wasm: add support for hi-dpi displays

Documentation/release/dev/add-hi-dpi-support-for-wasm.md

+# Add support for hi-dpi screens in vtkWebAssemblyRenderWindowInteractor
+
+The `vtkWebAssemblyRenderWindowInteractor` and `vtkSDL2OpenGLRenderWindow` classes
+now support hi-dpi screens.

Rendering/OpenGL2/vtkSDL2OpenGLRenderWindow.cxx

@@ -142,16 +142,26 @@ void vtkSDL2OpenGLRenderWindow::SetSize(int x, int y)
 {
   if ((this->Size[0] != x) || (this->Size[1] != y))
   {
-    this->Superclass::SetSize(x, y);
-
-    if (this->Interactor)
-    {
-      this->Interactor->SetSize(x, y);
-    }
     if (this->WindowId)
     {
       SDL_SetWindowSize(this->WindowId, x, y);
     }
+    // For high dpi screens, SDL2 recommends querying the GL drawable size.
+    // This is needed for the glViewport call in vtkOpenGLCamera::Render to
+    // work correctly.
+    // See https://wiki.libsdl.org/SDL2/SDL_GL_GetDrawableSize
+    if (this->GetDPI() > 72)
+    {
+      SDL_GL_GetDrawableSize(this->WindowId, &this->Size[0], &this->Size[1]);
+    }
+    else
+    {
+      SDL_GetWindowSize(this->WindowId, &this->Size[0], &this->Size[1]);
+    }
+    if (this->Interactor)
+    {
+      this->Interactor->SetSize(this->Size[0], this->Size[1]);
+    }
   }
 }
 
@@ -225,8 +235,8 @@ void vtkSDL2OpenGLRenderWindow::CreateAWindow()
   SDL_SetHint(SDL_HINT_EMSCRIPTEN_KEYBOARD_ELEMENT, "#canvas");
 #endif
 
-  this->WindowId = SDL_CreateWindow(
-    this->WindowName, x, y, width, height, SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
+  this->WindowId = SDL_CreateWindow(this->WindowName, x, y, width, height,
+    SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI);
   SDL_SetWindowResizable(this->WindowId, SDL_TRUE);
   if (this->WindowId)
   {
@@ -293,15 +303,22 @@ void vtkSDL2OpenGLRenderWindow::DestroyWindow()
 // Get the current size of the window.
 int* vtkSDL2OpenGLRenderWindow::GetSize(void)
 {
-  // if we aren't mapped then just return the ivar
-  if (this->WindowId && this->Mapped)
+  if (this->WindowId)
   {
     int w = 0;
     int h = 0;
-
-    SDL_GetWindowSize(this->WindowId, &w, &h);
-    this->Size[0] = w;
-    this->Size[1] = h;
+    if (this->GetDPI() > 72)
+    {
+      SDL_GL_GetDrawableSize(this->WindowId, &w, &h);
+      this->Size[0] = w;
+      this->Size[1] = h;
+    }
+    else
+    {
+      SDL_GetWindowSize(this->WindowId, &w, &h);
+      this->Size[0] = w;
+      this->Size[1] = h;
+    }
   }
 
   return this->vtkOpenGLRenderWindow::GetSize();

Rendering/UI/vtkWebAssemblyRenderWindowInteractor.cxx

@@ -160,7 +160,8 @@ bool vtkWebAssemblyRenderWindowInteractor::ProcessEvent(void* arg)
 
     case SDL_MOUSEMOTION:
     {
-      this->SetEventInformationFlipY(event->motion.x, event->motion.y, ctrl, shift);
+      const double dpr = emscripten_get_device_pixel_ratio();
+      this->SetEventInformationFlipY(event->motion.x * dpr, event->motion.y * dpr, ctrl, shift);
       this->SetAltKey(alt);
       this->InvokeEvent(vtkCommand::MouseMoveEvent, nullptr);
     }
@@ -169,7 +170,8 @@ bool vtkWebAssemblyRenderWindowInteractor::ProcessEvent(void* arg)
     case SDL_MOUSEBUTTONDOWN:
     case SDL_MOUSEBUTTONUP:
     {
-      this->SetEventInformationFlipY(event->button.x, event->button.y, ctrl, shift);
+      const double dpr = emscripten_get_device_pixel_ratio();
+      this->SetEventInformationFlipY(event->button.x * dpr, event->button.y * dpr, ctrl, shift);
       this->SetAltKey(alt);
 
       int ev = -1;