// dear imgui: Renderer Backend for DirectX9
// This needs to be used along with a Platform Backend (e.g. Win32)

// Implemented features:
//  [X] Renderer: User texture binding. Use 'LPDIRECT3DTEXTURE9' as ImTextureID. Read the FAQ about ImTextureID!
//  [X] Renderer: Multi-viewport support. Enable with 'io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable'.
//  [X] Renderer: Support for large meshes (64k+ vertices) with 16-bit indices.

// You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
// Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
// If you are new to Dear ImGui, read documentation from the docs/ folder + read the top of imgui.cpp.
// Read online: https://github.com/ocornut/imgui/tree/master/docs

// CHANGELOG
// (minor and older changes stripped away, please see git history for details)
//  2021-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
//  2021-06-29: Reorganized backend to pull data from a single structure to facilitate usage with multiple-contexts (all g_XXXX access changed to bd->XXXX).
//  2021-06-25: DirectX9: Explicitly disable texture state stages after >= 1.
//  2021-05-19: DirectX9: Replaced direct access to ImDrawCmd::TextureId with a call to ImDrawCmd::GetTexID(). (will become a requirement)
//  2021-04-23: DirectX9: Explicitly setting up more graphics states to increase compatibility with unusual non-default states.
//  2021-03-18: DirectX9: Calling IDirect3DStateBlock9::Capture() after CreateStateBlock() as a workaround for state restoring issues (see #3857).
//  2021-03-03: DirectX9: Added support for IMGUI_USE_BGRA_PACKED_COLOR in user's imconfig file.
//  2021-02-18: DirectX9: Change blending equation to preserve alpha in output buffer.
//  2019-05-29: DirectX9: Added support for large mesh (64K+ vertices), enable ImGuiBackendFlags_RendererHasVtxOffset flag.
//  2019-04-30: DirectX9: Added support for special ImDrawCallback_ResetRenderState callback to reset render state.
//  2019-03-29: Misc: Fixed erroneous assert in ImGui_ImplDX9_InvalidateDeviceObjects().
//  2019-01-16: Misc: Disabled fog before drawing UI's. Fixes issue #2288.
//  2018-11-30: Misc: Setting up io.BackendRendererName so it can be displayed in the About Window.
//  2018-06-08: Misc: Extracted imgui_impl_dx9.cpp/.h away from the old combined DX9+Win32 example.
//  2018-06-08: DirectX9: Use draw_data->DisplayPos and draw_data->DisplaySize to setup projection matrix and clipping rectangle.
//  2018-05-07: Render: Saving/restoring Transform because they don't seem to be included in the StateBlock. Setting shading mode to Gouraud.
//  2018-02-16: Misc: Obsoleted the io.RenderDrawListsFn callback and exposed ImGui_ImplDX9_RenderDrawData() in the .h file so you can call it yourself.
//  2018-02-06: Misc: Removed call to ImGui::Shutdown() which is not available from 1.60 WIP, user needs to call CreateContext/DestroyContext themselves.

#include "imgui.h"
#include "imgui_impl_dx9.h"

// DirectX
#include <d3d9.h>

// DirectX data
struct ImGui_ImplDX9_Data
{
    LPDIRECT3DDEVICE9           pd3dDevice;
    LPDIRECT3DVERTEXBUFFER9     pVB;
    LPDIRECT3DINDEXBUFFER9      pIB;
    LPDIRECT3DTEXTURE9          FontTexture;
    int                         VertexBufferSize;
    int                         IndexBufferSize;

    ImGui_ImplDX9_Data()        { memset(this, 0, sizeof(*this)); VertexBufferSize = 5000; IndexBufferSize = 10000; }
};

struct CUSTOMVERTEX
{
    float    pos[3];
    D3DCOLOR col;
    float    uv[2];
};
#define D3DFVF_CUSTOMVERTEX (D3DFVF_XYZ|D3DFVF_DIFFUSE|D3DFVF_TEX1)

