Routines
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BC74: Write Attribute Block (3-Wide)
Used by the routine at ApplySpriteAttributes3Wide.
Writes a colour attribute to a 3-wide block of attribute cells at the position derived from the screen buffer address in HL. The height is 2 rows if Y-aligned, or 3 rows if not. The width is 2 or 3 columns depending on bit 0 of D (X alignment).
Input
C Attribute base high byte (58 for screen, F8 for room)
D Bit 0: extra column needed, Bit 1: extra row needed
E Attribute value to write (ink bits 0-2)
HL Screen buffer address
Check if the Y position crosses a character boundary; if so, an extra row of attributes is needed.
WriteAttributeBlock3Wide BC74 LD A,H A=H.
BC75 AND %00000111 Keep only bits 0-2 (sub-character Y offset).
BC77 OR A Jump to WriteAttributeBlock3Wide_CalcAddress if Y-aligned.
BC78 JR Z,WriteAttributeBlock3Wide_CalcAddress
BC7A SET 1,D Set bit 1 of D (extra row needed).
Convert the screen buffer address to the corresponding attribute address.
WriteAttributeBlock3Wide_CalcAddress BC7C LD A,H A=H.
BC7D RRCA Rotate right three positions.
BC7E RRCA
BC7F RRCA
BC80 AND %00000011 Keep only bits 0-1.
BC82 OR C Merge with the attribute base in C.
BC83 LD H,A H=A.
Branch based on whether an extra column is needed.
BC84 BIT 0,D Test bit 0 of D.
BC86 JR Z,WriteAttributeBlock3Wide_2Columns Jump to WriteAttributeBlock3Wide_2Columns if X-aligned (2 columns wide).
Not X-aligned: write attributes across 3 columns.
Write attribute to the first row (3 cells).
WriteAttributeBlock3Wide_3Columns BC88 LD A,(HL) Write the ink bits to *HL (preserve paper/brightness).
BC89 AND %11111000
BC8B OR E
BC8C LD (HL),A
BC8D INC HL Move to the next column.
BC8E LD A,(HL) Write the ink bits to *HL.
BC8F AND %11111000 Keep only bits 3-7.
BC91 OR E
BC92 LD (HL),A
BC93 INC HL Move to the next column.
BC94 LD A,(HL) Write the ink bits to *HL.
BC95 AND %11111000
BC97 OR E
BC98 LD (HL),A
Move back to the first column and down one attribute row.
BC99 DEC HL Move back two columns.
BC9A DEC HL
BC9B LD BC,$0020 HL+=0020 (move down one row).
BC9E ADD HL,BC
Write attribute to the second row (3 cells).
BC9F LD A,(HL) Write the ink bits to *HL.
BCA0 AND %11111000
BCA2 OR E
BCA3 LD (HL),A
BCA4 INC HL Move to the next column.
BCA5 LD A,(HL) Write the ink bits to *HL.
BCA6 AND %11111000
BCA8 OR E
BCA9 LD (HL),A
BCAA INC HL Move to the next column.
BCAB LD A,(HL) Write the ink bits to *HL.
BCAC AND %11111000
BCAE OR E
BCAF LD (HL),A
If Y-aligned, we're done. Otherwise write a third row.
BCB0 BIT 1,D Test bit 1 of D.
BCB2 RET Z Return if Y-aligned (no extra row needed).
Move back and down to the third row.
BCB3 DEC HL Move back two columns.
BCB4 DEC HL
BCB5 ADD HL,BC HL+=BC (move down one row).
Write attribute to the third row (3 cells).
BCB6 LD A,(HL) Write the ink bits to *HL.
BCB7 AND %11111000
BCB9 OR E
BCBA LD (HL),A
BCBB INC HL Move to the next column.
BCBC LD A,(HL) Write the ink bits to *HL.
BCBD AND %11111000
BCBF OR E
BCC0 LD (HL),A
BCC1 INC HL Move to the next column.
BCC2 LD A,(HL) Write the ink bits to *HL.
BCC3 AND %11111000
BCC5 OR E
BCC6 LD (HL),A
BCC7 RET Return.
X-aligned: write attributes across 2 columns only.
Write attribute to the first row (2 cells).
WriteAttributeBlock3Wide_2Columns BCC8 LD A,(HL) Write the ink bits to *HL.
BCC9 AND %11111000
BCCB OR E
BCCC LD (HL),A
BCCD INC HL Move to the next column.
BCCE LD A,(HL) Write the ink bits to *HL.
BCCF AND %11111000
BCD1 OR E
BCD2 LD (HL),A
Move back and down one attribute row.
BCD3 DEC HL Move back one column.
BCD4 LD BC,$0020 HL+=0020 (move down one row).
BCD7 ADD HL,BC
Write attribute to the second row (2 cells).
BCD8 LD A,(HL) Write the ink bits to *HL.
BCD9 AND %11111000
BCDB OR E
BCDC LD (HL),A
BCDD INC HL Move to the next column.
BCDE LD A,(HL) Write the ink bits to *HL.
BCDF AND %11111000
BCE1 OR E
BCE2 LD (HL),A
If Y-aligned, we're done. Otherwise write a third row.
BCE3 BIT 1,D Test bit 1 of D.
BCE5 RET Z Return if Y-aligned.
Move back and down to the third row.
BCE6 DEC HL Move back one column.
BCE7 ADD HL,BC HL+=BC (move down one row).
Write attribute to the third row (2 cells).
BCE8 LD A,(HL) Write the ink bits to *HL.
BCE9 AND %11111000
BCEB OR E
BCEC LD (HL),A
BCED INC HL Move to the next column.
BCEE LD A,(HL) Write the ink bits to *HL.
BCEF AND %11111000
BCF1 OR E
BCF2 LD (HL),A
BCF3 RET Return.
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