util/font: Transition to 8-bit anti-aliased font generation
Update generate_font.py to produce 8-bit alpha maps instead of 1-bit packed bitmaps. This enables text smoothing (anti-aliasing) during framebuffer rendering by providing pixel intensity values (0-255). Key changes: - Switch PIL image mode from "1" (monochrome) to "L" (8-bit grayscale). - Change C data type from uint32_t bit-packed rows to uint8_t byte arrays. - Implement vertical centering logic using font metrics (ascent/descent). - Add glyph clipping detection and warnings for both width and height. - Format C output so each source line represents one glyph row. Change-Id: Iec8a0123456789abcdef0123456789abcdef0123 Signed-off-by: Subrata Banik <subratabanik@google.com> Reviewed-on: https://review.coreboot.org/c/coreboot/+/91178 Reviewed-by: Kapil Porwal <kapilporwal@google.com> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
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Subrata Banik
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1 changed files with 46 additions and 57 deletions
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@ -2,10 +2,10 @@
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# SPDX-License-Identifier: GPL-2.0-or-later
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"""
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This utility generates a compressed bitmapped font table from a TTF/OTF file.
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This utility generates an anti-aliased (smoothed) font table from a TTF/OTF file.
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The output is a C source file containing:
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1. Font dimensions and range macros.
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2. A normalized (left-aligned) bitmapped font table.
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2. An 8-bit alpha map font table (0=transparent, 255=opaque).
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3. A character width table for proportional spacing.
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Usage:
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@ -26,11 +26,10 @@ def generate_c_table(font_path, canvas_width, canvas_height):
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print(f"Error: Font file '{font_path}' not found.", file=sys.stderr)
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sys.exit(1)
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# Validation: Width must not exceed 32 bits for uint32_t storage
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if canvas_width > 32:
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print(f"Error: Requested width ({canvas_width}) exceeds 32-bit capacity. "
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"The current renderer supports up to 32 pixels wide.", file=sys.stderr)
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sys.exit(1)
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# RESTRICTION: Width and Height checks for firmware safety
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if canvas_width > 64 or canvas_height > 64:
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print(f"Warning: Large dimensions ({canvas_width}x{canvas_height}) "
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"will consume significant flash memory.", file=sys.stderr)
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# Validation: Basic sanity check for positive dimensions
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if canvas_width <= 0 or canvas_height <= 0:
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@ -39,7 +38,6 @@ def generate_c_table(font_path, canvas_width, canvas_height):
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# Use canvas_width as font size to maintain original calculation style
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font_size = canvas_width
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y_offset = 0
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try:
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font = ImageFont.truetype(font_path, font_size)
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@ -47,6 +45,16 @@ def generate_c_table(font_path, canvas_width, canvas_height):
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print(f"Error: Could not open font file '{font_path}'.", file=sys.stderr)
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sys.exit(1)
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# Check for vertical clipping based on font metrics
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ascent, descent = font.getmetrics()
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total_font_height = ascent + descent
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if total_font_height > canvas_height:
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print(f"Warning: Font vertical size ({total_font_height}px) exceeds "
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f"canvas height ({canvas_height}px).", file=sys.stderr)
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y_offset = 0
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else:
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y_offset = (canvas_height - total_font_height) // 2
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# Header for the generated C file
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print("/* SPDX-License-Identifier: GPL-2.0-or-later */\n")
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print("/*")
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@ -65,72 +73,50 @@ def generate_c_table(font_path, canvas_width, canvas_height):
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widths = []
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# Choose data type based on width
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data_type = "uint32_t"
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hex_format = "08x" if canvas_width > 16 else "04x"
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bit_depth = 32 if canvas_width > 16 else 16
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print(f"const uint8_t font_table[FONT_NUM_CHARS][FONT_HEIGHT * FONT_WIDTH] = {{")
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# 2. Generate packed font table
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print(f"const {data_type} font_table[FONT_NUM_CHARS][FONT_HEIGHT] = {{")
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clipped_glyphs = []
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for char_code in range(START_CHAR, END_CHAR + 1):
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char = chr(char_code)
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image = Image.new("1", (canvas_width, canvas_height), 0)
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image = Image.new("L", (canvas_width, canvas_height), 0)