#ifdef IMGUI_USE_BGRA_PACKED_COLOR
#define IMGUI_COL_TO_DX9_ARGB(_COL)     (_COL)
#else
#define IMGUI_COL_TO_DX9_ARGB(_COL)     (((_COL) & 0xFF00FF00) | (((_COL) & 0xFF0000) >> 16) | (((_COL) & 0xFF) << 16))
#endif

// Backend data stored in io.BackendRendererUserData to allow support for multiple Dear ImGui contexts
// It is STRONGLY preferred that you use docking branch with multi-viewports (== single Dear ImGui context + multiple windows) instead of multiple Dear ImGui contexts.
static ImGui_ImplDX9_Data* ImGui_ImplDX9_GetBackendData()
{
    return ImGui::GetCurrentContext() ? (ImGui_ImplDX9_Data*)ImGui::GetIO().BackendRendererUserData : NULL;
}

// Forward Declarations
static void ImGui_ImplDX9_InitPlatformInterface();
static void ImGui_ImplDX9_ShutdownPlatformInterface();
static void ImGui_ImplDX9_CreateDeviceObjectsForPlatformWindows();
static void ImGui_ImplDX9_InvalidateDeviceObjectsForPlatformWindows();

// Functions
static void ImGui_ImplDX9_SetupRenderState(ImDrawData* draw_data)
{
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();

    // Setup viewport
    D3DVIEWPORT9 vp;
    vp.X = vp.Y = 0;
    vp.Width = (DWORD)draw_data->DisplaySize.x;
    vp.Height = (DWORD)draw_data->DisplaySize.y;
    vp.MinZ = 0.0f;
    vp.MaxZ = 1.0f;
    bd->pd3dDevice->SetViewport(&vp);

    // Setup render state: fixed-pipeline, alpha-blending, no face culling, no depth testing, shade mode (for gradient)
    bd->pd3dDevice->SetPixelShader(NULL);
    bd->pd3dDevice->SetVertexShader(NULL);
    bd->pd3dDevice->SetRenderState(D3DRS_FILLMODE, D3DFILL_SOLID);
    bd->pd3dDevice->SetRenderState(D3DRS_SHADEMODE, D3DSHADE_GOURAUD);
    bd->pd3dDevice->SetRenderState(D3DRS_ZWRITEENABLE, FALSE);
    bd->pd3dDevice->SetRenderState(D3DRS_ALPHATESTENABLE, FALSE);
    bd->pd3dDevice->SetRenderState(D3DRS_CULLMODE, D3DCULL_NONE);
    bd->pd3dDevice->SetRenderState(D3DRS_ZENABLE, FALSE);
    bd->pd3dDevice->SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE);
    bd->pd3dDevice->SetRenderState(D3DRS_BLENDOP, D3DBLENDOP_ADD);
    bd->pd3dDevice->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_SRCALPHA);
    bd->pd3dDevice->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_INVSRCALPHA);
    bd->pd3dDevice->SetRenderState(D3DRS_SEPARATEALPHABLENDENABLE, TRUE);
    bd->pd3dDevice->SetRenderState(D3DRS_SRCBLENDALPHA, D3DBLEND_ONE);
    bd->pd3dDevice->SetRenderState(D3DRS_DESTBLENDALPHA, D3DBLEND_INVSRCALPHA);
    bd->pd3dDevice->SetRenderState(D3DRS_SCISSORTESTENABLE, TRUE);
    bd->pd3dDevice->SetRenderState(D3DRS_FOGENABLE, FALSE);
    bd->pd3dDevice->SetRenderState(D3DRS_RANGEFOGENABLE, FALSE);
    bd->pd3dDevice->SetRenderState(D3DRS_SPECULARENABLE, FALSE);
    bd->pd3dDevice->SetRenderState(D3DRS_STENCILENABLE, FALSE);
    bd->pd3dDevice->SetRenderState(D3DRS_CLIPPING, TRUE);
    bd->pd3dDevice->SetRenderState(D3DRS_LIGHTING, FALSE);
    bd->pd3dDevice->SetTextureStageState(0, D3DTSS_COLOROP, D3DTOP_MODULATE);
    bd->pd3dDevice->SetTextureStageState(0, D3DTSS_COLORARG1, D3DTA_TEXTURE);
    bd->pd3dDevice->SetTextureStageState(0, D3DTSS_COLORARG2, D3DTA_DIFFUSE);
    bd->pd3dDevice->SetTextureStageState(0, D3DTSS_ALPHAOP, D3DTOP_MODULATE);
    bd->pd3dDevice->SetTextureStageState(0, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);
    bd->pd3dDevice->SetTextureStageState(0, D3DTSS_ALPHAARG2, D3DTA_DIFFUSE);
    bd->pd3dDevice->SetTextureStageState(1, D3DTSS_COLOROP, D3DTOP_DISABLE);
    bd->pd3dDevice->SetTextureStageState(1, D3DTSS_ALPHAOP, D3DTOP_DISABLE);
    bd->pd3dDevice->SetSamplerState(0, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);
    bd->pd3dDevice->SetSamplerState(0, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);

