fix(font): Prevent VLW spaces from erasing previous rows. - #279
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Some VLW exporters encode a blank space bitmap with offsets outside the text line. Rendering that bitmap can fill the background above the current line and erase previously drawn text. Treat spaces as advance-only glyphs while retaining the xAdvance stored in the font. Keep the guessed advance for fonts without a space glyph. Validate 54 space cases across three fonts with ASan/UBSan and confirm that 294 non-space glyph renderings remain unchanged. Signed-off-by: hlym123 <lwylwt@qq.com>
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Some VLW exporters encode a blank space bitmap with offsets outside the text line. Rendering that bitmap can fill the background above the current line and erase previously drawn text.
Treat spaces as advance-only glyphs while retaining the xAdvance stored in the font. Keep the guessed advance for fonts without a space glyph.
Validate 54 space cases across three fonts with ASan/UBSan and confirm that 294 non-space glyph renderings remain unchanged.