Improvements to docs.

FONT_TO_PY.md

@@ -13,7 +13,7 @@ is known as frozen bytecode.
 
 17 Oct 2019 V0.33 With thanks to Stephen Irons (@ironss).
  1. Fix bug where input rather than output filename was checked.
- 2. Add `baseline()` to ouput file returning the maximum descent.
+ 2. Add `baseline()` to ouput file returning the maximum ascent.
  3. Correct left position of rendered glyph.
 
 21 Sept 2019 V0.22
@@ -116,6 +116,10 @@ character set.
 Any requirement for arguments -xr will be specified in the device driver
 documentation. Bit reversal is required by some display hardware.
 
+Using the -f argument with a variable pitch source font will produce a fixed
+pitch result. A better apearance would be achieved by using a font designed as
+monospaced.
+
 There have been reports that producing fonts with Unicode characters outside
 the ASCII set from ttf files is unreliable. If expected results are not
 achieved, use an otf font. I have successfully created Cyrillic and extended
@@ -150,6 +154,26 @@ to render strings on demand. A practical example may be studied
 [here](./writer/writer_demo.py).
 The detailed layout of the Python file may be seen [here](./writer/DRIVERS.md).
 
+### Python font files
+
+These start with a comment which is the command line used to create the font.
+
+They include the following functions:
+ 1. `height()` Height of bitmaps in pixels (all are the same height).
+ 2. `max_width()` Width of widest glyph in pixels.
+ 3. `baseline()` Offset from top of the bitmap to the baseline. This is a
+ notional "ruler line" where glyphs are drawn. Enables rendering different
+ fonts on a common baseline. It is a positive number of pixels.
+ 4. `hmap()` `True` if bitmaps are horizonataly mapped.
+ 5. `reverse()` `True` if bit reversal is used.
+ 6. `monospaced()` `True` if bitmaps were created with fixed pitch.
+ 7. `min_ch()` Returns smallest ordinal value in font.
+ 8. `max_ch()` Largest ordinal value in font.
+ 9. `get_ch()` Arg: a Unicode character. Returns three items:
+   1. A memoryview into the bitmap for that character.  
+   2. Bitmap height in pixels. Equal to `height()` above.  
+   3. Bitmap width in pixels.  
+
 ### Binary font files
 
 There is an option to create a binary font file, specified with a `-b` or

README.md

@@ -45,8 +45,8 @@ This comprises three components, links to docs below:
 
 This command line utility is written in Python 3 and runs on a PC. It takes
 as input a font file in `ttf` or `otf` form together with a height in pixels
-and outputs a Python source file containing the font data. Fixed and variable
-pitch rendering are supported. The design has the following aims:
+and outputs a Python source file containing the font as a bitmap. Fixed and
+variable pitch rendering are supported. The design has the following aims:
 
  * Independence of specific display hardware.
  * The path from font file to Python code to be fully open source.
@@ -71,35 +71,36 @@ size.
 
 By default the `font_to_py.py` utility produces the ASCII character set from
 `chr(32)` to `chr(126)` inclusive. Command line options enable the character
-set to be modified to include extended ASCII. Alternative sets may be specified
-such as non-English languages or limited, non-contiguous sets for specialist
-applications.
+set to be modified to include arbitrary Unicode characters. Alternative sets
+may be specified such as for non-English languages. Efficient support is now
+provided for sparse character sets.
 
 # Font file interface
 
-A font file is imported in the usual way e.g. `import font14`. It contains
-the following methods which return values defined by the arguments which were
-provided to `font_to_py.py`:
+A font file is imported in the usual way e.g. `import font14`. Python font
+files contain the following functions. These return values defined by the
+arguments which were provided to `font_to_py.py`:
 
 `height` Returns height in pixels.  
 `max_width` Returns maximum width of a glyph in pixels.  
+`baseline` Offset from top of glyph to the baseline.  
 `hmap` Returns `True` if font is horizontally mapped.  
 `reverse` Returns `True` if bit reversal was specified.  
 `monospaced` Returns `True` if monospaced rendering was specified.  
 `min_ch` Returns the ordinal value of the lowest character in the file.  
 `max_ch` Returns the ordinal value of the highest character in the file.
 
-Glyphs are returned with the `get_ch` method. Its argument is a character
-and it returns the following values:
+Glyphs are returned with the `get_ch` function. Its argument is a Unicode
+character and it returns the following values:
 
- * A `memoryview` object containg the glyph bytes.
+ * A `memoryview` object containing the glyph bytes.
  * The height in pixels.
  * The character width in pixels.
 
 The `font_to_py.py` utility allows a default glyph to be specified (typically
 `?`). If called with an undefined character, this glyph will be returned.
 
-The `min_ch` and `max_ch` methods are mainly relevant to contiguous character
+The `min_ch` and `max_ch` functions are mainly relevant to contiguous character
 sets.
 
 # Licence