Added class simplifiing ledbar output

* also added rainbow.py, which uses this class to create rainbow effect

host_python/README

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+INTRODUCTION:
+
+The scripts in this directory try to work according to the KISS principle. It 
+contains a script which redirects its stdin to serial device 
+(send_to_serial.py), one that simulates the ledbar and sends the data unaltered 
+from its stdin to its stdout, a module that helps programmers to program 
+various graphical effects and some example effect generators using this module.
+
+
+EXAMPLES:
+
+./rainbow.py | ./demo.py >/dev/null
+    - only simulate the rainbow effect, do not send it anywhere
+
+./rainbow.py | ./send_to_serial.py
+    - only send the data to the serial device, do not show the simulation
+
+./rainbow.py | ./demo.py | ./send_to_serial.py
+    - combine both options, show a simulation and send the data to the serial
+      device
+
+
+DEPENDENCIES:
+
+demo.py requires PyGame, Python wrapper around SDL
+send_to_serial.py requires PySerial, Python library for work with serial ports

host_python/ledbar.py

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+#!/usr/bin/python
+# vim:et:sw=4:ts=4:sts=4
+
+import sys
+import time
+
+class Ledbar:
+
+    def __init__(self, boxes=10, secs_per_frame=0.025):
+        self.boxes = boxes
+        self.secs_per_frame = secs_per_frame
+        self.last_update = time.time()
+        self.pixels = []
+        for i in xrange(boxes):
+            self.pixels.append([0, 0, 0])
+
+    def set_pixel(self, pixel, red, green, blue):
+        self.set_red(pixel, red)
+        self.set_green(pixel, green)
+        self.set_blue(pixel, blue)
+
+    def set_red(self, pixel, red):
+        if red < 0.0 or red > 1.0: raise ValueError('red has to be between 0.0 and 1.0')
+        self.pixels[pixel][0] = int(red*255.99)
+
+    def set_green(self, pixel, green):
+        if green < 0.0 or green > 1.0: raise ValueError('green has to be between 0.0 and 1.0')
+        self.pixels[pixel][1] = int(green*255.99)
+
+    def set_blue(self, pixel, blue):
+        if blue < 0.0 or blue > 1.0: raise ValueError('blue has to be between 0.0 and 1.0')
+        self.pixels[pixel][2] = int(blue*255.99)
+
+    def echo(self, s, no_newline=False):
+        sys.stderr.write(str(s) + ('' if no_newline else '\n'))
+
+    def update(self):
+        now = time.time()
+        delta = now - self.last_update
+        if delta < self.secs_per_frame:
+            time.sleep(self.secs_per_frame - delta)
+        try:
+            for p in self.pixels:
+                for c in p:
+                    sys.stdout.write(chr(c))
+            sys.stdout.flush()
+        except IOError:
+            return False
+        self.last_update += self.secs_per_frame
+        return True

host_python/rainbow.py

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+#!/usr/bin/python
+# vim:et:sw=4:ts=4:sts=4
+
+import sys
+
+from ledbar import Ledbar
+
+PIXELS = 10
+
+def update(t, i):
+    offset = float(i)/PIXELS
+    time = 0.005*t
+    phi = 6*offset+time
+    phase = int(phi%6)
+    part = phi % 1.0
+    inc = part
+    dec = 1-part
+    if   phase == 0: return (  1, inc,   0)
+    elif phase == 1: return (dec,   1,   0)
+    elif phase == 2: return (  0,   1, inc)
+    elif phase == 3: return (  0, dec,   1)
+    elif phase == 4: return (inc,   0,   1)
+    elif phase == 5: return (  1,   0, dec)
+
+l = Ledbar(PIXELS)
+t = 0
+work = True
+while work:
+    for i in xrange(PIXELS):
+        c = update(t, i)
+        l.set_pixel(i, c[0], c[1], c[2])
+    work = l.update()
+    t += 1