What does AWT.GetDrawingSurface do?

Question

I'm on a project where I need to use vtk with Java and JavaFX. And to give VTK the correct canvas where it can draw, I was wondering what does the function GetDrawingSurface() do in the code below. awt is a JAWT object described in jawt.h from the jawt library.

It's in order to rewrite a Java class to give the C++ the correct canvas.

extern "C" JNIEXPORT jint  JNICALL
Java_vtk_vtkPanel_RenderCreate(JNIEnv *env, jobject canvas, jobject id0)
{
#if defined(WIN32_JAWT_LOCK_HACK)
  int hash;
  WJLH_HASH_FUNC(env, canvas, hash);
  WJLH_lock_map[hash] = 0;
#endif

  JAWT awt;
  JAWT_DrawingSurface* ds;
  JAWT_DrawingSurfaceInfo* dsi;
  jint lock;

  // get the render window pointer
  vtkRenderWindow *temp0;
  temp0 = (vtkRenderWindow *)(vtkJavaGetPointerFromObject(env,id0));

  /* Get the AWT */
  awt.version = JAWT_VERSION_1_3;
  if (JAWT_GetAWT(env, &awt) == JNI_FALSE)
    {
#ifndef VTK_JAVA_DEBUG
    printf("AWT Not found\n");
#endif
    return 1;
    }

  /* Get the drawing surface */
  ds = awt.GetDrawingSurface(env, canvas);
  if (ds == NULL)
    {
#ifndef VTK_JAVA_DEBUG
    printf("NULL drawing surface\n");
#endif
    return 1;
    }

  /* Lock the drawing surface */
  lock = ds->Lock(ds);
  if((lock & JAWT_LOCK_ERROR) != 0)
    {
#ifndef VTK_JAVA_DEBUG
    printf("Error locking surface\n");
#endif
    awt.FreeDrawingSurface(ds);
    return 1;
    }

  /* Get the drawing surface info */
  dsi = ds->GetDrawingSurfaceInfo(ds);
  if (dsi == NULL)
    {
    printf("Error getting surface info\n");
    ds->Unlock(ds);
    awt.FreeDrawingSurface(ds);
    return 1;
    }

// Here is the win32 drawing code
#if defined(_WIN32) || defined(WIN32)
  temp0->Finalize();
  JAWT_Win32DrawingSurfaceInfo* dsi_win;
  dsi_win = (JAWT_Win32DrawingSurfaceInfo*)dsi->platformInfo;
  temp0->SetWindowId((void *)dsi_win->hwnd);
  temp0->SetDisplayId((void *)dsi_win->hdc);
  // also set parent id to avoid border sizes being added
  temp0->SetParentId((void *)dsi_win->hdc);
// use mac code
#elif defined(__APPLE__)
  JAWT_MacOSXDrawingSurfaceInfo* dsi_mac;
  dsi_mac = (JAWT_MacOSXDrawingSurfaceInfo*)dsi->platformInfo;
  temp0->SetWindowId(dsi_mac->cocoaViewRef);
// otherwise use X11 code
#else
  JAWT_X11DrawingSurfaceInfo* dsi_x11;
  dsi_x11 = (JAWT_X11DrawingSurfaceInfo*)dsi->platformInfo;
  temp0->SetDisplayId((void *)dsi_x11->display);
  temp0->SetWindowId((void *)dsi_x11->drawable);
  temp0->SetParentId((void *)dsi_x11->display);
#endif

  /* Free the drawing surface info */
  ds->FreeDrawingSurfaceInfo(dsi);

  /* Unlock the drawing surface */
  ds->Unlock(ds);

  /* Free the drawing surface */
  awt.FreeDrawingSurface(ds);

#if defined(WIN32_JAWT_LOCK_HACK)
  if (WJLH_init_check == 0)
    {
    WJLH_init_check = 1;
    }
  WJLH_lock_map[hash] = 1;
#endif
  return 0;
}

Answer 1

Well, I figured out by myself that it was returning information on the window manager use on the system.

It uses the getPeer function of java to get the right information and give it to the C code. So it is not possible to give where i want to draw because the javadoc tells clearly that it is computer specific and could not be rewritten.

Hopefully, the last VTK version (6.1.0) gives a new option to have VTK in JavaFX by using vtkJoGLPanelComponent. It's supposed to be lightweight I guess because the other option, vtkJoGLCanvasComponent is not working at all.