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Routines |
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Draws the columns of a sprite which is shifted to the right by two, four or six pixels. There is a piece of code for each of up to five columns of the sprite, and the code for the width of the sprite is where the jump at SpriteJumpOpcode starts. Each piece puts a column into two bytes of the buffer, using the table for the shift to split the mask and the pixels in two. The buffer address is in BC.
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The jump at SpriteJumpOpcode starts here for five columns.
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| DrawShiftedColumns | BE8A | CPL | Invert the screen byte, and fetch the mask into E and the pixels into D. | |
| BE8B | POP DE | |||
| BE8C | LD L,E | Clear the screen bits under the part of the mask which is in this byte. | ||
| BE8D | OR (HL) | |||
| BE8E | CPL | |||
| BE8F | LD L,D | Add the part of the pixels which is in this byte. | ||
| BE90 | OR (HL) | |||
| BE91 | LD (BC),A | Store the byte and move on to the next. | ||
| BE92 | INC BC | |||
| BE93 | INC H | Point H at the table for the bits which move into the next byte, and fetch that screen byte. | ||
| BE94 | LD L,E | |||
| BE95 | LD A,(BC) | |||
| BE96 | CPL | Clear the screen bits under the part of the mask which has moved into it. | ||
| BE97 | OR (HL) | |||
| BE98 | CPL | |||
| BE99 | LD L,D | Add the part of the pixels which has moved into it. | ||
| BE9A | OR (HL) | |||
| BE9B | DEC H | Point H back at the first table. | ||
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The jump at SpriteJumpOpcode starts here for four columns.
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| BE9C | CPL | Invert the screen byte, and fetch the mask into E and the pixels into D. | ||
| BE9D | POP DE | |||
| BE9E | LD L,E | Clear the screen bits under the part of the mask which is in this byte. | ||
| BE9F | OR (HL) | |||
| BEA0 | CPL | |||
| BEA1 | LD L,D | Add the part of the pixels which is in this byte. | ||
| BEA2 | OR (HL) | |||
| BEA3 | LD (BC),A | Store the byte and move on to the next. | ||
| BEA4 | INC BC | |||
| BEA5 | INC H | Point H at the table for the bits which move into the next byte, and fetch that screen byte. | ||
| BEA6 | LD L,E | |||
| BEA7 | LD A,(BC) | |||
| BEA8 | CPL | Clear the screen bits under the part of the mask which has moved into it. | ||
| BEA9 | OR (HL) | |||
| BEAA | CPL | |||
| BEAB | LD L,D | Add the part of the pixels which has moved into it. | ||
| BEAC | OR (HL) | |||
| BEAD | DEC H | Point H back at the first table. | ||
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The jump at SpriteJumpOpcode starts here for three columns.
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| BEAE | CPL | Invert the screen byte, and fetch the mask into E and the pixels into D. | ||
| BEAF | POP DE | |||
| BEB0 | LD L,E | Clear the screen bits under the part of the mask which is in this byte. | ||
| BEB1 | OR (HL) | |||
| BEB2 | CPL | |||
| BEB3 | LD L,D | Add the part of the pixels which is in this byte. | ||
| BEB4 | OR (HL) | |||
| BEB5 | LD (BC),A | Store the byte and move on to the next. | ||
| BEB6 | INC BC | |||
| BEB7 | INC H | Point H at the table for the bits which move into the next byte, and fetch that screen byte. | ||
| BEB8 | LD L,E | |||
| BEB9 | LD A,(BC) | |||
| BEBA | CPL | Clear the screen bits under the part of the mask which has moved into it. | ||
| BEBB | OR (HL) | |||
| BEBC | CPL | |||
| BEBD | LD L,D | Add the part of the pixels which has moved into it. | ||
| BEBE | OR (HL) | |||
| BEBF | DEC H | Point H back at the first table. | ||
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The jump at SpriteJumpOpcode starts here for two columns.
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| BEC0 | CPL | Invert the screen byte, and fetch the mask into E and the pixels into D. | ||
| BEC1 | POP DE | |||
| BEC2 | LD L,E | Clear the screen bits under the part of the mask which is in this byte. | ||
| BEC3 | OR (HL) | |||
| BEC4 | CPL | |||
| BEC5 | LD L,D | Add the part of the pixels which is in this byte. | ||
| BEC6 | OR (HL) | |||
| BEC7 | LD (BC),A | Store the byte and move on to the next. | ||
| BEC8 | INC BC | |||
| BEC9 | INC H | Point H at the table for the bits which move into the next byte, and fetch that screen byte. | ||
| BECA | LD L,E | |||
| BECB | LD A,(BC) | |||
| BECC | CPL | Clear the screen bits under the part of the mask which has moved into it. | ||
| BECD | OR (HL) | |||
| BECE | CPL | |||
| BECF | LD L,D | Add the part of the pixels which has moved into it. | ||
| BED0 | OR (HL) | |||
| BED1 | DEC H | Point H back at the first table. | ||
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The jump at SpriteJumpOpcode starts here for one column.
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| BED2 | CPL | Invert the screen byte, and fetch the mask into E and the pixels into D. | ||
| BED3 | POP DE | |||
| BED4 | LD L,E | Clear the screen bits under the part of the mask which is in this byte. | ||
| BED5 | OR (HL) | |||
| BED6 | CPL | |||
| BED7 | LD L,D | Add the part of the pixels which is in this byte. | ||
| BED8 | OR (HL) | |||
| BED9 | LD (BC),A | Store the byte and move on to the next. | ||
| BEDA | INC BC | |||
| BEDB | INC H | Point H at the table for the bits which move into the next byte, and fetch that screen byte. | ||
| BEDC | LD L,E | |||
| BEDD | LD A,(BC) | |||
| BEDE | CPL | Clear the screen bits under the part of the mask which has moved into it. | ||
| BEDF | OR (HL) | |||
| BEE0 | CPL | |||
| BEE1 | LD L,D | Add the part of the pixels which has moved into it. | ||
| BEE2 | OR (HL) | |||
| BEE3 | DEC H | Point H back at the first table. | ||
| BEE4 | LD (BC),A | Store the last byte of the row. | ||
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Continue on to FinishSpriteRow.
View the equivalent code in;
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| Prev: BE85 | Up: Map | Next: BEE5 |