    // Setup orthographic projection matrix
    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayPos is (0,0) for single viewport apps.
    // Being agnostic of whether <d3dx9.h> or <DirectXMath.h> can be used, we aren't relying on D3DXMatrixIdentity()/D3DXMatrixOrthoOffCenterLH() or DirectX::XMMatrixIdentity()/DirectX::XMMatrixOrthographicOffCenterLH()
    {
        float L = draw_data->DisplayPos.x + 0.5f;
        float R = draw_data->DisplayPos.x + draw_data->DisplaySize.x + 0.5f;
        float T = draw_data->DisplayPos.y + 0.5f;
        float B = draw_data->DisplayPos.y + draw_data->DisplaySize.y + 0.5f;
        D3DMATRIX mat_identity = { { { 1.0f, 0.0f, 0.0f, 0.0f,  0.0f, 1.0f, 0.0f, 0.0f,  0.0f, 0.0f, 1.0f, 0.0f,  0.0f, 0.0f, 0.0f, 1.0f } } };
        D3DMATRIX mat_projection =
        { { {
            2.0f/(R-L),   0.0f,         0.0f,  0.0f,
            0.0f,         2.0f/(T-B),   0.0f,  0.0f,
            0.0f,         0.0f,         0.5f,  0.0f,
            (L+R)/(L-R),  (T+B)/(B-T),  0.5f,  1.0f
        } } };
        bd->pd3dDevice->SetTransform(D3DTS_WORLD, &mat_identity);
        bd->pd3dDevice->SetTransform(D3DTS_VIEW, &mat_identity);
        bd->pd3dDevice->SetTransform(D3DTS_PROJECTION, &mat_projection);
    }
}

// Render function.
void ImGui_ImplDX9_RenderDrawData(ImDrawData* draw_data)
{
    // Avoid rendering when minimized
    if (draw_data->DisplaySize.x <= 0.0f || draw_data->DisplaySize.y <= 0.0f)
        return;

    // Create and grow buffers if needed
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
    if (!bd->pVB || bd->VertexBufferSize < draw_data->TotalVtxCount)
    {
        if (bd->pVB) { bd->pVB->Release(); bd->pVB = NULL; }
        bd->VertexBufferSize = draw_data->TotalVtxCount + 5000;
        if (bd->pd3dDevice->CreateVertexBuffer(bd->VertexBufferSize * sizeof(CUSTOMVERTEX), D3DUSAGE_DYNAMIC | D3DUSAGE_WRITEONLY, D3DFVF_CUSTOMVERTEX, D3DPOOL_DEFAULT, &bd->pVB, NULL) < 0)
            return;
    }
    if (!bd->pIB || bd->IndexBufferSize < draw_data->TotalIdxCount)
    {
        if (bd->pIB) { bd->pIB->Release(); bd->pIB = NULL; }
        bd->IndexBufferSize = draw_data->TotalIdxCount + 10000;
        if (bd->pd3dDevice->CreateIndexBuffer(bd->IndexBufferSize * sizeof(ImDrawIdx), D3DUSAGE_DYNAMIC | D3DUSAGE_WRITEONLY, sizeof(ImDrawIdx) == 2 ? D3DFMT_INDEX16 : D3DFMT_INDEX32, D3DPOOL_DEFAULT, &bd->pIB, NULL) < 0)
            return;
    }

