ngl::Matrix vs Imath::Matrix44

As I've been working with the Alembic file I/O system for a while I've been using some of the IMath functions as Alembic is build upon IMath / OpenEXR base code. IMath is a templated maths library that, to quote the website, "Imath, a math library with support for matrices, 2d- and 3d-transformations, solvers for linear/quadratic/cubic equations, and more".

Half way through using this I started wanting to use my own ngl::Matrix library as this is integrated into my code base, it when that I discovered that the two were not fully compatible.

Whilst both have very similar functions, the one core difference was how the matrix*matrix multiplication worked, (pre / post multiplication of values). In the end I decided to modify how the ngl::Matrix * operator worked so that it is compatible with IMath::Matrix44

Using IMath in ngl::
To start using IMath in ngl (or other programs) we need to set the compiler include paths to the correct place. By default they are installed in /usr/local (with the headers being in a directory OpenEXR)

A number of the classes in IMath are templated header only files so we don't need to add any additional libs, however some of the functions may also need the additional libImath.so (or static .a version)

To add these in a Qt project file add the following lines

INCLUDEPATH+=/usr/include/
LIBS +=-lImath

Once these have been added to the project we need to add the following header to the program

#include <OpenEXR/ImathMatrix.h>
#include <OpenEXR/ImathVec.h>

The IMath::Matrix44 class is a templated class so we need to construct it to be compatible with the ngl::Matrix class using a float. The following code is going to construct both an ngl::Matrix and a IMath::Matrix44

float xRotation=45.0f;
// Imath
Imath::Matrix44 <float> iXMatrix;
iXMatrix.setAxisAngle(Imath::Vec3<float>(1,0,0),ngl::radians(xRotation));
// ngl
ngl::Matrix nXMatrix;
nXMatrix.rotateX(xRotation);

In the above example the Imath matrix is constructed and will be set to the identity matrix as default. We then use the setAxisAngle method to set the matrix as a rotation around the x axis by xRotation degrees. This method is passed a vector for the axis to rotate around and a value for the rotation which must be converted into radians.

The ngl::Matrix class is also set to the identity when it's constructed, and to set the rotation value we use the rotateX method (which expects the rotation values in degrees).

We can check the output of this by using the overloaded << operators as shown

std::cout<<"X rotation "<<xRotation<<"\n"<<nXMatrix<<"\n"<<iXMatrix<<"\n";


X rotation 45
[+1.0000000000000000,+0.0000000000000000,+0.0000000000000000,+0.0000000000000000]
[+0.0000000000000000,+0.7071067690849304,+0.7071067690849304,+0.0000000000000000]
[+0.0000000000000000,-0.7071067690849304,+0.7071067690849304,+0.0000000000000000]
[+0.0000000000000000,+0.0000000000000000,+0.0000000000000000,+1.0000000000000000]

(  +1.0000000000000000   +0.0000000000000000   +0.0000000000000000   +0.0000000000000000
   +0.0000000000000000   +0.7071067690849304   +0.7071067690849304   +0.0000000000000000
   +0.0000000000000000   -0.7071067690849304   +0.7071067690849304   +0.0000000000000000
   +0.0000000000000000   +0.0000000000000000   +0.0000000000000000   +1.0000000000000000)

Another useful feature of the ngl::Matrix class is that is can be constructed from a float [4][4] as shown here

Matrix::Matrix(Real _m[4][4])
{
  for(int y=0; y<4; ++y)
  {
    for(int x=0; x<4; ++x)
    {
      m_m[y][x]=_m[y][x];
    }
  }

}

This means we can construct an ngl::Matrix from an Imath matrix as shown

  
Imath::Matrix44 <float> iZMatrix;
iZMatrix.setAxisAngle(Imath::Vec3<float>(0,0,1),ngl::radians(zRotation));
// alternativly we can construct from an Matrix.x array
ngl::Matrix nZMatrix(iZMatrix.x);

The listing below show the complete program and the output

int main()
{
  float xRotation=45.0f;
  float yRotation=35.0f;
  float zRotation=15.0f;


