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feat(render): anti-aliased embedded Adwaita Mono atlas, generated and committed

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Martino Ferrari committed 2026-09-28 10:40:23 +02:00
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commit 5ca3587325
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include/plot/render/bitmap_font.hpp
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#pragma once
#include <plot/core/types.hpp>
#include <plot/math/vec2.hpp>
#include <plot/render/text.hpp>
namespace plot::render {
/// 8x8 bitmap font, the text backend of the renderer.
///
/// The glyphs are 1-bit, one byte per row, bit 0 the leftmost pixel; the table
/// and its provenance are in `src/render/bitmap_font.cpp`. Nothing here needs a
/// font file, FreeType or stb_truetype: `plot_core` stays dependency-free.
///
/// Metrics are proportional, not fixed width: an advance is the glyph's ink
/// width plus one pixel of spacing, floored at two pixels, derived from the
/// same bitmaps the atlas uploads, so a second width table cannot drift from the
/// artwork. Whitespace is a blank glyph with a nonzero advance, and every
/// codepoint without a glyph draws a visible box, so a missing glyph is obvious
/// rather than silently blank.
///
/// Metrics are in unscaled font pixels, one per glyph texel, and the atlas is a
/// grid of `kGlyphPx` cells: every glyph's rect is its own cell, so a run drawn
/// at `s` pixels per font pixel measures `measure(utf8) * s` and sits in a cell
/// of `s * kGlyphPx` pixels. `TextBatch::add_text` takes that factor and applies
/// it to the pen it advances.
class BitmapFont final : public TextBackend {
public:
// Atlas geometry: a grid of `kGlyphPx` cells whose width is a whole number of
// them. A glyph's rect is its own cell, normalised by these sizes, so the grid
// is all the text pipeline has to know about the atlas.
static constexpr u32 kGlyphPx = 8; ///< glyph cell edge, texels
static constexpr u32 kFirstChar = 32; ///< U+0020
static constexpr u32 kAsciiGlyphs = 95; ///< U+0020..U+007E
static constexpr u32 kDegreeSlot = kAsciiGlyphs; ///< U+00B0 DEGREE SIGN
static constexpr u32 kMicroSlot = kAsciiGlyphs + 1u; ///< U+00B5 MICRO SIGN
static constexpr u32 kOhmSlot = kAsciiGlyphs + 2u; ///< U+03A9 OHM
static constexpr u32 kFallbackSlot = kAsciiGlyphs + 3u; ///< missing-glyph box
static constexpr u32 kGlyphCount = kAsciiGlyphs + 4u;
static constexpr u32 kAtlasCols = 16;
static constexpr u32 kAtlasRows = 7;
static constexpr u32 kAtlasWidth = kAtlasCols * kGlyphPx; ///< 128 texels
static constexpr u32 kAtlasHeight = kAtlasRows * kGlyphPx; ///< 56 texels
/// The atlas cell, normalised: one `kGlyphPx` square of the grid. Every glyph's
/// rect is this, and `cell_uv()` reports it -- one number, derived from the same
/// two constants `pack_atlas()` packs, so the grid the pipeline draws and the
/// grid the ink was written into cannot disagree.
static constexpr Vec2 kCellUV{static_cast<f32>(kGlyphPx) / static_cast<f32>(kAtlasWidth),
static_cast<f32>(kGlyphPx) / static_cast<f32>(kAtlasHeight)};
static_assert(kAtlasCols * kAtlasRows >= kGlyphCount, "atlas too small for the glyph set");
BitmapFont() noexcept = default;
/// Width of `utf8`, the sum of the glyph advances: zero for the empty string
/// and for null. The ASCII path allocates nothing.
f32 measure(const char* utf8) const override;
/// Cell height in pixels (one glyph row of text occupies `height()` pixels).
f32 height() const override;
/// Top of the cell to the baseline, in pixels.
f32 ascent() const override;
/// Advance of one ASCII character in pixels. A byte that is not printable
/// ASCII reports the missing-glyph box, matching what `measure` gives that
/// byte on its own.
f32 advance(char c) const noexcept;
/// Advance of a decoded Unicode codepoint, in pixels.
