imgui/backends/imgui_impl_sdlrenderer3.cpp

// dear imgui: Renderer Backend for SDL_Renderer for SDL3
// (Requires: SDL 3.1.8+)

// Note that SDL_Renderer is an _optional_ component of SDL3, which IMHO is now largely obsolete.
// For a multi-platform app consider using other technologies:
// - SDL3+SDL_GPU: SDL_GPU is SDL3 new graphics abstraction API.
// - SDL3+DirectX, SDL3+OpenGL, SDL3+Vulkan: combine SDL with dedicated renderers.
// If your application wants to render any non trivial amount of graphics other than UI,
// please be aware that SDL_Renderer currently offers a limited graphic API to the end-user
// and it might be difficult to step out of those boundaries.

// Implemented features:
//  [X] Renderer: User texture binding. Use 'SDL_Texture*' as ImTextureID. Read the FAQ about ImTextureID!
//  [X] Renderer: Large meshes support (64k+ vertices) even with 16-bit indices (ImGuiBackendFlags_RendererHasVtxOffset).
//  [X] Renderer: Expose selected render state for draw callbacks to use. Access in '(ImGui_ImplXXXX_RenderState*)GetPlatformIO().Renderer_RenderState'.
// Missing features:
//  [ ] Renderer: Multi-viewport support (multiple windows).

// You can copy and 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.
// Learn about Dear ImGui:
// - FAQ                  https://dearimgui.com/faq
// - Getting Started      https://dearimgui.com/getting-started
// - Documentation        https://dearimgui.com/docs (same as your local docs/ folder).
// - Introduction, links and more at the top of imgui.cpp

// CHANGELOG
//  2025-01-18: Use endian-dependent RGBA32 texture format, to match SDL_Color.
//  2024-10-09: Expose selected render state in ImGui_ImplSDLRenderer3_RenderState, which you can access in 'void* platform_io.Renderer_RenderState' during draw callbacks.
//  2024-07-01: Update for SDL3 api changes: SDL_RenderGeometryRaw() uint32 version was removed (SDL#9009).
//  2024-05-14: *BREAKING CHANGE* ImGui_ImplSDLRenderer3_RenderDrawData() requires SDL_Renderer* passed as parameter.
//  2024-02-12: Amend to query SDL_RenderViewportSet() and restore viewport accordingly.
//  2023-05-30: Initial version.

#include "imgui.h"
#ifndef IMGUI_DISABLE
#include "imgui_impl_sdlrenderer3.h"
#include <stdint.h>     // intptr_t

// Clang warnings with -Weverything
#if defined(__clang__)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wsign-conversion"    // warning: implicit conversion changes signedness
#endif

// SDL
#include <SDL3/SDL.h>
#if !SDL_VERSION_ATLEAST(3,0,0)
#error This backend requires SDL 3.0.0+
#endif

// SDL_Renderer data
struct ImGui_ImplSDLRenderer3_Data
{
    SDL_Renderer*           Renderer;       // Main viewport's renderer
    SDL_Texture*            FontTexture;
    ImVector<SDL_FColor>    ColorBuffer;

    ImGui_ImplSDLRenderer3_Data()   { memset((void*)this, 0, sizeof(*this)); }
};

// 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_ImplSDLRenderer3_Data* ImGui_ImplSDLRenderer3_GetBackendData()
{
    return ImGui::GetCurrentContext() ? (ImGui_ImplSDLRenderer3_Data*)ImGui::GetIO().BackendRendererUserData : nullptr;
}

// Functions
bool ImGui_ImplSDLRenderer3_Init(SDL_Renderer* renderer)
{
    ImGuiIO& io = ImGui::GetIO();
    IMGUI_CHECKVERSION();
    IM_ASSERT(io.BackendRendererUserData == nullptr && "Already initialized a renderer backend!");
    IM_ASSERT(renderer != nullptr && "SDL_Renderer not initialized!");

    // Setup backend capabilities flags
    ImGui_ImplSDLRenderer3_Data* bd = IM_NEW(ImGui_ImplSDLRenderer3_Data)();
    io.BackendRendererUserData = (void*)bd;
    io.BackendRendererName = "imgui_impl_sdlrenderer3";
    io.BackendFlags |= ImGuiBackendFlags_RendererHasVtxOffset;  // We can honor the ImDrawCmd::VtxOffset field, allowing for large meshes.

    bd->Renderer = renderer;

    return true;
}

void ImGui_ImplSDLRenderer3_Shutdown()
{
    ImGui_ImplSDLRenderer3_Data* bd = ImGui_ImplSDLRenderer3_GetBackendData();
    IM_ASSERT(bd != nullptr && "No renderer backend to shutdown, or already shutdown?");
    ImGuiIO& io = ImGui::GetIO();

