Chase H.Q.: Routine at BDC1

BDC1: Clears the playfield then sets its attributes

The playfield is the lower two thirds of the screen - where the action happens. clear_playfield clears it, then the bitmap is reset to $FF and three bands of attributes are laid in: two rows of plain sky, three rows of bright sky and eleven rows of the stage's ground colour. Both edge columns of every playfield row are then stamped black on black, which hides the road overdraw at the screen borders. Used by the routines at load_stage, run_pregame_screen and set_up_stage.
set_playfield_attrs	BDC1	CALL clear_playfield	Call clear_playfield
	BDC4	LD HL,$4800	Clear the game screen pixels to $FF (bug: duplicates work just done)
	BDC7	LD DE,$4801
	BDCA	LD BC,$0FFF
	BDCD	LD (HL),$FF
	BDCF	LDIR
	BDD1	LD HL,$5900	Clear the game screen attributes to $28 (black over cyan) - first two rows only
	BDD4	LD DE,$5901
	BDD7	LD (HL),$28
	BDD9	LD C,$40
	BDDB	LDIR
	BDDD	LD (HL),$68	Clear the next three rows to $68 (bright, black over cyan)
	BDDF	LD C,$60
	BDE1	LDIR
	BDE3	LD A,($5CF4)	Clear the next 11 rows to the current ground colour
	BDE6	LD (HL),A
	BDE7	LD BC,$015F
	BDEA	LDIR
	BDEC	LD HL,$5900	Clear the edges of the game screen to black on black
	BDEF	LD DE,$001F
	BDF2	LD B,$10
cpsa_clear_edges_loop	BDF4	LD (HL),D
	BDF5	ADD HL,DE
	BDF6	LD (HL),D
	BDF7	INC HL
	BDF8	DJNZ cpsa_clear_edges_loop
	BDFA	RET	Return