Crafter.Graphics/implementations/Crafter.Graphics-UIAtlas.cpp

/*
Crafter®.Graphics
Copyright (C) 2026 Catcrafts®
catcrafts.net

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License version 3.0 as published by the Free Software Foundation;

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
*/
module;
#include "vulkan/vulkan.h"
#include "../lib/stb_truetype.h"
module Crafter.Graphics:UIAtlas_impl;
import :UIAtlas;
import :Font;
import :ImageVulkan;
import :Device;
import std;

using namespace Crafter;
using namespace Crafter::UI;

void FontAtlas::Initialize(VkCommandBuffer cmd) {
    image.Create(
        kAtlasSize, kAtlasSize, /*mipLevels*/ 1, cmd,
        VK_FORMAT_R8_UNORM,
        VK_IMAGE_USAGE_TRANSFER_DST_BIT | VK_IMAGE_USAGE_SAMPLED_BIT,
        VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL
    );
    // Staging buffer is mapped; clear it so empty atlas regions sample as
    // distance < onedge (i.e. fully outside any glyph).
    std::memset(image.buffer.value, 0, kAtlasSize * kAtlasSize);
    dirty = true;
}

bool FontAtlas::ShelfPlace(int w, int h, int& outX, int& outY) {
    // Try existing shelves first — same height heuristic keeps fragmentation low.
    for (Shelf& s : shelves_) {
        if (h <= s.height && s.cursorX + w <= kAtlasSize) {
            outX = s.cursorX;
            outY = s.y;
            s.cursorX += w;
            return true;
        }
    }
    // New shelf below current ones.
    if (nextShelfY_ + h > kAtlasSize) return false;
    Shelf s{};
    s.y       = nextShelfY_;
    s.height  = h;
    s.cursorX = w;
    outX = 0;
    outY = s.y;
    shelves_.push_back(s);
    nextShelfY_ += h;
    return true;
}

bool FontAtlas::Ensure(Font& font, std::uint32_t codepoint) {
    Key key{&font, codepoint};
    if (cache_.contains(key)) return true;

    float fontScale = stbtt_ScaleForPixelHeight(&font.font, kBaseSize);

    // Advance is always present, even for empty glyphs (e.g. space).
    int advanceUnits = 0, lsb = 0;
    stbtt_GetCodepointHMetrics(&font.font, static_cast<int>(codepoint), &advanceUnits, &lsb);

    int sw = 0, sh = 0, xoff = 0, yoff = 0;
    unsigned char* sdf = stbtt_GetCodepointSDF(
        &font.font, fontScale, static_cast<int>(codepoint),
        kPadding, static_cast<unsigned char>(kOnEdgeValue), kPixelDistScale,
        &sw, &sh, &xoff, &yoff
    );

    Glyph g{};
    g.advance = advanceUnits * fontScale;
    g.xoff = static_cast<float>(xoff);
    g.yoff = static_cast<float>(yoff);

    if (sdf && sw > 0 && sh > 0) {
        int px = 0, py = 0;
        if (!ShelfPlace(sw, sh, px, py)) {
            stbtt_FreeSDF(sdf, nullptr);
            return false;       // V1: silently drop overflow; V2: grow atlas
        }
        // Blit row-by-row into the mapped staging buffer.
        for (int row = 0; row < sh; ++row) {
            std::memcpy(
                image.buffer.value + (py + row) * kAtlasSize + px,
                sdf + row * sw,
                static_cast<std::size_t>(sw)
            );
        }
        stbtt_FreeSDF(sdf, nullptr);

        g.w  = static_cast<float>(sw);
        g.h  = static_cast<float>(sh);
        g.u0 = static_cast<float>(px) / kAtlasSize;
        g.v0 = static_cast<float>(py) / kAtlasSize;
        g.u1 = static_cast<float>(px + sw) / kAtlasSize;
        g.v1 = static_cast<float>(py + sh) / kAtlasSize;
        dirty = true;
    }
    // For empty glyphs (whitespace) we still cache the entry — the size-0
    // fields tell the emitter to skip the quad but advance the cursor.

    cache_.emplace(key, g);
    return true;
}

const Glyph* FontAtlas::Lookup(Font& font, std::uint32_t codepoint) const {
    auto it = cache_.find(Key{&font, codepoint});
    return it == cache_.end() ? nullptr : &it->second;
}

void FontAtlas::Update(VkCommandBuffer cmd) {
    if (!dirty) return;
    image.Update(cmd, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL);
    dirty = false;
}