From 347ac79e7b7cc5006be9263d79c97325049a2f3e Mon Sep 17 00:00:00 2001
From: Andreas Kling <andreas@ladybird.org>
Date: Mon, 8 Jun 2026 21:23:51 +0200
Subject: [PATCH] UI/Qt: Preserve bitmap fallback for Vulkan web view

Hide the native Vulkan child window whenever the current paintable
cannot be imported and rendered through the dmabuf path. This lets the
existing QWidget paint path remain visible for shareable bitmap frames
instead of covering it with a clear-only Vulkan frame.
---
 UI/Qt/WebContentView.h        |  1 +
 UI/Qt/WebContentViewLinux.cpp | 48 ++++++++++++++++++++++++++++++++---
 2 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/UI/Qt/WebContentView.h b/UI/Qt/WebContentView.h
index dfff861a0a..0d2562d09c 100644
--- a/UI/Qt/WebContentView.h
+++ b/UI/Qt/WebContentView.h
@@ -184,6 +184,7 @@ private:
 
     void create_vulkan_window();
     void destroy_vulkan_window();
+    bool current_paintable_can_use_vulkan_window() const;
     void schedule_vulkan_window_update();
     void update_vulkan_window_geometry();
     void set_vulkan_window_cursor(QCursor const&);
diff --git a/UI/Qt/WebContentViewLinux.cpp b/UI/Qt/WebContentViewLinux.cpp
index cbbaae7cca..8c28eaa7e1 100644
--- a/UI/Qt/WebContentViewLinux.cpp
+++ b/UI/Qt/WebContentViewLinux.cpp
@@ -517,6 +517,11 @@ struct WebContentView::VulkanRenderer {
         return imported_textures[slot].ptr();
     }
 
+    bool can_render(Gfx::SharedImageBuffer const& shared_image_buffer)
+    {
+        return imported_texture_for(shared_image_buffer);
+    }
+
     OwnPtr<ImportedTexture> import_texture(Gfx::LinuxDmaBufHandle const& dmabuf, DmaBufIdentity const& dmabuf_identity)
     {
         auto vk_format = vk_format_from_drm_format(dmabuf.drm_format);
@@ -794,6 +799,19 @@ struct WebContentView::VulkanWindowRenderer final : public QVulkanWindowRenderer
             return;
         }
 
+        auto paintable = m_view.current_paintable();
+        bool can_render = paintable.has_value()
+            && !paintable->bitmap_size.is_empty()
+            && m_renderer.prepare(m_window)
+            && m_renderer.can_render(*paintable->shared_image_buffer);
+        if (!can_render) {
+            if (m_view.m_vulkan_window_container)
+                m_view.m_vulkan_window_container->hide();
+            m_view.update();
+            m_window.frameReady();
+            return;
+        }
+
         auto background_color = m_view.page_background_color();
         VkClearColorValue clear_color {
             {
@@ -825,11 +843,14 @@ struct WebContentView::VulkanWindowRenderer final : public QVulkanWindowRenderer
         };
         vkCmdBeginRenderPass(command_buffer, &render_pass_begin_info, VK_SUBPASS_CONTENTS_INLINE);
 
-        auto paintable = m_view.current_paintable();
-        if (paintable.has_value() && !paintable->bitmap_size.is_empty() && m_renderer.prepare(m_window))
-            m_renderer.render(command_buffer, *paintable->shared_image_buffer, paintable->bitmap_size, target_size);
+        bool rendered = m_renderer.render(command_buffer, *paintable->shared_image_buffer, paintable->bitmap_size, target_size);
 
         vkCmdEndRenderPass(command_buffer);
+        if (!rendered) {
+            if (m_view.m_vulkan_window_container)
+                m_view.m_vulkan_window_container->hide();
+            m_view.update();
+        }
         m_window.frameReady();
     }
 
@@ -885,6 +906,7 @@ void WebContentView::create_vulkan_window()
     m_vulkan_window_container->setFocusPolicy(Qt::FocusPolicy::StrongFocus);
     m_vulkan_window_container->setMouseTracking(true);
     m_vulkan_window_container->setGeometry(rect());
+    m_vulkan_window_container->hide();
     setFocusProxy(m_vulkan_window_container);
 }
 
@@ -905,9 +927,29 @@ void WebContentView::destroy_vulkan_window()
     m_vulkan_window = nullptr;
 }
 
+bool WebContentView::current_paintable_can_use_vulkan_window() const
+{
+    auto paintable = current_paintable();
+    if (!paintable.has_value())
+        return false;
+
+    return paintable->shared_image_buffer->linux_dmabuf_handle();
+}
+
 void WebContentView::schedule_vulkan_window_update()
 {
     if (m_vulkan_window) {
+        if (!current_paintable_can_use_vulkan_window()) {
+            if (m_vulkan_window_container)
+                m_vulkan_window_container->hide();
+            update();
+            return;
+        }
+
+        if (m_vulkan_window_container && !m_vulkan_window_container->isVisible()) {
+            m_vulkan_window_container->setGeometry(rect());
+            m_vulkan_window_container->show();
+        }
         m_vulkan_window->requestUpdate();
         return;
     }