    // Backup the DX9 state
    IDirect3DStateBlock9* d3d9_state_block = NULL;
    if (bd->pd3dDevice->CreateStateBlock(D3DSBT_ALL, &d3d9_state_block) < 0)
        return;
    if (d3d9_state_block->Capture() < 0)
    {
        d3d9_state_block->Release();
        return;
    }

    // Backup the DX9 transform (DX9 documentation suggests that it is included in the StateBlock but it doesn't appear to)
    D3DMATRIX last_world, last_view, last_projection;
    bd->pd3dDevice->GetTransform(D3DTS_WORLD, &last_world);
    bd->pd3dDevice->GetTransform(D3DTS_VIEW, &last_view);
    bd->pd3dDevice->GetTransform(D3DTS_PROJECTION, &last_projection);

    // Allocate buffers
    CUSTOMVERTEX* vtx_dst;
    ImDrawIdx* idx_dst;
    if (bd->pVB->Lock(0, (UINT)(draw_data->TotalVtxCount * sizeof(CUSTOMVERTEX)), (void**)&vtx_dst, D3DLOCK_DISCARD) < 0)
    {
        d3d9_state_block->Release();
        return;
    }
    if (bd->pIB->Lock(0, (UINT)(draw_data->TotalIdxCount * sizeof(ImDrawIdx)), (void**)&idx_dst, D3DLOCK_DISCARD) < 0)
    {
        bd->pVB->Unlock();
        d3d9_state_block->Release();
        return;
    }

    // Copy and convert all vertices into a single contiguous buffer, convert colors to DX9 default format.
    // FIXME-OPT: This is a minor waste of resource, the ideal is to use imconfig.h and
    //  1) to avoid repacking colors:   #define IMGUI_USE_BGRA_PACKED_COLOR
    //  2) to avoid repacking vertices: #define IMGUI_OVERRIDE_DRAWVERT_STRUCT_LAYOUT struct ImDrawVert { ImVec2 pos; float z; ImU32 col; ImVec2 uv; }
    for (int n = 0; n < draw_data->CmdListsCount; n++)
    {
        const ImDrawList* cmd_list = draw_data->CmdLists[n];
        const ImDrawVert* vtx_src = cmd_list->VtxBuffer.Data;
        for (int i = 0; i < cmd_list->VtxBuffer.Size; i++)
        {
            vtx_dst->pos[0] = vtx_src->pos.x;
            vtx_dst->pos[1] = vtx_src->pos.y;
            vtx_dst->pos[2] = 0.0f;
            vtx_dst->col = IMGUI_COL_TO_DX9_ARGB(vtx_src->col);
            vtx_dst->uv[0] = vtx_src->uv.x;
            vtx_dst->uv[1] = vtx_src->uv.y;
            vtx_dst++;
            vtx_src++;
        }
        memcpy(idx_dst, cmd_list->IdxBuffer.Data, cmd_list->IdxBuffer.Size * sizeof(ImDrawIdx));
        idx_dst += cmd_list->IdxBuffer.Size;
    }
    bd->pVB->Unlock();
    bd->pIB->Unlock();
    bd->pd3dDevice->SetStreamSource(0, bd->pVB, 0, sizeof(CUSTOMVERTEX));
    bd->pd3dDevice->SetIndices(bd->pIB);
    bd->pd3dDevice->SetFVF(D3DFVF_CUSTOMVERTEX);

