app_server: add new BView layers API

* Add new methods
    BView::BeginLayer(uint8 opacity)
    BView::EndLayer()

* All drawing between begin and end of a layer is redirected onto an
  intermediate bitmap. When ending the layer, this bitmap is
  composited onto the view with the opacity given when the layer was
  started.

* Layers can be nested arbitrarily and will be blended onto each
  other in order. There can also be any arbitrary interleaving of
  layer begin/end and drawing operations.

* Internally, drawing commands are redirected into a BPicture between
  BeginLayer and EndLayer (but client code need not know or care
  about this). Client code can also start/end other BPictures while
  inside a layer.

* Uses the PictureBoundingBoxPlayer to determine the size of the
  layer bitmap before allocating and drawing into it, so it does not
  allocate more memory than necessary and -- more importantly -- it
  will not alpha-composite more pixels than necessary.

* Drawing mode is always set to B_OP_ALPHA, blend mode to
  (B_PIXEL_ALPHA, B_ALPHA_COMPOSITE) while inside layers. This is
  necessary for (a) correct compositing output and (b) for
  redirection of drawing into the intermediate bitmap, which uses the
  renderer_region offset (in B_OP_COPY, the Painter does not use the
  AGG renderer methods, it directly accesses the pixel data. This
  would access out-of-bounds without the offset, so B_OP_COPY cannot
  be allowed.)
  To ensure these modes aren't changed, BView::SetDrawingMode()
  and BView::SetBlendingMode() are ignored while inside a layer.

* The main motivation behind this new API is WebKit, which internally
  expects such a layers functionality to be present. A performant and
  reusable implementation of this functionality can only be done
  server-side in app_server.

headers/os/interface/View.h

@@ -505,6 +505,9 @@ public:
 			void				DrawPictureAsync(const char* filename,
 									long offset, BPoint where);
 
+			void				BeginLayer(uint8 opacity);
+			void				EndLayer();
+
 			status_t			SetEventMask(uint32 mask, uint32 options = 0);
 			uint32				EventMask();
 			status_t			SetMouseEventMask(uint32 mask,

headers/private/app/ServerProtocol.h

@@ -7,6 +7,7 @@
  *		Jérôme Duval, jerome.duval@free.fr
  *		Axel Dörfler, axeld@pinc-software.de
  *		Andrej Spielmann, <andrej.spielmann@seh.ox.ac.uk>
+ *		Julian Harnath, <julian.harnath@rwth-aachen.de>
  */
 #ifndef APP_SERVER_PROTOCOL_H
 #define APP_SERVER_PROTOCOL_H
@@ -319,6 +320,8 @@ enum {
 	AS_VIEW_SET_VIEW_BITMAP,
 	AS_VIEW_SET_PATTERN,
 	AS_SET_CURRENT_VIEW,
+	AS_VIEW_BEGIN_LAYER,
+	AS_VIEW_END_LAYER,
 
 	// BDirectWindow/BWindowScreen codes
 	AS_DIRECT_WINDOW_GET_SYNC_DATA,

headers/private/interface/PictureDataWriter.h

@@ -1,9 +1,10 @@
 /*
- * Copyright 2006-2007 Haiku, Inc. All rights reserved.
+ * Copyright 2006-2015 Haiku, Inc. All rights reserved.
  * Distributed under the terms of the MIT License.
  *
  * Authors:
  *		Stefano Ceccherini, burton666@libero.it
+ *		Julian Harnath, <julian.harnath@rwth-achen.de>
  */
 #ifndef _PICTURE_DATA_WRITER_H
 #define _PICTURE_DATA_WRITER_H
@@ -17,6 +18,7 @@
 #include <stack>
 
 
+class Layer;
 class BPositionIO;
 class BRegion;
 
@@ -91,6 +93,8 @@ public:
 			status_t			WriteDrawPicture(const BPoint& where,
 									const int32& token);
 
+			status_t			WriteBlendLayer(Layer* layer);
+
 protected:
 	// throw a status_t on error
 			void				BeginOp(const int16& op);

headers/private/interface/PictureProtocol.h

@@ -52,10 +52,11 @@ enum {
 	B_PIC_SET_FONT_BPP			= 0x0388,
 	B_PIC_SET_FONT_FACE			= 0x0389,
 	B_PIC_SET_TRANSFORM			= 0x0390,
+	B_PIC_BLEND_LAYER			= 0x0391
 };
 
