[chore]: move imgui HDRI switching to vulkan

3 files changed, 70 insertions, 5 deletions

diff --git a/src/core/application.cpp b/src/core/application.cpp
index 667fc73..701e088 100644
--- a/src/core/application.cpp
+++ b/src/core/application.cpp
@@ -2,6 +2,7 @@
 
 #include "rendering/renderer.h"
 #include "settings_manager.h"
+#include "hdri_manager.h"
 
 #include "states/simulation_state.h"
 #include "states/config_state.h"
@@ -80,15 +81,32 @@ namespace Donut
 
     auto Application::build_vulkan_ui() -> void
     {
-        // Placeholder UI proving the ImGui Vulkan backend renders. The real
-        // application UI (states' on_im_ui_render) moves here once the scene is
-        // ported to Vulkan (B-3).
         ImGui::Begin("Donut - Vulkan backend");
         ImGui::Text("Geodesic black hole through Vulkan (MoltenVK).");
         ImGui::Text("%.1f FPS", ImGui::GetIO().Framerate);
         ImGui::Separator();
-        ImGui::TextWrapped("Drag to orbit, scroll to zoom. HDRI starfield is live; "
-                           "next is porting the simulation UI to Vulkan.");
+
+        if (m_vulkan_renderer)
+        {
+            auto& hdri = HDRIManager::get();
+            std::string current = m_vulkan_renderer->current_hdri();
+            std::string preview = hdri.get_hdri_name(current);
+            if (ImGui::BeginCombo("HDRI", preview.c_str()))
+            {
+                for (const auto& path : hdri.get_available_hdri())
+                {
+                    bool selected = (path == current);
+                    if (ImGui::Selectable(hdri.get_hdri_name(path).c_str(), selected))
+                        m_vulkan_renderer->set_hdri(path);
+                    if (selected) ImGui::SetItemDefaultFocus();
+                }
+                ImGui::EndCombo();
+            }
+            ImGui::TextDisabled("Switching rebuilds the cubemap (brief pause).");
+        }
+
+        ImGui::Separator();
+        ImGui::TextWrapped("Drag to orbit, scroll to zoom.");
         ImGui::End();
     }
 
diff --git a/src/platform/vulkan/vulkan_renderer.cpp b/src/platform/vulkan/vulkan_renderer.cpp
index 95a546b..104bb62 100644
--- a/src/platform/vulkan/vulkan_renderer.cpp
+++ b/src/platform/vulkan/vulkan_renderer.cpp
@@ -99,6 +99,7 @@ namespace Donut
         bool left_was_down = false;
         VkImage cube_image = VK_NULL_HANDLE; VkDeviceMemory cube_mem = VK_NULL_HANDLE;
         VkImageView cube_view = VK_NULL_HANDLE; VkSampler cube_sampler = VK_NULL_HANDLE;
+        std::string hdri_path;  // path backing the current cubemap (UI display + no-op switch guard)
         VkDescriptorSetLayout geo_set_layout = VK_NULL_HANDLE;
         VkDescriptorPool geo_pool = VK_NULL_HANDLE;
         VkDescriptorSet geo_set = VK_NULL_HANDLE;
@@ -132,6 +133,7 @@ namespace Donut
         auto create_sync_objects() -> bool;
         auto create_geodesic_resources() -> bool;
         auto create_hdri_cubemap(const char* path) -> bool;
+        auto rebuild_hdri_cubemap(const char* path) -> void;
         auto create_present_resources() -> bool;
         auto process_input() -> void;
         auto update_geodesic_uniforms() -> void;
@@ -601,6 +603,7 @@ namespace Donut
 
     auto VulkanRenderer::Impl::create_hdri_cubemap(const char* path) -> bool
     {
+        hdri_path = path;
         const VkMemoryPropertyFlags host_vis = VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT | VK_MEMORY_PROPERTY_HOST_COHERENT_BIT;
         const uint32_t FACE = 1024;
         const VkFormat cube_fmt = VK_FORMAT_R16G16B16A16_SFLOAT;
@@ -845,6 +848,28 @@ namespace Donut
         return true;
     }
 
+    // Runtime HDRI switch: drain the device, tear down the old cubemap, build the
+    // new one, and repoint the geodesic set's samplerCube (binding 4) at it.
+    auto VulkanRenderer::Impl::rebuild_hdri_cubemap(const char* path) -> void
+    {
+        vkDeviceWaitIdle(device);
+
+        if (cube_sampler) vkDestroySampler(device, cube_sampler, nullptr);
+        if (cube_view)    vkDestroyImageView(device, cube_view, nullptr);
+        if (cube_image)   vkDestroyImage(device, cube_image, nullptr);
+        if (cube_mem)     vkFreeMemory(device, cube_mem, nullptr);
+        cube_sampler = VK_NULL_HANDLE; cube_view = VK_NULL_HANDLE;
+        cube_image   = VK_NULL_HANDLE; cube_mem  = VK_NULL_HANDLE;
+
+        create_hdri_cubemap(path);
+
+        VkDescriptorImageInfo cube_info{ cube_sampler, cube_view, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL };
+        VkWriteDescriptorSet write{ VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET };
+        write.dstSet = geo_set; write.dstBinding = 4; write.descriptorCount = 1;
+        write.descriptorType = VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER; write.pImageInfo = &cube_info;
+        vkUpdateDescriptorSets(device, 1, &write, 0, nullptr);
+    }
+
     auto VulkanRenderer::Impl::create_present_resources() -> bool
     {
         VkSamplerCreateInfo smci{ VK_STRUCTURE_TYPE_SAMPLER_CREATE_INFO };
@@ -1138,6 +1163,19 @@ namespace Donut
         m_impl->width = width; m_impl->height = height;
     }
 
+    auto VulkanRenderer::set_hdri(const std::string& path) -> void
+    {
+        Impl& v = *m_impl;
+        if (v.device == VK_NULL_HANDLE || v.geo_set == VK_NULL_HANDLE) return;
+        if (v.hdri_path == path) return;
+        v.rebuild_hdri_cubemap(path.c_str());
+    }
+
+    auto VulkanRenderer::current_hdri() const -> const std::string&
+    {
+        return m_impl->hdri_path;
+    }
+
     auto VulkanRenderer::draw_frame(const glm::vec4& clear_color, const std::function<void()>& build_ui) -> void
     {
         Impl& v = *m_impl;
diff --git a/src/platform/vulkan/vulkan_renderer.h b/src/platform/vulkan/vulkan_renderer.h
index 97a4e38..68a1602 100644
--- a/src/platform/vulkan/vulkan_renderer.h
+++ b/src/platform/vulkan/vulkan_renderer.h
@@ -2,6 +2,7 @@
 
 #include <glm/glm.hpp>
 #include <functional>
+#include <string>
 
 // Live-window Vulkan backend: owns the instance, surface, device, swapchain,
 // render pass, framebuffers and per-frame synchronization, and drives the
@@ -33,6 +34,14 @@ namespace Donut
 
         auto on_resize(int width, int height) -> void;
 
+        // Rebuilds the starfield environment cubemap from another equirect .hdr
+        // at runtime (device-idle teardown + rebuild + descriptor rewrite).
+        // No-op if path is already the active HDRI.
+        auto set_hdri(const std::string& path) -> void;
+
+        // Filesystem path of the HDRI currently backing the cubemap.
+        auto current_hdri() const -> const std::string&;
+
     private:
         struct Impl;
         Impl* m_impl = nullptr;