| ← C3C1 | Map | C41E → |
C3D0: Advance the credits marquee one pixel and report exhaustion
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Scrolls the credits marquee left by one pixel and reports whether the message is finished. The text scrolls two pixels per frame.
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A phase counter cycles through eight pixel steps. On the eighth it drops the next glyph into the rightmost cell. One whole character is therefore consumed per eight pixel steps.
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| credits_scroll_step | C3D0 | LD A,(credits_scroll_phase) | Bump the phase counter; every 8th call (one full character width) it is time to feed the next glyph. | ||||
| C3D3 | INC A | ||||||
| C3D4 | CP $08 | ||||||
| C3D6 | JR NZ,credits_scroll_step_0 | ||||||
| C3D8 | CALL credits_scroll_feed | Feed the next glyph. On the message terminator, discard this frame's return and return $FF in A straight to the attract loop, past the shift below. | |||||
| C3DB | XOR A | On the feed path, restart the phase at 0. | |||||
| credits_scroll_step_0 | C3DC | LD (credits_scroll_phase),A | Store the phase counter (0 just after a feed, otherwise the incremented value). | ||||
| C3DF | LD HL,SCREEN_BASE+$1077 | Point at the top pixel row of the rightmost marquee cell (row 19 column 23). | |||||
| C3E2 | LD B,$08 | Walk the cell's pixel rows. | |||||
| C3E4 | LD C,$00 | Dead: C only feeds the two dead loads below. SLA shifts a blank pixel in at the right edge on its own. | |||||
| credits_scroll_step_1 | C3E6 | PUSH HL | Save the row's start byte for the next pixel row. | ||||
| C3E7 | LD A,C | Dead: A and D are reloaded from the seed each row but never read. | |||||
| C3E8 | LD D,C | ||||||
| C3E9 | SLA (HL) | Shift this 128-pixel row left one pixel. SLA seeds 0 into the rightmost pixel and its high bit into carry. The RL chain walks that carry leftward across the rest of the strip's cells, one byte at a time. | |||||
| C3EB | DEC L | ||||||
| C3EC | RL (HL) | ||||||
| C3EE | DEC L | ||||||
| C3EF | RL (HL) | ||||||
| C3F1 | DEC L | ||||||
| C3F2 | RL (HL) | ||||||
| C3F4 | DEC L | ||||||
| C3F5 | RL (HL) | ||||||
| C3F7 | DEC L | ||||||
| C3F8 | RL (HL) | ||||||
| C3FA | DEC L | ||||||
| C3FB | RL (HL) | ||||||
| C3FD | DEC L | ||||||
| C3FE | RL (HL) | ||||||
| C400 | DEC L | ||||||
| C401 | RL (HL) | ||||||
| C403 | DEC L | ||||||
| C404 | RL (HL) | ||||||
| C406 | DEC L | ||||||
| C407 | RL (HL) | ||||||
| C409 | DEC L | ||||||
| C40A | RL (HL) | ||||||
| C40C | DEC L | ||||||
| C40D | RL (HL) | ||||||
| C40F | DEC L | ||||||
| C410 | RL (HL) | ||||||
| C412 | DEC L | ||||||
| C413 | RL (HL) | ||||||
| C415 | DEC L | ||||||
| C416 | RL (HL) | ||||||
| C418 | POP HL | Advance to the next pixel row of the cell and repeat for all 8 rows. | |||||
| C419 | INC H | ||||||
| C41A | DJNZ credits_scroll_step_1 | ||||||
| C41C | XOR A | Return 0 in A: the message still has bytes to come. | |||||
| C41D | RET | ||||||
| ← C3C1 | Map | C41E → |