feat(glyph): add --byte-align option

Author: kisvegabor

README.md

@@ -60,6 +60,11 @@ Common:
   grayscale icons. Since gray tones are emulated via transparency, result
   will be good on contrast background only.
 - `--lv-include` - only with `--format lvgl`, set alternate path for `lvgl.h`.
+- `--no-compress` - disable built-in RLE compression.
+- `--no-prefilter` - disable bitmap lines filter (XOR), used to improve
+  compression ratio.
+- `--byte-align` - pad the line ends of the bitmaps to a whole byte (requires `--no-compress` and `--bpp != 3`)
+- `--no-kerning` - drop kerning info to reduce size (not recommended).
 
 Per font:
 
@@ -79,11 +84,6 @@ Per font:
 - `--autohint-strong` - use more strong autohinting (will break kerning).
 
 Additional debug options:
-
-- `--no-compress` - disable built-in RLE compression.
-- `--no-prefilter` - disable bitmap lines filter (XOR), used to improve
-  compression ratio.
-- `--no-kerning` - drop kerning info to reduce size (not recommended).
 - `--full-info` - don't shorten 'font_info.json' (include pixels data).
 
 

lib/cli.js

@@ -263,6 +263,13 @@ List of characters to copy, belongs to previously declared "--font". Examples:
     help: 'Drop kerning info to reduce size (not recommended).'
   });
 
+  parser.add_argument('--byte-align', {
+    dest: 'byte_align',
+    action: 'store_true',
+    default: false,
+    help: 'Pad bitmap line endings to whole bytes.'
+  });
+
   parser.add_argument('--lv-include', {
     metavar: '<path>',
     help: 'Set alternate "lvgl.h" path (for --format lvgl).'
@@ -302,6 +309,16 @@ List of characters to copy, belongs to previously declared "--font". Examples:
     }
   }
 
+  if (args.byte_align) {
+    if (args.no_compress === false) {
+      parser.error('--byte_align requires --no-compress');
+    }
+
+    if (args.bpp === 3) {
+      parser.error('--byte_align requires --bpp 1, 2, 4, or 8');
+    }
+  }
+
   //
   // Convert
   //

lib/font/table_glyf.js

@@ -60,18 +60,30 @@ class Glyf {
   }
 
   storePixels(bitStream, pixels) {
-    if (this.getCompressionCode() === 0) this.storePixelsRaw(bitStream, pixels);
+    if (this.getCompressionCode() === 0 || this.getCompressionCode() === 3) this.storePixelsRaw(bitStream, pixels);
     else this.storePixelsCompressed(bitStream, pixels);
   }
 
   storePixelsRaw(bitStream, pixels) {
+    if (pixels.length == 0) return;
+
     const bpp = this.font.opts.bpp;
+    let pad = 0;
+    if (this.font.opts.byte_align) {
+      const pxPerByte = 8 / bpp;
+      pad = pxPerByte - (pixels[0].length % pxPerByte);
+    }
 
     for (let y = 0; y < pixels.length; y++) {
       const line = pixels[y];
       for (let x = 0; x < line.length; x++) {
         bitStream.writeBits(line[x], bpp);
       }
+      if (pad) {
+        for (let x = 0; x < pad; x++) {
+          bitStream.writeBits(0, bpp);
+        }
+      }
     }
   }
 
@@ -135,9 +147,10 @@ class Glyf {
   }
 
   getCompressionCode() {
+    if (this.font.opts.byte_align) return 3;
     if (this.font.opts.no_compress) return 0;
     if (this.font.opts.bpp === 1) return 0;
-
+    
     if (this.font.opts.no_prefilter) return 2;
     return 1;
   }