# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1323044439 -3600
# Node ID 69e7ee0e99dd530760ecb6359ef40573d156bd5d
# Parent  4460129be79e86a60bc3cc9f548694504aa95f86
Added spacing between character rows and fixed the number of rows in the modes involved.

diff -r 4460129be79e -r 69e7ee0e99dd ula.py
--- a/ula.py	Sun Dec 04 21:43:45 2011 +0100
+++ b/ula.py	Mon Dec 05 01:20:39 2011 +0100
@@ -10,12 +10,13 @@
 
 WIDTH = 640
 HEIGHT = 512
+INTENSITY = 255
 
 LINES_PER_ROW = 8
 MAX_HEIGHT = 256
 SCREEN_LIMIT = 0x8000
 MAX_MEMORY = 0x10000
-INTENSITY = 255
+BLANK = (0, 0, 0)
 
 def update(screen, ula):
 
@@ -41,8 +42,8 @@
 
     modes = [
         (640, 1, 32), (320, 2, 32), (160, 4, 32),   # (width, depth, rows)
-        (640, 1, 24), (320, 1, 32), (160, 2, 32),
-        (320, 1, 24)
+        (640, 1, 25), (320, 1, 32), (160, 2, 32),
+        (320, 1, 25)
         ]
 
     palette = range(0, 8) * 2
@@ -75,15 +76,29 @@
           * number of entries in the pixel buffer
         """
 
-        self.width, self.depth, self.rows = self.modes[mode]
+        self.width, self.depth, rows = self.modes[mode]
+
+        row_size = (self.width * self.depth * LINES_PER_ROW) / 8            # bits per row -> bytes per row
 
-        row_size = (self.width * self.depth * LINES_PER_ROW) / 8    # bits per row -> bytes per row
+        # Memory access configuration.
+
+        self.screen_size = row_size * rows
+        self.screen_start = (SCREEN_LIMIT - self.screen_size) & 0xff00      # limitation on positioning
+
+        # Scanline configuration.
 
-        self.screen_size = row_size * self.rows
-        self.screen_start = SCREEN_LIMIT - self.screen_size
-        self.xscale = WIDTH / self.width                            # pixel width in display pixels
-        self.yscale = HEIGHT / (self.rows * LINES_PER_ROW)          # pixel height in display pixels
-        self.spacing = MAX_HEIGHT / self.rows - LINES_PER_ROW       # pixels between rows
+        self.xscale = WIDTH / self.width                                    # pixel width in display pixels
+        self.yscale = HEIGHT / (rows * LINES_PER_ROW)                       # pixel height in display pixels
+
+        self.spacing = MAX_HEIGHT / rows - LINES_PER_ROW                    # pixels between rows
+
+        # Start of unused region.
+
+        self.footer = rows * LINES_PER_ROW
+        self.margin = MAX_HEIGHT - rows * (LINES_PER_ROW + self.spacing) + self.spacing
+
+        # Internal pixel buffer size.
+
         self.buffer_limit = 8 / self.depth
 
     def vsync(self):
@@ -93,6 +108,7 @@
         self.line_start = self.address = self.screen_start
         self.line = 0
         self.ysub = 0
+        self.ssub = 0
         self.reset_horizontal()
 
     def reset_horizontal(self):
@@ -106,6 +122,12 @@
 
         "Signal the end of a line."
 
+        # Support spacing between character rows.
+
+        if self.ssub:
+            self.ssub -= 1
+            return
+
         self.reset_horizontal()
 
         # Scale pixels vertically.
@@ -123,7 +145,9 @@
         self.ysub = 0
         self.line += 1
 
-        if self.line < LINES_PER_ROW:
+        # If not on a row boundary, move to the next line.
+
+        if self.line % LINES_PER_ROW:
             self.address = self.line_start + 1
             self.wrap_address()
 
@@ -134,12 +158,17 @@
             self.address -= LINES_PER_ROW - 1
             self.wrap_address()
 
-        self.line_start = self.address
+            # Test for the footer region.
+
+            if self.spacing and self.line == self.footer:
+                self.ssub = self.margin * self.yscale
+                return
 
-        # Move on to the next row if appropriate.
+            # Support spacing between character rows.
 
-        if self.line == LINES_PER_ROW:
-            self.line = 0
+            self.ssub = self.spacing * self.yscale
+
+        self.line_start = self.address
 
     def get_pixel_colour(self):
 
@@ -147,6 +176,11 @@
         Return a pixel colour by reading from the pixel buffer.
         """
 
+        # Detect spacing between character rows.
+
+        if self.ssub:
+            return BLANK
+
         # Scale pixels horizontally.
 
         if self.xsub == self.xscale:
@@ -268,4 +302,17 @@
     update(a, ula)
     mainloop()
 
+    # Test MODE 6.
+
+    ula.set_mode(6)
+
+    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)
+    mainloop()
+
+    ula.screen_start = 0x6f00 + 160
+    update(a, ula)
+    mainloop()
+
 # vim: tabstop=4 expandtab shiftwidth=4