scale interpolated line step count according to line length, so all lines appear with the same brightness.

Makefile

@@ -27,11 +27,11 @@ output:
 	mkdir output
 
 output/%.wav: %.svg
-	./render.py -s 192000 -o $@ $<
+	./render.py -s 192000 -i 5 -o $@ $<
 
 output/%_rotate.wav: %.svg
 	for number in {000..360..5} ; do \
-	   ./render.py -s 192000 -t 0.1 -o output/$(@F)_$$number.wav -r $$number $< ; \
+	   ./render.py -s 192000 -i 5 -t 0.1 -o output/$(@F)_$$number.wav -r $$number $< ; \
 	done
 	ffmpeg -f concat -safe 0 -i <( for f in output/$(@F)_*.wav; do echo "file '$$(pwd)/$$f'"; done ) $@
 	rm output/$(@F)_*.wav

render.py

@@ -70,7 +70,7 @@ def read_image(filename, path_steps, volume_percent, angle_d):
         if dist_curr < dist_min:
             dist_min = dist_curr
 
-    p_center = [ p_min[0] + (p_max[0] - p_min[0] )/2  ,  p_min[1] + (p_max[1] - p_min[1] )/2]
+    p_center = [ p_min[0] + (p_max[0] - p_min[0]) / 2, p_min[1] + (p_max[1] - p_min[1]) / 2 ]
 
     # find min max for all rotatations
     for segment in path:
@@ -127,16 +127,20 @@ def read_image(filename, path_steps, volume_percent, angle_d):
         p = interpolate(p1, p2, f)
         add_point(p)
 
-    for n in range(0, len(points) - 1):
-        for step in range(0, path_steps):
-            add_segment(points[n], points[n + 1], step / path_steps)
+    def add_path(p1, p2):
+        l = math.sqrt((p2[0] - p1[0]) ** 2 + (p2[1] - p1[1]) ** 2)
+        ps = max(1, int(path_steps * l))
+        for step in range(0, ps):
+            add_segment(p1, p2, step / ps)
 
-    #add_point(points[len(points) - 1])
+    # walk path forwards
+    for n in range(0, len(points) - 1):
+        add_path(points[n], points[n + 1])
+    add_point(points[len(points) - 1])
 
+    # walk path backwards
     for n in range(len(points) - 2, -1, -1):
-        for step in range(0, path_steps):
-            add_segment(points[n + 1], points[n], step / path_steps)
-
+        add_path(points[n + 1], points[n])
     add_point(points[0])
 
     return data
@@ -163,8 +167,8 @@ def main():
                         help="Samplerate of output file in Hz. Defaults to 44.1kHz.")
     parser.add_argument("-v", "--volume", dest="volume", default=100.0, type=float,
                         help="Volume of output file in percent. Defaults to 100%%.")
-    parser.add_argument("-i", "--interpolate", dest="interpolate", default=10, type=int,
-                        help="Steps on interpolated paths. Defaults to 10.")
+    parser.add_argument("-i", "--interpolate", dest="interpolate", default=3, type=int,
+                        help="Steps on interpolated paths. Defaults to 3.")
     parser.add_argument("-r", "--rotate", dest="angle_d", default=0.0, type=float,
                         help="Angle to rotate image, in degrees. Defaults to 0 deg.")