  Imath::Matrix44 <float> iXMatrix;
  iXMatrix.setAxisAngle(Imath::Vec3<float>(1,0,0),ngl::radians(xRotation));
  ngl::Matrix nXMatrix;
  nXMatrix.rotateX(xRotation);

  Imath::Matrix44 <float> iYMatrix;
  iYMatrix.setAxisAngle(Imath::Vec3<float>(0,1,0),ngl::radians(yRotation));
  ngl::Matrix nYMatrix;//(iYMatrix.x);
  nYMatrix.rotateY(yRotation);

  Imath::Matrix44 <float> iZMatrix;
  iZMatrix.setAxisAngle(Imath::Vec3<float>(0,0,1),ngl::radians(zRotation));
  // alternativly we can construct from an Matrix.x array
  ngl::Matrix nZMatrix(iZMatrix.x);

  std::cout<<"X rotation "<<xRotation<<"\n"<<nXMatrix<<"\n"<<iXMatrix<<"\n";
  std::cout<<"y rotation "<<yRotation<<"\n"<<nYMatrix<<"\n"<<iYMatrix<<"\n";
  std::cout<<"z rotation "<<zRotation<<"\n"<<nZMatrix<<"\n"<<iZMatrix<<"\n";

  std::cout<<"ngl mult y*x \n"<<nYMatrix*nXMatrix<<"\n";
  std::cout<<"iMath mult y*x \n"<<iYMatrix*iXMatrix<<"\n";
  ngl::Matrix nxyz=nXMatrix*nYMatrix*nZMatrix;
  std::cout<<"ngl mult x*y*z \n"<<nxyz<<"\n";
  Imath::Matrix44 <float> ixyz=iXMatrix*iYMatrix*iZMatrix;
  std::cout<<"iMath mult x*y*z \n"<<ixyz<<"\n";

  Imath::Matrix44 <float> iInverse=ixyz.inverse();
  std::cout<<"inverse \n"<<iInverse<<"\n";
  ngl::Matrix nInverse=nxyz.inverse();
  std::cout<<"inverse \n"<<nInverse<<"\n";

  Imath::Vec3<float> iPos(1,2,3);
  std::cout<<"i V*M "<<iPos*ixyz<<"\n";
  ngl::Vector nPos(1,2,3,1);
  std::cout<<"n V*M"<<nPos*nxyz<<"\n";
  std::cout<<"n M*V"<<nxyz*nPos<<"\n";
}

Which gives the following output

X rotation 45
[+1.0000000000000000,+0.0000000000000000,+0.0000000000000000,+0.0000000000000000]
[+0.0000000000000000,+0.7071067690849304,+0.7071067690849304,+0.0000000000000000]
[+0.0000000000000000,-0.7071067690849304,+0.7071067690849304,+0.0000000000000000]
[+0.0000000000000000,+0.0000000000000000,+0.0000000000000000,+1.0000000000000000]

(  +1.0000000000000000   +0.0000000000000000   +0.0000000000000000   +0.0000000000000000
   +0.0000000000000000   +0.7071067690849304   +0.7071067690849304   +0.0000000000000000
   +0.0000000000000000   -0.7071067690849304   +0.7071067690849304   +0.0000000000000000
   +0.0000000000000000   +0.0000000000000000   +0.0000000000000000   +1.0000000000000000)

y rotation +35.0000000000000000
[+0.8191520571708679,+0.0000000000000000,-0.5735764503479004,+0.0000000000000000]
[+0.0000000000000000,+1.0000000000000000,+0.0000000000000000,+0.0000000000000000]
[+0.5735764503479004,+0.0000000000000000,+0.8191520571708679,+0.0000000000000000]
[+0.0000000000000000,+0.0000000000000000,+0.0000000000000000,+1.0000000000000000]

