# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1466437834 -7200
# Node ID 59d7fe6a9ba069922c713917213d6aac8258ca07
# Parent  ea19ad85988b2cea60688ffaaf549202edc823fe
Tidied, introducing a write_pixels function, removing PIXEL_POSITIONS.

diff -r ea19ad85988b -r 59d7fe6a9ba0 ula.py
--- a/ula.py	Mon Jun 20 16:57:12 2016 +0200
+++ b/ula.py	Mon Jun 20 17:50:34 2016 +0200
@@ -37,9 +37,6 @@
 
 MAX_PIXELPOS = MIN_PIXELPOS + MAX_WIDTH
 
-PIXEL_POSITIONS = 8     # the number of pixel positions per byte
-                        # (doubled or quadrupled in lower resolutions)
-
 SCREEN_LIMIT = 0x8000   # the first address after the screen memory
 MAX_MEMORY = 0x10000    # the number of addressable memory locations
 MAX_RAM = 0x10000       # the number of addressable RAM locations (64Kb in each IC)
@@ -304,8 +301,9 @@
     def in_frame(self): return MIN_PIXELLINE <= self.y < (MIN_PIXELLINE + self.display_height)
     def inside_frame(self): return MIN_PIXELLINE < self.y < (MIN_PIXELLINE + self.display_height)
     def read_pixels(self): return MIN_PIXELPOS <= self.x < MAX_PIXELPOS and self.in_frame()
+    def write_pixels(self): return self.pcycle != 0
+    def next_pixel(self): return self.xscale == 1 or (self.xscale == 2 and self.cycle & 0b10101010) or (self.xscale == 4 and self.cycle & 0b10001000)
     def end_pixels(self): return self.pcycle == 1
-    def next_pixel(self): return self.xscale == 1 or (self.xscale == 2 and self.cycle & 0b10101010) or (self.xscale == 4 and self.cycle & 0b10001000)
 
     def update(self):
 
@@ -467,7 +465,7 @@
 
         # Detect spacing between character rows.
 
-        if not self.pcycle:
+        if not self.write_pixels():
             self.video.colour = BLANK
 
         # For pixels within the frame, obtain and output the value.
@@ -480,7 +478,6 @@
 
             if self.next_pixel():
                 self.next_pixel_value()
-                self.pcycle = rotate(self.pcycle, self.depth)
 
                 # Finish writing pixels.
 
@@ -501,6 +498,7 @@
 
     def next_pixel_value(self):
         self.pdata = rotate(self.pdata, self.depth)
+        self.pcycle = rotate(self.pcycle, self.depth)
 
     def wrap_address(self):
         if self.address >= SCREEN_LIMIT: