src/lua/lua_image_decode.cpp

#ifdef WITH_RIVE_SCRIPTING

#include "rive/lua/rive_lua_libs.hpp"
#include "lua.h"
#include "lualib.h"

#include <cassert>
#include <cstring>
#include <vector>
#include <unordered_map>

// ============================================================================
// Native path — uses Bitmap::decode via WorkPool
// ============================================================================

#ifndef __EMSCRIPTEN__

#include "rive/async/work_pool.hpp"
#ifdef RIVE_DECODERS
#include "rive/decoders/bitmap_decoder.hpp"
#endif

namespace rive
{

#ifdef RIVE_DECODERS
class ImageDecodeTask : public WorkTask
{
public:
    std::vector<uint8_t> m_encodedData;
    uint32_t m_width = 0;
    uint32_t m_height = 0;
    lua_State* m_state = nullptr;
    int m_promiseRef = LUA_NOREF;
    std::unique_ptr<Bitmap> m_bitmap;

    bool execute() override
    {
        m_bitmap = Bitmap::decode(m_encodedData.data(), m_encodedData.size());
        if (!m_bitmap)
        {
            m_errorMessage = "failed to decode image data";
            return false;
        }
        if (m_bitmap->pixelFormat() != Bitmap::PixelFormat::RGBAPremul)
        {
            m_bitmap->pixelFormat(Bitmap::PixelFormat::RGBAPremul);
        }
        m_width = m_bitmap->width();
        m_height = m_bitmap->height();
        return true;
    }

    void onComplete() override
    {
        if (!m_state || m_promiseRef == LUA_NOREF)
            return;
        lua_State* L = m_state;
        lua_rawgeti(L, LUA_REGISTRYINDEX, m_promiseRef);
        auto* promise = lua_torive<ScriptedPromise>(L, -1, true);
        lua_pop(L, 1);
        if (promise && promise->isPending())
        {
            if (m_bitmap->pixelFormat() != Bitmap::PixelFormat::RGBAPremul)
            {
                lua_pushstring(L,
                               "internal error: decoded image is not "
                               "RGBAPremul");
                promise->reject(L, lua_gettop(L));
                lua_pop(L, 1);
                m_bitmap.reset();
                lua_unref(L, m_promiseRef);
                m_promiseRef = LUA_NOREF;
                return;
            }
            lua_newtable(L);
            size_t pixelSize = (size_t)m_width * m_height * 4;
            void* buf = lua_newbuffer(L, pixelSize);
            memcpy(buf, m_bitmap->bytes(), pixelSize);
            lua_setfield(L, -2, "data");
            lua_pushnumber(L, m_width);
            lua_setfield(L, -2, "width");
            lua_pushnumber(L, m_height);
            lua_setfield(L, -2, "height");
            promise->resolve(L, lua_gettop(L));
            lua_pop(L, 1);
        }
        // Release decoded bitmap immediately — the pixels have been
        // copied to the Lua buffer. The TaskRef userdata in the onCancel
        // closure may keep this task alive until GC, so eagerly free the
        // large allocation.
        m_bitmap.reset();
        m_encodedData.clear();
        m_encodedData.shrink_to_fit();
        lua_unref(L, m_promiseRef);
        m_promiseRef = LUA_NOREF;
    }

    void onError(const std::string& error) override
    {
        if (!m_state || m_promiseRef == LUA_NOREF)
            return;
        lua_State* L = m_state;
        lua_rawgeti(L, LUA_REGISTRYINDEX, m_promiseRef);
        auto* promise = lua_torive<ScriptedPromise>(L, -1, true);
        lua_pop(L, 1);
        if (promise && promise->isPending())
        {
            lua_pushstring(L, error.c_str());
            promise->reject(L, lua_gettop(L));
            lua_pop(L, 1);
        }
        lua_unref(L, m_promiseRef);
        m_promiseRef = LUA_NOREF;
    }

    void onCancel() override
    {
        m_promiseRef = LUA_NOREF;
        m_state = nullptr;
    }
};
#endif // RIVE_DECODERS

} // namespace rive

int context_decodeImage_impl(lua_State* L)
{
    using namespace rive;

    size_t len = 0;
    const void* data = nullptr;
    if (lua_isbuffer(L, 2))
        data = lua_tobuffer(L, 2, &len);
    else
    {
        luaL_typeerror(L, 2, "buffer");
        return 0;
    }
    if (!data || len == 0)
    {
        luaL_error(L, "decodeImage: empty buffer");
        return 0;
    }

#ifndef RIVE_DECODERS
    luaL_error(L, "decodeImage: not supported on this platform");
    return 0;
#else
    auto* ctx = static_cast<ScriptingContext*>(lua_getthreaddata(L));
    WorkPool* wp = ctx->workPool();

    lua_State* mainThread = lua_mainthread(L);
    lua_newrive<ScriptedPromise>(L, mainThread);
    int promiseIdx = lua_gettop(L);
    lua_pushvalue(L, promiseIdx);
    int promiseRef = lua_ref(L, -1);
    lua_pop(L, 1);

    auto task = make_rcp<ImageDecodeTask>();
    task->m_encodedData.assign(static_cast<const uint8_t*>(data),
                               static_cast<const uint8_t*>(data) + len);
    task->m_state = mainThread;
    task->m_promiseRef = promiseRef;
    task->setOwnerId(ctx->ownerId());

    // Wrap the rcp<WorkTask> in a Lua userdata with a destructor so the
    // task stays alive as long as the onCancel closure exists. This
    // prevents a use-after-free if the WorkPool is destroyed (dropping
    // its rcp) before the promise is cancelled.
    struct TaskRef
    {
        rcp<WorkTask> ref;
    };
    auto* taskUD = static_cast<TaskRef*>(
        lua_newuserdatadtor(L, sizeof(TaskRef), [](void* p) {
            static_cast<TaskRef*>(p)->~TaskRef();
        }));
    new (taskUD) TaskRef{task}; // copy rcp before submit moves it
    int taskUDIdx = lua_gettop(L);

    wp->submit(std::move(task));

    // Register onCancel hook: cancel the WorkPool task so the decode
    // thread skips execution (or the result is discarded), and release
    // the promise registry reference so the Promise can be collected.
    auto* promise = lua_torive<ScriptedPromise>(L, promiseIdx);
    lua_pushvalue(L, taskUDIdx);
    lua_remove(L, taskUDIdx); // remove original, closure upvalue has it
    lua_pushinteger(L, promiseRef);
    lua_pushcclosurek(
        L,
        [](lua_State* L) -> int {
            auto* tr =
                static_cast<TaskRef*>(lua_touserdata(L, lua_upvalueindex(1)));
            if (tr && tr->ref)
                tr->ref->cancel();
            int pRef = (int)lua_tointeger(L, lua_upvalueindex(2));
            lua_unref(L, pRef);
            return 0;
        },
        nullptr,
        2,
        nullptr);
    promise->m_onCancelRef = lua_ref(L, -1);
    lua_pop(L, 1);

    lua_pushvalue(L, promiseIdx);
    return 1;
#endif // RIVE_DECODERS
}

// ============================================================================
// WASM path — uses browser's createImageBitmap, no WorkPool
// ============================================================================

#else // __EMSCRIPTEN__

#include <emscripten.h>

namespace
{

// Track in-flight decodes so the JS callback can find the Lua state + promise.
struct PendingDecode
{
    lua_State* state;
    int promiseRef;
};
std::unordered_map<uint32_t, PendingDecode> s_pendingDecodes;
uint32_t s_nextDecodeId = 1;

// Generate a unique decode ID, skipping any that are still in-flight.
uint32_t nextDecodeId()
{
    uint32_t id = s_nextDecodeId++;
    // On wraparound, skip IDs that collide with in-flight decodes.
    while (id == 0 || s_pendingDecodes.count(id))
        id = s_nextDecodeId++;
    return id;
}

} // namespace

// Start a browser-native image decode. createImageBitmap is async; the JS
// callback fires between frames and calls back into C++ to resolve the promise.
EM_JS(void,
      wasm_start_image_decode,
      (uint32_t requestId, const uint8_t* data, int dataLen),
      {
          // Copy from WASM heap (SharedArrayBuffer can't be used for Blob).
          var sourceView = Module["HEAP8"].subarray(data, data + dataLen);
          var buffer = new Uint8Array(dataLen);
          buffer.set(sourceView);

          var blob = new Blob([buffer]);
          createImageBitmap(blob)
              .then(function(bmp) {
                  // Draw to OffscreenCanvas to extract raw RGBA pixels.
                  var canvas = new OffscreenCanvas(bmp.width, bmp.height);
                  var ctx2d = canvas.getContext("2d");
                  ctx2d.drawImage(bmp, 0, 0);
                  var imageData =
                      ctx2d.getImageData(0, 0, bmp.width, bmp.height);

                  // Allocate WASM memory and copy pixels.
                  var numBytes = imageData.data.length;
                  var ptr = Module._malloc(numBytes);
                  Module.HEAPU8.set(imageData.data, ptr);

                  Module._wasm_image_decode_complete(requestId,
                                                     bmp.width,
                                                     bmp.height,
                                                     ptr,
                                                     numBytes);
              })
              .catch(function(err) {
                  var msg = err.message || "decode failed";
                  var msgLen = Module.lengthBytesUTF8(msg) + 1;
                  var msgPtr = Module._malloc(msgLen);
                  Module.stringToUTF8(msg, msgPtr, msgLen);
                  Module._wasm_image_decode_error(requestId, msgPtr);
                  Module._free(msgPtr);
              });
      });

// C callbacks invoked by JS when createImageBitmap resolves/rejects.
extern "C"
{
    using namespace rive;

