Routines
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44295: Prepare Entity Item
Used by the routine at BuildDrawList.
Converts the position of the entity with ConvertEntityPosition and adds it to the draw list. Entity types 12 and 16 are only appended with AppendEntityItem. Any other type is also given a record in the table of item records, which holds a copy of the rows of the screen buffer (which are 24 bytes wide) that lie under the entity, so that RestoreItemRows can put them back after the entity has been drawn.
Input
IX The entity
HL Pointer to the next free byte in the table of item records
Output
HL Updated pointer
PrepareEntityItem 44295 PUSH HL Save the item record pointer.
44296 CALL ConvertEntityPosition Convert the position of the entity.
44299 POP HL Restore the item record pointer.
44300 LD A,(IX+0) Fetch the type of the entity.
44303 CP 12 Jump to AppendEntityItem if it is type 12.
44305 JR Z,AppendEntityItem
44307 CP 16 Jump to AppendEntityItem if it is type 16.
44309 JR Z,AppendEntityItem
This entry point is used by the routine at BuildDrawList.
Entry point used for the extra records, which are passed in IY.
Count the item.
PrepareEntityItem_Table 44311 LD A,(62720) Fetch the number of prepared items.
44314 INC A Add one.
44315 LD (62720),A Store it again.
44318 PUSH HL Save the item record pointer.
44319 CALL TestRecordsAgainstEntity Check the 20-byte records for any that overlap the entity.
Check the 20-byte records for any that overlap the entity.
44322 LD HL,(45164) Fetch the next free item address.
Fetch the type.
44325 LD A,(IX+0) Fetch the type of the entity.
44328 CP 2 Jump to PrepareEntityItem_Entity if it is not type 2.
44330 JR NZ,PrepareEntityItem_Entity
44332 LD (HL),A Use the type as the flag for the item.
44333 PUSH IY IY moves into DE.
44335 POP DE (via the stack).
44336 INC HL Move to the address bytes.
44337 LD (HL),E Store the low byte of the record address.
44338 INC HL Move on.
44339 LD (HL),D Store the high byte of the record address.
44340 JR PrepareEntityItem_Header Jump to PrepareEntityItem_Header.
Add an entity item (flag 1) to the draw list.
PrepareEntityItem_Entity 44342 LD (HL),1 Set the flag of the item to 1.
44344 INC HL Move to the address bytes.
44345 PUSH IX IX moves into DE.
44347 POP DE (via the stack).
44348 LD (HL),E Store the low byte of the entity address.
44349 INC HL Move on.
44350 LD (HL),D Store the high byte of the entity address.
PrepareEntityItem_Header 44351 INC HL Move to the next free item.
44352 LD (45164),HL Store it.
44355 POP HL Restore the item record pointer.
Fetch the address in the screen buffer.
44356 LD E,(IX+24) Fetch the low byte of the address in the screen buffer.
44359 LD D,(IX+25) Fetch the high byte of the address in the screen buffer.
Work out how many bytes wide the record is, from field 22 and field 14.
44362 LD A,(IX+22) Read field 22.
44365 AND %00001111 Keep the low nibble.
44367 LD C,A Copy it into C.
44368 LD A,(IX+14) Read field 14.
44371 AND %00000111 Use bits 0-2.
44373 JR Z,PrepareEntityItem_Width Jump to PrepareEntityItem_Width if they are all zero.
44375 INC C Otherwise add one to the width.
Patch the operand of the BC load at 44438 and write the record header: the first byte is the width plus 24 then the address in the screen buffer.
PrepareEntityItem_Width 44376 LD A,232 Start from 232.
44378 SUB C Subtract the width.
44379 LD (44438),A Patch the operand of the BC load at 44436 with it.
44382 NEG Negate it to give the width plus 24.
44384 LD (HL),A Write it as the first byte of the record.
44385 INC HL Move on.
44386 LD (HL),E Write the low byte of the address in the screen buffer.
44387 INC HL Move on.
44388 LD (HL),D Write the high byte of the address in the screen buffer.
44389 INC HL Move on.
Patch the jump back into the unrolled copy so that only C bytes of each row are copied.
44390 SLA C Double the width.
44392 LD A,248 Start from 248.
44394 SUB C Subtract twice the width.
44395 LD (44443),A Patch the displacement of the DJNZ at PrepareEntityItem_Loop with it (the displacement is the byte at 44443).
44398 SUB 2 Subtract 2.
44400 LD (HL),A Write it as the fourth byte of the record.
44401 INC HL Move on.
Work out the number of rows from fields 23 and 15 and write it to the header.
44402 LD A,(IX+23) Read field 23.
44405 AND %00111111 Use bits 0-5.
44407 INC A Add one.
44408 LD B,A Copy it into B.
44409 LD A,(IX+15) Read field 15.
44412 CP B Compare it with the value in B.
44413 JR NC,PrepareEntityItem_Skip Jump to 44418 if it is not less.
44415 ADD A,2 Otherwise use field 15 plus 2.
44417 LD B,A Copy it into B.
PrepareEntityItem_Skip 44418 LD (HL),B Write the number of rows as the fifth byte of the record.
44419 INC HL Move on.
Swap, ready to copy the rows from the data into the table.
44420 EX DE,HL Swap the screen buffer address into HL and the table pointer into DE.
44421 JP PrepareEntityItem_Loop Jump into the copy loop.
PrepareEntityItem_Copy 44424 LDI Copy a byte and move on.
44426 LDI Copy a byte and move on.
44428 LDI Copy a byte and move on.
44430 LDI Copy a byte and move on.
44432 LDI Copy a byte and move on.
44434 LDI Copy a byte and move on.
44436 LD A,B Save the row counter.
44437 LD BC,65280 Set up the step back to the start of the next row (the low byte is patched at 44438).
44440 ADD HL,BC Move HL back to the start of the next row of the screen buffer.
44441 LD B,A Restore the row counter.
PrepareEntityItem_Loop 44442 DJNZ PrepareEntityItem_Loop Decrease the row counter and jump back into the copy chain (the displacement is patched at 44443) until all rows are copied.
44444 EX DE,HL Swap the pointer to the next free byte back into HL.
44445 RET Return.
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