Crafter.Graphics/implementations/Crafter.Graphics-Font.cpp

//SPDX-License-Identifier: LGPL-3.0-only
//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

module;
#define STB_TRUETYPE_IMPLEMENTATION
#include "../lib/stb_truetype.h"
module Crafter.Graphics:Font_impl;
import :Font;
import std;

using namespace Crafter;

Font::Font(const std::filesystem::path& fontFilePath) {
    // 1. Load the font file into memory
    std::ifstream fontFile(fontFilePath, std::ios::binary | std::ios::ate);
    if (!fontFile.is_open()) {
        std::cerr << "Failed to open font file\n";
    }

    std::streamsize size = fontFile.tellg();
    fontFile.seekg(0, std::ios::beg);
    fontBuffer.resize(size);
    if (!fontFile.read((char*)fontBuffer.data(), size)) {
        std::cerr << "Failed to read font file\n";
    }

    // 2. Initialize the font
    if (!stbtt_InitFont(&font, fontBuffer.data(), stbtt_GetFontOffsetForIndex(fontBuffer.data(), 0))) {
        std::cout << "Test6" << std::endl;
        std::cerr << "Failed to initialize font.\n";
    }

    int ascent;
    int descent;
    int lineGap;

    stbtt_GetFontVMetrics(&font, &ascent, &descent, &lineGap);

    this->ascent = ascent;
    this->descent = descent;
    this->lineGap = lineGap;

    asciiAdvance_.fill(-1);
}

std::int32_t Font::AdvanceUnits(std::uint32_t cp) {
    if (cp < asciiAdvance_.size()) {
        if (asciiAdvance_[cp] < 0) {
            int advance = 0, lsb = 0;
            stbtt_GetCodepointHMetrics(&font, static_cast<int>(cp), &advance, &lsb);
            asciiAdvance_[cp] = advance;
        }
        return asciiAdvance_[cp];
    }
    if (auto it = advanceUnits_.find(cp); it != advanceUnits_.end()) return it->second;
    int advance = 0, lsb = 0;
    stbtt_GetCodepointHMetrics(&font, static_cast<int>(cp), &advance, &lsb);
    return advanceUnits_.emplace(cp, advance).first->second;
}

std::uint32_t Font::GetLineWidth(const std::string_view text, float size) {
    float scale = stbtt_ScaleForPixelHeight(&font, size);
    std::uint32_t lineWidth = 0;
    std::size_t i = 0;
    while (i < text.size()) {
        std::uint32_t cp = DecodeUtf8(text, i);
        if (cp == 0) break;
        lineWidth += (int)(AdvanceUnits(cp) * scale);
    }
    return lineWidth;
}

std::size_t Font::NearestCursorByte(std::string_view text, float size, float target) {
    if (target <= 0.0f) return 0;
    float scale = stbtt_ScaleForPixelHeight(&font, size);
    std::size_t best     = 0;        // byte offset 0 → caret before the first glyph
    float       bestDist = target;   // |target - 0|, and target > 0 here
    float       cumWidth = 0.0f;
    std::size_t i = 0;
    while (i < text.size()) {
        std::uint32_t cp = DecodeUtf8(text, i);   // i advances to the next boundary
        if (cp == 0) break;
        cumWidth += (int)(AdvanceUnits(cp) * scale);  // match GetLineWidth's per-glyph rounding
        float d = std::abs(target - cumWidth);
        if (d < bestDist) {
            bestDist = d;
            best     = i;            // byte offset just past this codepoint
        } else {
            break;                   // monotonic advance ⇒ already past the closest boundary
        }
    }
    return best;
}

float Font::LineHeight(float size) {
    float scale = stbtt_ScaleForPixelHeight(&font, size);
    return (ascent - descent + lineGap) * scale;
}

float Font::AscentPx(float size) {
    return ascent * stbtt_ScaleForPixelHeight(&font, size);
}

float Font::ScaleForSize(float size) {
    return stbtt_ScaleForPixelHeight(&font, size);
}