    // Setup desired DX state
    ImGui_ImplDX9_SetupRenderState(draw_data);

    // Render command lists
    // (Because we merged all buffers into a single one, we maintain our own offset into them)
    int global_vtx_offset = 0;
    int global_idx_offset = 0;
    ImVec2 clip_off = draw_data->DisplayPos;
    for (int n = 0; n < draw_data->CmdListsCount; n++)
    {
        const ImDrawList* cmd_list = draw_data->CmdLists[n];
        for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
        {
            const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
            if (pcmd->UserCallback != NULL)
            {
                // User callback, registered via ImDrawList::AddCallback()
                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
                if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
                    ImGui_ImplDX9_SetupRenderState(draw_data);
                else
                    pcmd->UserCallback(cmd_list, pcmd);
            }
            else
            {
                // Project scissor/clipping rectangles into framebuffer space
                ImVec2 clip_min(pcmd->ClipRect.x - clip_off.x, pcmd->ClipRect.y - clip_off.y);
                ImVec2 clip_max(pcmd->ClipRect.z - clip_off.x, pcmd->ClipRect.w - clip_off.y);
                if (clip_max.x <= clip_min.x || clip_max.y <= clip_min.y)
                    continue;

                // Apply Scissor/clipping rectangle, Bind texture, Draw
                const RECT r = { (LONG)clip_min.x, (LONG)clip_min.y, (LONG)clip_max.x, (LONG)clip_max.y };
                const LPDIRECT3DTEXTURE9 texture = (LPDIRECT3DTEXTURE9)pcmd->GetTexID();
                bd->pd3dDevice->SetTexture(0, texture);
                bd->pd3dDevice->SetScissorRect(&r);
                bd->pd3dDevice->DrawIndexedPrimitive(D3DPT_TRIANGLELIST, pcmd->VtxOffset + global_vtx_offset, 0, (UINT)cmd_list->VtxBuffer.Size, pcmd->IdxOffset + global_idx_offset, pcmd->ElemCount / 3);
            }
        }
        global_idx_offset += cmd_list->IdxBuffer.Size;
        global_vtx_offset += cmd_list->VtxBuffer.Size;
    }

    // When using multi-viewports, it appears that there's an odd logic in DirectX9 which prevent subsequent windows
    // from rendering until the first window submits at least one draw call, even once. That's our workaround. (see #2560)
    if (global_vtx_offset == 0)
        bd->pd3dDevice->DrawIndexedPrimitive(D3DPT_TRIANGLELIST, 0, 0, 0, 0, 0);

    // Restore the DX9 transform
    bd->pd3dDevice->SetTransform(D3DTS_WORLD, &last_world);
    bd->pd3dDevice->SetTransform(D3DTS_VIEW, &last_view);
    bd->pd3dDevice->SetTransform(D3DTS_PROJECTION, &last_projection);

    // Restore the DX9 state
    d3d9_state_block->Apply();
    d3d9_state_block->Release();
}

bool ImGui_ImplDX9_Init(IDirect3DDevice9* device)
{
    ImGuiIO& io = ImGui::GetIO();
    IM_ASSERT(io.BackendRendererUserData == NULL && "Already initialized a renderer backend!");

    // Setup backend capabilities flags
    ImGui_ImplDX9_Data* bd = IM_NEW(ImGui_ImplDX9_Data)();
    io.BackendRendererUserData = (void*)bd;
    io.BackendRendererName = "imgui_impl_dx9";
    io.BackendFlags |= ImGuiBackendFlags_RendererHasVtxOffset;  // We can honor the ImDrawCmd::VtxOffset field, allowing for large meshes.
    io.BackendFlags |= ImGuiBackendFlags_RendererHasViewports;  // We can create multi-viewports on the Renderer side (optional)

    bd->pd3dDevice = device;
    bd->pd3dDevice->AddRef();

    if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable)
        ImGui_ImplDX9_InitPlatformInterface();

    return true;
}

void ImGui_ImplDX9_Shutdown()
{
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
    IM_ASSERT(bd != NULL && "No renderer backend to shutdown, or already shutdown?");
    ImGuiIO& io = ImGui::GetIO();

