328 lines
11 KiB
Python
328 lines
11 KiB
Python
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#!/usr/bin/env python3
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"""Generate the megademo's vaporwave picture, and its six frames of video.
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The picture is composed directly in akbasic's 16-colour palette space at
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160x120 -- one cell is a 5x5 pixel block on the 800x600 window -- then
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run-length encoded into string literals the demo decodes with INSTR and
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draws with three WIDTH-2 lines per run.
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The video is delta frames. Six phases of a perfect loop -- the floor
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grid advancing on a geometric progression parameterised so phase 6 lands
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exactly on phase 0, and the sun's slice pattern crawling on a period-six
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cycle -- and each frame encodes only the rows that differ from the one
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before it: an 'R' record carrying the row in two base-36 digits, then
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ordinary runs, with unreachable colour 'Q' as a skip. The rays are not
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in the encoding at all; the demo overdraws them live, which is what
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turns a thirty-run grid row back into a five-run one.
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Why strings and not DATA: the interpreter's DATA pool is 512 items and
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the stroke font already holds ~350 of them. A string literal carries one
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RLE run in two characters. TODO.md section 4 records the gap.
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Why the dithering is by row and not by pixel: per-pixel ordered dither
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shatters every gradient into one-cell runs, which is death for RLE.
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Row-phase dither keeps the runs long, and horizontal banding is what a
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CRT did to a gradient anyway.
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Usage:
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python3 vaporwave.py --preview OUT.png write a x5 preview of
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phase 0, rays included
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python3 vaporwave.py --splice MEGADEMO.BAS rewrite the generated
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block between the
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PICTURE-BEGIN/END markers
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"""
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import argparse
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import struct
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import sys
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import zlib
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W, H = 160, 120
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PHASES = 6
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# src/graphics_tables.c, Pepto's PAL measurement. Index 0 unused.
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PALETTE = [
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(0x00, 0x00, 0x00), (0x00, 0x00, 0x00), (0xff, 0xff, 0xff),
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(0x88, 0x39, 0x32), (0x67, 0xb6, 0xbd), (0x8b, 0x3f, 0x96),
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(0x55, 0xa0, 0x49), (0x40, 0x31, 0x8d), (0xbf, 0xce, 0x72),
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(0x8b, 0x54, 0x29), (0x57, 0x42, 0x00), (0xb8, 0x69, 0x62),
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(0x50, 0x50, 0x50), (0x78, 0x78, 0x78), (0x94, 0xe0, 0x89),
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(0x78, 0x69, 0xc4), (0x9f, 0x9f, 0x9f),
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]
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# Run encoding alphabets. Position decides meaning, so overlap is fine.
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# 'Q' is a skip (INSTR misses the colour table and the decoder's guard
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# draws nothing) and 'R' opens a row record.
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COLORCH = "ABCDEFGHIJKLMNOP"
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SKIP = "Q"
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ROWREC = "R"
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LENCH = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
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MAXRUN = len(LENCH)
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PAYLOAD = 240
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SUN_CX, SUN_CY, SUN_R = 80, 50, 30
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HORIZON = 74
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GRID_R = 1.55
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RAY_SPREAD = 26
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def band_mix(y, x, frac, a, b):
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threshold = (((y * 5) + ((x // 8) * 3)) % 8) / 8.0
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return b if frac > threshold else a
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def sky_color(y, x):
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bands = [(7, 5), (5, 11), (11, 9)]
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seg = HORIZON / len(bands)
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i = min(int(y / seg), len(bands) - 1)
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frac = (y - (i * seg)) / seg
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a, b = bands[i]
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return band_mix(y, x, frac, a, b)
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def sun_color(y):
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frac = (y - (SUN_CY - SUN_R)) / (2.0 * SUN_R)
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if frac < 0.4:
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return 8
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if frac < 0.7:
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return 9
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return 3
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def sun_sliced(y, phase):
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"""Period-six cuts below the sun's midline, crawling with the phase."""
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if y < SUN_CY:
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return False
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