27 lines
1.2 KiB
C++
27 lines
1.2 KiB
C++
#pragma once
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#include <plot/core/types.hpp>
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namespace plot::render::detail {
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/// The factor a text run is drawn by: `requested_px / em_px`, a plain ratio.
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///
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/// It is a ratio rather than a whole multiple because the renderer's built-in
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/// face is anti-aliased: a style asking for 12 px from a 13 px bake is drawn at
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/// 12/13, where a 1-bit glyph would have had to snap to the nearest multiple of
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/// its cell. Everything the renderer stages is scaled by this one factor, so the
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/// labels a plot laid out and the glyphs the pipeline draws cannot disagree.
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///
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/// A backend that cannot state an em -- `em_px()` at or below zero, or NaN --
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/// yields a 1:1 scale rather than dividing by it or propagating a NaN into every
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/// vertex. The requested size being NaN, zero or negative does the same. The rule
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/// lives here, not inline in the renderer, so it is one function and can be
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/// asserted without a GL context; it is instrumentation-free and part of no
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/// public surface (`*/detail/` headers stay out of the umbrella).
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inline f32 text_scale(f32 requested_px, f32 em_px) noexcept {
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const f32 ratio = requested_px / em_px;
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return (em_px > 0.0f && ratio > 0.0f) ? ratio : 1.0f;
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}
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} // namespace plot::render::detail
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