    ImGui_ImplSDLRenderer3_DestroyDeviceObjects();

    io.BackendRendererName = nullptr;
    io.BackendRendererUserData = nullptr;
    io.BackendFlags &= ~ImGuiBackendFlags_RendererHasVtxOffset;
    IM_DELETE(bd);
}

static void ImGui_ImplSDLRenderer3_SetupRenderState(SDL_Renderer* renderer)
{
    // Clear out any viewports and cliprect set by the user
    // FIXME: Technically speaking there are lots of other things we could backup/setup/restore during our render process.
    SDL_SetRenderViewport(renderer, nullptr);
    SDL_SetRenderClipRect(renderer, nullptr);
}

void ImGui_ImplSDLRenderer3_NewFrame()
{
    ImGui_ImplSDLRenderer3_Data* bd = ImGui_ImplSDLRenderer3_GetBackendData();
    IM_ASSERT(bd != nullptr && "Context or backend not initialized! Did you call ImGui_ImplSDLRenderer3_Init()?");

    if (!bd->FontTexture)
        ImGui_ImplSDLRenderer3_CreateDeviceObjects();
}

// https://github.com/libsdl-org/SDL/issues/9009
static int SDL_RenderGeometryRaw8BitColor(SDL_Renderer* renderer, ImVector<SDL_FColor>& colors_out, SDL_Texture* texture, const float* xy, int xy_stride, const SDL_Color* color, int color_stride, const float* uv, int uv_stride, int num_vertices, const void* indices, int num_indices, int size_indices)
{
    const Uint8* color2 = (const Uint8*)color;
    colors_out.resize(num_vertices);
    SDL_FColor* color3 = colors_out.Data;
    for (int i = 0; i < num_vertices; i++)
    {
        color3[i].r = color->r / 255.0f;
        color3[i].g = color->g / 255.0f;
        color3[i].b = color->b / 255.0f;
        color3[i].a = color->a / 255.0f;
        color2 += color_stride;
        color = (const SDL_Color*)color2;
    }
    return SDL_RenderGeometryRaw(renderer, texture, xy, xy_stride, color3, sizeof(*color3), uv, uv_stride, num_vertices, indices, num_indices, size_indices);
}

void ImGui_ImplSDLRenderer3_RenderDrawData(ImDrawData* draw_data, SDL_Renderer* renderer)
{
    ImGui_ImplSDLRenderer3_Data* bd = ImGui_ImplSDLRenderer3_GetBackendData();

    // If there's a scale factor set by the user, use that instead
    // If the user has specified a scale factor to SDL_Renderer already via SDL_RenderSetScale(), SDL will scale whatever we pass
    // to SDL_RenderGeometryRaw() by that scale factor. In that case we don't want to be also scaling it ourselves here.
    float rsx = 1.0f;
    float rsy = 1.0f;
    SDL_GetRenderScale(renderer, &rsx, &rsy);
    ImVec2 render_scale;
    render_scale.x = (rsx == 1.0f) ? draw_data->FramebufferScale.x : 1.0f;
    render_scale.y = (rsy == 1.0f) ? draw_data->FramebufferScale.y : 1.0f;

    // Avoid rendering when minimized, scale coordinates for retina displays (screen coordinates != framebuffer coordinates)
    int fb_width = (int)(draw_data->DisplaySize.x * render_scale.x);
    int fb_height = (int)(draw_data->DisplaySize.y * render_scale.y);
    if (fb_width == 0 || fb_height == 0)
        return;

    // Backup SDL_Renderer state that will be modified to restore it afterwards
    struct BackupSDLRendererState
    {
        SDL_Rect    Viewport;
        bool        ViewportEnabled;
        bool        ClipEnabled;
        SDL_Rect    ClipRect;
    };
    BackupSDLRendererState old = {};
    old.ViewportEnabled = SDL_RenderViewportSet(renderer);
    old.ClipEnabled = SDL_RenderClipEnabled(renderer);
    SDL_GetRenderViewport(renderer, &old.Viewport);
    SDL_GetRenderClipRect(renderer, &old.ClipRect);

    // Setup desired state
    ImGui_ImplSDLRenderer3_SetupRenderState(renderer);

    // Setup render state structure (for callbacks and custom texture bindings)
    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
    ImGui_ImplSDLRenderer3_RenderState render_state;
    render_state.Renderer = renderer;
    platform_io.Renderer_RenderState = &render_state;

    // Will project scissor/clipping rectangles into framebuffer space
    ImVec2 clip_off = draw_data->DisplayPos;         // (0,0) unless using multi-viewports
    ImVec2 clip_scale = render_scale;

