# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1323545060 -3600
# Node ID 82c1556ff0a9c73b3773b553d242739f40b11d39
# Parent  0ac34bc9f1179e82f873552cdb91fdde7d1cba81# Parent  0eb49bcc609b6981dc61a83dc53cab555cd22021
Merged Shedskin-related and general changes.

diff -r 0ac34bc9f117 -r 82c1556ff0a9 ULA.txt
--- a/ULA.txt	Sat Dec 10 20:23:37 2011 +0100
+++ b/ULA.txt	Sat Dec 10 20:24:20 2011 +0100
@@ -21,9 +21,9 @@
 One argument for a 2 byte resolution is smooth vertical scrolling. A pitfall
 of changing the screen address by 2 bytes is the change in the number of lines
 from the initial and final character rows that need reading by the ULA, which
-would need to maintain this state information. Another pitfall is the
-complication that might be introduced to software writing bitmaps of character
-height to the screen.
+would need to maintain this state information (although this is a relatively
+trivial change). Another pitfall is the complication that might be introduced
+to software writing bitmaps of character height to the screen.
 
 Region Blanking
 ---------------
@@ -123,8 +123,8 @@
 that hardware to reduce the load on the system CPU which was responsible for
 producing the video output.
 
-Hardware Sprites
-----------------
+Hardware Sprites and Colour Planes
+----------------------------------
 
 An enhanced ULA might provide hardware sprites, but this would be done in an
 way that is incompatible with the standard ULA, since no &FE*X locations are
@@ -137,6 +137,14 @@
 particular state after each write. For example: read LSB of region, read MSB
 of region, read size, read height.
 
+Providing hardware sprites can be awkward without having some kind of working
+area, since the ULA would need to remember where each sprite is to be plotted
+and then deduce which sprites would be contributing to any given pixel. An
+alternative is to use memory into which the sprites would be plotted, and this
+memory would be combined with the main screen memory, taking a particular
+colour as the "colourkey" which is to be considered transparent, and only
+overwriting the main screen pixels with pixel values for other colours.
+
 Enhanced Graphics
 -----------------
 
@@ -158,6 +166,12 @@
 the given framework. The BBC Micro ULA employs &FE40-&FE4F for sound control,
 and an enhanced ULA could adopt this interface.
 
+The BBC Micro uses the SN76489 chip to produce sound, and the entire
+functionality of this chip could be emulated for enhanced sound, with a subset
+of the functionality exposed via the &FE*6 interface.
+
+See: http://en.wikipedia.org/wiki/Texas_Instruments_SN76489
+
 Waveform Upload
 ---------------
 
diff -r 0ac34bc9f117 -r 82c1556ff0a9 main.py
--- a/main.py	Sat Dec 10 20:23:37 2011 +0100
+++ b/main.py	Sat Dec 10 20:24:20 2011 +0100
@@ -7,6 +7,9 @@
 from ula import *
 import pygame
 
+def update_surface(surface_array, screen_array):
+    surface_array[:] = screen_array
+
 def mainloop():
     while 1:
         pygame.display.flip()
@@ -21,6 +24,7 @@
 
     memory = get_memory()
     ula = ULA(memory)
+    ula_screen = get_screen()
 
     # Test MODE 2.
 
@@ -28,11 +32,13 @@
 
     fill(memory, 0x3000, 0x5800 - 320, encode((1, 6), 4))
     fill(memory, 0x5800 - 320, 0x8000, encode((2, 7), 4))
-    update(a, ula)
+    update(ula_screen, ula)
+    update_surface(a, ula_screen)
     mainloop()
 
     ula.screen_start = 0x3000 + 2
-    update(a, ula)
+    update(ula_screen, ula)
+    update_surface(a, ula_screen)
     mainloop()
 
     # Test MODE 6.
@@ -41,11 +47,13 @@
 
     fill(memory, 0x6000, 0x6f00 + 160, encode((1, 0, 1, 1, 0, 0, 1, 1), 1))
     fill(memory, 0x6f00 + 160, 0x7f40, encode((1, 0, 1, 0, 1, 0, 1, 0), 1))
-    update(a, ula)
+    update(ula_screen, ula)
+    update_surface(a, ula_screen)
     mainloop()
 
     ula.screen_start = 0x6f00 + 160
-    update(a, ula)
+    update(ula_screen, ula)
+    update_surface(a, ula_screen)
     mainloop()
 
 # vim: tabstop=4 expandtab shiftwidth=4
diff -r 0ac34bc9f117 -r 82c1556ff0a9 ula.py
--- a/ula.py	Sat Dec 10 20:23:37 2011 +0100
+++ b/ula.py	Sat Dec 10 20:24:20 2011 +0100
@@ -271,8 +271,27 @@
     return result
 
 def get_memory():
+
+    "Return an array representing the computer's memory."
+
     return array.array("B", itertools.repeat(0, MAX_MEMORY))
 
+def get_screen():
+
+    "Return a list of arrays representing the display."
+
+    x = 0
+    screen = []
+    while x < WIDTH:
+        y = 0
+        column = []
+        while y < HEIGHT:
+            column.append((0, 0, 0))
+            y += 1
+        screen.append(column)
+        x += 1
+    return screen
+
 def fill(memory, start, end, value):
     for i in xrange(start, end):
         memory[i] = value
@@ -289,11 +308,7 @@
     # Make a simple two-dimensional array of tuples (three-dimensional in pygame
     # terminology).
 
-    a = [
-        [(0, 0, 0), (0, 0, 0), (0, 0, 0)],
-        [(0, 0, 0), (0, 0, 0), (0, 0, 0)],
-        [(0, 0, 0), (0, 0, 0), (0, 0, 0)]
-        ]
+    a = get_screen()
     update(a, ula)
 
 # vim: tabstop=4 expandtab shiftwidth=4