 
-const static uint32 kOpsTableSize = 49;
+const static uint32 kOpsTableSize = 50;
 
 
 #endif

src/kits/interface/PictureDataWriter.cpp

@@ -1,9 +1,10 @@
 /*
- * Copyright 2006-2009 Haiku, Inc. All rights reserved.
+ * Copyright 2006-2015 Haiku, Inc. All rights reserved.
  * Distributed under the terms of the MIT License.
  *
  * Authors:
  *		Stefano Ceccherini, stefano.ceccherini@gmail.com
+ *		Julian Harnath, <julian.harnath@rwth-achen.de>
  */
 
 #include <PictureDataWriter.h>
@@ -641,6 +642,21 @@ PictureDataWriter::WritePopState()
 }
 
 
+status_t
+PictureDataWriter::WriteBlendLayer(Layer* layer)
+{
+	try {
+		BeginOp(B_PIC_BLEND_LAYER);
+		Write<Layer*>(layer);
+		EndOp();
+	} catch (status_t& status) {
+		return status;
+	}
+
+	return B_OK;
+}
+
+
 // private
 void
 PictureDataWriter::BeginOp(const int16& op)

src/kits/interface/PicturePlayer.cpp

@@ -1,11 +1,12 @@
 /*
- * Copyright 2001-2007, Haiku Inc.
+ * Copyright 2001-2015, Haiku Inc.
  * Distributed under the terms of the MIT License.
  *
  * Authors:
  *		Marc Flerackers (mflerackers@androme.be)
  *		Stefano Ceccherini (stefano.ceccherini@gmail.com)
  *		Marcus Overhagen (marcus@overhagen.de)
+ *		Julian Harnath (julian.harnath@rwth-aachen.de)
  */
 
 /**	PicturePlayer is used to play picture data. */
@@ -23,6 +24,9 @@
 using BPrivate::PicturePlayer;
 
 
+class Layer;
+
+
 typedef void (*fnc)(void*);
 typedef void (*fnc_BPoint)(void*, BPoint);
 typedef void (*fnc_BPointBPoint)(void*, BPoint, BPoint);
@@ -47,6 +51,7 @@ typedef void (*fnc_DrawPixels)(void *, BRect, BRect, int32, int32, int32,
 typedef void (*fnc_DrawPicture)(void *, BPoint, int32);
 typedef void (*fnc_BShape)(void*, BShape*);
 typedef void (*fnc_BAffineTransform)(void*, BAffineTransform);
+typedef void (*fnc_Layer)(void*, const Layer*);
 
 
 static void
@@ -160,7 +165,7 @@ PicturePlayer::Play(void **callBackTable, int32 tableEntries, void *userData)
 		(void *)nop, (void *)nop, (void *)nop, (void *)nop,
 		(void *)nop, (void *)nop, (void *)nop, (void *)nop,
 		(void *)nop, (void *)nop, (void *)nop, (void *)nop,
-		(void *)nop
+		(void *)nop, (void *)nop
 	};
 
 	if ((uint32)tableEntries < kOpsTableSize) {
@@ -546,6 +551,13 @@ PicturePlayer::Play(void **callBackTable, int32 tableEntries, void *userData)
 				break;
 			}
 
+			case B_PIC_BLEND_LAYER:
+			{
+				((fnc_Layer)functionTable[49])(userData,
+					*reinterpret_cast<Layer* const*>(data));
+				break;
+			}
+
 			default:
 				break;
 		}

src/kits/interface/View.cpp

@@ -7,6 +7,7 @@
  *		Axel Dörfler, axeld@pinc-software.de
  *		Adrian Oanca, adioanca@cotty.iren.ro
  *		Ingo Weinhold. ingo_weinhold@gmx.de
+ *		Julian Harnath, julian.harnath@rwth-aachen.de
  */
 
 
@@ -3933,6 +3934,27 @@ BView::DrawPictureAsync(const char* filename, long offset, BPoint where)
 }
 
