Build and use 1-bit font, saves a good amount of space

lib/EpdFont/EpdFontData.h

@@ -6,13 +6,13 @@
 
 /// Font data stored PER GLYPH
 typedef struct {
-  uint8_t width;            ///< Bitmap dimensions in pixels
-  uint8_t height;           ///< Bitmap dimensions in pixels
-  uint8_t advanceX;         ///< Distance to advance cursor (x axis)
-  int16_t left;             ///< X dist from cursor pos to UL corner
-  int16_t top;              ///< Y dist from cursor pos to UL corner
-  uint16_t compressedSize;  ///< Size of the zlib-compressed font data.
-  uint32_t dataOffset;      ///< Pointer into EpdFont->bitmap
+  uint8_t width;        ///< Bitmap dimensions in pixels
+  uint8_t height;       ///< Bitmap dimensions in pixels
+  uint8_t advanceX;     ///< Distance to advance cursor (x axis)
+  int16_t left;         ///< X dist from cursor pos to UL corner
+  int16_t top;          ///< Y dist from cursor pos to UL corner
+  uint16_t dataLength;  ///< Size of the font data.
+  uint32_t dataOffset;  ///< Pointer into EpdFont->bitmap
 } EpdGlyph;
 
 /// Glyph interval structure
@@ -28,7 +28,6 @@ typedef struct {
   const EpdGlyph* glyph;                ///< Glyph array
   const EpdUnicodeInterval* intervals;  ///< Valid unicode intervals for this font
   uint32_t intervalCount;               ///< Number of unicode intervals.
-  bool compressed;                      ///< Does this font use compressed glyph bitmaps?
   uint8_t advanceY;                     ///< Newline distance (y axis)
   int ascender;                         ///< Maximal height of a glyph above the base line
   int descender;                        ///< Maximal height of a glyph below the base line

lib/EpdFont/scripts/fontconvert.py

@@ -7,20 +7,18 @@ import math
 import argparse
 from collections import namedtuple
 
-# From: https://github.com/vroland/epdiy
+# Originally from https://github.com/vroland/epdiy
 
 parser = argparse.ArgumentParser(description="Generate a header file from a font to be used with epdiy.")
 parser.add_argument("name", action="store", help="name of the font.")
 parser.add_argument("size", type=int, help="font size to use.")
 parser.add_argument("fontstack", action="store", nargs='+', help="list of font files, ordered by descending priority.")
-parser.add_argument("--compress", dest="compress", action="store_true", help="compress glyph bitmaps.")
 parser.add_argument("--additional-intervals", dest="additional_intervals", action="append", help="Additional code point intervals to export as min,max. This argument can be repeated.")
 args = parser.parse_args()
 
-GlyphProps = namedtuple("GlyphProps", ["width", "height", "advance_x", "left", "top", "compressed_size", "data_offset", "code_point"])
+GlyphProps = namedtuple("GlyphProps", ["width", "height", "advance_x", "left", "top", "data_length", "data_offset", "code_point"])
 
 font_stack = [freetype.Face(f) for f in args.fontstack]
-compress = args.compress
 size = args.size
 font_name = args.name
 
@@ -148,19 +146,18 @@ for i_start, i_end in unvalidated_intervals:
         intervals.append((start, i_end))
 
 for face in font_stack:
-    # shift by 6 bytes, because sizes are given as 6-bit fractions
-    # the display has about 150 dpi.
     face.set_char_size(size << 6, size << 6, 150, 150)
 
 total_size = 0
-total_packed = 0
 all_glyphs = []
 
 for i_start, i_end in intervals:
     for code_point in range(i_start, i_end + 1):
         face = load_glyph(code_point)
         bitmap = face.glyph.bitmap
-        pixels = []
+
+        # Build out 4-bit greyscale bitmap
+        pixels4g = []
         px = 0
         for i, v in enumerate(bitmap.buffer):
             y = i / bitmap.width
@@ -169,31 +166,49 @@ for i_start, i_end in intervals:
                 px = (v >> 4)
             else:
                 px = px | (v & 0xF0)
-                pixels.append(px);
+                pixels4g.append(px);
                 px = 0
             # eol
             if x == bitmap.width - 1 and bitmap.width % 2 > 0:
-                pixels.append(px)
+                pixels4g.append(px)
                 px = 0
 
-        packed = bytes(pixels);
-        total_packed += len(packed)
-        compressed = packed
-        if compress:
-            compressed = zlib.compress(packed)
+        # Downsample to 1-bit bitmap - treat any non-zero as black
+        pixelsbw = []
+        px = 0
+        pitch = (bitmap.width // 2) + (bitmap.width % 2)
+        for localY in range(bitmap.rows):
+            for xx in range(bitmap.width):
+                px = px << 1
+                bm = pixels4g[localY * pitch + (xx // 2)]
+                if (xx & 1) == 0:
+                    if bm & 0xF > 0:
+                        px += 1
+                else:
+                    if bm & 0xF0 > 0:
+                        px += 1
 
+                if (localY * bitmap.width + xx) % 8 == 7:
+                    pixelsbw.append(px)
+                    px = 0
+        if (bitmap.width * bitmap.rows) % 8 != 0:
+            pixelsbw.append(px)
+
+
+        # Build output data
+        packed = bytes(pixelsbw)
         glyph = GlyphProps(
             width = bitmap.width,
             height = bitmap.rows,
             advance_x = norm_floor(face.glyph.advance.x),
             left = face.glyph.bitmap_left,
             top = face.glyph.bitmap_top,
-            compressed_size = len(compressed),
+            data_length = len(packed),
             data_offset = total_size,
             code_point = code_point,
         )
-        total_size += len(compressed)
-        all_glyphs.append((glyph, compressed))
+        total_size += len(packed)
+        all_glyphs.append((glyph, packed))
 
 # pipe seems to be a good heuristic for the "real" descender
 face = load_glyph(ord('|'))
@@ -201,11 +216,11 @@ face = load_glyph(ord('|'))
 glyph_data = []
 glyph_props = []
 for index, glyph in enumerate(all_glyphs):
-    props, compressed = glyph
-    glyph_data.extend([b for b in compressed])
+    props, packed = glyph
+    glyph_data.extend([b for b in packed])
     glyph_props.append(props)
 
-print(f"/**\n * generated by fontconvert.py\n * name: {font_name}\n * size: {size}\n * compressed: {compress}\n */")
+print(f"/**\n * generated by fontconvert.py\n * name: {font_name}\n * size: {size}\n */")
 print("#pragma once")
 print("#include \"EpdFontData.h\"\n")
 print(f"static const uint8_t {font_name}Bitmaps[{len(glyph_data)}] = {{")
@@ -230,7 +245,6 @@ print(f"    {font_name}Bitmaps,")
 print(f"    {font_name}Glyphs,")
 print(f"    {font_name}Intervals,")
 print(f"    {len(intervals)},")
-print(f"    {1 if compress else 0},")
 print(f"    {norm_ceil(face.size.height)},")
 print(f"    {norm_ceil(face.size.ascender)},")
 print(f"    {norm_floor(face.size.descender)},")