    ImGui_ImplDX9_ShutdownPlatformInterface();
    ImGui_ImplDX9_InvalidateDeviceObjects();
    if (bd->pd3dDevice) { bd->pd3dDevice->Release(); }
    io.BackendRendererName = NULL;
    io.BackendRendererUserData = NULL;
    IM_DELETE(bd);
}

static bool ImGui_ImplDX9_CreateFontsTexture()
{
    // Build texture atlas
    ImGuiIO& io = ImGui::GetIO();
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
    unsigned char* pixels;
    int width, height, bytes_per_pixel;
    io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height, &bytes_per_pixel);

    // Convert RGBA32 to BGRA32 (because RGBA32 is not well supported by DX9 devices)
#ifndef IMGUI_USE_BGRA_PACKED_COLOR
    if (io.Fonts->TexPixelsUseColors)
    {
        ImU32* dst_start = (ImU32*)ImGui::MemAlloc((size_t)width * height * bytes_per_pixel);
        for (ImU32* src = (ImU32*)pixels, *dst = dst_start, *dst_end = dst_start + (size_t)width * height; dst < dst_end; src++, dst++)
            *dst = IMGUI_COL_TO_DX9_ARGB(*src);
        pixels = (unsigned char*)dst_start;
    }
#endif

    // Upload texture to graphics system
    bd->FontTexture = NULL;
    if (bd->pd3dDevice->CreateTexture(width, height, 1, D3DUSAGE_DYNAMIC, D3DFMT_A8R8G8B8, D3DPOOL_DEFAULT, &bd->FontTexture, NULL) < 0)
        return false;
    D3DLOCKED_RECT tex_locked_rect;
    if (bd->FontTexture->LockRect(0, &tex_locked_rect, NULL, 0) != D3D_OK)
        return false;
    for (int y = 0; y < height; y++)
        memcpy((unsigned char*)tex_locked_rect.pBits + (size_t)tex_locked_rect.Pitch * y, pixels + (size_t)width * bytes_per_pixel * y, (size_t)width * bytes_per_pixel);
    bd->FontTexture->UnlockRect(0);

    // Store our identifier
    io.Fonts->SetTexID((ImTextureID)bd->FontTexture);

#ifndef IMGUI_USE_BGRA_PACKED_COLOR
    if (io.Fonts->TexPixelsUseColors)
        ImGui::MemFree(pixels);
#endif

    return true;
}

bool ImGui_ImplDX9_CreateDeviceObjects()
{
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
    if (!bd || !bd->pd3dDevice)
        return false;
    if (!ImGui_ImplDX9_CreateFontsTexture())
        return false;
    ImGui_ImplDX9_CreateDeviceObjectsForPlatformWindows();
    return true;
}

void ImGui_ImplDX9_InvalidateDeviceObjects()
{
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
    if (!bd || !bd->pd3dDevice)
        return;
    if (bd->pVB) { bd->pVB->Release(); bd->pVB = NULL; }
    if (bd->pIB) { bd->pIB->Release(); bd->pIB = NULL; }
    if (bd->FontTexture) { bd->FontTexture->Release(); bd->FontTexture = NULL; ImGui::GetIO().Fonts->SetTexID(NULL); } // We copied bd->pFontTextureView to io.Fonts->TexID so let's clear that as well.
    ImGui_ImplDX9_InvalidateDeviceObjectsForPlatformWindows();
}

void ImGui_ImplDX9_NewFrame()
{
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplDX9_Init()?");

    if (!bd->FontTexture)
        ImGui_ImplDX9_CreateDeviceObjects();
}

//--------------------------------------------------------------------------------------------------------
// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
// This is an _advanced_ and _optional_ feature, allowing the backend to create and handle multiple viewports simultaneously.
// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
//--------------------------------------------------------------------------------------------------------