(  +0.8191520571708679   +0.0000000000000000   -0.5735764503479004   +0.0000000000000000
   +0.0000000000000000   +1.0000000000000000   +0.0000000000000000   +0.0000000000000000
   +0.5735764503479004   +0.0000000000000000   +0.8191520571708679   +0.0000000000000000
   +0.0000000000000000   +0.0000000000000000   +0.0000000000000000   +1.0000000000000000)

z rotation +15.0000000000000000
[+0.9659258127212524,+0.2588190436363220,+0.0000000000000000,+0.0000000000000000]
[-0.2588190436363220,+0.9659258127212524,+0.0000000000000000,+0.0000000000000000]
[+0.0000000000000000,+0.0000000000000000,+1.0000000000000000,+0.0000000000000000]
[+0.0000000000000000,+0.0000000000000000,+0.0000000000000000,+1.0000000000000000]

(  +0.9659258127212524   +0.2588190436363220   +0.0000000000000000   +0.0000000000000000
   -0.2588190436363220   +0.9659258127212524   +0.0000000000000000   +0.0000000000000000
   +0.0000000000000000   +0.0000000000000000   +1.0000000000000000   +0.0000000000000000
   +0.0000000000000000   +0.0000000000000000   +0.0000000000000000   +1.0000000000000000)

ngl mult y*x 
[+0.8191520571708679,+0.4055798053741455,-0.4055798053741455,+0.0000000000000000]
[+0.0000000000000000,+0.7071067690849304,+0.7071067690849304,+0.0000000000000000]
[+0.5735764503479004,-0.5792279839515686,+0.5792279839515686,+0.0000000000000000]
[+0.0000000000000000,+0.0000000000000000,+0.0000000000000000,+1.0000000000000000]

iMath mult y*x 
(  +0.8191520571708679   +0.4055798053741455   -0.4055798053741455   +0.0000000000000000
   +0.0000000000000000   +0.7071067690849304   +0.7071067690849304   +0.0000000000000000
   +0.5735764503479004   -0.5792279839515686   +0.5792279839515686   +0.0000000000000000
   +0.0000000000000000   +0.0000000000000000   +0.0000000000000000   +1.0000000000000000)

ngl mult x*y*z 
[+0.7912400960922241,+0.2120121568441391,-0.5735764503479004,+0.0000000000000000]
[+0.2087472975254059,+0.7879844307899475,+0.5792279839515686,+0.0000000000000000]
[+0.5747727155685425,-0.5780408978462219,+0.5792279839515686,+0.0000000000000000]
[+0.0000000000000000,+0.0000000000000000,+0.0000000000000000,+1.0000000000000000]

iMath mult x*y*z 
(  +0.7912400960922241   +0.2120121568441391   -0.5735764503479004   +0.0000000000000000
   +0.2087472975254059   +0.7879844307899475   +0.5792279839515686   +0.0000000000000000
   +0.5747727155685425   -0.5780408978462219   +0.5792279839515686   +0.0000000000000000
   +0.0000000000000000   +0.0000000000000000   +0.0000000000000000   +1.0000000000000000)

inverse 
(  +0.7912400960922241   +0.2087472826242447   +0.5747727155685425   +0.0000000000000000
   +0.2120121717453003   +0.7879844903945923   -0.5780409574508667   +0.0000000000000000
   -0.5735764503479004   +0.5792279243469238   +0.5792278647422791   +0.0000000000000000
   +0.0000000000000000   -0.0000000000000000   +0.0000000000000000   +1.0000000000000000)

inverse 
[+0.7912402153015137,+0.2087473124265671,+0.5747727751731873,+0.0000000000000000]
[+0.2120122015476227,+0.7879846096038818,-0.5780410170555115,+0.0000000000000000]
[-0.5735765099525452,+0.5792279839515686,+0.5792279243469238,+0.0000000000000000]
[+0.0000000000000000,+0.0000000000000000,+0.0000000000000000,+1.0000000000000000]

i V*M (+2.9330530166625977 +0.0538582801818848 +2.3225636482238770)
n V*M[+2.9330530166625977,+0.0538582801818848,+2.3225636482238770,+1.0000000000000000]
n M*V[-0.5054649114608765,+3.5224001407623291,+1.1563749313354492,+1.0000000000000000]

The main upshot from these changes occur in the ngl demos where the code to load the matrices to the shader have been modified as shown in the code here

ngl::Matrix MV;
ngl::Matrix MVP;
ngl::Mat3x3 normalMatrix;
ngl::Matrix M;

