Adding sdl2 and sdl3 SDL_Renderer backend

build.zig

@@ -11,9 +11,11 @@ pub const Backend = enum {
     sdl2_opengl3,
     osx_metal,
     sdl2,
+    sdl2_renderer,
     sdl3,
-    sdl3_gpu,
     sdl3_opengl3,
+    sdl3_renderer,
+    sdl3_gpu,
 };
 
 pub fn build(b: *std.Build) void {
@@ -348,6 +350,18 @@ pub fn build(b: *std.Build) void {
                 .flags = cflags,
             });
         },
+        .sdl2_renderer => {
+            if (b.lazyDependency("zsdl", .{})) |zsdl| {
+                imgui.addIncludePath(zsdl.path("libs/sdl2/include"));
+            }
+            imgui.addCSourceFiles(.{
+                .files = &.{
+                    "libs/imgui/backends/imgui_impl_sdl2.cpp",
+                    "libs/imgui/backends/imgui_impl_sdlrenderer2.cpp",
+                },
+                .flags = cflags,
+            });
+        },
         .sdl3_gpu => {
             if (b.lazyDependency("zsdl", .{})) |zsdl| {
                 imgui.addIncludePath(zsdl.path("libs/sdl3/include"));
@@ -360,6 +374,18 @@ pub fn build(b: *std.Build) void {
                 .flags = cflags,
             });
         },
+        .sdl3_renderer => {
+            if (b.lazyDependency("zsdl", .{})) |zsdl| {
+                imgui.addIncludePath(zsdl.path("libs/sdl3/include"));
+            }
+            imgui.addCSourceFiles(.{
+                .files = &.{
+                    "libs/imgui/backends/imgui_impl_sdl3.cpp",
+                    "libs/imgui/backends/imgui_impl_sdlrenderer3.cpp",
+                },
+                .flags = cflags,
+            });
+        },
         .sdl3_opengl3 => {
             if (b.lazyDependency("zsdl", .{})) |zsdl| {
                 imgui.addIncludePath(zsdl.path("libs/sdl3/include/SDL3"));

libs/imgui/backends/imgui_impl_sdl2.cpp

@@ -137,8 +137,9 @@ static const Uint32 SDL_WINDOW_VULKAN = 0x10000000;
 // FIX(zig-gamedev):
 extern "C" {
 
-bool     ImGui_ImplSDL2_InitForOpenGL(SDL_Window* window, void* sdl_gl_context);
 bool     ImGui_ImplSDL2_InitForOther(SDL_Window* window);
+bool     ImGui_ImplSDL2_InitForOpenGL(SDL_Window* window, void* sdl_gl_context);
+bool	 ImGui_ImplSDL2_InitForSDLRenderer(SDL_Window* window, SDL_Renderer* renderer);
 void     ImGui_ImplSDL2_Shutdown();
 void     ImGui_ImplSDL2_NewFrame();
 bool     ImGui_ImplSDL2_ProcessEvent(const SDL_Event* event);

