80 lines
3.3 KiB
C
80 lines
3.3 KiB
C
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/**
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* .epdfont Binary Font Format Specification
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*
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* This format is designed for on-demand loading from SD card
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* with minimal RAM usage on embedded devices.
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*
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* File Layout:
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* ┌─────────────────────────────────────────────────────┐
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* │ Header (32 bytes) │
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* ├─────────────────────────────────────────────────────┤
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* │ Intervals[] (intervalCount × 12 bytes) │
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* ├─────────────────────────────────────────────────────┤
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* │ Glyphs[] (glyphCount × 16 bytes) │
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* ├─────────────────────────────────────────────────────┤
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* │ Bitmap data (variable size) │
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* └─────────────────────────────────────────────────────┘
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*/
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#pragma once
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#include <cstdint>
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// Magic number: "EPDF" in little-endian
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#define EPDFONT_MAGIC 0x46445045
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// Current format version
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#define EPDFONT_VERSION 1
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#pragma pack(push, 1)
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/**
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* File header - 32 bytes
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*/
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struct EpdFontHeader {
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uint32_t magic; // 0x46445045 ("EPDF")
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uint16_t version; // Format version (1)
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uint8_t is2Bit; // 1 = 2-bit grayscale, 0 = 1-bit
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uint8_t reserved1; // Reserved for alignment
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uint8_t advanceY; // Line height
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int8_t ascender; // Max height above baseline
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int8_t descender; // Max depth below baseline (negative)
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uint8_t reserved2; // Reserved for alignment
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uint32_t intervalCount; // Number of unicode intervals
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uint32_t glyphCount; // Total number of glyphs
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uint32_t intervalsOffset; // File offset to intervals array
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uint32_t glyphsOffset; // File offset to glyphs array
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uint32_t bitmapOffset; // File offset to bitmap data
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};
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/**
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* Unicode interval - 12 bytes
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* Same as EpdUnicodeInterval but with explicit packing
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*/
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struct EpdFontInterval {
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uint32_t first; // First unicode code point
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uint32_t last; // Last unicode code point
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uint32_t offset; // Index into glyph array
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};
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/**
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* Glyph data - 16 bytes
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* Same as EpdGlyph but with explicit packing
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*/
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struct EpdFontGlyph {
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uint8_t width; // Bitmap width in pixels
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uint8_t height; // Bitmap height in pixels
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uint8_t advanceX; // Horizontal advance
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uint8_t reserved; // Reserved for alignment
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int16_t left; // X offset from cursor
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int16_t top; // Y offset from cursor
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uint32_t dataLength; // Bitmap data size in bytes
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uint32_t dataOffset; // Offset into bitmap section
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};
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#pragma pack(pop)
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// Sanity checks for struct sizes
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static_assert(sizeof(EpdFontHeader) == 32, "EpdFontHeader must be 32 bytes");
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static_assert(sizeof(EpdFontInterval) == 12, "EpdFontInterval must be 12 bytes");
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static_assert(sizeof(EpdFontGlyph) == 16, "EpdFontGlyph must be 16 bytes");
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