--- fract/mandelzoom.cgi	2001/02/26 03:13:13	1.6
+++ fract/mandelzoom.cgi	2001/06/26 12:43:34	1.10
@@ -1,8 +1,15 @@
 #!/usr/bin/python
 
-import cgi, Image, ImageDraw, sys, math
+import cgi, Image, ImageDraw, sys, math, signal, errno, os
 from string import atoi, atof
 
+def handler(signum, frame):
+    signal.alarm(0)
+    raise os.error, (errno.ETIME, "Timer expired")
+
+signal.alarm(55)
+signal.signal(signal.SIGALRM, handler)
+
 # This is to get backtrace output
 sys.stderr = sys.stdout
 
@@ -35,6 +42,8 @@
 else:
     cy= 0.0
 
+# The length of the diagonal line from corner to corner.
+# Used as a measure of image size independent of aspect ratio.
 if form.has_key('diag'):
     diag= atof(form['diag'].value)
 else:
@@ -68,21 +77,23 @@
         ds="&debug=on"
     else:
         ds=""
+    # If the user has selected a specific point on the image
     if form.has_key('image.x') and form.has_key('image.y'):
         # Adjust cx and cy
-        ix= atof(form['image.x'].value)
-        iy= atof(form['image.y'].value)
+        ix= atof(form['image.x'].value) # Intermediate value
+        iy= atof(form['image.y'].value) # Intermediate value
         owidth= atof(form['owidth'].value)
         oheight= atof(form['oheight'].value)
-        diagp= math.sqrt(width**2 + height**2)
-        scale= diagp/diag
-        cx= (ix/scale) + (cx - (width / (scale*2)))
-        cy= ((height-iy)/scale) + (cy - (height / (scale*2)))
+        diagp= math.sqrt(owidth**2 + oheight**2) # Intermediate value
+        scale= diagp/diag               # Intermediate value
+        cx= (ix/scale) + (cx - (owidth / (scale*2)))
+        cy= ((oheight-iy)/scale) + (cy - (oheight / (scale*2)))
     if form.has_key('zoom'):
         zoom=atof(form['zoom'].value)
         diag=diag/zoom
     else:
-        # If no zoom provided, don't actually zoom
+        # If no zoom provided, don't actually zoom, but keep the
+        # default of ×2 zoom.
         zoom= 2.0
     print 'SRC="mandelzoom.cgi?type=image&width=%s&height=%s&iter=%s%s&diag=%s&cx=%s&cy=%s"' % (str(width), str(height), str(maxiter), ds, str(diag), str(cx), str(cy)),
     print 'ALIGN=BOTTOM HEIGHT="%s"' % (str(height)),
@@ -117,31 +128,38 @@
         print '<INPUT TYPE=HIDDEN NAME="%s" VALUE="%s">' % var
     print '<INPUT TYPE=HIDDEN NAME=type VALUE="html">'
 
-    print """</FORM>
+    print """</FORM><P>
+After changing any settings, don't forget to change the "Zoom" setting
+to "Pan" if you don't want to zoom when applying them.
 </BODY></HTML>"""
+    # Just exit, don't calculate an image.
     sys.exit(0)
 
+# c1 and c2 are the coordinates of two opposite corners.
 # Figure out c1 and c2 from width, height, diag, cx, and cy.
+
 # Diagonal in pixels
 diagp= math.sqrt(width**2 + height**2)
 # Scale between pixels and coordinates
 scale= diagp/diag
+# half the width/height in real numbers; intermediate values
 x= (width/2.0)/scale
 y= (height/2.0)/scale
 
+# The coordinates of two opposite corners
 c1= cx - x + (cy - y) * (0+1j)
 c2= cx + x + (cy + y) * (0+1j)
 
 #print width, height, diag, cx, cy, diagp, scale, x, y, c1, c2
 #sys.exit(0)
 
-#c1, c2 = (-2+2j), (2-2j)                # Corner coordinates
-
 # Force c1 to be upper left and c2 to be lower right
 c1, c2= complex(min(c1.real, c2.real), max(c1.imag, c2.imag)), \
         complex(max(c1.real, c2.real), min(c1.imag, c2.imag))
 
+# New image object
 mandel= Image.new("L", (width, height))
+# shortcut to the "Draw" method on the image object
 draw= ImageDraw.Draw(mandel)
 
 def drawrect((x1, y1), (x2, y2)):
@@ -203,6 +221,7 @@
                 draw.rectangle([x1, y1m, x2, y2m], fill= color)
 
 def constant(x, y):
+    "Return complex number from pixel coordinates x and y."
     creal= (float(x)/xmax)*(c2.real - c1.real)+c1.real
     cimag= (float(y)/ymax)*(c2.imag - c1.imag)+c1.imag
     return complex(creal, cimag)
@@ -247,7 +266,13 @@
     else:
         yto= yorig # End at x axis
 
-drawrect((0, yfrom), (xmax, yto))
+try:
+    drawrect((0, yfrom), (xmax, yto))
+except os.error, the_error:
+    if the_error[0] != errno.ETIME:
+        raise os.error, the_error
+
+signal.alarm(0)
 
 print "Content-type: image/png"
 print