// load matrix to shader before changes to ngl::Matrix

M=_tx.getCurrentTransform().getMatrix();
MV=m_cam->getViewMatrix() *_tx.getCurrAndGlobal().getMatrix();
MVP=m_cam->getProjectionMatrix()*MV*;

// new version with compatible matrix
M=_tx.getCurrentTransform().getMatrix();
MV=_tx.getCurrAndGlobal().getMatrix()*m_cam->getViewMatrix() ;
MVP=MV*m_cam->getProjectionMatrix();

As you can see when we calculated the previous MVP matrix it was done using the P*V*M calculation order, now we use M*V*P instead. If you are having any issues just swap the matrix order in these type of functions.

Pipeline Stuff

As we are starting the group project section of the Masters term I thought it would be a good idea to do some basic pipeline stuff.

This example is going to write some simulation data created in a C++ program and then we will write some simple Python scripts to load this data into Maya and Houdini.

The following video shows the program in action as well as the Maya and Houdini versions.

As this is an ad-hoc system the output file format is very simple, the C++ program writes out the following data :-


NumParticles 500
Frame 0
P0 64.301 -57.7284 49.8516

....

Frame 1

....

Where the particle data consists of The name of the Particle (in this case P0,P1....Pn) and the x,y,z positions of the particle per frame.

Maya Version

The maya version of the program will popup a dialog box to prompt the user to select an input file, it will then parse the file and create a locator for each of the particle names found.

Then for every frame a keyframe is created for the locator replicating the animation from the C++ simulation.

import maya.OpenMaya as OM
import maya.OpenMayaAnim as OMA
import maya.cmds as cmds

The code above loads in the maya elements we need, OpenMaya contains the core maya elements we need, the OpenMayaAnim namespace has the controls for all the animation transports such as setting the current frame and maya.cmds gives us access to all the maya cmds similar to the mel commands printed in the console when we generate things.

def createLocator(_name,_x,_y,_z) :
    cmds.spaceLocator( name=_name)
    cmds.move(_x,_y,_z)
    cmds.setKeyframe()

The createLocator function creates a simple space locator then moves it to the current x,y,z position we then set the keyframe to make the initial key at the currently set frame (more on this later)

def moveLocator(_name,x,y,z) :
    cmds.select(_name)
    cmds.move(x,y,z)
    cmds.setKeyframe()

The move locator function, first selects the locator (based on the name passed in), it then calles the move command which will move the currently selected object, finally we set the keyframe.

def importParticleFile() :
    basicFilter = "*.out"

    fileName=cmds.fileDialog2(caption="Please select file to import",fileFilter=basicFilter, fm=1)
    if fileName[0] !=None :

 file=open(str(fileName[0]))
 frame=0
 numParticles=0
 #set to frame 0
 animControl=OMA.MAnimControl()
 animControl.setCurrentTime(OM.MTime(frame))

 for line in file :
  line=line.split(" ")
  if line[0]=="NumParticles" :
   numParticles=int(line[1])
  elif line[0]=="Frame" :
   frame=int(line[1])
   animControl.setCurrentTime(OM.MTime(frame))
  else :
   name=line[0]
   x=float(line[1])
   y=float(line[2])
   z=float(line[3])
   if frame==0 :
    #we need to create our initial locators
    createLocator(name,x,y,z)
   else :
    moveLocator(name,x,y,z)

Houdini Version
The houdini version of the script will generate a null which is the houdini equivalent of a locator. By default a houdini null doesn't contain any geometry so we also need to parent this to some axis (houdini call these controls).