 
+void
+BView::BeginLayer(uint8 opacity)
+{
+	if (_CheckOwnerLockAndSwitchCurrent()) {
+		fOwner->fLink->StartMessage(AS_VIEW_BEGIN_LAYER);
+		fOwner->fLink->Attach<uint8>(opacity);
+		_FlushIfNotInTransaction();
+	}
+}
+
+
+void
+BView::EndLayer()
+{
+	if (_CheckOwnerLockAndSwitchCurrent()) {
+		fOwner->fLink->StartMessage(AS_VIEW_END_LAYER);
+		_FlushIfNotInTransaction();
+	}
+}
+
+
 void
 BView::Invalidate(BRect invalRect)
 {
@@ -5225,7 +5247,7 @@ BView::_ClipToPicture(BPicture* picture, BPoint where, bool invert, bool sync)
 	if (picture == NULL) {
 		fOwner->fLink->StartMessage(AS_VIEW_CLIP_TO_PICTURE);
 		fOwner->fLink->Attach<int32>(-1);
-		
+
 		// NOTE: No need to sync here, since the -1 token cannot
 		// become invalid on the server.
 	} else {
@@ -5240,7 +5262,7 @@ BView::_ClipToPicture(BPicture* picture, BPoint where, bool invert, bool sync)
 		// the client creates BPictures on the stack, these BPictures may
 		// have issued a AS_DELETE_PICTURE command to the ServerApp when Draw()
 		// goes out of scope, and the command is processed earlier in the
-		// ServerApp thread than the AS_VIEW_CLIP_TO_PICTURE command in the 
+		// ServerApp thread than the AS_VIEW_CLIP_TO_PICTURE command in the
 		// ServerWindow thread, which will then have the result that no
 		// ServerPicture is found of the token.
 		if (sync)

src/servers/app/Canvas.cpp

@@ -19,8 +19,10 @@
 
 #include <Region.h>
 
+#include "AlphaMask.h"
 #include "DrawingEngine.h"
 #include "DrawState.h"
+#include "Layer.h"
 
 
 #if __GNUC__ >= 3
@@ -218,6 +220,46 @@ Canvas::ScreenToPenTransform() const GCC_2_NRV(transform)
 }
 
 
+void
+Canvas::BlendLayer(Layer* layer)
+{
+	UtilityBitmap* layerBitmap = layer->RenderToBitmap(this);
+	if (layerBitmap == NULL)
+		return;
+
+	BRect destination = layerBitmap->Bounds();
+	destination.OffsetBy(layer->LeftTopOffset());
+	LocalToScreenTransform().Apply(&destination);
+
+	PushState();
+
+	fDrawState->SetDrawingMode(B_OP_ALPHA);
+	fDrawState->SetBlendingMode(B_PIXEL_ALPHA, B_ALPHA_COMPOSITE);
+	fDrawState->SetTransformEnabled(false);
+
+	AlphaMask* mask = new AlphaMask(layer->Opacity());
+	if (mask == NULL) {
+		layerBitmap->ReleaseReference();
+		return;
+	}
+
+	SetAlphaMask(mask);
+	mask->ReleaseReference();
+	ResyncDrawState();
+
+	GetDrawingEngine()->DrawBitmap(layerBitmap, layerBitmap->Bounds(),
+		destination, 0);
+
+	fDrawState->SetTransformEnabled(true);
+
+	PopState();
+	ResyncDrawState();
+
+	layerBitmap->ReleaseReference();
+	layer->ReleaseReference();
+}
+
+
 // #pragma mark - OffscreenCanvas
 
 

src/servers/app/Canvas.h

@@ -27,6 +27,7 @@ class DrawingEngine;
 class DrawState;
 class IntPoint;
 class IntRect;
+class Layer;
 class ServerPicture;
 
 
@@ -61,6 +62,8 @@ public:
 			SimpleTransform PenToLocalTransform() const;
 			SimpleTransform ScreenToPenTransform() const;
 
+			void			BlendLayer(Layer* layer);
+
 	virtual	DrawingEngine*	GetDrawingEngine() const = 0;
 	virtual ServerPicture*	GetPicture(int32 token) const = 0;
 	virtual	void			RebuildClipping(bool deep) = 0;

src/servers/app/Jamfile

@@ -67,6 +67,7 @@ Server app_server :
 	InputManager.cpp
 	IntPoint.cpp
 	IntRect.cpp
+	Layer.cpp
 	MessageLooper.cpp
 	MultiLocker.cpp
 	OffscreenServerWindow.cpp