// Helper structure we store in the void* RenderUserData field of each ImGuiViewport to easily retrieve our backend data.
struct ImGui_ImplDX9_ViewportData
{
    IDirect3DSwapChain9*    SwapChain;
    D3DPRESENT_PARAMETERS   d3dpp;

    ImGui_ImplDX9_ViewportData()  { SwapChain = NULL; ZeroMemory(&d3dpp, sizeof(D3DPRESENT_PARAMETERS)); }
    ~ImGui_ImplDX9_ViewportData() { IM_ASSERT(SwapChain == NULL); }
};

static void ImGui_ImplDX9_CreateWindow(ImGuiViewport* viewport)
{
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
    ImGui_ImplDX9_ViewportData* vd = IM_NEW(ImGui_ImplDX9_ViewportData)();
    viewport->RendererUserData = vd;

    // PlatformHandleRaw should always be a HWND, whereas PlatformHandle might be a higher-level handle (e.g. GLFWWindow*, SDL_Window*).
    // Some backends will leave PlatformHandleRaw NULL, in which case we assume PlatformHandle will contain the HWND.
    HWND hwnd = viewport->PlatformHandleRaw ? (HWND)viewport->PlatformHandleRaw : (HWND)viewport->PlatformHandle;
    IM_ASSERT(hwnd != 0);

    ZeroMemory(&vd->d3dpp, sizeof(D3DPRESENT_PARAMETERS));
    vd->d3dpp.Windowed = TRUE;
    vd->d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
    vd->d3dpp.BackBufferWidth = (UINT)viewport->Size.x;
    vd->d3dpp.BackBufferHeight = (UINT)viewport->Size.y;
    vd->d3dpp.BackBufferFormat = D3DFMT_UNKNOWN;
    vd->d3dpp.hDeviceWindow = hwnd;
    vd->d3dpp.EnableAutoDepthStencil = FALSE;
    vd->d3dpp.AutoDepthStencilFormat = D3DFMT_D16;
    vd->d3dpp.PresentationInterval = D3DPRESENT_INTERVAL_IMMEDIATE;   // Present without vsync

    HRESULT hr = bd->pd3dDevice->CreateAdditionalSwapChain(&vd->d3dpp, &vd->SwapChain); IM_UNUSED(hr);
    IM_ASSERT(hr == D3D_OK);
    IM_ASSERT(vd->SwapChain != NULL);
}

static void ImGui_ImplDX9_DestroyWindow(ImGuiViewport* viewport)
{
    // The main viewport (owned by the application) will always have RendererUserData == NULL since we didn't create the data for it.
    if (ImGui_ImplDX9_ViewportData* vd = (ImGui_ImplDX9_ViewportData*)viewport->RendererUserData)
    {
        if (vd->SwapChain)
            vd->SwapChain->Release();
        vd->SwapChain = NULL;
        ZeroMemory(&vd->d3dpp, sizeof(D3DPRESENT_PARAMETERS));
        IM_DELETE(vd);
    }
    viewport->RendererUserData = NULL;
}

static void ImGui_ImplDX9_SetWindowSize(ImGuiViewport* viewport, ImVec2 size)
{
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
    ImGui_ImplDX9_ViewportData* vd = (ImGui_ImplDX9_ViewportData*)viewport->RendererUserData;
    if (vd->SwapChain)
    {
        vd->SwapChain->Release();
        vd->SwapChain = NULL;
        vd->d3dpp.BackBufferWidth = (UINT)size.x;
        vd->d3dpp.BackBufferHeight = (UINT)size.y;
        HRESULT hr = bd->pd3dDevice->CreateAdditionalSwapChain(&vd->d3dpp, &vd->SwapChain); IM_UNUSED(hr);
        IM_ASSERT(hr == D3D_OK);
    }
}

static void ImGui_ImplDX9_RenderWindow(ImGuiViewport* viewport, void*)
{
    ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
    ImGui_ImplDX9_ViewportData* vd = (ImGui_ImplDX9_ViewportData*)viewport->RendererUserData;
    ImVec4 clear_color = ImVec4(0.0f, 0.0f, 0.0f, 1.0f);

