# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1466348971 -7200
# Node ID 195f22f028483889edfffa0ecbfa75614af61f54
# Parent  1f4007ddc332fb0a5770c598a13648a6b921f80b
Replaced row spacing variables with row height and row offset variables.

diff -r 1f4007ddc332 -r 195f22f02848 ula.py
--- a/ula.py	Sun Jun 19 16:33:20 2016 +0200
+++ b/ula.py	Sun Jun 19 17:09:31 2016 +0200
@@ -241,8 +241,8 @@
           * screen size in bytes
           * default screen start address
           * horizontal pixel scaling factor
-          * line spacing in pixels
-          * number of entries in the pixel buffer
+          * row height in pixels
+          * display height in pixels
 
         The ULA should be reset after a mode switch in order to cleanly display
         a full screen.
@@ -264,12 +264,8 @@
         # Scanline configuration.
 
         self.xscale = MAX_WIDTH / self.width                                # pixel width 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_SCANLINE - rows * (LINES_PER_ROW + self.spacing) + self.spacing
+        self.row_height = MAX_HEIGHT / rows                                 # row height in display pixels
+        self.display_height = rows * self.row_height                        # display height in pixels
 
     def vsync(self, value=0):
 
@@ -291,7 +287,6 @@
 
         self.line_start = self.address = self.screen_start
         self.line = self.line_start % LINES_PER_ROW
-        self.ssub = 0
         self.y = 0
         self.x = 0
 
@@ -312,41 +307,35 @@
         if not self.inside_frame():
             return
 
-        # Support spacing between character rows.
-
-        if self.ssub:
-            self.ssub -= 1
-            return
-
         self.line += 1
 
-        # 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()
-
         # After the end of the last line in a row, the address should already
         # have been positioned on the last line of the next column.
 
+        if self.line == self.row_height:
+            self.address -= LINES_PER_ROW - 1
+            self.wrap_address()
+            self.line = 0
+
+        # Support spacing between character rows.
+
+        elif not self.in_line():
+            return
+
+        # If not on a row boundary, move to the next line. Here, the address
+        # needs bringing back to the previous character row.
+
         else:
-            self.address -= LINES_PER_ROW - 1
+            self.address = self.line_start + 1
             self.wrap_address()
 
-            # Test for the footer region.
-
-            if self.spacing and self.line == self.footer:
-                self.ssub = self.margin
-                return
-
-            # Support spacing between character rows.
-
-            self.ssub = self.spacing
+        # Record the position of the start of the pixel row.
 
         self.line_start = self.address
 
-    def in_frame(self): return MIN_PIXELLINE <= self.y < MAX_PIXELLINE
-    def inside_frame(self): return MIN_PIXELLINE < self.y < MAX_PIXELLINE
+    def in_line(self): return self.line < LINES_PER_ROW
+    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 update(self):
@@ -370,7 +359,7 @@
 
         # Clock management.
 
-        would_access_ram = self.access == 0 and self.read_pixels() and not self.ssub
+        would_access_ram = self.access == 0 and self.read_pixels() and self.in_line()
         access_ram = not self.nmi and would_access_ram
 
         # Set row address (for ULA access only).
@@ -511,7 +500,7 @@
 
         # Detect spacing between character rows.
 
-        if not self.writing_pixels or self.ssub:
+        if not self.writing_pixels or not self.in_line():
             self.video.colour = BLANK
 
         # For pixels within the frame, obtain and output the value.