Crop glyphs

README.rst

@@ -179,6 +179,9 @@ Resource script entries look like this:
         "<name>": {
             "codepoints": "<filter>", // Which character glyphs to include. See below.
             "chars": "<text string>", // List of required character codepoints
+            "alpha",                  // Optional: maximum number of bits per pixel (1, 2, 4 or 8). Default is 8.
+            "mono",                   // Optional: Set to *true* to use 1 bit per pixel. Default is *false*.
+            "size",                   // Optional parameter for freetype fonts
             "normal": "<filename>",
             "italic": "<filename>",
             "bold": "<filename>",
@@ -188,7 +191,7 @@ Resource script entries look like this:
 
 Styles are optional but a font must have at least one typeface.
 
-By default, all ASCII characters from 0x20 (space) to 0x7e (~).
+By default, all ASCII characters from 0x20 (space) to 0x7e (~) are generated.
 The ``codepoints`` parameter is a comma-separated list of ranges:
 
     a-z,A-Z,0-9,0x4000-0x4050
@@ -228,12 +231,17 @@ The following font classes are currently supported:
 
         The ``freetype`` library supports other types so if required these are easily added.
 
-        These fonts have some additional parameters:
-            "mono": <True/False>
-                Whether to produce monochrome (1-bit) or grayscale (8-bit alpha) glyphs.
-                If not specified, defaults to grayscale.
-            "size": <Point size of font>
-                e.g. 16, 14.5
+        An optional **size** parameter indicates the point size for the font to generate.
+        If omitted, the first typeface defined for that font is used.
+
+The **alpha** parameter sets a limit on the number of bits per pixel used for the generate glyphs.
+The freetype and VLW fonts are generated using 8 bits per pixel for smoother appearance.
+This can be reduced to 4, 2 or 1 bit (monochrome) to reduce storage space.
+
+The **mono** parameter is equivalent to **alpha: 1**, and is ignored if **alpha** is specified.
+
+Generated glyphs are cropped to remove any blank space around the image, then packed to minimise memory usage.
+This means that the bitmap data is contiguous, without breaks, from top left to bottom right.
 
 
 Images

Tools/rc/rclib/font.py

@@ -25,7 +25,7 @@
 import sys
 import struct
 from .base import Resource, findFile, StructSize, fstrSize
-from PIL import Image
+from PIL import Image, ImageChops
 
 class FontStyle(enum.Enum):
     """Style is a set of these values, using strings here but bitfields in library"""
@@ -67,10 +67,21 @@ def set_bitmap(self, img: Image):
         """ Convert bitmap to internal (GFX) format and set width, height.
         We remove space round the glyph, update glyph offsets and pack the resulting bits.
         """
+
+        # Find smallest bounding box and crop
         w, h = img.width, img.height
+        bg = Image.new('L', (w, h), 0)
+        diff = ImageChops.difference(img, bg)
+        diff = ImageChops.add(diff, diff, 2.0, -100)
+        bbox = diff.getbbox()
+        if bbox:
+            img = img.crop(bbox)
+            w, h = img.width, img.height
+            self.xOffset += bbox[0]
+            self.yOffset += bbox[1]
+
         self.width = w
         self.height = h
-        stride = w # All modes 1 byte per pixel
         alpha = 1 if img.mode == '1' else self.typeface.font.alpha
         self.alpha = alpha
         pixels_per_byte = 8 // alpha