    EMSCRIPTEN_KEEPALIVE
    void wasm_image_decode_complete(uint32_t requestId,
                                    int width,
                                    int height,
                                    uint8_t* pixels,
                                    int numBytes)
    {
        auto it = s_pendingDecodes.find(requestId);
        if (it == s_pendingDecodes.end())
        {
            free(pixels);
            return;
        }

        auto [state, promiseRef] = it->second;
        s_pendingDecodes.erase(it);

        if (!state)
        {
            free(pixels);
            return;
        }

        lua_State* L = state;
        lua_rawgeti(L, LUA_REGISTRYINDEX, promiseRef);
        auto* promise = lua_torive<ScriptedPromise>(L, -1, true);
        lua_pop(L, 1);

        if (promise && promise->isPending())
        {
            // getImageData() returns straight RGBA; premultiply in-place so
            // the scripting API always delivers premultiplied RGBA8.
            for (int i = 0; i < numBytes; i += 4)
            {
                uint8_t a = pixels[i + 3];
                if (a < 255)
                {
                    pixels[i + 0] = (uint16_t(pixels[i + 0]) * a + 127) / 255;
                    pixels[i + 1] = (uint16_t(pixels[i + 1]) * a + 127) / 255;
                    pixels[i + 2] = (uint16_t(pixels[i + 2]) * a + 127) / 255;
                }
            }

            lua_newtable(L);

            void* buf = lua_newbuffer(L, numBytes);
            memcpy(buf, pixels, numBytes);
            lua_setfield(L, -2, "data");

            lua_pushnumber(L, width);
            lua_setfield(L, -2, "width");

            lua_pushnumber(L, height);
            lua_setfield(L, -2, "height");

            promise->resolve(L, lua_gettop(L));
            lua_pop(L, 1);
        }

        lua_unref(L, promiseRef);
        free(pixels);
    }

    EMSCRIPTEN_KEEPALIVE
    void wasm_image_decode_error(uint32_t requestId, const char* msg)
    {
        auto it = s_pendingDecodes.find(requestId);
        if (it == s_pendingDecodes.end())
            return;

        auto [state, promiseRef] = it->second;
        s_pendingDecodes.erase(it);

        if (state)
        {
            lua_State* L = state;
            lua_rawgeti(L, LUA_REGISTRYINDEX, promiseRef);
            auto* promise = lua_torive<ScriptedPromise>(L, -1, true);
            lua_pop(L, 1);

            if (promise && promise->isPending())
            {
                lua_pushstring(L, msg);
                promise->reject(L, lua_gettop(L));
                lua_pop(L, 1);
            }
            lua_unref(L, promiseRef);
        }
    }

} // extern "C"

// Cancel all pending decodes for a Lua state (called on shutdown).
// Must be called while mainThread is still valid so we can unref promises.
namespace rive
{
void wasm_cancelPendingDecodes(lua_State* mainThread)
{
    for (auto it = s_pendingDecodes.begin(); it != s_pendingDecodes.end();)
    {
        if (it->second.state == mainThread)
        {
            lua_unref(mainThread, it->second.promiseRef);
            it = s_pendingDecodes.erase(it);
        }
        else
        {
            ++it;
        }
    }
}
} // namespace rive

int context_decodeImage_impl(lua_State* L)
{
    using namespace rive;

    size_t len = 0;
    const void* data = nullptr;
    if (lua_isbuffer(L, 2))
        data = lua_tobuffer(L, 2, &len);
    else
    {
        luaL_typeerror(L, 2, "buffer");
        return 0;
    }
    if (!data || len == 0)
    {
        luaL_error(L, "decodeImage: empty buffer");
        return 0;
    }

    lua_State* mainThread = lua_mainthread(L);
    lua_newrive<ScriptedPromise>(L, mainThread);
    int promiseIdx = lua_gettop(L);
    lua_pushvalue(L, promiseIdx);
    int promiseRef = lua_ref(L, -1);
    lua_pop(L, 1);

    // Register the pending decode so the JS callback can find the promise.
    uint32_t id = nextDecodeId();
    s_pendingDecodes[id] = {mainThread, promiseRef};

    // Start the browser-native decode. This returns immediately.
    wasm_start_image_decode(id,
                            static_cast<const uint8_t*>(data),
                            static_cast<int>(len));

    // Register onCancel hook: erase from pending decodes so the JS
    // callback becomes a no-op (the browser will still finish decoding,
    // but the result is discarded).
    auto* promise = lua_torive<ScriptedPromise>(L, promiseIdx);
    lua_pushinteger(L, id);
    lua_pushinteger(L, promiseRef);
    lua_pushcclosurek(
        L,
        [](lua_State* L) -> int {
            uint32_t decodeId = (uint32_t)lua_tointeger(L, lua_upvalueindex(1));
            int pRef = (int)lua_tointeger(L, lua_upvalueindex(2));
            s_pendingDecodes.erase(decodeId);
            lua_unref(L, pRef);
            return 0;
        },
        nullptr,
        2,
        nullptr);
    promise->m_onCancelRef = lua_ref(L, -1);
    lua_pop(L, 1);

    lua_pushvalue(L, promiseIdx);
    return 1;
}

#endif // __EMSCRIPTEN__

#endif // WITH_RIVE_SCRIPTING