    // Render command lists
    for (int n = 0; n < draw_data->CmdListsCount; n++)
    {
        const ImDrawList* draw_list = draw_data->CmdLists[n];
        const ImDrawVert* vtx_buffer = draw_list->VtxBuffer.Data;
        const ImDrawIdx* idx_buffer = draw_list->IdxBuffer.Data;

        for (int cmd_i = 0; cmd_i < draw_list->CmdBuffer.Size; cmd_i++)
        {
            const ImDrawCmd* pcmd = &draw_list->CmdBuffer[cmd_i];
            if (pcmd->UserCallback)
            {
                // 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_ImplSDLRenderer3_SetupRenderState(renderer);
                else
                    pcmd->UserCallback(draw_list, pcmd);
            }
            else
            {
                // Project scissor/clipping rectangles into framebuffer space
                ImVec2 clip_min((pcmd->ClipRect.x - clip_off.x) * clip_scale.x, (pcmd->ClipRect.y - clip_off.y) * clip_scale.y);
                ImVec2 clip_max((pcmd->ClipRect.z - clip_off.x) * clip_scale.x, (pcmd->ClipRect.w - clip_off.y) * clip_scale.y);
                if (clip_min.x < 0.0f) { clip_min.x = 0.0f; }
                if (clip_min.y < 0.0f) { clip_min.y = 0.0f; }
                if (clip_max.x > (float)fb_width) { clip_max.x = (float)fb_width; }
                if (clip_max.y > (float)fb_height) { clip_max.y = (float)fb_height; }
                if (clip_max.x <= clip_min.x || clip_max.y <= clip_min.y)
                    continue;

                SDL_Rect r = { (int)(clip_min.x), (int)(clip_min.y), (int)(clip_max.x - clip_min.x), (int)(clip_max.y - clip_min.y) };
                SDL_SetRenderClipRect(renderer, &r);

                const float* xy = (const float*)(const void*)((const char*)(vtx_buffer + pcmd->VtxOffset) + offsetof(ImDrawVert, pos));
                const float* uv = (const float*)(const void*)((const char*)(vtx_buffer + pcmd->VtxOffset) + offsetof(ImDrawVert, uv));
                const SDL_Color* color = (const SDL_Color*)(const void*)((const char*)(vtx_buffer + pcmd->VtxOffset) + offsetof(ImDrawVert, col)); // SDL 2.0.19+

                // Bind texture, Draw
                SDL_Texture* tex = (SDL_Texture*)pcmd->GetTexID();
                SDL_RenderGeometryRaw8BitColor(renderer, bd->ColorBuffer, tex,
                    xy, (int)sizeof(ImDrawVert),
                    color, (int)sizeof(ImDrawVert),
                    uv, (int)sizeof(ImDrawVert),
                    draw_list->VtxBuffer.Size - pcmd->VtxOffset,
                    idx_buffer + pcmd->IdxOffset, pcmd->ElemCount, sizeof(ImDrawIdx));
            }
        }
    }
    platform_io.Renderer_RenderState = nullptr;

    // Restore modified SDL_Renderer state
    SDL_SetRenderViewport(renderer, old.ViewportEnabled ? &old.Viewport : nullptr);
    SDL_SetRenderClipRect(renderer, old.ClipEnabled ? &old.ClipRect : nullptr);
}

// Called by Init/NewFrame/Shutdown
bool ImGui_ImplSDLRenderer3_CreateFontsTexture()
{
    ImGuiIO& io = ImGui::GetIO();
    ImGui_ImplSDLRenderer3_Data* bd = ImGui_ImplSDLRenderer3_GetBackendData();

    // Build texture atlas
    unsigned char* pixels;
    int width, height;
    io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height);   // Load as RGBA 32-bit (75% of the memory is wasted, but default font is so small) because it is more likely to be compatible with user's existing shaders. If your ImTextureId represent a higher-level concept than just a GL texture id, consider calling GetTexDataAsAlpha8() instead to save on GPU memory.

    // Upload texture to graphics system
    // (Bilinear sampling is required by default. Set 'io.Fonts->Flags |= ImFontAtlasFlags_NoBakedLines' or 'style.AntiAliasedLinesUseTex = false' to allow point/nearest sampling)
    bd->FontTexture = SDL_CreateTexture(bd->Renderer, SDL_PIXELFORMAT_RGBA32, SDL_TEXTUREACCESS_STATIC, width, height);
    if (bd->FontTexture == nullptr)
    {
        SDL_Log("error creating texture");
        return false;
    }
    SDL_UpdateTexture(bd->FontTexture, nullptr, pixels, 4 * width);
    SDL_SetTextureBlendMode(bd->FontTexture, SDL_BLENDMODE_BLEND);
    SDL_SetTextureScaleMode(bd->FontTexture, SDL_SCALEMODE_LINEAR);

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

    return true;
}

void ImGui_ImplSDLRenderer3_DestroyFontsTexture()
{
    ImGuiIO& io = ImGui::GetIO();
    ImGui_ImplSDLRenderer3_Data* bd = ImGui_ImplSDLRenderer3_GetBackendData();
    if (bd->FontTexture)
    {
        io.Fonts->SetTexID(0);
        SDL_DestroyTexture(bd->FontTexture);
        bd->FontTexture = nullptr;
    }
}

bool ImGui_ImplSDLRenderer3_CreateDeviceObjects()
{
    return ImGui_ImplSDLRenderer3_CreateFontsTexture();
}

void ImGui_ImplSDLRenderer3_DestroyDeviceObjects()
{
    ImGui_ImplSDLRenderer3_DestroyFontsTexture();
}

//-----------------------------------------------------------------------------

#if defined(__clang__)
#pragma clang diagnostic pop
#endif

#endif // #ifndef IMGUI_DISABLE