Wheelie: Routine at 6424

6424: Copy Level Data to Level Buffer

Used by the routine at InitialiseLevel.

Input
HL	Source data pointer
DE	Destination buffer pointer

CopyLevelDataToBuffer

6424

LD C,$05

Set a counter in C for 05 rows to copy.

CopyLevelDataToBuffer_CopyRow

6426

LD B,$20

Set a counter in B for 20 bytes per row.

CopyLevelDataToBuffer_CopyByte

6428

LD A,(HL)

Fetch a terrain byte from the source data.

6429

INC HL

Move to the next source data byte.

642A

LD (DE),A

Write the byte to the destination buffer.

642B

INC E

Move to the next destination buffer position.

642C

DJNZ CopyLevelDataToBuffer_CopyByte

Decrease the bytes-per-row counter by one and loop back to CopyLevelDataToBuffer_CopyByte until the whole row has been copied.

Handle updating the destination pointer positioning after each row.

642E

DEC E

Step back one position.

642F

LD A,E

Align to a 20 byte boundary.

6430

AND %11100000

Keep only the upper 3 bits of the E co-ordinate.

6432

LD E,A

Reset to the start of the current 20 byte block.

6433

INC D

Move down one row.

6434

DEC C

Decrease the row counter by one.

6435

JR NZ,CopyLevelDataToBuffer_CopyRow

Jump back to CopyLevelDataToBuffer_CopyRow until all the rows have been copied.

Adjust the destination pointer after copying a complete 05x20 block.

6437

ADD A,$20

Move to the next block horizontally.

6439

LD E,A

Load the new horizontal position into E.

643A

RET Z

Return if E wrapped around to 00 (we reached the end of the buffer).

Move the destination pointer back up 05 rows to the original vertical position.

643B

LD A,D

D-=05.

643C

SUB $05

643E

LD D,A

643F

RET

Return.