NPAPI:AsyncDrawing: Difference between revisions

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= Status =
= Status =


Under consideration.
Accepted, ready for implementation.  


= Contributors =
= Contributors =


* Last modified: November 28, 2011
* Last modified: April 19, 2012
* Authors: Bas Schouten (Mozilla Corporation), Josh Aas (Mozilla Corporation)
* Authors: Bas Schouten (Mozilla Corporation), Josh Aas (Mozilla Corporation)
* Contributors: Robert O'Callahan (Mozilla Corporation)
* Contributors: Robert O'Callahan (Mozilla Corporation)
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For documentation on negotiating drawing models, see [[NPAPI:Models]]. This specification covers all async models, which use the same drawing mechanics with platform-specific data structures. The following models are currently specified:
For documentation on negotiating drawing models, see [[NPAPI:Models]]. This specification covers all async models, which use the same drawing mechanics with platform-specific data structures. The following models are currently specified:


* NPDrawingModelAsyncBitmapSurface (NPDrawingModel = TBA)
* NPDrawingModelAsyncBitmapSurface (NPDrawingModel = 7)
* NPDrawingModelAsyncWindowsDXGISurface (NPDrawingModel = TBA)
* NPDrawingModelAsyncWindowsDXGISurface (NPDrawingModel = 8)
* NPDrawingModelAsyncWindowsDX9ExSurface (NPDrawingModel = TBA)


Support query variables are:
Support query variables are:


* NPNVsupportsAsyncBitmapSurfaceBool (NPNVariable = TBA)
* NPNVsupportsAsyncBitmapSurfaceBool (NPNVariable = 2007)
* NPNVsupportsAsyncWindowsDXGISurfaceBool (NPNVariable = TBA)
* NPNVsupportsAsyncWindowsDXGISurfaceBool (NPNVariable = 2008)
* NPNVsupportsAsyncWindowsDX9ExSurfaceBool (NPNVariable = TBA)
* NPNVpreferredDXGIAdapter (NPNVariable = 2009)


Since these are the first new models for Windows and Linux the existing models will be assigned names:
Since these are the first new models for Windows and Linux the existing models will be assigned names:


* NPDrawingModelSyncWin (NPDrawingModel = TBA)
* NPDrawingModelSyncWin (NPDrawingModel = 5)
* NPDrawingModelSyncX (NPDrawingModel = TBA)
* NPDrawingModelSyncX (NPDrawingModel = 6)


= General Async Drawing Mechanics =
= General Async Drawing Mechanics =
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Surfaces cannot be modified while they are current. A modified rectangle may be provided in the <code>changed</code> argument to give the host a hint on which part of the surface was modified with respect to the previous current surface so that the browser can choose to optimize the composition process. There is no guarantee only this rectangle will be recomposed though and the entire surface needs to be valid.
Surfaces cannot be modified while they are current. A modified rectangle may be provided in the <code>changed</code> argument to give the host a hint on which part of the surface was modified with respect to the previous current surface so that the browser can choose to optimize the composition process. There is no guarantee only this rectangle will be recomposed though and the entire surface needs to be valid.


SetCurrent can take NULL as the surface. This removes the previous current surface. The plugin will render nothing. This should be used before finalizing the last surface.
SetCurrent can take NULL as pthe surface. This removes the previous current surface. The plugin will render nothing. This should be used before finalizing the last surface. All three functions must be called on the plugin thread.


The Init and Finalize functions must be called from the main plugin thread. The SetCurrent function may be called from any thread. Reentrant calls from the browser into the plugin do not occur during a SetCurrent invocation from the main thread. The browser is expected to implement SetCurrent using a locking protocol that cannot block for long. For example, SetCurrent might block only while the previous surface is being read by the browser's compositing.
Reentrant calls from the browser into the plugin do not occur during a SetCurrent invocation from the main thread. The browser is expected to implement SetCurrent using a locking protocol that cannot block for long. For example, SetCurrent might block only while the previous surface is being read by the browser's compositing.


= Throttling Painting =
= Throttling Painting =
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Plugins should finalize Windows shared surfaces by calling <code>NPN_FinalizeAsyncSurface</code> when they are done with the surface.
Plugins should finalize Windows shared surfaces by calling <code>NPN_FinalizeAsyncSurface</code> when they are done with the surface.
== Creating the Device ==
On dual-GPU systems, the browser and plugin process may unintentionally bind to different GPUs if default DXGI parameters are used. When this happens the plugin's draw calls will most likely fail, or crash. To address this, it is necessary to open the browser's shared DXGI surfaces on the same adapter. The adapter can be found using <tt>NPNVpreferredDXGIAdapter</tt>. For example,
<pre>
static IDXGIAdapter1*
FindDXGIAdapter(NPP npp, IDXGIFactory1* factory)
{
  DXGI_ADAPTER_DESC preferred;
  if (NPN_GetValue(npp, NPNVpreferredDXGIAdapter, &preferred) != NPERR_NO_ERROR) {
    return NULL;
  }
  for (UINT index = 0; ; index++) {
    IDXGIAdapter* adapter = NULL;
    if (FAILED(factory1->EnumAdapters1(index, &adapter)) || !adapter) {
      return nullptr;
    }
    DXGI_ADAPTER_DESC desc;
    if (SUCCEEDED(adapter->GetDesc(&desc)) &&
        desc.AdapterLuid.LowPart == preferred.AdapterLuid.LowPart &&
        desc.AdapterLuid.HighPart == preferred.AdapterLuid.HighPart)
    {
      return adapter;
    }
    adapter->Release();
  }
  return NULL;
}
</pre>
The adapter returned by this function can then be used with any DXGI device creation function, such as <tt>D3D10CreateDevice</tt>. Failure to negotiate the adapter properly (or failure to use an IDXGIAdapter1) will result in undefined behavior.
If no matching adapter can be found, the safest course of action for the plugin is to switch to a different drawing model (such the AsyncBitmap model).
== Sample Code ==