src/servers/app/Layer.cpp

@@ -0,0 +1,216 @@
+/*
+ * Copyright 2015 Julian Harnath <julian.harnath@rwth-aachen.de>
+ * All rights reserved. Distributed under the terms of the MIT license.
+ */
+#include "Layer.h"
+
+#include "AlphaMask.h"
+#include "BitmapHWInterface.h"
+#include "DrawingEngine.h"
+#include "DrawState.h"
+#include "IntRect.h"
+#include "PictureBoundingBoxPlayer.h"
+#include "ServerBitmap.h"
+#include "View.h"
+
+
+class LayerCanvas : public Canvas {
+public:
+	LayerCanvas(DrawingEngine* drawingEngine, DrawState* drawState)
+		:
+		Canvas(),
+		fDrawingEngine(drawingEngine)
+	{
+		delete fDrawState;
+		fDrawState = drawState;
+	}
+
+	virtual DrawingEngine* GetDrawingEngine() const
+	{
+		return fDrawingEngine;
+	}
+
+	virtual ServerPicture* GetPicture(int32 token) const
+	{
+		return NULL;
+	}
+
+	virtual void RebuildClipping(bool)
+	{
+	}
+
+	virtual void ResyncDrawState()
+	{
+		fDrawingEngine->SetDrawState(fDrawState);
+	}
+
+protected:
+	virtual void _LocalToScreenTransform(SimpleTransform&) const
+	{
+	}
+
+	virtual void _ScreenToLocalTransform(SimpleTransform&) const
+	{
+	}
+
+private:
+	DrawingEngine*	fDrawingEngine;
+};
+
+
+Layer::Layer(uint8 opacity)
+	:
+	fOpacity(opacity),
+	fLeftTopOffset(0, 0)
+{
+}
+
+
+Layer::~Layer()
+{
+}
+
+
+void
+Layer::PushLayer(Layer* layer)
+{
+	PushPicture(layer);
+}
+
+
+Layer*
+Layer::PopLayer()
+{
+	Layer* const previousLayer = static_cast<Layer*>(PopPicture());
+	if (previousLayer != NULL)
+		previousLayer->ReleaseReference();
+	return previousLayer;
+}
+
+
+UtilityBitmap*
+Layer::RenderToBitmap(Canvas* canvas)
+{
+	BRect boundingBox = _DetermineBoundingBox(canvas);
+	if (!boundingBox.IsValid())
+		return NULL;
+
+	fLeftTopOffset = boundingBox.LeftTop();
+
+	UtilityBitmap* const layerBitmap = _AllocateBitmap(boundingBox);
+	if (layerBitmap == NULL)
+		return NULL;
+
+	BitmapHWInterface layerInterface(layerBitmap);
+	DrawingEngine* const layerEngine = layerInterface.CreateDrawingEngine();
+	if (layerEngine == NULL) {
+		layerBitmap->ReleaseReference();
+		return NULL;
+	}
+	layerEngine->SetRendererOffset(boundingBox.left, boundingBox.top);
+		// Drawing commands of the layer's picture use coordinates in the
+		// coordinate space of the underlying canvas. The coordinate origin
+		// of the layer bitmap is at boundingBox.LeftTop(). So all the drawing
+		// from the picture needs to be offset to be moved into the bitmap.
+		// We use a low-level offsetting via the AGG renderer here because the
+		// offset needs to be processed independently, after all other
+		// transforms, even after the BAffineTransforms (which are processed in
+		// Painter), to prevent this origin from being further transformed by
+		// e.g. scaling.
+
+	LayerCanvas layerCanvas(layerEngine, canvas->CurrentState());
+
+	AlphaMask* const mask = layerCanvas.GetAlphaMask();
+	BPoint oldOffset;
+	if (mask != NULL) {
+		// Move alpha mask to bitmap origin
+		oldOffset = mask->Update(BPoint(0, 0));
+	}
+
+	canvas->CurrentState()->SetDrawingMode(B_OP_ALPHA);
+	canvas->CurrentState()->SetBlendingMode(B_PIXEL_ALPHA, B_ALPHA_COMPOSITE);
+
+	layerCanvas.ResyncDrawState();
+		// Apply state to the new drawing engine of the layer canvas
+
+	if (layerEngine->LockParallelAccess()) {
+		const BRegion region(boundingBox);
+		layerEngine->ConstrainClippingRegion(&region);
+
+		// Draw recorded picture into bitmap
+		Play(&layerCanvas);
+		layerEngine->UnlockParallelAccess();
+	}
+
+	if (mask != NULL) {
+		// Move alpha mask back to its old position
+		// Note: this needs to be adapted if setting alpha masks is
+		// implemented as BPicture command (the mask now might be a different
+		// one than before).
+		mask->Update(oldOffset);
+		layerCanvas.ResyncDrawState();
+	}
+
+	canvas->SetDrawState(layerCanvas.CurrentState());
+		// Update state in canvas (the top-of-stack state could be a different
+		// state instance now, if the picture commands contained push/pop
+		// commands)
+
+	delete layerEngine;
+
+	return layerBitmap;
+}
+
+
+IntPoint
+Layer::LeftTopOffset() const
+{
+	return fLeftTopOffset;
+}
+
+
+uint8
+Layer::Opacity() const
+{
+	return fOpacity;
+}
+
+
+BRect
+Layer::_DetermineBoundingBox(Canvas* canvas)
+{
+	BRect boundingBox;
+	PictureBoundingBoxPlayer::Play(this, canvas->CurrentState(), &boundingBox);
+
+	if (!boundingBox.IsValid())
+		return boundingBox;
+
+	// Round up and add an additional 2 pixels on the bottom/right to
+	// compensate for the various types of rounding used in Painter.
+	boundingBox.left = floorf(boundingBox.left);
+	boundingBox.right = ceilf(boundingBox.right) + 2;
+	boundingBox.top = floorf(boundingBox.top);
+	boundingBox.bottom = ceilf(boundingBox.bottom) + 2;
+
+	// TODO: for optimization, crop the bounding box to the underlying
+	// view bounds here
+
+	return boundingBox;
+}
+
+
+UtilityBitmap*
+Layer::_AllocateBitmap(const BRect& bounds)
+{
+	UtilityBitmap* const layerBitmap = new(std::nothrow) UtilityBitmap(bounds,
+		B_RGBA32, 0);
+	if (layerBitmap == NULL)
+		return NULL;
+	if (!layerBitmap->IsValid()) {
+		delete layerBitmap;
+		return NULL;
+	}
+	memset(layerBitmap->Bits(), 0, layerBitmap->BitsLength());
+
+	return layerBitmap;
+}

src/servers/app/Layer.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2015 Julian Harnath <julian.harnath@rwth-aachen.de>
+ * All rights reserved. Distributed under the terms of the MIT license.
+ */
+#ifndef LAYER_H
+#define LAYER_H
+
+
+#include "ServerPicture.h"
+
+#include "IntPoint.h"
+
+
+class AlphaMask;
+class Canvas;
+class UtilityBitmap;
+
+
+class Layer : public ServerPicture {
+public:
+								Layer(uint8 opacity);
+	virtual						~Layer();
+
+			void				PushLayer(Layer* layer);
+			Layer*				PopLayer();
+
+			UtilityBitmap*		RenderToBitmap(Canvas* canvas);
+
+			IntPoint			LeftTopOffset() const;
+			uint8				Opacity() const;
+
+private:
+			BRect				_DetermineBoundingBox(Canvas* canvas);
+			UtilityBitmap*		_AllocateBitmap(const BRect& bounds);
+
+private:
+			uint8				fOpacity;
+			IntPoint			fLeftTopOffset;
+};
+
+
+#endif // LAYER_H

src/servers/app/PictureBoundingBoxPlayer.cpp

@@ -16,6 +16,7 @@
 
 #include "DrawState.h"
 #include "FontManager.h"
+#include "Layer.h"
 #include "ServerApp.h"
 #include "ServerBitmap.h"
 #include "ServerFont.h"
@@ -704,6 +705,18 @@ set_transform(BoundingBoxState* state, BAffineTransform transform)
 }
 
 
+static void
+determine_bounds_nested_layer(BoundingBoxState* state, Layer* layer)
+{
+	TRACE_BB("%p nested layer\n", state);
+
+	BRect boundingBox;
+	PictureBoundingBoxPlayer::Play(layer, state->GetDrawState(), &boundingBox);
+	if (boundingBox.IsValid())
+		state->IncludeRect(boundingBox);
+}
+
+
 const static void* kTableEntries[] = {
 	(const void*)nop,									//	0
 	(const void*)move_pen_by,
@@ -753,7 +766,8 @@ const static void* kTableEntries[] = {
 	(const void*)nop,									//	45
 	(const void*)set_font_face,
 	(const void*)set_blending_mode,
-	(const void*)set_transform							//	48
+	(const void*)set_transform,
+	(const void*)determine_bounds_nested_layer			//	49
 };
 
