CF	LD L,A
	B5D0	LD A,(IX+$03)	Subtract it from the height of the bottom of the object considered.
	B5D3	SUB L
	B5D4	JR NC,DrawObjectsInOrder_CompareY	Jump to DrawObjectsInOrder_CompareY if the object considered is above the other.
	B5D6	LD A,(IX+$03)	Fetch the height of the top of the object considered.
	B5D9	ADD A,(IX+$06)
	B5DC	LD L,A
	B5DD	LD A,(IY+$03)	Subtract it from the height of the bottom of the other object.
	B5E0	SUB L
	B5E1	JR C,DrawObjectsInOrder_HeightCode	Jump to DrawObjectsInOrder_HeightCode if the two overlap.
	B5E3	INC C	Add one to the code, as the object considered is below the other.
DrawObjectsInOrder_HeightCode	B5E4	INC C	Add one to the number along z.
Add the number along y.
DrawObjectsInOrder_CompareY	B5E5	LD A,(IY+$02)	Fetch the highest y position of the other object.
	B5E8	ADD A,(IY+$05)
	B5EB	LD L,A
	B5EC	LD A,(IX+$02)	Subtract it from the lowest y position of the object considered.
	B5EF	SUB (IX+$05)
	B5F2	SUB L
	B5F3	JR NC,DrawObjectsInOrder_CompareX	Jump to DrawObjectsInOrder_CompareX if the object considered has the higher y position, and is behind.
	B5F5	LD A,(IX+$02)	Fetch the highest y position of the object considered.
	B5F8	ADD A,(IX+$05)
	B5FB	LD L,A
	B5FC	LD A,(IY+$02)	Subtract it from the lowest y position of the other object.
	B5FF	SUB (IY+$05)
	B602	SUB L
	B603	LD A,C	Fetch the number so far.
	B604	JR C,DrawObjectsInOrder_YCode	Jump to DrawObjectsInOrder_YCode if the two overlap.
	B606	ADD A,$03	Add three to the code, as the object considered has the lower y position.
DrawObjectsInOrder_YCode	B608	ADD A,$03	Add 03 to the number along y.
	B60A	LD C,A	Store the number.
Add the number along x.
DrawObjectsInOrder_CompareX	B60B	LD A,(IY+$01)	Fetch the highest x position of the other object.
	B60E	ADD A,(IY+$04)
	B611	LD L,A
	B612	LD A,(IX+$01)	Subtract it from the lowest x position of the object considered.
	B615	SUB (IX+$04)
	B618	SUB L
	B619	JR NC,DrawObjectsInOrder_Dispatch	Jump to DrawObjectsInOrder_Dispatch if the object considered has the higher x position, and is in front.
	B61B	LD A,(IX+$01)	Fetch the highest x position of the object considered.
	B61E	ADD A,(IX+$04)
	B621	LD L,A
	B622	LD A,(IY+$01)	Subtract it from the lowest x position of the other object.
	B625	SUB (IY+$04)
	B628	SUB L
	B629	LD A,C	Fetch the number so far.
	B62A	JR C,DrawObjectsInOrder_XCode	Jump to DrawObjectsInOrder_XCode if the two overlap.
	B62C	ADD A,$09	Add nine to the code, as the object considered has the lower x position.
DrawObjectsInOrder_XCode	B62E	ADD A,$09	Add 09 to the number along x.
	B630	LD C,A	Store the number.
Jump to the routine for the number.
DrawObjectsInOrder_Dispatch	B631	LD L,C	Use the number as the index into the table.
	B632	LD BC,$B638	Point BC at SortJumpTable.
	B635	JP RunGame_JumpViaTable	Jump to RunGame_JumpViaTable.
View the equivalent code in; Knight Lore Alien 8