To start with we need to get the name of the file, this is done using the getAbsoluteFilename function described here http://jonmacey.blogspot.com/2011/01/houdini-python-ascode.html

def createNull(parent,_name,x,y,z) :
 #create a null this will set loads of default values
 null = parent.createNode("null", _name, run_init_scripts=False, load_contents=True)
 # set the x,y,z values
 null.parm("tx").set(x)
 null.parm("ty").set(y)
 null.parm("tz").set(z)
 # now add a control to the null so we have something to visualise
 null.createNode("control", "ctrl"+_name, run_init_scripts=False, load_contents=True)
 # now grab the keyframe
 setKey = hou.Keyframe()
 # set to frame 0
 setKey.setFrame(0)
 # now key the tx/y and z values
 setKey.setValue(x)
 null.parm("tx").setKeyframe(setKey)
 setKey.setValue(y)
 null.parm("ty").setKeyframe(setKey)
 setKey.setValue(z)
 null.parm("tz").setKeyframe(setKey)
 # now add to our network node

This function is passed the parent node, which in this case will be the houdini path "/obj/" from this we create a new node called a "null" and set it's parameters. In Houdini all parameters can be access using the parm(...) method of the object passing in the name of the parameter we wish to access, in this case "tx/ty/tz". Next we set the keyframes using the hou.keyframe class.

def moveNull(_name,frame,x,y,z) :
 null=hou.node("/obj/"+_name)
 setKey = hou.Keyframe()
 setKey.setFrame(frame)
 setKey.setValue(x)
 null.parm("tx").setKeyframe(setKey)
 setKey.setValue(y)
 null.parm("ty").setKeyframe(setKey)
 setKey.setValue(z)
 null.parm("tz").setKeyframe(setKey)

In this function we grab the object by name then set the keyframes using the same method as above. Finally we are going to create our nodes and import the file, the file reading code is exactly the same, however we create a subNetwork first to make the houdini scene neater.

def importParticleFile() :

 fileName=GetAbsoluteFileName("Select particle File","*.out",hou.fileType.Any)
 # get the the object leve as our parent
 if locals().get("hou_parent") is None:
  parent = hou.node("/obj")

 # make sure we got a filename
 if fileName !=None :
  subNetName=hou.ui.readInput("Please Enter name for the subnet")
  ## @brief we now copy this to a new string
  subNetName=subNetName[1]

  subNet=parent.createNode("subnet", subNetName, run_init_scripts=False, load_contents=True)
  #open the file (could do a proper check here)
  file=open(fileName)
  frame=0
  numParticles=0
  # now process the file and create the nulls
  for line in file :
   line=line.split(" ")
   if line[0]=="NumParticles" :
    numParticles=int(line[1])
   elif line[0]=="Frame" :
    frame=int(line[1])
   else :
    name=line[0]
    x=float(line[1])
    y=float(line[2])
    z=float(line[3])
    if frame==0 :
     #we need to create our initial locators
     createNull(subNet,name,x,y,z)
    else :
     moveNull(subNetName+"/"+name,frame,x,y,z)

To grab the full code use the following

DemoProgram (requires NGL)
particles.out (the output of the program which the python files read)
Houdini Script
Maya Script

Getting Started with Alembic

I've just started looking at the Alembic interchange format which looks like a really promising system for passing baked animation data plus a whole lot more around. With big players like ILM, Sony Image Works, The Foundry etc all using it I thought it would be good to get started with implementing my own wrapper for the ngl:: library and just have a general look at what it can do so I can do a lecture or two on it.

Installation is fairly straight forward, you need boost++,  HDF5 and cmake and the OpenEXR framework libraries ( ILMBase which has IMath etc).  On the mac the latest version get placed in /usr/local/alembic-1.0.3 and this will have the static libs, headers and maya plugins needed to get started.

I'm not going to dwell too long on the structures etc of Alembic at present and just have a look at getting started on some very basic loading of meshes etc. A good overview can be found here.

Getting some geometry

To get some sample geometry to test I decided to generate a very simple scene of primitives in maya

I have named each of the primitives to I can see how they fit into the alembic structure, also as transforms are present within the alembic structure, I decided to duplicate and transform some of the elements to see how this worked.

To export the data we can use the maya exported which comes with Alembic. This is called AbcExport and can be run from the Mel script window. I've not really managed to figure out how selection / grouping works with the exporter as yet, and it seems best to make each individual element in the scene a root and export in turn. This can be done with the following command.

