NPAPI:AsyncDrawing: Difference between revisions

The Init and Finalize functions must be called from the main plugin thread. The SetCurrent function may be called from any thread. Reentrant calls into the plugin do not occur during a SetCurrent invocation. Therefore 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 browser compositing.

This model should be available on all platforms. It allows calls to SetCurrent on any thread.

Plugins should create a Windows shared surface by calling <code>NPN_InitAsyncSurface</code> with a <code>NULL</code> value for <code>initData</code>. The resulting <code>NPAsyncSurface</code> will point to a <code>HANDLE</code> that can be used, for example, through [http://msdn.microsoft.com/en-us/library/bb173598%28v=VS.85%29.aspx OpenSharedResource] in order to create a texture for the user. In order to allow fast drawing to any hardware surfaces, the host will acquire the handle from [http://msdn.microsoft.com/en-us/library/bb174562%28v=VS.85%29.aspx IDXGISurface::GetSharedHandle]. This shared handle will represent a texture which is usable as a render target and is valid as a shader resource. The plugin can open this shared handle as a texture and then use it as a render target for any drawing operations. SetCurrent may only be called on the main thread in this model.

  NPSize size;

size.width = pluginwidth;

size.height = pluginheight;

NPN_InitAsyncSurface(instance, size, NPImageFormatBGRX32, NULL, npFrontBuffer);

NPN_InitAsyncSurface(instance, size, NPImageFormatBGRX32, NULL, npBackBuffer);

pDevice10->OpenSharedResource(npFrontBuffer->handle,

                              __uuidof(ID3D10Texture2D),

                              (void**)(&frontBuffer));

pDevice10->OpenSharedResource(npBackBuffer->handle,

                              __uuidof(ID3D10Texture2D),

                              (void**)(&backBuffer));

  while (painting) {

   // Draw to backBuffer texture

frontBuffer->Release();

backBuffer->Release();

NPN_FinalizeAsyncSurface(instance, npFrontBuffer);

NPN_FinalizeAsyncSurface(instance, npBackBuffer);

   

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. SetCurrent may only be called on the main thread in this model.

size.width = pluginwidth;

size.height = pluginheight;

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);

  while (painting) {

   // Draw to backBuffer texture

   // Synchronize by one of the methods described above

  frontBuffer->Release();

backBuffer->Release();

  NPN_SetCurrentAsyncSurface(instance, NULL);

NPN_FinalizeAsyncSurface(instance, npFrontBuffer);

NPN_FinalizeAsyncSurface(instance, npBackBuffer);

  delete npFrontBuffer;

delete npBackBuffer;