Routines
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C856: Draw Narrow Entity Sprite
Used by the routines at Main_Game_Loop, Remove_Entity_From_List, Process_Cluster_Entity and Apply_Entity_Velocity.
Entry point for drawing a narrow entity sprite. Sets draw mode (attribute writes enabled) and falls through to Render_Narrow_Entity_Sprite. XOR-renders 8 rows of 2 bytes each; the sprite type is looked up in Sprite_Pixel_Data_Table for the pixel data address, and the entity colour is written to the 2 attribute cells flanking each pixel row.
Input
HL Entity record pointer
Draw_Narrow_Entity_Sprite C856 EXX Set draw mode: set the attribute-write flag in D'.
C857 LD D,$01
C859 EXX
This entry point is used by the routine at Erase_Narrow_Entity_Sprite.
Compute the sprite pixel data pointer and screen coordinate.
Render_Narrow_Entity_Sprite C85A LD B,H Copy the entity record pointer to BC.
C85B LD C,L
C85C LD E,(HL) Read the sprite type byte and form a word offset in DE.
C85D SLA E
C85F LD D,$00
C861 LD HL,$C60C Look up the sprite pixel data address in the table at Sprite_Pixel_Data_Table.
C864 ADD HL,DE
C865 LD E,(HL)
C866 INC HL
C867 LD D,(HL)
C868 LD H,B Restore the entity record pointer to HL.
C869 LD L,C
C86A INC HL Advance past the sprite type byte and load the screen row address high byte from the entity record.
C86B LD B,$46
C86D LD C,(HL)
C86E INC HL
C86F SLA C Shift the coordinate into B to build the screen address high byte.
C871 RL B
C873 PUSH BC Stash the screen coordinate on the stack.
C874 LD A,(HL) Load the column byte, clear HL, and distribute its bits into L via successive right-rotations to form the pixel offset.
C875 AND A
C876 LD HL,$0000
C879 RRA
C87A RR L
C87C RRA
C87D RR L
C87F RRA
C880 RR L
C882 RRC L
C884 ADD HL,DE Add the sprite data base to the offset, set BC as the sprite pixel data pointer, and restore the screen coordinate.
C885 LD B,H
C886 LD C,L
C887 POP HL
C888 EXX
C889 LD C,A Stash the column offset in alternate C and return to the main register set.
C88A EXX
Row 1: XOR-render the first sprite row and optionally write the entity colour to the flanking attribute cells.
C88B ADD A,(HL) Compute the first screen row address from the entity record into DE.
C88C LD E,A
C88D INC HL
C88E LD D,(HL)
C88F INC HL
C890 LD A,(BC) XOR-render 2 sprite pixel bytes at the first screen row.
C891 EX DE,HL
C892 XOR (HL)
C893 LD (HL),A
C894 INC BC
C895 INC HL
C896 LD A,(BC)
C897 INC BC
C898 XOR (HL)
C899 LD (HL),A
C89A EXX Check whether attribute writes are enabled; jump to Render_Narrow_Entity_Sprite_Row2 to skip the colour write in erase mode.
C89B LD A,D
C89C AND A
C89D EXX
C89E JR Z,Render_Narrow_Entity_Sprite_Row2
C8A0 LD A,H Convert the screen address high byte to an attribute address.
C8A1 RRCA
C8A2 RRCA
C8A3 RRCA
C8A4 AND %00000011 Mask to the attribute page bits.
C8A6 OR %01011000 Set the attribute area high byte.
C8A8 LD H,A Update H to point into attribute RAM.
C8A9 EXX Fetch the entity colour via B' and write it to the first attribute cell.
C8AA LD A,B
C8AB EXX
C8AC LD (HL),A
C8AD DEC HL
C8AE LD (HL),A Write the entity colour to the second attribute cell.
Rows 2–7: XOR-render the remaining sprite rows without attribute writes (attribute colour was set once on row 1).
Render_Narrow_Entity_Sprite_Row2 C8AF EX DE,HL Restore the entity record pointer and fetch the column offset from alternate C.
C8B0 EXX
C8B1 LD A,C
C8B2 EXX
C8B3 ADD A,(HL) Compute the second screen row address from the entity record.
C8B4 LD E,A
C8B5 INC HL
C8B6 LD D,(HL)
C8B7 INC HL
C8B8 LD A,(BC) XOR-render 2 sprite bytes at the second screen row and restore the entity record pointer.
C8B9 EX DE,HL
C8BA XOR (HL)
C8BB LD (HL),A
C8BC INC BC
C8BD INC HL
C8BE LD A,(BC)
C8BF INC BC
C8C0 XOR (HL)
C8C1 LD (HL),A
C8C2 EX DE,HL
C8C3 EXX Fetch the column offset from alternate C.
