# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1466372259 -7200
# Node ID d5e05e69b3266e0f76c7ab8fc5eb4d19b03911f7
# Parent  3594df6469c1ac8588478ef9c4703e5c1629046f
Replaced the pixel buffer with translated byte data and a function converting
this data to colour values for each pixel.

diff -r 3594df6469c1 -r d5e05e69b326 ula.py
--- a/ula.py	Sun Jun 19 21:21:28 2016 +0200
+++ b/ula.py	Sun Jun 19 23:37:39 2016 +0200
@@ -219,7 +219,7 @@
         self.access = 0         # counter used to determine whether a byte needs reading
         self.have_pixels = 0    # whether pixel data has been read
         self.writing_pixels = 0 # whether pixel data can be written
-        self.buffer = [BLANK]*8 # pixel buffer for decoded RAM data
+        self.pdata = [0]*8      # decoded RAM data for pixel output
 
         self.cycle = ShiftRegister()    # 8-state counter within each 2MHz period
 
@@ -377,7 +377,6 @@
 
             if not self.writing_pixels and self.have_pixels:
                 self.buffer_index = 0
-                self.fill_pixel_buffer()
                 self.writing_pixels = 1
 
         # Latch row address, set column address (for ULA access only).
@@ -445,6 +444,10 @@
             if access_ram:
                 self.data = self.data | self.ram.data
                 self.have_pixels = 1
+
+                # Rearrange the byte value.
+
+                self.pdata = decode(self.data, self.depth)
             else:
                 self.cpu_transfer_low()
 
@@ -506,37 +509,28 @@
         # For pixels within the frame, obtain and output the value.
 
         else:
-            self.video.colour = self.buffer[self.buffer_index]
+            self.video.colour = self.get_pixel()
 
             # Scale pixels horizontally, only accessing the next pixel value
             # after the required number of scan positions.
 
             if self.x % self.xscale == 0:
-                self.buffer_index += 1
+                self.buffer_index += self.depth
 
             # Finish writing pixels.
 
             if self.x % PIXEL_POSITIONS == 0:
                 self.writing_pixels = 0
 
-    def fill_pixel_buffer(self):
+    def get_pixel(self):
 
         """
-        Fill the pixel buffer by translating memory content for the current
+        Return the current pixel by translating memory content for the current
         mode.
         """
 
-        # Rearrange the byte value.
-
-        byte_value = decode(self.data, self.depth)
-
-        i = 0
-        o = 0
-        while i < 8:
-            colour = value_of_bits(byte_value[i:i+self.depth])
-            self.buffer[o] = get_physical_colour(self.palette[colour])
-            i += self.depth
-            o += 1
+        colour = value_of_bits(self.pdata[self.buffer_index:self.buffer_index+self.depth])
+        return get_physical_colour(self.palette[colour])
 
     def wrap_address(self):
         if self.address >= SCREEN_LIMIT: