ykcheungab
47 lines
1.8 KiB
Python
47 lines
1.8 KiB
Python
"""Convex camera-cell stroke shapes and perspective-preserving clipping."""
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import math
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import random
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from patch_geometry import clip_halfspace, interpolate_uv
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def capsule_in_cell(i, j, nx, ny, seed, width_ratio=0.42, length_ratio=0.84):
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"""Return a round-ended stroke wholly inside one normalized camera cell."""
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if not 0 < width_ratio <= length_ratio < 1:
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raise ValueError("require 0 < width_ratio <= length_ratio < 1")
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rng = random.Random((seed * 1000003 + i * 9176 + j * 6113) & 0xFFFFFFFF)
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angle = rng.uniform(0, math.pi)
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radius = width_ratio / 2
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half_body = (length_ratio - width_ratio) / 2
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outline = []
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for centre, start in ((half_body, -math.pi / 2), (-half_body, math.pi / 2)):
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for step in range(9):
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theta = start + math.pi * step / 8
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x = centre + radius * math.cos(theta)
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y = radius * math.sin(theta)
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xr = x * math.cos(angle) - y * math.sin(angle)
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yr = x * math.sin(angle) + y * math.cos(angle)
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outline.append(((i + 0.5 + xr) / nx, (j + 0.5 + yr) / ny))
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return outline
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def clip_to_stroke(fragment, outline):
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"""Clip a projected triangle while retaining its perspective attributes."""
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points = fragment
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for a, b in zip(outline, outline[1:] + outline[:1]):
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dx, dy = b[0] - a[0], b[1] - a[1]
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points = clip_halfspace(
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points,
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lambda p, a=a, dx=dx, dy=dy: dx * (p[1] - a[1]) - dy * (p[0] - a[0]),
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)
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if len(points) < 3:
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return []
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return points
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def projected_stroke_uv(fragment, loop_uvs, outline):
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"""Resolve a clipped camera stroke through the same UV interpolation as patches."""
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return [interpolate_uv(point, loop_uvs)
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for point in clip_to_stroke(fragment, outline)]
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