jkim202@xxxxxxxxxxxxxxxxx wrote: > > Hello Haiku developers! > > My name is James and I have been working on a layout manager called ALM. > In particular, I have been porting it from original C# version. As you > will see in the lib directory, ALM is already available in Haiku. I am > currently working on porting an extension of ALM. > > I need some help with converting a BControl (or BView) object, such as > BButton, to an image (BBitmap). For example, an image of BButton in a GUI > needs to be created and rendered in a window, replacing the original > BButton. Obviously, this rendered image would look the same as the > original BButton, but it would have no functionality because it is no > longer a real button. > > I have looked into BBitmap in bebook and also some drawing methods such > as BView::DrawBitmap(). After reading those documents, my initial thought > was to create a BBitmap object and then add a BView as a child and draw a > BControl inside that BView. If my understanding is correct, everything > drawn inside BBitmap's child BView is drawn onto BBitmap. But I don't > know how to draw a BControl inside the BView. I can add a BControl inside > BView, but does that mean that it is actually "drawing"? > > For C# users, this is done using Control.DrawToBitmap() followed by > Graphics.DrawImage() methods. Is this possible in Haiku? What you want to do is possible, but is a little more tricky. I will first give you the reason and then the solution. In BeOS/Haiku controls are usually drawn asynchronously. The BWindow in which the view is embedded receives a message from the app_server for regions that have to be redrawn. Then the window calls the Draw() hook function of every affected view. This will dispatch drawing commands to the app_server. At the app_server side, the drawing commands are handled by an object that represents the rendering backend and is attached to a "chunk of memory". For normal windows, this memory is the frame buffer, for BBitmaps which can have child views this is the bitmaps memory. As far as the app_server is concerned, there is no difference between receiving and rendering drawing commands for normal BWindows and offscreen windows. But on the client side, there is a difference. A BBitmap which are supposed to contain BViews will create a BWindow to make the app_server connection. But the messaging thread of this window is never run. Therefor it cannot receive any messages from the app_server and the app_server will not even try to send any. So the connection works only in one direction. Calls like "BView::Invalidate()" will not have any effect. If you want a view to draw anything, you will have to call Draw() on this view yourself, and you will also have to wait for the app_server to finish executing the commands (BView::Sync()). If you want to render a view hierarchy, you will have to iterate recursively over the children of the view and call Draw() on each one. It would be nice if BView or BBitmap offered a method like that already. Would probably be nicest in the BBitmap class, I can add such a call. For the time being, you should do something like this: void DrawViewAndChildren(BView* view, BRect updateRect) { int32 count = view->CountChildren(); for (int32 i = 0; i < count; i++) { BView* child = view->ChildAt(i); BRect childUpdateRect(updateRect); child->ConvertFromParent(&childUpdateRect); DrawViewAndChildren(child, childUpdateRect); } view->Draw(updateRect); } Then you can draw the hierarchy like this: if (bitmap->Lock()) { DrawViewAndChildren(topLevelView, topLevelView->Bounds()); topLevelView->Sync(); bitmap->Unlock(); } viewAttachedToRealWindow->DrawBitmap(bitmap); Best regards, -Stephan