horizontal: default to max width

src/overlay.cpp

@@ -579,12 +579,15 @@ void render_imgui(swapchain_stats& data, struct overlay_params& params, ImVec2&
    HUDElements.is_vulkan = is_vulkan;
    ImGui::GetIO().FontGlobalScale = params.font_scale;
    static float ralign_width = 0, old_scale = 0;
+   auto io = ImGui::GetIO();
    if (params.enabled[OVERLAY_PARAM_ENABLED_fps_only]){
       window_size = ImVec2((to_string(int(HUDElements.sw_stats->fps)).length() * ImGui::CalcTextSize("A").x) + 15.f, params.height);
+   } else if (params.enabled[OVERLAY_PARAM_ENABLED_horizontal]) {
+      window_size = ImVec2(io.DisplaySize.x, params.height);
    } else {
       window_size = ImVec2(params.width, params.height);
    }
-   unsigned height = ImGui::GetIO().DisplaySize.y;
+   unsigned height = io.DisplaySize.y;
    auto now = Clock::now();
 
    if (old_scale != params.font_scale) {