C8C4 LD A,C
C8C5 EXX
C8C6 ADD A,(HL) Compute the third screen row address from the entity record.
C8C7 LD E,A
C8C8 INC HL
C8C9 LD D,(HL)
C8CA INC HL
C8CB LD A,(BC) XOR-render 2 sprite bytes at the third screen row and restore.
C8CC EX DE,HL
C8CD XOR (HL)
C8CE LD (HL),A
C8CF INC BC
C8D0 INC HL
C8D1 LD A,(BC)
C8D2 INC BC
C8D3 XOR (HL)
C8D4 LD (HL),A
C8D5 EX DE,HL
C8D6 EXX Fetch the column offset from alternate C.
C8D7 LD A,C
C8D8 EXX
C8D9 ADD A,(HL) Compute the fourth screen row address from the entity record.
C8DA LD E,A
C8DB INC HL
C8DC LD D,(HL)
C8DD INC HL
C8DE LD A,(BC) XOR-render 2 sprite bytes at the fourth screen row and restore.
C8DF EX DE,HL
C8E0 XOR (HL)
C8E1 LD (HL),A
C8E2 INC BC
C8E3 INC HL
C8E4 LD A,(BC)
C8E5 INC BC
C8E6 XOR (HL)
C8E7 LD (HL),A
C8E8 EX DE,HL
C8E9 EXX Fetch the column offset from alternate C.
C8EA LD A,C
C8EB EXX
C8EC ADD A,(HL) Compute the fifth screen row address from the entity record.
C8ED LD E,A
C8EE INC HL
C8EF LD D,(HL)
C8F0 INC HL
C8F1 LD A,(BC) XOR-render 2 sprite bytes at the fifth screen row and restore.
C8F2 EX DE,HL
C8F3 XOR (HL)
C8F4 LD (HL),A
C8F5 INC BC
C8F6 INC HL
C8F7 LD A,(BC)
C8F8 INC BC
C8F9 XOR (HL)
C8FA LD (HL),A
C8FB EX DE,HL
C8FC EXX Fetch the column offset from alternate C.
C8FD LD A,C
C8FE EXX
C8FF ADD A,(HL) Compute the sixth screen row address from the entity record.
C900 LD E,A
C901 INC HL
C902 LD D,(HL)
C903 INC HL
C904 LD A,(BC) XOR-render 2 sprite bytes at the sixth screen row and restore.
C905 EX DE,HL
C906 XOR (HL)
C907 LD (HL),A
C908 INC BC
C909 INC HL
C90A LD A,(BC)
C90B INC BC
C90C XOR (HL)
C90D LD (HL),A
C90E EX DE,HL
C90F EXX Fetch the column offset from alternate C.
C910 LD A,C
C911 EXX
C912 ADD A,(HL) Compute the seventh screen row address from the entity record.
C913 LD E,A
C914 INC HL
C915 LD D,(HL)
C916 INC HL
C917 LD A,(BC) XOR-render 2 sprite bytes at the seventh screen row and restore the entity record pointer.
C918 EX DE,HL
C919 XOR (HL)
C91A LD (HL),A
C91B INC BC
C91C INC HL
C91D LD A,(BC)
C91E INC BC
C91F XOR (HL)
C920 LD (HL),A
C921 EX DE,HL
Row 8: XOR-render the final sprite row and write the entity colour to the flanking attribute cells if in draw mode.
C922 EXX Fetch the column offset from alternate C.
C923 LD A,C
C924 EXX
C925 ADD A,(HL) Compute the eighth screen row address from the entity record.
C926 LD E,A
C927 INC HL
C928 LD D,(HL)
C929 INC HL
C92A LD A,(BC) XOR-render 2 sprite bytes at the eighth screen row.
C92B EX DE,HL
C92C XOR (HL)
C92D LD (HL),A
C92E INC BC
C92F INC HL
C930 LD A,(BC)
C931 INC BC
C932 XOR (HL)
C933 LD (HL),A
C934 EXX Return without writing attributes if in erase mode.
C935 LD A,D
C936 AND A
C937 EXX
C938 RET Z
C939 LD A,H Convert the screen address high byte to an attribute address.
C93A RRCA
C93B RRCA
C93C RRCA
C93D AND %00000011 Mask to the attribute page bits.
C93F OR %01011000 Set the attribute area high byte.
C941 LD H,A Update H to point into attribute RAM.
C942 EXX Fetch the entity colour via B' and write it to the first attribute cell.
C943 LD A,B
C944 EXX
C945 LD (HL),A
C946 DEC HL Write the entity colour to the second attribute cell.
C947 LD (HL),A
C948 RET Return.
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