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draw = ImageDraw.Draw(image)
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draw.text((0, y_offset), char, font=font, fill=1)
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draw.text((0, y_offset), char, font=font, fill=255)
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pixels = list(image.getdata())
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rows = []
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global_mask = 0
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leftmost = canvas_width
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rightmost = 0
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has_pixels = False
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for y in range(canvas_height):
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row_val = 0
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base = y * canvas_width
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for x in range(canvas_width):
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if pixels[base + x]:
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# Map pixels to bits: Leftmost pixel is highest bit
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row_val |= (1 << ((canvas_width - 1) - x))
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rows.append(row_val)
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global_mask |= row_val
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if pixels[y * canvas_width + x] > 0:
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if x < leftmost: leftmost = x
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if x > rightmost: rightmost = x
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has_pixels = True
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# Dead space removal / Normalization
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left_shift = 0
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actual_width = 0
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if global_mask > 0:
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# Find the leftmost pixel column
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leftmost_col = 0
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for i in range(canvas_width):
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if (global_mask >> (canvas_width - 1 - i)) & 1:
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leftmost_col = i
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break
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# Find the rightmost pixel column
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rightmost_col = 0
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for i in range(canvas_width):
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if (global_mask >> i) & 1:
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rightmost_col = (canvas_width - 1) - i
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break
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# Width is the horizontal span of active pixels
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actual_width = rightmost_col - leftmost_col + 1
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# left_shift ensures character is left-aligned to MSB of the data type
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left_shift = (bit_depth - canvas_width) + leftmost_col
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if has_pixels:
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actual_width = rightmost - leftmost + 1
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if actual_width >= canvas_width:
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clipped_glyphs.append(char)
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else:
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actual_width = canvas_width // 3 # Default width for space
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widths.append(actual_width)
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# Pre-shift values to be MSB-aligned and mask based on bit depth
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mask_val = 0xFFFFFFFF if bit_depth == 32 else 0xFFFF
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hex_values = [f"0x{(row << left_shift) & mask_val:{hex_format}}" for row in rows]
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char_repr = f"'{char}'" if char not in ["'", "\\"] else f"'\\{char}'"
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print(f"\t[0x{char_code:02x} - FONT_START_CHAR] = {{")
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for i in range(0, len(hex_values), 8):
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line = ", ".join(hex_values[i:i+8])
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print(f"\t\t{line},")
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# Format with line breaks every 8 entries
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for i in range(0, len(pixels), canvas_width):
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row = pixels[i : i + canvas_width]
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for j in range(0, len(row), 8):
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chunk = row[j : j + 8]
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line = ", ".join([f"0x{p:02x}" for p in chunk])
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print(f"\t\t{line},")
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print(f"\t}}, /* {char_repr} */")
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print("};\n")
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@ -142,8 +128,11 @@ def generate_c_table(font_path, canvas_width, canvas_height):
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print(f"\t[0x{char_code:02x} - FONT_START_CHAR] = {w},")
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print("};")
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if clipped_glyphs:
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print(f"/* Warning: Characters clipped: {' '.join(clipped_glyphs)} */", file=sys.stderr)
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if __name__ == "__main__":
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parser = argparse.ArgumentParser(description="Generate bitmapped font table.")
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parser = argparse.ArgumentParser(description="Generate anti-aliased font table.")
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parser.add_argument("font_path", help="Path to TTF/OTF font file")
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parser.add_argument("--width", type=int, default=24, help="Canvas width (default: 24)")
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parser.add_argument("--height", type=int, default=32, help="Canvas height (default: 32)")
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