AbcExport -v -j " -ws -root pasted__Platonic -root pasted__Helix -root pasted__Pipe -root pasted__Solid -root pasted__Torus -root pasted__Cone -root pasted__Cylinder -root pasted__Sphere -root pasted__Plane -root Platonic -root Helix -root Pipe -root Solid -root Torus -root Cone -root Cylinder -root Sphere -root Plane -file /Users/jmacey/teaching/AlembicTests/MayaTest.abc";

You will see that the -j option is basically a command string that specifies the job, in this case we are exporting world space root nodes (-ws) where -root  indicates each of the objects to store.

Finally I'm writing to the file MayaTest.abc with an absolute directory.

Basic Qt Project

To get started I've created a basic Qt project based on the installation directory  /usr/local/alembic-1.0.3 to build and link agains the libs using a qt program can be done using the following

INCLUDEPATH+=/usr/local/alembic-1.0.3/include/
INCLUDEPATH+=/usr/local/include/OpenEXR
LIBS+=-L/usr/local/alembic-1.0.3/lib/static/
LIBS+=-lAlembicAbc
LIBS+=-lAlembicAbcGeom
LIBS+=-lAlembicAbcCoreAbstract
LIBS+=-lAlembicUtil
LIBS+=-lAlembicAbcCoreHDF5
LIBS+=-lImath
LIBS+=-lHalf
LIBS+=-lIex
LIBS+=-lhdf5
LIBS+=-lhdf5_hl

You will notice that we need to include both the hdf5 and ILM libs as well as the static alembic libraries.

Basic File read / echo

The first program I wrote was a basic traversal of the structure looking for nodes / meshes.  From initial reading of the docs It seems that the internal structure of an alembic file closely resembles as unix file system. With a root node / then nodes following down a tree structure. Each of these nodes is a distinct object that we can access and gather attribute values from.

In most of the sample code / demos a recursive visitor pattern seems to have been used for initial test I wanted a simple iterative solution for quick testing and debugging so I decided to use static loops instead. 

The following code is the basic opening of a Alembic archive.

#include <Alembic/AbcGeom/All.h>
#include <Alembic/AbcCoreAbstract/All.h>
#include <Alembic/AbcCoreHDF5/All.h>
#include <Alembic/Abc/ErrorHandler.h>

using namespace Alembic::AbcGeom; 
...

IArchive  archive( Alembic::AbcCoreHDF5::ReadArchive(),argv[1] );

One of the key design philosophies behind Alembic is that the API is split into In and Out classes similar to iostream. This is summed up well by the following quote in the documents

"Because Alembic is intended as a caching system, and not a live scenegraph, the API is split into two roughly symmetrical halves: one for writing, and one for reading. At the Abc and AbcGeom layers, classes that start with ‘O’ are for writing (or “output”), and classes that start with ‘I’ are for reading (or “input”). This is analogous to the C++ iostreams conceptual separation of istreams and ostreams."

So in the above we are opening an input (I) archive.

The next section of code will get the top of the archive and see how many children there are 

std::cout<<"traversing archive for elements\n";
IObject obj=archive.getTop();
unsigned int numChildren=obj.getNumChildren();
std::cout<< "found "<<numChildren<<" children in file\n";

Once we have the number of children we can iterate for each child in the node and traverse the tree (it must be noted in this example I know the tree is of a set depth, in reality we would need to traverse using recursion / visitor pattern to cope with more complex scene / geometry data however for a proof of concept this is fine)

for(int i=0; i<numChildren; ++i)
{
 std::cout<<obj.getChildHeader(i).getFullName()<<"\n";
 IObject child(obj,obj.getChildHeader(i).getName());
 
 std::cout<<"Children "<<child.getNumChildren()<<"\n";
 const MetaData &md = child.getMetaData();
 std::cout<<md.serialize() <<"\n";
 
 for(int x=0; x<child.getNumChildren(); x++)
 {
  IObject child2(child,child.getChildHeader(x).getName());
  const MetaData &md2 = child2.getMetaData();
  if( IPolyMeshSchema::matches( md2 ) || ISubDSchema::matches( md2 ))
  {
   std::cout<<"Found a mesh "<<child2.getName()<<"\n"; 
  }
 }
}

The code above grabs the child header of the current object and prints out the name. We then create a new IObject from the current object branch (getChildHeader(i).getName() ), this is the next object in the tree and we can then traverse this.

