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synced 2026-10-21 13:34:12 +00:00
[font] Crop blank space from glyph bitmaps (#21235)
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Jesse Hills
@@ -612,7 +612,14 @@ class GlyphInfo:
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self.height = height
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def glyph_to_glyphinfo(glyph, font, size, bpp):
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def glyph_to_glyphinfo(glyph, font, size, bpp, crop: bool = True):
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"""Render a glyph and pack its bitmap at the given bits per pixel.
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With ``crop``, blank rows and columns around the set pixels are dropped and the
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offsets adjusted to match. Bitmap fonts (BDF/PCF) render every glyph as a whole
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character cell, so this keeps their empty space out of flash. A blank glyph keeps
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its offsets and stores no pixels.
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"""
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# Convert to 32 bit unicode codepoint
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glyph = ord(glyph)
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scale = 256 // (1 << bpp)
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@@ -632,19 +639,36 @@ def glyph_to_glyphinfo(glyph, font, size, bpp):
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height = font.glyph.bitmap.rows
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buffer = font.glyph.bitmap.buffer
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pitch = font.glyph.bitmap.pitch
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glyph_data = [0] * ((height * width * bpp + 7) // 8)
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src_mode = font.glyph.bitmap.pixel_mode
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if src_mode == ft_pixel_mode_mono:
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rows = [
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[
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(1 << bpp) - 1 if buffer[y * pitch + x // 8] & (1 << (7 - x % 8)) else 0
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for x in range(width)
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]
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for y in range(height)
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]
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else:
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rows = [
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[buffer[y * pitch + x] // scale for x in range(width)]
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for y in range(height)
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]
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left = 0
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top = 0
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if crop and width * height > 1:
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used_rows = [y for y, row in enumerate(rows) if any(row)]
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used_cols = [x for x in range(width) if any(row[x] for row in rows)]
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if used_rows:
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left = used_cols[0]
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top = used_rows[0]
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width = used_cols[-1] + 1 - left
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height = used_rows[-1] + 1 - top
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else:
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width = height = 0
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glyph_data = [0] * ((height * width * bpp + 7) // 8)
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pos = 0
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for y in range(height):
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for x in range(width):
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if src_mode == ft_pixel_mode_mono:
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pixel = (
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(1 << bpp) - 1
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if buffer[y * pitch + x // 8] & (1 << (7 - x % 8))
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else 0
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)
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else:
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pixel = buffer[y * pitch + x] // scale
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for row in rows[top : top + height]:
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for pixel in row[left : left + width]:
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for bit_num in range(bpp):
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if pixel & (1 << (bpp - bit_num - 1)):
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glyph_data[pos // 8] |= 0x80 >> (pos % 8)
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@@ -663,8 +687,8 @@ def glyph_to_glyphinfo(glyph, font, size, bpp):
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glyph,
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glyph_data,
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pt_to_px(font.glyph.metrics.horiAdvance),
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font.glyph.bitmap_left,
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ascender - font.glyph.bitmap_top,
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font.glyph.bitmap_left + left,
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ascender - font.glyph.bitmap_top + top,
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width,
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height,
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)
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@@ -733,9 +757,9 @@ async def to_code(config):
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font_height = pt_to_px(base_font.size.height)
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ascender = pt_to_px(base_font.size.ascender)
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descender = abs(pt_to_px(base_font.size.descender))
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g = glyph_to_glyphinfo("x", base_font, size, bpp)
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g = glyph_to_glyphinfo("x", base_font, size, bpp, crop=False)
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xheight = g.height if len(g.bitmap_data) > 1 else 0
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g = glyph_to_glyphinfo("X", base_font, size, bpp)
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g = glyph_to_glyphinfo("X", base_font, size, bpp, crop=False)
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capheight = g.height if len(g.bitmap_data) > 1 else 0
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if font_height == 0:
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if not base_font.is_scalable:
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@@ -0,0 +1,72 @@
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STARTFONT 2.1
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FONT -Test-Cell-Medium-R-Normal--8-80-75-75-C-60-ISO10646-1
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SIZE 8 75 75
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FONTBOUNDINGBOX 6 8 0 -2
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STARTPROPERTIES 4
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PIXEL_SIZE 8
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FONT_ASCENT 6
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FONT_DESCENT 2
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SPACING "C"
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ENDPROPERTIES
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CHARS 4
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STARTCHAR space
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ENCODING 32
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SWIDTH 720 0
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DWIDTH 6 0
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BBX 6 8 0 -2
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BITMAP
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00
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00
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00
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00
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00
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00
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00
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00
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ENDCHAR
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STARTCHAR X
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ENCODING 88
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SWIDTH 720 0
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DWIDTH 6 0
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BBX 6 8 0 -2
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BITMAP
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84
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00
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00
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30
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00
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00
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00
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84
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ENDCHAR
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STARTCHAR x
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ENCODING 120
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SWIDTH 720 0
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DWIDTH 6 0
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BBX 6 8 0 -2