f32 advance_codepoint(u32 codepoint) const noexcept;
/// Glyph slot for a codepoint: printable ASCII is its own slot, the three SI
/// codepoints `format_si` emits map to real glyphs, and anything else maps to
/// the visible missing-glyph box.
static u32 glyph_index(u32 codepoint) noexcept;
/// The glyph for `codepoint`: its atlas cell as a normalised rect (see
/// `Glyph`), a zero bearing and its ink-derived advance. Never null -- a
/// codepoint with no artwork maps to the visible missing-glyph box, which is
/// what a label outside the coverage set should show.
const Glyph* glyph(u32 codepoint) const override;
/// `kCellUV`: the 8x8 cell every glyph occupies.
Vec2 cell_uv() const override { return kCellUV; }
/// The packed atlas, as `TextBackend` sees it: the bytes `atlas_image()`
/// returns, `kAtlasWidth` by `kAtlasHeight`, GL_R8-ready. Never null.
const u8* atlas_pixels() const override;
u32 atlas_width() const override;
u32 atlas_height() const override;
/// Always zero: the atlas is a compile-time constant, so it never changes and
/// the renderer uploads it once.
u32 revision() const override;
/// Rows in a glyph bitmap, always `kGlyphPx`.
u32 glyph_rows(char c) const noexcept;
/// The `kGlyphPx` rows of one ASCII character's bitmap, top row first.
const u8* glyph_bitmap(char c) const noexcept;
/// The `kGlyphPx` rows of a glyph slot.
static const u8* glyph_bitmap_of(u32 slot) noexcept;
/// The packed atlas image, ready for `plot::gl::Texture::upload_r8`: rows of
/// `kAtlasWidth` bytes, top row first, 255 for ink and 0 for background
/// (straight alpha, no dilation or gamma applied).
static const u8* atlas_image() noexcept;
/// Texel origin of a glyph slot in the atlas, in texels; `glyph()` gives the
/// same rectangle normalised, which is what the text pipeline stages.
static Vec2 atlas_origin(u32 slot) noexcept;
private:
/// Every slot's rect, bearing and advance, derived from the bitmaps above at
/// compile time. This replaced a per-instance `advances_` array holding the
/// same numbers, so the advances the pen uses and the ones `glyph()` publishes
/// cannot drift apart.
static const Glyph* glyph_table() noexcept;
};
} // namespace plot::render
include/plot/render/embedded_mono_font.hpp
+107
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@@ -0,0 +1,107 @@
#pragma once
#include <plot/core/types.hpp>
#include <plot/math/vec2.hpp>
#include <plot/render/text.hpp>
namespace plot::render {
/// The renderer's built-in text backend: an anti-aliased greyscale atlas of
/// Adwaita Mono, baked at authoring time and committed as data.
///
/// There is no font file, FreeType or stb_truetype behind this: the coverage
/// bytes and the glyph table are generated by `tools/fonts/gen_atlas.py` into
/// `src/render/embedded_mono_font.cpp`, so `plot_core` stays dependency-free and
/// nothing rasterises at build or run time. That file carries the provenance --
/// source face, its version, the em size, the supersample factor and the
/// coverage set -- and `gen_atlas.py --check` fails if it has drifted from its
/// input. Adwaita Mono is SIL OFL 1.1 (a copy is committed at
/// `licences/OFL-1.1.txt`); the class is named neutrally because OFL reserves
/// the font name for modified redistributions.
///
/// **One cell, every glyph.** The atlas is a fixed-cell grid -- `cell_uv()` is
/// the contract, and the staging path asserts it per glyph. Each cell is the
/// face's maximum advance wide and its ascent-to-descent extent tall, and every
/// glyph is drawn into its cell with its bearing preserved, never trimmed to its
/// ink. Because the face is monospaced the pen advances by the same amount for
/// every glyph, which is the face's own `hmtx` advance and not an assumption.
