Adding upstream version 115.7.0esr.upstream/115.7.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+Graphics Overview
+=========================
+
+Work in progress. Possibly incorrect or incomplete.
+---------------------------------------------------
+
+Jargon
+------
+
+There's a lot of jargon in the graphics stack. We try to maintain a list
+of common words and acronyms `here <https://wiki.mozilla.org/Platform/GFX/Jargon>`__.
+
+Overview
+--------
+
+The graphics systems is responsible for rendering (painting, drawing)
+the frame tree (rendering tree) elements as created by the layout
+system. Each leaf in the tree has content, either bounded by a rectangle
+(or perhaps another shape, in the case of SVG.)
+
+The simple approach for producing the result would thus involve
+traversing the frame tree, in a correct order, drawing each frame into
+the resulting buffer and displaying (printing non-withstanding) that
+buffer when the traversal is done. It is worth spending some time on the
+“correct order” note above. If there are no overlapping frames, this is
+fairly simple - any order will do, as long as there is no background. If
+there is background, we just have to worry about drawing that first.
+Since we do not control the content, chances are the page is more
+complicated. There are overlapping frames, likely with transparency, so
+we need to make sure the elements are draw “back to front”, in layers,
+so to speak. Layers are an important concept, and we will revisit them
+shortly, as they are central to fixing a major issue with the above
+simple approach.
+
+While the above simple approach will work, the performance will suffer.
+Each time anything changes in any of the frames, the complete process
+needs to be repeated, everything needs to be redrawn. Further, there is
+very little space to take advantage of the modern graphics (GPU)
+hardware, or multi-core computers. If you recall from the previous
+sections, the frame tree is only accessible from the UI thread, so while
+we’re doing all this work, the UI is basically blocked.
+
+(Retained) Layers
+~~~~~~~~~~~~~~~~~
+
+Layers framework was introduced to address the above performance issues,
+by having a part of the design address each item. At the high level:
+
+1. We create a layer tree. The leaf elements of the tree contain all
+   frames (possibly multiple frames per leaf).
+2. We render each layer tree element and cache (retain) the result.
+3. We composite (combine) all the leaf elements into the final result.
+
+Let’s examine each of these steps, in reverse order.
+
+Compositing
+~~~~~~~~~~~
+
+We use the term composite as it implies that the order is important. If
+the elements being composited overlap, whether there is transparency
+involved or not, the order in which they are combined will effect the
+result. Compositing is where we can use some of the power of the modern
+graphics hardware. It is optimal for doing this job. In the scenarios
+where only the position of individual frames changes, without the
+content inside them changing, we see why caching each layer would be
+advantageous - we only need to repeat the final compositing step,
+completely skipping the layer tree creation and the rendering of each
+leaf, thus speeding up the process considerably.
+
+Another benefit is equally apparent in the context of the stated
+deficiencies of the simple approach. We can use the available graphics
+hardware accelerated APIs to do the compositing step. Direct3D, OpenGL
+can be used on different platforms and are well suited to accelerate
+this step.
+
+Finally, we can now envision performing the compositing step on a
+separate thread, unblocking the UI thread for other work, and doing more
+work in parallel. More on this below.
+
+It is important to note that the number of operations in this step is
+proportional to the number of layer tree (leaf) elements, so there is
+additional work and complexity involved, when the layer tree is large.
+
+Render and retain layer elements
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+As we saw, the compositing step benefits from caching the intermediate
+result. This does result in the extra memory usage, so needs to be
+considered during the layer tree creation. Beyond the caching, we can
+accelerate the rendering of each element by (indirectly) using the
+available platform APIs (e.g., Direct2D, CoreGraphics, even some of the
+3D APIs like OpenGL or Direct3D) as available. This is actually done
+through a platform independent API (see Moz2D) below, but is important
+to realize it does get accelerated appropriately.
+
+Creating the layer tree
+~~~~~~~~~~~~~~~~~~~~~~~
+
+We need to create a layer tree (from the frames tree), which will give
+us the correct result while striking the right balance between a layer
+per frame element and a single layer for the complete frames tree. As
+was mentioned above, there is an overhead in traversing the whole tree
+and caching each of the elements, balanced by the performance
+improvements. Some of the performance improvements are only noticed when
+something changes (e.g., one element is moving, we only need to redo the
+compositing step).
+
+Refresh Driver
+~~~~~~~~~~~~~~
+
+Layers
+~~~~~~
+
+Rendering each layer
+~~~~~~~~~~~~~~~~~~~~
+
+Tiling vs. Buffer Rotation vs. Full paint
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Compositing for the final result
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Graphics API
+~~~~~~~~~~~~
+
+Compositing
+~~~~~~~~~~~
+
+Image Decoding
+~~~~~~~~~~~~~~
+
+Image Animation
+~~~~~~~~~~~~~~~
+
+`Historical Documents <http://www.youtube.com/watch?v=lLZQz26-kms>`__
+---------------------------------------------------------------------
+
+A number of posts and blogs that will give you more details or more
+background, or reasoning that led to different solutions and approaches.
+
+-  2010-01 `Layers: Cross Platform Acceleration <http://www.basschouten.com/blog1.php/layers-cross-platform-acceleration>`__
+-  2010-04 `Layers <http://robert.ocallahan.org/2010/04/layers_01.html>`__
+-  2010-07 `Retained Layers <http://robert.ocallahan.org/2010/07/retained-layers_16.html>`__
+-  2011-04 `Introduction <https://web.archive.org/web/20140604005804/https://blog.mozilla.org/joe/2011/04/26/introducing-the-azure-project/>`__
+-  2011-07 `Layers <http://chrislord.net/index.php/2011/07/25/shadow-layers-and-learning-by-failing/%20Shadow>`__
+-  2011-09 `Graphics API Design <http://robert.ocallahan.org/2011/09/graphics-api-design.html>`__
+-  2012-04 `Moz2D Canvas on OSX <http://muizelaar.blogspot.ca/2012/04/azure-canvas-on-os-x.html>`__
+-  2012-05 `Mask Layers <http://featherweightmusings.blogspot.co.uk/2012/05/mask-layers_26.html>`__
+-  2013-07 `Graphics related <http://www.basschouten.com/blog1.php>`__