libs/imgui/backends/imgui_impl_sdlrenderer2.cpp

@@ -0,0 +1,288 @@
+// dear imgui: Renderer Backend for SDL_Renderer for SDL2
+// (Requires: SDL 2.0.17+)
+
+// Note that SDL_Renderer is an _optional_ component of SDL2, 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. You will need to update to SDL3.
+// - SDL2+DirectX, SDL2+OpenGL, SDL2+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'.
+
+// 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_ImplSDLRenderer2_RenderState, which you can access in 'void* platform_io.Renderer_RenderState' during draw callbacks.
+//  2024-05-14: *BREAKING CHANGE* ImGui_ImplSDLRenderer3_RenderDrawData() requires SDL_Renderer* passed as parameter.
+//  2023-05-30: Renamed imgui_impl_sdlrenderer.h/.cpp to imgui_impl_sdlrenderer2.h/.cpp to accommodate for upcoming SDL3.
+//  2022-10-11: Using 'nullptr' instead of 'NULL' as per our switch to C++11.
+//  2021-12-21: Update SDL_RenderGeometryRaw() format to work with SDL 2.0.19.
+//  2021-12-03: Added support for large mesh (64K+ vertices), enable ImGuiBackendFlags_RendererHasVtxOffset flag.
+//  2021-10-06: Backup and restore modified ClipRect/Viewport.
+//  2021-09-21: Initial version.
+
+#include "imgui.h"
+#ifndef IMGUI_DISABLE
+#include "imgui_impl_sdlrenderer2.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 <SDL.h>
+#if !SDL_VERSION_ATLEAST(2,0,17)
+#error This backend requires SDL 2.0.17+ because of SDL_RenderGeometry() function
+#endif
+
+// FIX(zig-gamedev):
+extern "C" {
+
+bool     ImGui_ImplSDLRenderer2_Init(SDL_Renderer* renderer);
+void     ImGui_ImplSDLRenderer2_Shutdown();
+void     ImGui_ImplSDLRenderer2_NewFrame();
+void     ImGui_ImplSDLRenderer2_RenderDrawData(ImDrawData* draw_data, SDL_Renderer* renderer);
+
+}
+
+// SDL_Renderer data
+struct ImGui_ImplSDLRenderer2_Data
+{
+    SDL_Renderer*   Renderer;       // Main viewport's renderer
+    SDL_Texture*    FontTexture;
+    ImGui_ImplSDLRenderer2_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_ImplSDLRenderer2_Data* ImGui_ImplSDLRenderer2_GetBackendData()
+{
+    return ImGui::GetCurrentContext() ? (ImGui_ImplSDLRenderer2_Data*)ImGui::GetIO().BackendRendererUserData : nullptr;
+}
+
+// Functions
+bool ImGui_ImplSDLRenderer2_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_ImplSDLRenderer2_Data* bd = IM_NEW(ImGui_ImplSDLRenderer2_Data)();
+    io.BackendRendererUserData = (void*)bd;
+    io.BackendRendererName = "imgui_impl_sdlrenderer2";
+    io.BackendFlags |= ImGuiBackendFlags_RendererHasVtxOffset;  // We can honor the ImDrawCmd::VtxOffset field, allowing for large meshes.
+
+    bd->Renderer = renderer;
+
+    return true;
+}
+
+void ImGui_ImplSDLRenderer2_Shutdown()
+{
+    ImGui_ImplSDLRenderer2_Data* bd = ImGui_ImplSDLRenderer2_GetBackendData();
+    IM_ASSERT(bd != nullptr && "No renderer backend to shutdown, or already shutdown?");
+    ImGuiIO& io = ImGui::GetIO();
+
+    ImGui_ImplSDLRenderer2_DestroyDeviceObjects();
+
+    io.BackendRendererName = nullptr;
+    io.BackendRendererUserData = nullptr;
+    io.BackendFlags &= ~ImGuiBackendFlags_RendererHasVtxOffset;
+    IM_DELETE(bd);
+}
+
+static void ImGui_ImplSDLRenderer2_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_RenderSetViewport(renderer, nullptr);
+	SDL_RenderSetClipRect(renderer, nullptr);
+}
+
+void ImGui_ImplSDLRenderer2_NewFrame()
+{
+    ImGui_ImplSDLRenderer2_Data* bd = ImGui_ImplSDLRenderer2_GetBackendData();
+    IM_ASSERT(bd != nullptr && "Context or backend not initialized! Did you call ImGui_ImplSDLRenderer2_Init()?");
+
+    if (!bd->FontTexture)
+        ImGui_ImplSDLRenderer2_CreateDeviceObjects();
+}
+
+void ImGui_ImplSDLRenderer2_RenderDrawData(ImDrawData* draw_data, SDL_Renderer* renderer)
+{
+	// 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_RenderGetScale(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        ClipEnabled;
+        SDL_Rect    ClipRect;
+    };
+    BackupSDLRendererState old = {};
+    old.ClipEnabled = SDL_RenderIsClipEnabled(renderer) == SDL_TRUE;
+    SDL_RenderGetViewport(renderer, &old.Viewport);
+    SDL_RenderGetClipRect(renderer, &old.ClipRect);
+
+    // Setup desired state
+    ImGui_ImplSDLRenderer2_SetupRenderState(renderer);
+
+    // Setup render state structure (for callbacks and custom texture bindings)
+    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
+    ImGui_ImplSDLRenderer2_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_ImplSDLRenderer2_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_RenderSetClipRect(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));
+#if SDL_VERSION_ATLEAST(2,0,19)
+                const SDL_Color* color = (const SDL_Color*)(const void*)((const char*)(vtx_buffer + pcmd->VtxOffset) + offsetof(ImDrawVert, col)); // SDL 2.0.19+
+#else
+                const int* color = (const int*)(const void*)((const char*)(vtx_buffer + pcmd->VtxOffset) + offsetof(ImDrawVert, col)); // SDL 2.0.17 and 2.0.18
+#endif
+
+                // Bind texture, Draw
+				SDL_Texture* tex = (SDL_Texture*)pcmd->GetTexID();
+                SDL_RenderGeometryRaw(renderer, 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_RenderSetViewport(renderer, &old.Viewport);
+    SDL_RenderSetClipRect(renderer, old.ClipEnabled ? &old.ClipRect : nullptr);
+}
+
+// Called by Init/NewFrame/Shutdown
+bool ImGui_ImplSDLRenderer2_CreateFontsTexture()
+{
+    ImGuiIO& io = ImGui::GetIO();
+    ImGui_ImplSDLRenderer2_Data* bd = ImGui_ImplSDLRenderer2_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_ScaleModeLinear);
+
+    // Store our identifier
+    io.Fonts->SetTexID((ImTextureID)(intptr_t)bd->FontTexture);
+
+    return true;
+}
+
+void ImGui_ImplSDLRenderer2_DestroyFontsTexture()
+{
+    ImGuiIO& io = ImGui::GetIO();
+    ImGui_ImplSDLRenderer2_Data* bd = ImGui_ImplSDLRenderer2_GetBackendData();
+    if (bd->FontTexture)
+    {
+        io.Fonts->SetTexID(0);
+        SDL_DestroyTexture(bd->FontTexture);
+        bd->FontTexture = nullptr;
+    }
+}
+
+bool ImGui_ImplSDLRenderer2_CreateDeviceObjects()
+{
+    return ImGui_ImplSDLRenderer2_CreateFontsTexture();
+}
+
+void ImGui_ImplSDLRenderer2_DestroyDeviceObjects()
+{
+    ImGui_ImplSDLRenderer2_DestroyFontsTexture();
+}
+
+//-----------------------------------------------------------------------------
+
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
+
+#endif // #ifndef IMGUI_DISABLE