d0f7acf9eb
An x86-64 operating system built from xv6, now largely rewritten: SMP, a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF rasteriser, and a Linux-numbered syscall ABI. No history before this point -- the tree was never under version control. This commit exists so the rename that follows has something to undo to.
49 lines
2 KiB
C
49 lines
2 KiB
C
#pragma once
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// TrueType outlines, as a font provider for include/text.h.
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//
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// Scope, and why it is this and not "TTF and OTF":
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//
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// .ttf and .otf are both sfnt containers -- the same table directory, the same
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// cmap, the same hmtx. What differs is how outlines are stored. TrueType puts
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// quadratic B-spline contours in a `glyf` table; OpenType/PostScript puts cubic
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// béziers in a `CFF ` table encoded as Type 2 charstrings, which is a
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// stack-based interpreted format and a separate project.
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//
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// Checked before writing any of it: JetBrains Mono and Roboto -- the two fonts
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// this system is going to use -- both ship `glyf` and neither ships `CFF `. So
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// CFF support would buy nothing today, and the honest thing is to implement the
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// format the fonts actually use and say so, rather than half-implement two.
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//
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// Everything here is from Apple's TrueType Reference Manual and the OpenType
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// specification, both public documents.
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struct ttf {
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const unsigned char *data;
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uint32 len;
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uint32 glyf, glyf_len;
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uint32 loca, loca_len;
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uint32 cmap4; // offset of the format 4 subtable, 0 if none
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uint32 hmtx;
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int num_glyphs;
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int num_hmetrics;
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int units_per_em;
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int long_loca; // indexToLocFormat: 0 = 16-bit offsets, 1 = 32
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int ascent, descent;
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// Rasterisation target size, in pixels per em. Set by ttf_open.
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int px;
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};
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// Parse a font already in memory. Returns 0, or -1 if it is not a TrueType
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// font this can read. `data` must outlive the struct -- nothing is copied.
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int ttf_open(struct ttf *, const void *data, uint32 len, int pixels_per_em);
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// Rasterise one codepoint into `cov`. Returns 0, or -1 if the font has no such
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// glyph or it will not fit. Exposed because the host harness uses it directly.
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int ttf_render(struct ttf *, uint32 cp, struct glyph *out, unsigned char *cov,
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int covcap, int *ox, int *oy);
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// A font provider over it, for text.h. The struct must outlive the font.
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struct font *ttf_font(struct ttf *);
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