feat: prefer SDL.h instead of SDL/SDL.h on all supported platforms

TODO: What happens on Windows? macOS?

build.zig

@@ -105,6 +105,28 @@ pub fn package(
             zgui_c_cpp.linkSystemLibraryName("dwmapi");
         },
         .sdl2_opengl3 => {
+            if (target.isWindows()) blk: {
+                // see: https://github.com/MasterQ32/SDL.zig/blob/37f4ba9e31bea895fa19ef8b90d1f51111e52e67/Sdk.zig#L182-L199
+
+                zgui_c_cpp.addVcpkgPaths(if (args.options.shared) .dynamic else .static) catch break :blk;
+
+                const vcpkg_triplet = zgui_c_cpp.target.vcpkgTriplet(b.allocator, if (args.options.shared) .Dynamic else .Static) catch |e| {
+                    std.debug.panic("failed to determing vcpkg triplet: {}", .{e});
+                };
+                defer b.allocator.free(vcpkg_triplet);
+
+                const include_path = b.pathJoin(&.{ b.vcpkg_root.found, "installed", vcpkg_triplet, "include", "SDL2" });
+                zgui_c_cpp.include_dirs.append(.{ .raw_path = include_path }) catch @panic("out of memory");
+
+                const bin_path = zgui_c_cpp.vcpkg_bin_path orelse @panic("vcpkg paths were found, so vcpkg_bin_path should be set ");
+                const dll_path = std.fs.path.join(b.allocator, &.{ bin_path, "SDL2.dll" }) catch @panic("out of memory");
+
+                std.fs.cwd().access(dll_path, .{}) catch break :blk;
+                b.installBinFile(dll_path, "SDL2.dll");
+            }
+
+            zgui_c_cpp.linkSystemLibrary("SDL2");
+
             zgui_c_cpp.addCSourceFile(thisDir() ++ "/libs/imgui/backends/imgui_impl_sdl.cpp", cflags);
             zgui_c_cpp.addCSourceFile(thisDir() ++ "/libs/imgui/backends/imgui_impl_opengl3.cpp", cflags);
         },

libs/imgui/backends/imgui_impl_sdl.cpp

@@ -69,6 +69,7 @@
 // SDL
 #include <SDL.h>
 #include <SDL_syswm.h>
+
 #if defined(__APPLE__)
 #include <TargetConditionals.h>
 #endif

src/backend_sdl2_opengl3.zig

@@ -0,0 +1,42 @@
+const zgui = @import("gui.zig");
+
+const SDL_GL_Context = *anyopaque;
+
+pub fn init(window: *anyopaque, context: SDL_GL_Context, glsl_version: []const u8) void {
+    if (!ImGui_ImplSDL2_InitForOpenGL(window, context)) unreachable;
+    if (!ImGui_ImplOpenGL3_Init(glsl_version.ptr)) unreachable;
+}
+
+pub fn deinit() void {
+    ImGui_ImplOpenGL3_Shutdown();
+    ImGui_ImplSDL2_Shutdown();
+}
+
+pub fn newFrame(width: f32, height: f32) void {
+    ImGui_ImplOpenGL3_NewFrame();
+    ImGui_ImplSDL2_NewFrame();
+
+    zgui.io.setDisplaySize(width, height);
+    zgui.io.setDisplayFramebufferScale(1.0, 1.0);
+
+    zgui.newFrame();
+}
+
+pub fn draw() void {
+    zgui.render();
+    ImGui_ImplOpenGL3_RenderDrawData(zgui.getDrawData());
+}
+
+pub fn processEvent(event: *anyopaque) bool {
+    return ImGui_ImplSDL2_ProcessEvent(event);
+}
+
+extern fn ImGui_ImplSDL2_InitForOpenGL(window: *anyopaque, sdl_gl_context: SDL_GL_Context) bool;
+extern fn ImGui_ImplSDL2_Shutdown() void;
+extern fn ImGui_ImplSDL2_NewFrame() void;
+extern fn ImGui_ImplSDL2_ProcessEvent(event: *anyopaque) bool;
+
+extern fn ImGui_ImplOpenGL3_Init(glsl_version: [*]const u8) bool;
+extern fn ImGui_ImplOpenGL3_Shutdown() void;
+extern fn ImGui_ImplOpenGL3_NewFrame() void;
+extern fn ImGui_ImplOpenGL3_RenderDrawData(draw_data: *anyopaque) void;

src/main.zig

@@ -9,7 +9,9 @@ pub const version = @import("std").SemanticVersion{ .major = 0, .minor = 9, .pat
 pub usingnamespace @import("gui.zig");
 pub const plot = @import("plot.zig");
 pub const backend = switch (@import("zgui_options").backend) {
-    .glfw_wgpu => @import("backend_glfw_wgpu.zig"),
     .glfw_opengl3 => @import("backend_glfw_opengl3.zig"),
-    .no_backend, .win32_dx12, .sdl2_opengl3 => @panic("unsupported backend"),
+    .sdl2_opengl3 => @import("backend_sdl2_opengl3.zig"),
+    .glfw_wgpu => @import("backend_glfw_wgpu.zig"),
+    .win32_dx12 => .{}, // TODO:
+    .no_backend => .{},
 };