///
/// A codepoint outside the coverage set draws the baked fallback box, so a label
/// the atlas cannot spell is visible rather than silently blank.
class EmbeddedMonoFont final : public TextBackend {
public:
/// The size the atlas was baked at, in font pixels, and the coverage samples
/// per texel. Repeated here so a caller can reason about the artwork without
/// opening the generated table; the generated translation unit is the
/// authority and pins the same values.
static constexpr u32 kEmPx = 13;
static constexpr u32 kSupersample = 4;
/// The codepoint value `codepoint_of_slot()` reports for the fallback slot. It
/// is deliberately not a Unicode scalar, so it can never collide with a
/// codepoint the atlas really holds.
static constexpr u32 kFallbackCodepoint = 0xFFFFFFFFu;
EmbeddedMonoFont() noexcept = default;
/// Width of `utf8` in font pixels: the sum of the glyphs' advances, zero for
/// the empty string and for null. Allocates nothing.
f32 measure(const char* utf8) const override;
/// Cell height in font pixels: one line of text occupies this many pixels.
f32 height() const override;
/// Top of the cell to the baseline, in font pixels.
f32 ascent() const override;
/// `kEmPx`: the size the face was baked at. The renderer scales a run by
/// `Style::axis_font_px / em_px()`, so the same backend draws the size the
/// style asked for whatever it was baked at.
f32 em_px() const override;
/// The glyph for `codepoint`: its atlas cell as a normalised rect, no extra
/// bearing -- the bearing is inside the cell's ink -- and its advance. Never
/// null: anything outside the coverage set maps to the fallback box.
const Glyph* glyph(u32 codepoint) const override;
/// `(kCellW / atlas_width(), kCellH / atlas_height())`: the cell every glyph's
/// rect is.
Vec2 cell_uv() const override;
/// The packed atlas, GL_R8-ready, rows of `atlas_width()` bytes, top row
/// first, one coverage byte per texel. Never null.
const u8* atlas_pixels() const override;
u32 atlas_width() const override;
u32 atlas_height() const override;
/// Always zero: the atlas is a compile-time constant, so the renderer uploads
/// it once and never re-uploads.
u32 revision() const override;
/// Advance of a decoded codepoint, in font pixels. A codepoint outside the
/// coverage set reports the fallback box's advance.
static f32 advance_codepoint(u32 codepoint) noexcept;
/// Slot a codepoint maps to: printable ASCII is a direct index, the bakes SI
/// and dash codepoints are a short switch, and everything else is the fallback
/// box -- so a missing glyph is always visible, never blank.
static u32 glyph_index(u32 codepoint) noexcept;
/// Number of cells in the atlas, the fallback included.
static u32 glyph_count() noexcept;
/// The codepoint a slot was baked for, or `kFallbackCodepoint` for the
/// fallback slot. Out-of-range slots report the fallback too.
static u32 codepoint_of_slot(u32 slot) noexcept;
/// The fixed cell size, in atlas texels. Every glyph's rect is exactly this.
static u32 cell_width() noexcept;
static u32 cell_height() noexcept;
/// Texel origin of a slot's cell in the atlas; `glyph()` gives the same
/// rectangle normalised, which is what the text pipeline stages.
static Vec2 atlas_origin(u32 slot) noexcept;
/// The packed atlas image: the bytes `atlas_pixels()` returns, as a
/// compile-time table. Never null.
static const u8* atlas_image() noexcept;
};
} // namespace plot::render
include/plot/render/renderer.hpp
+24 -17
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@@ -8,7 +8,7 @@
#include <plot/core/types.hpp>
#include <plot/math/vec2.hpp>
#include <plot/plot/plot.hpp>
#include <plot/render/bitmap_font.hpp>
#include <plot/render/embedded_mono_font.hpp>
#include <plot/render/buffer.hpp>
#include <plot/render/primitives.hpp>
#include <plot/render/program.hpp>
@@ -155,9 +155,11 @@ class Renderer {
bool using_persistent_upload() const noexcept {
return line_vao_.persistent() && text_vao_.persistent();
}
/// The axis text size the renderer actually draws with: `style().axis_font_px`
/// rounded to the nearest whole multiple of `render::BitmapFont::kGlyphPx`,
/// because a 1-bit glyph only scales cleanly by whole factors.
