videodb: don't reset the source path if it is temporarily offline
videodb: add GetSourcePath() to get the path of the source another path belongs to
videodb: use the proper source path when checking for a temporarily offline source during library cleaning
[win32] update readme
Merge pull request #4795 from Montellese/videodb_clean_fix

videodb: fixes for support of temporarily offline sources during library cleaning
More efficient infobool expression evaluator

Expession infobools are evaluated at runtime from one or more single infobools
and a combination of boolean NOT, AND and OR operators. Previously, parsing
produced a vector of operands (leaf nodes) and operators in postfix
(reverse-Polish) form, and evaluated all leaf nodes every time the expression
was evaluated. But this ignores the fact that in many cases, once one operand
of an AND or OR operation has been evaluated, there is no need to evaluate the
other operand because its value can have no effect on the ultimate result. It
is also worth noting that AND and OR operations are associative, meaning they
can be rearranged at runtime to better suit the selected skin.

This patch rewrites the expression parsing and evaluation code. Now the
internal repreentation is in the form of a tree where leaf nodes represent a
single infobool, and branch nodes represent either an AND or an OR operation
on two or more child nodes.

Expressions are rewritten at parse time into a form which favours the
formation of groups of associative nodes. These groups are then reordered at
evaluation time such that nodes whose value renders the evaluation of the
remainder of the group unnecessary tend to be evaluated first (these are
true nodes for OR subexpressions, or false nodes for AND subexpressions).
The end effect is to minimise the number of leaf nodes that need to be
evaluated in order to determine the value of the expression. The runtime
adaptability has the advantage of not being customised for any particular skin.

The modifications to the expression at parse time fall into two groups:
1) Moving logical NOTs so that they are only applied to leaf nodes.
   For example, rewriting ![A+B]|C as !A|!B|C allows reordering such that
   any of the three leaves can be evaluated first.
2) Combining adjacent AND or OR operations such that each path from the root
   to a leaf encounters a strictly alternating pattern of AND and OR
   operations. So [A|B]|[C|D+[[E|F]|G] becomes A|B|C|[D+[E|F|G]].

I measured the effect while the Videos window of the default skin was open
(but idle) on a Raspberry Pi, and this reduced the CPU usage by 2.8% from
41.9% to 39.1%:

          Before          After
          Mean   StdDev   Mean   StdDev  Confidence  Change
IdleCPU%  41.9   0.5      39.1   0.9     100.0%      +7.0%
Where an infobool expression failed to parse, evaluate the infobool as false. Previously, this would result in a segfault due to the dereferencing of an uninitialised pointer to the head of the expression tree.
Add caching of infolabels

The functions CGUIInfoLabel::GetLabel and CGUIInfoLabel::GetItemLabel take
a number of strings returned from CGUIInfoManager::GetImage or
CGUIInfoManager::GetLabel, and combine them with various constant strings
which were determined during CGUIInfoLabel::Parse.

Rather than perform all the string operations on every call, this patch
changes to use a two-pass process: first it queries all the GetImage/GetLabel
strings, and then only if at least one of them has changed does it bother
rebuilding the resultant string - otherwise it re-uses the copy built on a
preceding call.

CGUIInfoLabel::GetLabel/GetItemLabel are also changed to return string
references, rather than forcing an additional string copy.

I have measured the effect while the Videos window of the default skin was
open (but idle) on a Raspberry Pi, and this reduced the CPU usage by 0.8%
from 36.2% to 35.4%:

          Before          After
          Mean   StdDev   Mean   StdDev  Confidence  Change
IdleCPU%  36.2   0.5      35.4   0.5     99.9%       +2.2%
De-duplication of string cache for non-item and item labels
Faster and simpler portable implementation of MathUtils::round_int().

