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Routines |
| Prev: 46769 | Up: Map | Next: 46841 |
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Handles a block that slides to and fro along the X axis. It works in the same way as HandleBlockMovingNorthSouth but with the X coordinate and the speed in X.
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| HandleBlockMovingEastWest | 46777 | CALL PlaySoundFromXPosition | Play the sound of a block moving along the X axis. | |||||
| 46780 | LD HL,265 | Set H to the offset of the X coordinate and L to the offset of the speed in X. | ||||||
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This entry point is used by the routine at HandleBlockMovingNorthSouth.
Modify the instructions that fetch the coordinate and store the speed.
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| HandleMovingBlock | 46783 | LD A,H | Fetch the offset of the coordinate. | |||||
| 46784 | LD (46816),A | Change the instruction at HandleMovingBlock_Coordinate to use it. | ||||||
| 46787 | LD A,L | Fetch the offset of the speed. | ||||||
| 46788 | LD (46833),A | Change the instruction at HandleMovingBlock_Speed to use it. | ||||||
| 46791 | CALL SetPixelAdjustments_Block | Set the pixel adjustments of a block. | ||||||
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Work out where the block should be: a position from 0 to 15 that goes up and down with the frame counter. The two blocks of a room are half a cycle apart, depending on the address of the object.
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| 46794 | PUSH IX | Copy IX to BC (using the stack). | ||||||
| 46796 | POP BC | |||||||
| 46797 | LD A,C | Fetch the low byte of the address of the object. | ||||||
| 46798 | RRCA | Rotate it right. | ||||||
| 46799 | AND %00010000 | Keep the bit which is different for the neighbouring objects. | ||||||
| 46801 | LD C,A | Stash it in C. | ||||||
| 46802 | LD A,(23458) | Fetch the frame counter from FrameCounter. | ||||||
| 46805 | ADD A,C | Add the offset of this block. | ||||||
| 46806 | BIT 4,A | Jump to HandleMovingBlock_Target if bit 4, which is the direction of the wave, is clear. | ||||||
| 46808 | JR Z,HandleMovingBlock_Target | |||||||
| 46810 | CPL | Invert the value, so that the wave goes down again. | ||||||
| HandleMovingBlock_Target | 46811 | AND %00001111 | Keep the lowest four bits as the position to go to. | |||||
| 46813 | LD C,A | Stash it in C. | ||||||
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Compare the block with the target. Redraw it if it is already there, otherwise set a speed of 1 towards the target.
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| HandleMovingBlock_Coordinate | 46814 | LD A,(IX+1) | Fetch the coordinate of the block. This is the instruction that is modified. | |||||
| 46817 | ADD A,8 | Add 8 to it. | ||||||
| 46819 | AND %00001111 | Keep the position of the block within its 16 steps. | ||||||
| 46821 | CP C | Compare it with the position that it should go to. | ||||||
| 46822 | JP Z,SetWipeAndDrawFlags | Jump to SetWipeAndDrawFlags if it is already there. | ||||||
| 46825 | LD A,1 | Set the speed to 1. | ||||||
| 46827 | JR C,HandleMovingBlock_Speed | Jump to HandleMovingBlock_Speed if the block is below the position that it should go to. | ||||||
| 46829 | NEG | Make the speed negative. | ||||||
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Set that speed, hold the block up, and move it.
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| HandleMovingBlock_Speed | 46831 | LD (IX+9),A | Set the speed of the block. This is the instruction that is modified. | |||||
| 46834 | LD (IX+11),1 | Set the speed in Z to 1, so that the block does not fall. | ||||||
| 46838 | JP MoveAndDrawObject | Move the block and flag it to be drawn again. | ||||||
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View the equivalent code in;
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| Prev: 46769 | Up: Map | Next: 46841 |