 

src/servers/app/ServerPicture.cpp

@@ -18,6 +18,7 @@
 #include "DrawingEngine.h"
 #include "DrawState.h"
 #include "FontManager.h"
+#include "Layer.h"
 #include "ServerApp.h"
 #include "ServerBitmap.h"
 #include "ServerFont.h"
@@ -784,6 +785,13 @@ set_transform(Canvas* canvas, BAffineTransform transform)
 }
 
 
+static void
+blend_layer(Canvas* canvas, Layer* layer)
+{
+	canvas->BlendLayer(layer);
+}
+
+
 static void
 reserved()
 {
@@ -839,7 +847,8 @@ const static void* kTableEntries[] = {
 	(const void*)reserved,				//	45
 	(const void*)set_font_face,
 	(const void*)set_blending_mode,
-	(const void*)set_transform			//  48
+	(const void*)set_transform,
+	(const void*)blend_layer			//	49
 };
 
 

src/servers/app/ServerPicture.h

@@ -1,10 +1,11 @@
 /*
- * Copyright 2001-2010, Haiku.
+ * Copyright 2001-2015, Haiku.
  * Distributed under the terms of the MIT License.
  *
  * Authors:
  *		DarkWyrm <bpmagic@columbus.rr.com>
  *		Stefano Ceccherini <stefano.ceccherini@gmail.com>
+ *		Julian Harnath <julian.harnath@rwth-aachen.de>
  */
 #ifndef SERVER_PICTURE_H
 #define SERVER_PICTURE_H
@@ -35,7 +36,7 @@ public:
 								ServerPicture(const ServerPicture& other);
 								ServerPicture(const char* fileName,
 									int32 offset);
-								~ServerPicture();
+	virtual						~ServerPicture();
 
 			int32				Token() { return fToken; }
 			bool				SetOwner(ServerApp* owner);

src/servers/app/ServerWindow.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2010, Haiku.
+ * Copyright 2001-2015, Haiku.
  * Distributed under the terms of the MIT License.
  *
  * Authors:
@@ -11,6 +11,7 @@
  *		Artur Wyszynski <harakash@gmail.com>
  *		Philippe Saint-Pierre <stpere@gmail.com>
  *		Brecht Machiels <brecht@mos6581.org>
+ *		Julian Harnath <julian.harnath@rwth-aachen.de>
  */
 
 
@@ -61,6 +62,7 @@
 #include "DrawingEngine.h"
 #include "DrawState.h"
 #include "HWInterface.h"
+#include "Layer.h"
 #include "Overlay.h"
 #include "ProfileMessageSupport.h"
 #include "RenderingBuffer.h"
@@ -2184,6 +2186,21 @@ fDesktop->LockSingleWindow();
 			break;
 		}
 
+		case AS_VIEW_BEGIN_LAYER:
+		{
+			DTRACE(("ServerWindow %s: Message AS_VIEW_BEGIN_LAYER\n",
+				Title()));
+
+			uint8 opacity;
+			link.Read<uint8>(&opacity);
+
+			Layer* layer = new(std::nothrow) Layer(opacity);
+			if (layer == NULL)
+				break;
+			fCurrentView->SetPicture(layer);
+			break;
+		}
+
 		default:
 			_DispatchViewDrawingMessage(code, link);
 			break;
@@ -2922,6 +2939,15 @@ ServerWindow::_DispatchViewDrawingMessage(int32 code,
 			break;
 		}
 
+		case AS_VIEW_END_LAYER:
+		{
+			DTRACE(("ServerWindow %s: Message AS_VIEW_END_LAYER\n",
+				Title()));
+			fCurrentView->BlendAllLayers();
+			fCurrentView->SetPicture(NULL);
+			break;
+		}
+
 		default:
 			BString codeString;
 			string_for_message_code(code, codeString);
@@ -2983,6 +3009,11 @@ ServerWindow::_DispatchPictureMessage(int32 code, BPrivate::LinkReceiver& link)
 			int8 drawingMode;
 			link.Read<int8>(&drawingMode);
 