/// The axis text size the renderer actually draws with: the on-screen cell
/// height of the backend it draws with. `Style::axis_font_px` is an em size, so
/// with an ascent-to-descent cell it is this that a host reads back as the line
/// height it got -- and it is the backend's own `height()` scaled, so it always
/// agrees with the metrics the plot laid the labels out with.
f32 axis_font_px() const noexcept { return font_backend_.cell_px(); }
/// Writes the framebuffer's viewport region as a binary PPM (P6, 8 bits per
@@ -174,23 +176,25 @@ class Renderer {
bool dump_frame_ppm(const char* path, Status* st = nullptr) const;
private:
/// The bitmap font as the plot layer sees it, at the size the text pipeline
/// draws it: `measure`/`height`/`ascent` scale with the glyph cell, so a label
/// can never be laid out for one size and drawn at another. The 8x8 font scales
/// by whole multiples of its cell only -- anything else lands a 1-bit glyph's
/// strokes unevenly -- so `reset()` picks the multiple nearest the requested
/// size.
/// The backend the plot layer sees, at the size the text pipeline draws it:
/// `measure`/`height`/`ascent` scale with the run, so a label can never be laid
/// out for one size and drawn at another.
///
/// It is also the backend the renderer uploads the atlas from, so it forwards
/// the whole interface: the metrics and the glyph bearings and advances are
/// scaled, while the artwork itself -- the atlas bytes, its size and its
/// revision -- is the font's own and passes through untouched.
/// It wraps a `TextBackend` and nothing more: the scale is
/// `axis_font_px / em_px()`, a plain ratio, so an anti-aliased face is drawn at
/// the size the style asked for rather than at a whole multiple of its cell,
/// and any backend -- the embedded font, a host's TrueType face -- is drawn the
/// same way. It forwards the whole interface: the metrics and the glyph
/// bearings and advances are scaled, while the artwork itself -- the atlas
/// bytes, its size and its revision -- is the backend's own and passes through
/// untouched.
class AxisFont final : public render::TextBackend {
public:
void reset(const render::BitmapFont& font, f32 requested_px) noexcept;
void reset(const render::TextBackend& font, f32 requested_px) noexcept;
f32 measure(const char* utf8) const override;
f32 height() const override;
f32 ascent() const override;
f32 em_px() const override;
/// The font's glyph at this wrapper's scale: the atlas rect is unchanged (it
/// is scale-free) and the bearing and advance are multiplied by it, so one
/// `Glyph` describes the glyph this backend draws. The result lives in the
@@ -213,7 +217,7 @@ class Renderer {
f32 scale() const noexcept { return scale_; }
private:
const render::BitmapFont* font_ = nullptr;
const render::TextBackend* font_ = nullptr;
f32 cell_px_ = 1.0f;
f32 scale_ = 1.0f;
/// `glyph()`'s scaled result, returned by pointer because the interface is
@@ -280,7 +284,10 @@ class Renderer {
void draw_measures(const Plot& plot, const PlotLayout& layout);
void draw_annotations(const Plot& plot);
render::BitmapFont font_;
/// The built-in backend the renderer owns. Every use of it goes through the
/// `TextBackend` interface -- `self`-typed nowhere -- so swapping it for
/// another face is a change to this member alone.
render::EmbeddedMonoFont default_font_;
AxisFont font_backend_;
render::Style style_;
include/plot/render/text.hpp
+12
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@@ -108,6 +108,18 @@ class TextBackend {
/// text bottoms instead of cell bottoms.
virtual f32 ascent() const = 0;
/// The face's em size in font pixels: the size the atlas was baked at, in the
/// same units as `height()` and `ascent()`.
///
/// It exists so a run can be drawn at the size a caller asked for whatever the
/// backend was baked at: the renderer scales by `requested_px / em_px()`, so a
/// backend re-baked at another size -- or swapped for a different face -- keeps
/// drawing `Style::axis_font_px`, and the renderer never has to know which font
/// it holds. A backend with no meaningful em (one whose "font pixels" are an
/// arbitrary unit) returns something proportional, `height()` being the
/// natural choice.
virtual f32 em_px() const = 0;
/// The glyph for `codepoint`, or null when this backend has none -- the caller
/// then draws nothing for it (a backend that wants a visible missing-glyph box
/// publishes one as the glyph for the codepoints it cannot render). The