Much as I like a bit of inline assembler, I have also removed the ARM versions
of MathUtils::truncate_int() and MathUtils::round_int(). The former was just
how any sane compiler should have assembled a cast from double to signed int
anyway. The latter was a much too complicated way to achieve the desired
effect, and was switched out in most ARM builds anyway in favour of the old
portable implementation that used floor().

Verified that MathUtils::test() still passes, and that GCC is now able to
inline MathUtils::round_int(), where it didn't previously.

I tested on a Raspberry Pi with the default theme, displaying the front page
with the RSS ticker enabled. This saturates the CPU, so I'm measuring the
improvement using the debug window's FPS figure. This patch improves this from
~50.8 FPS to ~52.6 FPS.
Move the reference-counting of Begin and End calls from DX and GL source files into GUIFontTTF.cpp.
Convert CGUIFontTTFBase::m_vertex to be managed as a std::vector. Also retired CGUIFontTTFBase::m_vertex_count and CGUIFontTTFBase::m_vertex_size because these can be derived from vector member functions.
CGUIFontTTFBase::RenderCharacter can now append to arbitrary vectors of vertices rather than only CGUIFontTTFBase::m_vertex
Add a cache of font glyph bounding box vertices. This is implemented as a template because ultimately we will key on different parameters and store values of different types, depending upon whether we have a GLES or non-GLES backend, and for GLES, whether or not the currently applicable transformation matrices permit the use of hardware clipping.
Lay the groundwork for hardware clipping.

For glScissor() to replace CGraphicContext::ClipRect, a necessary condition
is that no shear or rotation is introduced between the coordinate systems
they use; this depends upon the settings of the GUI matrix m_finalTransform
as well as the OpenGL model-view and projection matrices. These all remain
unchanged between paired calls of CGUIShader::OnEnabled and
CGUIShader::OnDisabled, so we scan the matrices in CGUIShader::OnEnabled to
see whether hardware clipping is possible.

Then, in CGUIFontTTFBase::RenderCharacter, we don't apply software clipping
in such cases. However, because vertices arising from multiple
CGUIFontTTFBase::DrawTextInternal calls (each of which often uses a different
clip rectangle) get lumped into the same vector, which only at the end is
passed to OpenGL for rendering, we need to wait a few commits before we can
actually apply hardware clipping. In the meantime, expect to see rendering
errors.
Increase font cache hit rate by keying on the fractional part of m_originX and m_originY *after* they have been through the graphics context's transformation matrix, plus the scale/rotation elements of the matrix, rather than the origin in the original frame of reference plus the complete transformation matrix. All vertices of individual glyph bounding boxes are a constant offset from this position, and when the fractional part of the translation is a match, the rounding of each vertex will be in the same direction; this permits us to calculate the desired vertices from the cached ones simply by adding the integer parts of the translations with no additional rounding steps.

Note that this requires that software clipping is *not* performed.
Rewrite of scrolling text code.

No longer shuffles the string round to minimise the number of characters
before the clipping rectangle; this doesn't save much on rendering time but
does harm the effectiveness of the cache. Now uses a pixel offset into the
string rather than a character + pixel offset, and plots the entire string
every time (execpt when the wrap point is visible, in which case the entire
string is plotted twice).

It also makes motion smoother, because (possibly unintentionally) the
previous code preferred to align the scroll offset with character boundaries.
This would lead to uneven changes of position, especially when the width of
the character currently being scrolled off the edge was only slightly more
than an integral multiple of the scroll increment.
Move the application of the translation offsets into the GLES code. Still all pure software at this stage. Main change is in the data types at the interface between CGUIFontTTFBase and CGUIFontTTFGL. The old way (array of vertices in m_vertex) are retained in addition, for the sake`of cases that need to use software clipping on GLES, as well as for DX and GL support where the new scheme is not (yet?) used.
Rather than applying the translation offsets to the vertices, now applies them to the model view matrix from the top of the matrix stack and pushes it over to OpenGL. The vertices themselves are still all held client-side.
Enable hardware clipping.