Routines
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46027: Build Patterned Sprite
Used by the routine at DrawSprite.
Builds a copy of a sprite in the buffer at 23408 for an entity whose sprite has a pattern. The pattern is chosen by the entity and by the frame counter at FrameCounter, taken from the table at PatternTable, and each pair of bytes of the sprite is combined with a rotating mask from the table.
Input
A Bits 4-7 of field 22 of the entity, shifted
DE The address of the sprite
Output
DE The address of the buffer
The countdown nibble, already shifted down, selects the pattern. The low bits of the frame counter choose which mask, and which way it rotates.
BuildPatternedSprite 46027 RRA The pattern index is the countdown nibble, less four.
46028 RRA
46029 SUB 4
46031 LD B,A Keep the index.
46032 LD A,(41693) Read the frame counter.
46035 AND %00000011 Use its low two bits.
46037 OR B Combine them with the index.
46038 LD HL,46102 Look the mask up in the pattern table.
46041 CALL AddToAddress
46044 LD C,(HL) Read the mask.
46045 EX DE,HL The sprite is the source.
46046 LD A,(41693) Read the frame counter again.
46049 AND %00000001 Use its low bit.
46051 ADD A,A Turn that bit into a rotate one way or the other.
46052 ADD A,A
46053 ADD A,A
46054 INC A
46055 LD (46091),A Patch the rotate below with it.
46058 LD B,(HL) Remember the sprite's width and height at the front of the buffer.
46059 INC HL
46060 LD E,(HL)
46061 LD A,B
46062 LD (23408),A
46065 LD A,E
46066 LD (23409),A
46069 XOR A Move on to the sprite data and clear the total.
46070 INC HL
BuildPatternedSprite_Width 46071 ADD A,E Add the width once for every row.
46072 DJNZ BuildPatternedSprite_Width
46074 LD B,A The total is the number of byte pairs.
46075 LD (23770),SP Remember the stack and read the sprite through it.
46079 LD SP,HL
46080 LD HL,23410 The masked copy is built just after the width and height.
BuildPatternedSprite_Pairs 46083 POP DE Copy one byte and mask its partner.
46084 LD (HL),E
46085 INC HL
46086 LD A,D
46087 AND C
46088 LD (HL),A
46089 INC HL Move on to the next pair.
46090 RRC C Rotate the mask and repeat for the remaining pairs.
46092 DJNZ BuildPatternedSprite_Pairs
46094 LD SP,(23770) Restore the stack pointer.
46098 LD DE,23408 Return the buffer, width and height included.
46101 RET Return.
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