This sample code illustrates usage of this drawing model:
This sample code illustrates usage of this drawing model:


<pre>
  ID3D10Device *pDevice10;
  ID3D10Device *pDevice10;
  NPAsyncSurface *npFrontBuffer = new NPAsyncSurface;
  NPAsyncSurface *npFrontBuffer = new NPAsyncSurface;
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   backBuffer->QueryInterface(&mutex);
   backBuffer->QueryInterface(&mutex);
   mutex->AcquireSync(0);
   mutex->AcquireSync(0);
 
   ... Draw to backBuffer texture ...
   ... Draw to backBuffer texture ...
 
   mutex->ReleaseSync(0);
   mutex->ReleaseSync(0);
   mutex->Release();
   mutex->Release();
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   delete npBackBuffer;
   delete npBackBuffer;
  }
  }
 
</pre>
= NPDrawingModelAsyncWindowsDX9ExSurface =
 
This drawing model will only be valid on Windows Vista and higher in order to simplify hardware accelerated surface sharing for plugins wanting to use Direct3D 9Ex.
 
In this drawing model the plugin will be responsible for actual creation of the texture. The reason for this behavior is that textures created in Direct3D 10 cannot be shared using Direct3D 9/10 interoperability. Textures created with Direct3D 9 can be opened in Direct3D 10. In this model the plugin will create a texture using the <code>CreateTexture</code> call on a Direct3D 9Ex device. The <code>pSharedHandle</code> argument will be used to acquire a shared handle for that texture. This shared handle should be set as the <code>data</code> member of the <code>NPAsyncSurface</code> structure before <code>NPN_InitAsyncSurface</code> is called to initialize the surface. The plugin must also set the <code>stride</code> member of <code>NPAsyncSurface</code> before calling <code>NPN_InitAsyncSurface</code>.
 
The return value of the <code>NPN_InitAsyncSurface</code> call will indicate if the surface was successfully accessed by the host. When a surface is set current the plugin must make sure all drawing calls to that surface have finished execution. For Direct3D 9Ex this means making sure that the GPU has processed all graphics command queued to draw to that surface in order to prevent race condition with a host using another device. One way of doing this is do use a <code>D3DQUERYTYPE_EVENT</code> query to determine when the graphics pipeline has finished executing all events. Another method is to execute a blocking readback from a small (i.e. 1x1 pixel) portion of the texture. When the readback has successfully executed then the GPU has finished the drawing calls to the surface. Failure to follow these guidelines may result in incomplete drawing of the contents of the texture.
 
Plugins should finalize surfaces by calling <code>NPN_FinalizeAsyncSurface</code>.
 
IDirect3DDevice9Ex *pDevice9;
NPAsyncSurface *npFrontBuffer = new NPAsyncSurface;
NPAsyncSurface *npBackBuffer = new NPAsyncSurface;
IDirect3DTexture9 *frontBuffer;
IDirect3DTexture9 *backBuffer;
void Init() {
  ... Initialize pDevice9 ...
  NPSize size;
  size.width = pluginwidth;
  size.height = pluginheight;
  HANDLE frontBufferHandle = NULL;
  HANDLE backBufferHandle = NULL;
  pDevice9->CreateTexture(pluginWidth, pluginHeight, 0,
                          D3DUSAGE_RENDERTARGET,
                          D3DFMT_X8R8G8B8, D3DPOOL_DEFAULT,
                          &frontBuffer, &frontBufferHandle);
  pDevice9->CreateTexture(pluginWidth, pluginHeight, 0,
                          D3DUSAGE_RENDERTARGET,
                          D3DFMT_X8R8G8B8, D3DPOOL_DEFAULT,
                          &backBuffer, &backBufferHandle);
  NPN_InitAsyncSurface(instance, size, NPImageFormatBGRX32, frontBufferHandle, npFrontBuffer);
  NPN_InitAsyncSurface(instance, size, NPImageFormatBGRX32, backBufferHandle, npBackBuffer);
  DrawFrame();
}
void DrawFrame() {
  ... Draw to backBuffer texture ...
  ... Synchronize by one of the methods described above ...
  NPN_SetCurrentAsyncSurface(instance, npBackBuffer);
  IDirect3DDevice9 *tmp = frontBuffer;
  NPAsyncSurface *npTmp = npFrontBuffer;
  frontBuffer = backBuffer;
  npFrontBuffer = npBackBuffer;
  backBuffer = tmp;
  npBackBuffer = npTmp;
}
void NPP_DidComposite() {
  DrawFrame();
}
void Shutdown() {
  frontBuffer->Release();
  backBuffer->Release();
  NPN_SetCurrentAsyncSurface(instance, NULL);
  NPN_FinalizeAsyncSurface(instance, npFrontBuffer);
  NPN_FinalizeAsyncSurface(instance, npBackBuffer);
  delete npFrontBuffer;
  delete npBackBuffer;
}
 
= Open Issues =
 
* Add accelerated Linux drawing model.
Confirmed users
156

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