move design doc to CAD subfolder

docs/CAD/design/mate-connectors/render_stl.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+"""Flat-shade an ASCII/binary STL from several directions.
+
+Used to answer one question with a picture instead of an argument: does a RECESSED faceted
+pocket read as an oriented feature, or does a concave feature collapse into a dark hole?
+"""
+import struct
+import sys
+import numpy as np
+from PIL import Image, ImageDraw
+
+LIGHT = np.array([0.35, -0.5, 0.78]); LIGHT /= np.linalg.norm(LIGHT)
+
+
+def load_stl(path):
+    data = open(path, "rb").read()
+    if data[:5] == b"solid" and b"facet" in data[:2000]:
+        tris, cur = [], []
+        for line in data.decode("ascii", "ignore").splitlines():
+            s = line.split()
+            if s and s[0] == "vertex":
+                cur.append([float(x) for x in s[1:4]])
+                if len(cur) == 3:
+                    tris.append(cur); cur = []
+        return np.array(tris, dtype=float)
+    n = struct.unpack("<I", data[80:84])[0]
+    tris = np.empty((n, 3, 3), dtype=float)
+    off = 84
+    for i in range(n):
+        v = struct.unpack("<12f", data[off:off + 48])
+        tris[i] = np.array(v[3:12]).reshape(3, 3)
+        off += 50
+    return tris
+
+
+def render(tris, eye, target, path, size=(620, 460), scale=14.0, label=""):
+    eye = np.array(eye, float); target = np.array(target, float)
+    f = target - eye; f /= np.linalg.norm(f)
+    up = np.array([0, 0, 1.0])
+    if abs(np.dot(f, up)) > 0.999: up = np.array([0, 1.0, 0])
+    r = np.cross(f, up); r /= np.linalg.norm(r)
+    u = np.cross(r, f)
+    cam = np.stack([r, u, f])
+
+    w, h = size
+    img = Image.new("RGB", size, (238, 240, 243)); d = ImageDraw.Draw(img)
+    faces = []
+    for t in tris:
+        n = np.cross(t[1] - t[0], t[2] - t[0])
+        ln = np.linalg.norm(n)
+        if ln < 1e-12: continue
+        n /= ln
+        c = t.mean(axis=0)
+        if np.dot(n, c - eye) > 0: continue                  # cull back faces
+        P = (t - eye) @ cam.T
+        lam = max(0.0, float(np.dot(n, LIGHT)))
+        shade = 0.20 + 0.80 * lam
+        col = tuple(int(255 * shade * ch) for ch in (0.86, 0.72, 0.35))
+        poly = [(w / 2 + p[0] * scale, h / 2 - p[1] * scale) for p in P]
+        faces.append((P[:, 2].mean(), poly, col))
+    for _, poly, col in sorted(faces, key=lambda x: -x[0]):
+        d.polygon(poly, fill=col)
+    if label:
+        d.rectangle([8, 8, 8 + 9 * len(label), 30], fill=(255, 255, 255))
+        d.text((14, 14), label, fill=(20, 20, 20))
+    img.save(path)
+
+
+if __name__ == "__main__":
+    tris = load_stl(sys.argv[1])
+    print("triangles:", len(tris))
+    views = [((26, -22, 20), "iso"), ((0, 0, 34), "straight down +Z"),
+             ((4, -30, 9), "grazing"), ((-28, -10, 12), "from the tall end")]
+    for i, (eye, lab) in enumerate(views):
+        render(tris, eye, (0, 0, 0), f"fem-{i}.png", label=f"FEMALE POCKET — {lab}")
+        print(f"fem-{i}.png")