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BITMAP
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00
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00
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50
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20
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50
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00
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00
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00
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ENDCHAR
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STARTCHAR bar
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ENCODING 124
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SWIDTH 720 0
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DWIDTH 6 0
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BBX 6 8 0 -2
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BITMAP
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20
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20
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20
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20
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20
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20
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20
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20
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ENDCHAR
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ENDFONT
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@@ -0,0 +1,14 @@
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esphome:
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name: test
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host:
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font:
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- file: ../cell6x8.bdf
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id: cell
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size: 8
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glyphs: " Xx|"
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- file: ../NotoSans-Regular.ttf
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id: noto
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size: 12
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glyphs: " AB"
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@@ -10,6 +10,7 @@ from pathlib import Path
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import re
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from unittest.mock import MagicMock, patch
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from freetype import Face
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import pytest
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from esphome.components.font import (
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@@ -19,8 +20,10 @@ from esphome.components.font import (
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CONF_IGNORE_MISSING_GLYPHS,
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CONF_RAW_GLYPH_ID,
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FONT_CACHE,
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GlyphInfo,
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flatten,
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glyph_comparator,
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glyph_to_glyphinfo,
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to_code,
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validate_font_config,
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)
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@@ -345,3 +348,84 @@ def test_glyph_table_is_progmem(
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assert re.search(r"static constexpr font::Glyph \w+\[\] PROGMEM = ", main_cpp)
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assert "static const font::Glyph" not in main_cpp
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# ---------- glyph cropping ----------
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BDF_PATH = FONT_DIR / "cell6x8.bdf"
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def _glyph_table(main_cpp: str, glyph_table_id: str) -> dict[int, tuple[int, ...]]:
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"""Map each codepoint in a generated glyph table to (advance, offset_x, offset_y, width, height)."""
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table = re.search(
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rf"font::Glyph {glyph_table_id}\[\] PROGMEM = \{{(.*)\}};", main_cpp
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).group(1)
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return {
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int(code): tuple(int(x) for x in rest.split(", "))
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for code, rest in re.findall(r"\{(\d+), \([^)]*\), ([-\d, ]+)\}", table)
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}
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def test_bitmap_font_glyphs_are_cropped(
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generate_main: Callable[[str | Path], str],
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component_config_path: Callable[[str], Path],
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) -> None:
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"""Bitmap font glyphs drop blank rows and columns; outline glyphs are unchanged."""
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main_cpp = generate_main(component_config_path("bitmap_crop.yaml"))
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# Each 6x8 cell is reduced to its set pixels, and the offsets move to match
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assert _glyph_table(main_cpp, "font_glyph_id") == {
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32: (6, 0, 0, 0, 0), # blank: no pixels stored
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88: (6, 0, 0, 6, 8), # touches every edge of the cell: no crop
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120: (6, 1, 2, 3, 3), # blank border all round
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124: (6, 2, 0, 1, 8), # full height column
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}
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# 6 bytes for "X", 2 for the cropped "x", 1 for "|"
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assert (
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"uint8_t_id[] PROGMEM = "
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"{0x84, 0x00, 0x0C, 0x00, 0x00, 0x21, 0xAA, 0x80, 0xFF};" in main_cpp
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)
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# xheight and capheight still measure the uncropped cell
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assert "font::Font(font_glyph_id, 4, 6, 8, 2, 8, 8, 1);" in main_cpp
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# FreeType already crops outline glyphs, and a blank one stays 1x1
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assert _glyph_table(main_cpp, "font_glyph_id_2") == {
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32: (3, 0, 12, 1, 1),
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65: (8, 0, 4, 8, 9),
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66: (8, 1, 4, 6, 9),
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}
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def _render(glyph: GlyphInfo, bpp: int) -> dict[tuple[int, int], int]:
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"""Decode a packed glyph bitmap into its non-zero pixels at absolute positions."""
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pixels = {}
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pos = 0
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for y in range(glyph.height):
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for x in range(glyph.width):
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value = 0
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for _ in range(bpp):
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bit = glyph.bitmap_data[pos // 8] >> (7 - pos % 8) & 1
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value = value << 1 | bit
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pos += 1
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if value:
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pixels[(x + glyph.offset_x, y + glyph.offset_y)] = value
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return pixels
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@pytest.mark.parametrize("bpp", [1, 2, 4, 8])
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@pytest.mark.parametrize(
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("path", "size"),
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[(BDF_PATH, 8), (FONT_PATH, 12)],
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ids=["bitmap", "outline"],
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)
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def test_cropped_glyphs_render_identically(path: Path, size: int, bpp: int) -> None:
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"""Cropping only drops blank pixels, so every glyph renders the same as before."""
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face = Face(str(path))
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for char in " Xx|AB":
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if not face.get_char_index(char):
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continue
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full = glyph_to_glyphinfo(char, face, size, bpp, crop=False)
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cropped = glyph_to_glyphinfo(char, face, size, bpp)
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assert _render(cropped, bpp) == _render(full, bpp)
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assert cropped.advance == full.advance
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assert len(cropped.bitmap_data) <= len(full.bitmap_data)
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