ROOT stuff

DON'T PANIC

ROOT 6:23/01 changing branch name

The new (still experimental ) version of ROOT seems to have the brilliant idea to change the name of a TClonesArray branch ending with a dot, removing the dot.

Example: in previous ROOT version I had

t.

t..e

t..t

Now i have:

t

t.e

t.t

Checked with a modified version of tree0.C example.

Asking ROOT team

ROOT I/O

TFile reading online and local

It seems that TFile is more powerful than I knew. It allows to read both local files and files from a server, https and xROOTD

Checking a file while is being written

First, we need to save the file periodically. You can use once at the time or within your loop

mytree->SetAutoSave(nbytes) #saves every nbytes periodically
mytree->AutoSave() #saves now 

If we try to open the file now, we get warning message, and try to recover, but we can access the files. It is naturally safer to not rely on ROOT recovery system, but use the recommended procedure to access the TTree while being written (https://root-forum.cern.ch/t/errors-in-remote-client-reading-of-ttree-from-tfile-via-xrootd-while-simultaneously-updating-ttree-on-server/43479), also found in the TDirectory reference. Writing process calls:

#writing process
inputtree.AutoSave()
r.gDirectory.Saveself()

#reading process
inputfile = r.TFile.Open("testfile.root","READ") #done only first time
inputfile.ReadKeys() #everytime you want an update
inputtree = r.gDirectory.Get("testtree")

From ROOT forum:

Recreate the TFile object does everything you need (except you also need to delete the previous one) but also does more than you really need. In other word, doing multiple TFile::Open is simpler but a bit slower.

Cheers, Philippe.

Transparency

Volumes are made transparent with SetFillColorAlpha(color, alpha).

However, to actually see transparent volumes in the canvas, you need to set

OpenGL.CanvasPreferGL = 1

in the .rootrc file or in your HOME path (or, if you prefer, in $ROOTSYS/etc/system.rootrc)

TTree AutoSave, MaxTTreeSize

Related to how often a TFile is written:

• AutoSave(n>0): save each n entries;

• AutoSave(n<0): save each n bytes;

MaxTTreeSize, again in bytes.

Code Syntax (according to requests)

Auto

CONSIDER whether auto can reduce verbosity by avoiding repeating types

Use auto* instead of TGeoBBox*, for example;

Casts

NEVER use C-style casts (e.g. (TTree *)file->Get("some_tree");). INSTEAD, prefer static_cast, dynamic_cast (or if it's absolutely unavoidable reinterpret_cast), in that order.

Pointers

Please use nullptr, NULL should not be used in modern code.

Definition

Please don't define multiple things on the same line, this is unreadable. Also, Bool_t should be initialised to false, not 0 for readability

Ternary statements

TGeoBBox *Absorber = (fDesign < 4) ? true : false

Etc.

Remove trailing whitespace, single space between attribute and type