Qt: Refactor render widget state transitions

Recreate widget each time. Fixes fullscreen mode switches on D3D11 and
hopefully Wayland.

src/duckstation-qt/qthostdisplay.cpp

@@ -0,0 +1,130 @@
+#include "qthostdisplay.h"
+#include "common/assert.h"
+#include "frontend-common/imgui_styles.h"
+#include "imgui.h"
+#include "qtdisplaywidget.h"
+#include "qthostinterface.h"
+#include <cmath>
+
+QtHostDisplay::QtHostDisplay(QtHostInterface* host_interface) : m_host_interface(host_interface) {}
+
+QtHostDisplay::~QtHostDisplay() = default;
+
+QtDisplayWidget* QtHostDisplay::createWidget(QWidget* parent)
+{
+  Assert(!m_widget);
+  m_widget = new QtDisplayWidget(parent);
+
+  // We want a native window for both D3D and OpenGL.
+  m_widget->setAutoFillBackground(false);
+  m_widget->setAttribute(Qt::WA_NativeWindow, true);
+  m_widget->setAttribute(Qt::WA_NoSystemBackground, true);
+  m_widget->setAttribute(Qt::WA_PaintOnScreen, true);
+
+  return m_widget;
+}
+
+void QtHostDisplay::destroyWidget()
+{
+  Assert(m_widget);
+
+  delete m_widget;
+  m_widget = nullptr;
+}
+
+bool QtHostDisplay::hasDeviceContext() const
+{
+  return false;
+}
+
+bool QtHostDisplay::createDeviceContext(bool debug_device)
+{
+  return false;
+}
+
+bool QtHostDisplay::initializeDeviceContext(bool debug_device)
+{
+  if (!createImGuiContext() || !createDeviceResources())
+    return false;
+
+  return true;
+}
+
+bool QtHostDisplay::makeDeviceContextCurrent()
+{
+  return true;
+}
+
+void QtHostDisplay::moveContextToThread(QThread* new_thread) {}
+
+void QtHostDisplay::destroyDeviceContext()
+{
+  destroyImGuiContext();
+  destroyDeviceResources();
+}
+
+bool QtHostDisplay::createSurface()
+{
+  return false;
+}
+
+void QtHostDisplay::destroySurface() {}
+
+void* QtHostDisplay::GetRenderWindow() const
+{
+  return m_widget;
+}
+
+void QtHostDisplay::ChangeRenderWindow(void* new_window)
+{
+  Panic("Not implemented");
+}
+
+bool QtHostDisplay::createImGuiContext()
+{
+  ImGui::CreateContext();
+
+  auto& io = ImGui::GetIO();
+  io.IniFilename = nullptr;
+  io.DisplaySize.x = static_cast<float>(m_window_width);
+  io.DisplaySize.y = static_cast<float>(m_window_height);
+
+  const float framebuffer_scale = static_cast<float>(m_widget->devicePixelRatioFromScreen());
+  io.DisplayFramebufferScale.x = framebuffer_scale;
+  io.DisplayFramebufferScale.y = framebuffer_scale;
+  ImGui::GetStyle().ScaleAllSizes(framebuffer_scale);
+
+  ImGui::StyleColorsDarker();
+  ImGui::AddRobotoRegularFont(15.0f * framebuffer_scale);
+
+  return true;
+}
+
+void QtHostDisplay::destroyImGuiContext()
+{
+  ImGui::DestroyContext();
+}
+
+bool QtHostDisplay::createDeviceResources()
+{
+  return true;
+}
+
+void QtHostDisplay::destroyDeviceResources() {}
+
+void QtHostDisplay::WindowResized(s32 new_window_width, s32 new_window_height)
+{
+  HostDisplay::WindowResized(new_window_width, new_window_height);
+  updateImGuiDisplaySize();
+}
+
+void QtHostDisplay::updateImGuiDisplaySize()
+{
+  // imgui may not have been initialized yet
+  if (!ImGui::GetCurrentContext())
+    return;
+
+  auto& io = ImGui::GetIO();
+  io.DisplaySize.x = static_cast<float>(m_window_width);
+  io.DisplaySize.y = static_cast<float>(m_window_height);
+}