In such case gPad can be set to nullptr and function fails
Solving https://root-forum.cern.ch/t/43560

This pointer was not initialized properly

Created image may be cleaned up many time, causing ROOT crash
One also should initialize that pointer properly

Avoid streaming a copy of the TPaveStats parent during the TH1 cloning process.

Connection id can be used to provide client-dependent output
Also there is always master connection flag.
Use connection info in RFrame and RStatBox when processing ranges
requests

It is central place where it used and applied.
Move also Request and Reply classes into correspondent drawables

RFrame keep track of selected zoom range for each client.
Every client sends update when zooming is changed.
Statbox request changes when zooming is changed on client side.
On server side statbox gets necessary range settings, which was
transferred already by frame

Visible range may depend on different components like RFrame or
RHistDrawable. Such range required to calculate statistic for the
statbox or implement improved histogram display.

This object provided to RDrawable::Display() method as argument and
give contexts - canvas, sub-pad, primitive index. Same context made
available for RDrawableRequest

Visible range may depend on different components like RFrame or
RHistDrawable. Such range required to calculate statistic for the
statbox or implement improved histogram display.

This object provided to RDrawable::Display() method as argument and
give contexts - canvas, sub-pad, primitive index. Same context made
available for RDrawableRequest

* Implement SetRealAspectRatio

* Make the method SetRealAspectRatio visible in the canvas menu

* fix typos

* Implement the F option in RedrawAxis to redraw the plots frame

* update release notes

* Line style can be taken from the frame

[ROOT-10302] Move glew to ROOT builtins (part 2)

While RLine defined in primitives, it cannot be used only
with gpadv7

ROOT_STANDARD_LIBRARY_PACKAGE passes all DEPENDENCIES to roocling via
ROOT_GENERATE_DICTIONARY.

Try to exclude as much as possible ${CMAKE_BUILD_DIR)/include from includes paths.
By this one much better control library dependencies - includes from other ROOT libraries not "visible" during the build.

Several generated files placed first to ${CMAKE_BUILD_DIR)/ginclude and then copied to include.

Dictionary generation still uses only ${CMAKE_BUILD_DIR)/include

Co-authored-by: Axel Naumann <Axel.Naumann@cern.ch>

Let extract RPadLength directly from the css code.
Simplify implementation of custom attributes classes.

Provide generic Execute() for RDrawable class, 
allows to execute all methods markes as **MENU**
Later one can provides attributes changes via menu

Assign RCanvas, RPadBase and RDrawable to requests members,
which can be accessed in RDrawableRequest::Process() methods.
Use pointer for pad and canvas while shared_ptr is not possible for
RCanvas

Client can submit request to the server and can assign callback
to get reply. Requests are derived from dedicated class and via
sub-classing can get arbitrary access to RDrawable API

As first example, use RHistStatBox for this. When working online,
statistic will be filled by the server through such special requests

If drawable not changed since last update, just send dummy entry to
client. This ensure that client do not remove element from paint list

While painter used for bi-directional communication, it is required
to access non-const methods of RCanvas

Use version to detect which drawable need to be transfer to client
Idea to reduce transfer when only attributes of some objects are changed

It only reference RDrawable attributes, but not drawable itself.
Idea to be able transfer all graphical attributes of drawable, 
but be able to provide absolutely different data compared to the
drawable

First example is RHistStatBox. It will reference histogram, but this
histogram not required on client side. All statistic should be
calculated on the server side and send as ready-to-use data to client

Provide minimal demo in draw_rh2_colz.cxx tutorial

Add testing of gradient palette

* [TPad][docs] bring Print and SaveAs documentation into better alignment

* [TPad][docs] add notes that cannot save TMathText as PDF properly