text_layout.h

#pragma once
 
#include <cstddef>
#include <string_view>
 
#include "core/utf8.h"
#include "resource/asset/font_asset.h"
 
namespace Vkm::Engine {

template <typename Visit>
float walkGlyphs(const FontAsset& font, std::string_view text, float scale, Visit&& visit) {
    float       pen      = 0.0f;
    int         previous = -1;
    std::size_t at       = 0;
    while (at < text.size()) {
        const std::size_t start = at;
        const int index = FontAsset::glyphIndex(Utf8::next(text, at));
        if (index < 0) {
            previous = -1;
            continue;
        }
        if (previous >= 0) pen += font.kern(previous, index) * scale;
 
        const FontGlyph& glyph = font.glyphs[static_cast<std::size_t>(index)];
        if (!visit(start, glyph, pen)) return pen;
        pen     += glyph.advance * scale;
        previous = index;
    }
    return pen;
}

inline float measureText(const FontAsset& font, std::string_view text, float pixelSize) {
    if (font.pixelHeight <= 0.0f) return 0.0f;
    return walkGlyphs(
        font,
        text,
        pixelSize / font.pixelHeight,
        [](std::size_t, const FontGlyph&, float) { return true; }
    );
}
 
} // namespace Vkm::Engine