    LPDIRECT3DSURFACE9 render_target = NULL;
    LPDIRECT3DSURFACE9 last_render_target = NULL;
    LPDIRECT3DSURFACE9 last_depth_stencil = NULL;
    vd->SwapChain->GetBackBuffer(0, D3DBACKBUFFER_TYPE_MONO, &render_target);
    bd->pd3dDevice->GetRenderTarget(0, &last_render_target);
    bd->pd3dDevice->GetDepthStencilSurface(&last_depth_stencil);
    bd->pd3dDevice->SetRenderTarget(0, render_target);
    bd->pd3dDevice->SetDepthStencilSurface(NULL);

    if (!(viewport->Flags & ImGuiViewportFlags_NoRendererClear))
    {
        D3DCOLOR clear_col_dx = D3DCOLOR_RGBA((int)(clear_color.x*255.0f), (int)(clear_color.y*255.0f), (int)(clear_color.z*255.0f), (int)(clear_color.w*255.0f));
        bd->pd3dDevice->Clear(0, NULL, D3DCLEAR_TARGET, clear_col_dx, 1.0f, 0);
    }

    ImGui_ImplDX9_RenderDrawData(viewport->DrawData);

    // Restore render target
    bd->pd3dDevice->SetRenderTarget(0, last_render_target);
    bd->pd3dDevice->SetDepthStencilSurface(last_depth_stencil);
    render_target->Release();
    last_render_target->Release();
    if (last_depth_stencil) last_depth_stencil->Release();
}

static void ImGui_ImplDX9_SwapBuffers(ImGuiViewport* viewport, void*)
{
    ImGui_ImplDX9_ViewportData* vd = (ImGui_ImplDX9_ViewportData*)viewport->RendererUserData;
    HRESULT hr = vd->SwapChain->Present(NULL, NULL, vd->d3dpp.hDeviceWindow, NULL, 0);
    // Let main application handle D3DERR_DEVICELOST by resetting the device.
    IM_ASSERT(hr == D3D_OK || hr == D3DERR_DEVICELOST);
}

static void ImGui_ImplDX9_InitPlatformInterface()
{
    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
    platform_io.Renderer_CreateWindow = ImGui_ImplDX9_CreateWindow;
    platform_io.Renderer_DestroyWindow = ImGui_ImplDX9_DestroyWindow;
    platform_io.Renderer_SetWindowSize = ImGui_ImplDX9_SetWindowSize;
    platform_io.Renderer_RenderWindow = ImGui_ImplDX9_RenderWindow;
    platform_io.Renderer_SwapBuffers = ImGui_ImplDX9_SwapBuffers;
}

static void ImGui_ImplDX9_ShutdownPlatformInterface()
{
    ImGui::DestroyPlatformWindows();
}

static void ImGui_ImplDX9_CreateDeviceObjectsForPlatformWindows()
{
    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
    for (int i = 1; i < platform_io.Viewports.Size; i++)
        if (!platform_io.Viewports[i]->RendererUserData)
            ImGui_ImplDX9_CreateWindow(platform_io.Viewports[i]);
}

static void ImGui_ImplDX9_InvalidateDeviceObjectsForPlatformWindows()
{
    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
    for (int i = 1; i < platform_io.Viewports.Size; i++)
        if (platform_io.Viewports[i]->RendererUserData)
            ImGui_ImplDX9_DestroyWindow(platform_io.Viewports[i]);
}
