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77 lines
2.8 KiB
Python
77 lines
2.8 KiB
Python
#!/usr/bin/env python3
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"""Flat-shade an ASCII/binary STL from several directions.
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Used to answer one question with a picture instead of an argument: does a RECESSED faceted
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pocket read as an oriented feature, or does a concave feature collapse into a dark hole?
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"""
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import struct
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import sys
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import numpy as np
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from PIL import Image, ImageDraw
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LIGHT = np.array([0.35, -0.5, 0.78]); LIGHT /= np.linalg.norm(LIGHT)
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def load_stl(path):
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data = open(path, "rb").read()
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if data[:5] == b"solid" and b"facet" in data[:2000]:
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tris, cur = [], []
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for line in data.decode("ascii", "ignore").splitlines():
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s = line.split()
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if s and s[0] == "vertex":
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cur.append([float(x) for x in s[1:4]])
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if len(cur) == 3:
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tris.append(cur); cur = []
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return np.array(tris, dtype=float)
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n = struct.unpack("<I", data[80:84])[0]
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tris = np.empty((n, 3, 3), dtype=float)
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off = 84
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for i in range(n):
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v = struct.unpack("<12f", data[off:off + 48])
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tris[i] = np.array(v[3:12]).reshape(3, 3)
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off += 50
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return tris
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def render(tris, eye, target, path, size=(620, 460), scale=14.0, label=""):
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eye = np.array(eye, float); target = np.array(target, float)
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f = target - eye; f /= np.linalg.norm(f)
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up = np.array([0, 0, 1.0])
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if abs(np.dot(f, up)) > 0.999: up = np.array([0, 1.0, 0])
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r = np.cross(f, up); r /= np.linalg.norm(r)
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u = np.cross(r, f)
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cam = np.stack([r, u, f])
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w, h = size
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img = Image.new("RGB", size, (238, 240, 243)); d = ImageDraw.Draw(img)
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faces = []
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for t in tris:
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n = np.cross(t[1] - t[0], t[2] - t[0])
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ln = np.linalg.norm(n)
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if ln < 1e-12: continue
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n /= ln
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c = t.mean(axis=0)
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if np.dot(n, c - eye) > 0: continue # cull back faces
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P = (t - eye) @ cam.T
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lam = max(0.0, float(np.dot(n, LIGHT)))
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shade = 0.20 + 0.80 * lam
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col = tuple(int(255 * shade * ch) for ch in (0.86, 0.72, 0.35))
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poly = [(w / 2 + p[0] * scale, h / 2 - p[1] * scale) for p in P]
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faces.append((P[:, 2].mean(), poly, col))
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for _, poly, col in sorted(faces, key=lambda x: -x[0]):
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d.polygon(poly, fill=col)
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if label:
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d.rectangle([8, 8, 8 + 9 * len(label), 30], fill=(255, 255, 255))
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d.text((14, 14), label, fill=(20, 20, 20))
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img.save(path)
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if __name__ == "__main__":
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tris = load_stl(sys.argv[1])
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print("triangles:", len(tris))
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views = [((26, -22, 20), "iso"), ((0, 0, 34), "straight down +Z"),
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((4, -30, 9), "grazing"), ((-28, -10, 12), "from the tall end")]
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for i, (eye, lab) in enumerate(views):
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render(tris, eye, (0, 0, 0), f"fem-{i}.png", label=f"FEMALE POCKET — {lab}")
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print(f"fem-{i}.png")
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