calibs: optimise pixel-by-pixel mask

Calculating the focal-plane offset of each pixel is very slow (it always
has been, but it seems slower with the new Transform API), but the new
Transform API allows us to vectorise the calculation.

python/lsst/obs/hsc/calibs.py

@@ -78,17 +78,16 @@ def maskVignetting(self, mask, detector):
             mask |= bitMask
             return
         # We have to go pixel by pixel
-        x = np.empty((h, w))
-        y = np.empty_like(x)
-        for j in range(mask.getHeight()):
-            for i in range(mask.getWidth()):
-                x[j, i], y[j, i] = transform.applyForward(afwGeom.Point2D(i, j))
-        R = np.hypot(x - self.config.vignette.xCenter, y - self.config.vignette.yCenter)
-        isBad = R > self.config.vignette.radius
+        numPixels = w*h
+        xx, yy = np.meshgrid(np.arange(0, w, dtype=int), np.arange(0, h, dtype=int))
+        xyDetector = [afwGeom.Point2D(x, y) for x, y in zip(xx.reshape(numPixels), yy.reshape(numPixels))]
+        xyFocalPlane = transform.applyForward(xyDetector)
+        origin = afwGeom.Point2D(self.config.vignette.xCenter, self.config.vignette.yCenter)
+        r2 = np.array([pp.distanceSquared(origin) for pp in xyFocalPlane])
+        isBad = (r2 > self.config.vignette.radius**2).reshape((h, w))
         self.log.info("Detector %d has %f%% pixels vignetted" %
                       (detector.getId(), isBad.sum()/float(isBad.size)*100.0))
         maskArray = mask.getArray()
-        xx, yy = np.meshgrid(np.arange(w), np.arange(h))
         maskArray[yy[isBad], xx[isBad]] |= bitMask
 
     def maskBadAmps(self, mask, detector):