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Routines |
| Prev: 716D | Up: Map | Next: 71BC |
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Used by the routines at DisplayEntity, RemoveEntity, DrawEntity, DrawTwoBytes and ActorUpdateSizeNext.
Erases the old sprite and draws the new sprite, a line at a time going up the screen. One line of the old sprite is erased by clearing its bits from the screen, then one line of the new sprite is drawn, and so on until both are done. The old sprite is held in the normal registers and the new sprite in the shadow registers. In each set C holds the number of lines left, DE the sprite data and HL the screen address.
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| MaskSprite | 7170 | LD A,C | Jump to ActorUpdateSizeNext if there are no more lines of the old sprite. | |||||
| 7171 | AND A | |||||||
| 7172 | JR Z,ActorUpdateSizeNext | |||||||
| 7174 | DEC C | Decrease the number of lines left by one. | ||||||
| 7175 | PUSH HL | Stash the screen address on the stack. | ||||||
| 7176 | LD A,($5E40) | Fetch the number of pixels to shift by (OldSpriteShift) and keep the pixel shift in B. | ||||||
| 7179 | LD B,A | |||||||
| 717A | EX DE,HL | HL=sprite data and DE=screen address. | ||||||
| 717B | PUSH DE | Stash the screen address on the stack. | ||||||
| 717C | LD D,(HL) | D=the first byte of this line of the sprite. | ||||||
| 717D | INC HL | Increment the sprite data pointer by one. | ||||||
| 717E | LD E,(HL) | E=the second byte of this line of the sprite. | ||||||
| 717F | INC HL | Increment the sprite data pointer by one. | ||||||
| 7180 | AND A | Jump to MaskSprite_Unshifted if the sprite is not shifted. | ||||||
| 7181 | JR Z,MaskSprite_Unshifted | |||||||
| 7183 | EX DE,HL | HL=sprite data and DE=this line of the sprite. | ||||||
| 7184 | XOR A | A=00. | ||||||
| MaskSprite_ShiftErase | 7185 | ADD HL,HL | Shift the line of the sprite left. | |||||
| 7186 | ADC A,A | Rotate the bit that was shifted out into A. | ||||||
| 7187 | DJNZ MaskSprite_ShiftErase | Decrease counter by one and loop back to MaskSprite_ShiftErase until counter is zero. | ||||||
| 7189 | EX DE,HL | DE=the shifted line of the sprite and HL=sprite data. | ||||||
| 718A | EX (SP),HL | HL=screen address (the sprite data pointer goes on the stack). | ||||||
| 718B | CPL | Invert the bits of the first byte of the line. | ||||||
| 718C | AND (HL) | Remove the bits from the screen. | ||||||
| 718D | LD (HL),A | Write the byte back to the screen. | ||||||
| 718E | INC L | Move onto the next screen byte. | ||||||
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This entry point is used by the routine at MaskSprite_Unshifted.
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| MaskSprite_EraseBytes | 718F | LD A,D | A=D. | |||||
| 7190 | CPL | Invert the bits. | ||||||
| 7191 | AND (HL) | Remove the bits from the screen. | ||||||
| 7192 | LD (HL),A | Write the byte back to the screen. | ||||||
| 7193 | INC L | Move onto the next screen byte. | ||||||
| 7194 | LD A,E | A=E. | ||||||
| 7195 | CPL | Invert the bits. | ||||||
| 7196 | AND (HL) | Remove the bits from the screen. | ||||||
| 7197 | LD (HL),A | Write the byte back to the screen. | ||||||
| 7198 | POP DE | Restore the sprite data pointer from the stack. | ||||||
| 7199 | POP HL | Restore the screen address of the start of the line from the stack. | ||||||
| 719A | CALL ScreenPosition1PixelAbove | Call ScreenPosition1PixelAbove to move up a line. | ||||||
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Now draw one line of the new sprite.
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| 719D | EXX | Switch to the shadow registers (the new sprite). | ||||||
| 719E | LD A,C | A=C. | ||||||
| 719F | AND A | Jump to MaskSprite_Next if there are no more lines of the new sprite. | ||||||
| 71A0 | JR Z,MaskSprite_Next | |||||||
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This entry point is used by the routine at ActorUpdateSizeNext.
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| MaskSprite_Draw | 71A2 | DEC C | Decrease the number of lines left by one. | |||||
| 71A3 | PUSH HL | Stash the screen address on the stack. | ||||||
| 71A4 | LD A,($5E41) | Fetch the number of pixels to shift by (NewSpriteShift) and keep the pixel shift in B. | ||||||
| 71A7 | LD B,A | |||||||
| 71A8 | EX DE,HL | HL=sprite data and DE=screen address. | ||||||
| 71A9 | PUSH DE | Stash the screen address on the stack. | ||||||
| 71AA | LD D,(HL) | D=the first byte of this line of the sprite. | ||||||
| 71AB | INC HL | Increment the sprite data pointer by one. | ||||||
| 71AC | LD E,(HL) | E=the second byte of this line of the sprite. | ||||||
| 71AD | INC HL | Increment the sprite data pointer by one. | ||||||
| 71AE | AND A | Jump to MaskSprite_DrawUnshifted if the sprite is not shifted. | ||||||
| 71AF | JR Z,MaskSprite_DrawUnshifted | |||||||
| 71B1 | EX DE,HL | HL=sprite data and DE=this line of the sprite. | ||||||
| 71B2 | XOR A | A=00. | ||||||
| MaskSprite_ShiftDraw | 71B3 | ADD HL,HL | Shift the line of the sprite left. | |||||
| 71B4 | ADC A,A | Rotate the bit that was shifted out into A. | ||||||
| 71B5 | DJNZ MaskSprite_ShiftDraw | Decrease counter by one and loop back to MaskSprite_ShiftDraw until counter is zero. | ||||||
| 71B7 | EX DE,HL | DE=the shifted line of the sprite and HL=sprite data. | ||||||
| 71B8 | EX (SP),HL | HL=screen address (the sprite data pointer goes on the stack). | ||||||
| 71B9 | OR (HL) | Merge the first byte of the line with the screen. | ||||||
| 71BA | LD (HL),A | Write the byte back to the screen. | ||||||
| 71BB | INC L | Move onto the next screen byte. | ||||||
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View the equivalent code in;
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| Prev: 716D | Up: Map | Next: 71BC |