+			if (dynamic_cast<Layer*>(picture) != NULL) {
+				// drawing mode changes not allowed in layers
+				break;
+			}
+
 			picture->WriteSetDrawingMode((drawing_mode)drawingMode);
 
 			fCurrentView->CurrentState()->SetDrawingMode(
@@ -3416,6 +3447,42 @@ ServerWindow::_DispatchPictureMessage(int32 code, BPrivate::LinkReceiver& link)
 			fLink.Flush();
 			return true;
 		}
+
+		case AS_VIEW_BEGIN_LAYER:
+		{
+			uint8 opacity;
+			link.Read<uint8>(&opacity);
+
+			Layer* layer = dynamic_cast<Layer*>(picture);
+			if (layer == NULL)
+				break;
+
+			Layer* nextLayer = new(std::nothrow) Layer(opacity);
+			if (nextLayer == NULL)
+				break;
+
+			nextLayer->PushLayer(layer);
+			fCurrentView->SetPicture(nextLayer);
+			break;
+		}
+
+		case AS_VIEW_END_LAYER:
+		{
+			Layer* layer = dynamic_cast<Layer*>(picture);
+			if (layer == NULL)
+				break;
+
+			Layer* previousLayer = layer->PopLayer();
+			if (previousLayer == NULL) {
+				// End last layer
+				return false;
+			}
+			fCurrentView->SetPicture(previousLayer);
+
+			previousLayer->WriteBlendLayer(layer);
+			break;
+		}
+
 /*
 		case AS_VIEW_SET_BLENDING_MODE:
 		{

src/servers/app/View.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001-2014, Haiku, Inc.
+ * Copyright (c) 2001-2015, Haiku, Inc.
  * Distributed under the terms of the MIT license.
  *
  * Authors:
@@ -9,6 +9,7 @@
  *		Stephan Aßmus <superstippi@gmx.de>
  *		Marcus Overhagen <marcus@overhagen.de>
  *		Adrien Destugues <pulkomandy@pulkomandy.tk
+ *		Julian Harnath <julian.harnath@rwth-aachen.de>
  */
 #include "View.h"
 
@@ -19,6 +20,7 @@
 #include "Desktop.h"
 #include "DrawingEngine.h"
 #include "DrawState.h"
+#include "Layer.h"
 #include "Overlay.h"
 #include "ServerApp.h"
 #include "ServerBitmap.h"
@@ -27,6 +29,7 @@
 #include "ServerWindow.h"
 #include "Window.h"
 
+#include "BitmapHWInterface.h"
 #include "drawing_support.h"
 
 #include <List.h>
@@ -972,6 +975,18 @@ View::SetPicture(ServerPicture* picture)
 }
 
 
+void
+View::BlendAllLayers()
+{
+	if (fPicture == NULL)
+		return;
+	Layer* layer = dynamic_cast<Layer*>(fPicture);
+	if (layer == NULL)
+		return;
+	BlendLayer(layer);
+}
+
+
 void
 View::Draw(DrawingEngine* drawingEngine, BRegion* effectiveClipping,
 	BRegion* windowContentClipping, bool deep)

src/servers/app/View.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001-2014, Haiku, Inc.
+ * Copyright (c) 2001-2015, Haiku, Inc.
  * Distributed under the terms of the MIT license.
  *
  * Authors:
@@ -9,6 +9,7 @@
  *		Stephan Aßmus <superstippi@gmx.de>
  *		Marcus Overhagen <marcus@overhagen.de>
  *		Adrien Destugues <pulkomandy@pulkomandy.tk>
+ *		Julian Harnath <julian.harnath@rwth-aachen.de>
  */
 #ifndef	VIEW_H
 #define VIEW_H
@@ -156,6 +157,8 @@ public:
 			ServerPicture*	Picture() const
 								{ return fPicture; }
 
+			void			BlendAllLayers();
+
 			// for background clearing
 			virtual void	Draw(DrawingEngine* drawingEngine,
 								BRegion* effectiveClipping,

src/tests/servers/app/Jamfile

@@ -154,6 +154,7 @@ SharedLibrary libtestappserver.so :
 	BitmapHWInterface.cpp
 	Canvas.cpp
 	DesktopSettings.cpp
+	Layer.cpp
 	OffscreenServerWindow.cpp
 	OffscreenWindow.cpp
 	PictureBoundingBoxPlayer.cpp