1.1 --- a/ULA.txt Tue Feb 18 22:59:49 2014 +0100
1.2 +++ b/ULA.txt Sat Apr 05 00:36:04 2014 +0200
1.3 @@ -1,3 +1,6 @@
1.4 +The Acorn Electron ULA
1.5 +======================
1.6 +
1.7 Principal Design and Feature Constraints
1.8 ----------------------------------------
1.9
1.10 @@ -545,13 +548,16 @@
1.11 definitions containing a start column, region width and colour details. There
1.12 might be a certain number of definitions allowed per row, or the ULA might
1.13 just traverse an ordered list of such definitions with each one indicating the
1.14 -row, start column, region width and colour details. One could even compress
1.15 -this information further by requiring only the row, start column and colour
1.16 -details with each subsequent definition terminating the effect of the previous
1.17 -one. However, one would also need to consider the convenience of preparing
1.18 -such definitions and whether efficient access to definitions for a particular
1.19 -row might be desirable. It might also be desirable to avoid having to prepare
1.20 -definitions for "empty" areas of the screen.
1.21 +row, start column, region width and colour details.
1.22 +
1.23 +One could even compress this information further by requiring only the row,
1.24 +start column and colour details with each subsequent definition terminating
1.25 +the effect of the previous one. However, one would also need to consider the
1.26 +convenience of preparing such definitions and whether efficient access to
1.27 +definitions for a particular row might be desirable. It might also be
1.28 +desirable to avoid having to prepare definitions for "empty" areas of the
1.29 +screen, effectively making the definition of the screen contents employ
1.30 +run-length encoding and employ only colour plus length information.
1.31
1.32 One application of region filling is that of simple 2D and 3D shape rendering.
1.33 Although it is entirely possible to plot such shapes to the screen and have
1.34 @@ -559,6 +565,14 @@
1.35 bandwidth both in the initial plotting and in the final transfer to the
1.36 screen. Region filling would reduce such bandwidth usage substantially.
1.37
1.38 +This way of representing screen images would make certain kinds of images
1.39 +unfeasible to represent - consider alternating single pixel values which could
1.40 +easily occur in some character bitmaps - even if an internal queue of regions
1.41 +were to be supported such that the ULA could read ahead and buffer such
1.42 +"bandwidth intensive" areas. Thus, the ULA might be better served providing
1.43 +this feature for certain areas of the display only as some kind of special
1.44 +graphics window.
1.45 +
1.46 Enhancement: Hardware Sprites
1.47 -----------------------------
1.48
1.49 @@ -870,3 +884,14 @@
1.50 ----------
1.51
1.52 See: http://bbc.nvg.org/doc/A%20Hardware%20Guide%20for%20the%20BBC%20Microcomputer/bbc_hw.htm
1.53 +
1.54 +About this Document
1.55 +-------------------
1.56 +
1.57 +The most recent version of this document and accompanying distribution should
1.58 +be available from the following location:
1.59 +
1.60 +http://hgweb.boddie.org.uk/ULA
1.61 +
1.62 +Copyright and licence information can be found in the docs directory of this
1.63 +distribution - see docs/COPYING.txt for more information.