To access all of the data we can grab the meta data and call the serialize method, followed by traversing the data to see if we have a mesh and seeing what the name is. The output on the scene above looks like the following ( a partial listing )


traversing archive for elements
found 18 children in file

/Plane
Children 1
schema=AbcGeom_Xform_v3;schemaObjTitle=AbcGeom_Xform_v3:.xform
Found a mesh plane
/Platonic
Children 1
schema=AbcGeom_Xform_v3;schemaObjTitle=AbcGeom_Xform_v3:.xform
Found a mesh icosa
/Solid
Children 1
schema=AbcGeom_Xform_v3;schemaObjTitle=AbcGeom_Xform_v3:.xform
Found a mesh buckyball
/Sphere
Children 1
schema=AbcGeom_Xform_v3;schemaObjTitle=AbcGeom_Xform_v3:.xform
Found a mesh sphere
/Torus
Children 1
schema=AbcGeom_Xform_v3;schemaObjTitle=AbcGeom_Xform_v3:.xform
Found a mesh torus


Getting to the Points
Once I have the ability to grab the mesh in the file structure I can now look at accessing the point data and rendering it. This is a two stage process with the maya output as we have a top level transform node and then the point data. We need to get the transform matrix, then we need to multiply the points by it to get them in the correct world space.

Using the previous code frame work, we can grab the transform using the following

IXform x( child, kWrapExisting );
XformSample xs;
x.getSchema().get( xs );
M44d mat=xs.getMatrix();

You will see that this returns a M44d which is from the IMath library and is a 4x4 Matrix. We can also access the XformSample elements in a number of ways such as getTranslation, get[X/Y/Z]Rotation, getScale which will actually fit in well with the ngl::Transform class once I get to that stage. Initially I'm just going to use the raw matrix and use IMath to do the multiplication with the point.

We now do the check to see if we have a mesh as outlined above, If we do we can built a MeshObject and access the data as show below

// we have a mesh so build a mesh object
IPolyMesh mesh(child,child2.getName());
// grab the schema for the object
IPolyMeshSchema schema=mesh.getSchema();

// now grab the time sample data for the object

IPolyMeshSchema::Sample mesh_samp;
schema.get( mesh_samp );
// get how many points (positions) there are
uint32_t size=mesh_samp.getPositions()->size();

Another important concept of Alembic is the idea of sampling, again for the documentation

"Because Alembic is a sampling system, and does not natively store things like animation curves or natively provide interpolated values, there is a rich system for recording and recovering the time information associated with the data stored in it. In the classes AbcA::TimeSamplingType and AbcA::TimeSampling, you will find that interface."


We access the mesh sample at the current time value (0 as we've not set any frame data yet) and we can get the positions (and size) at this temporal sample.

The following code will now loop for each of the positions in the sample and multiply them by the current transform. I then save each in my own format Vec3

for(uint32_t m=0; m<size; ++m)
{
  // get the current point
  V3f p= mesh_samp.getPositions()->get()[m];

  // multiply by transform
  p=p*mat;
  // store for later use
  data.push_back(ngl::Vec3(p.x,p.y,p.z));
}

In the case of this demo I just create a point cloud into a Vertex Array object and draw using my ngl:: framework. This can be seen in the following video

A lot of this post is supposition /  basic rantings about what I've done so far, as this is a very new API and there is very little solid documentation at the moment, I think this post may well be updated / superseded very soon. It is my intention to fully integrate the mesh and possibly lights / cameras as much as I can into ngl, and we also intend to use this as a core data exchange format at the NCCA, so I hope to have much more detail about all this very soon.

iNGL

I've just release the initial version and a demo of the iNGL library for iOS devices (it's designed for iPhone 3Gs and above and both iPads as it uses OpenGLES 2.0)

You can see more here and I will do many a blog post about it soon

http://nccastaff.bournemouth.ac.uk/jmacey/GraphicsLib/iNGL/index.html

What's changed in NGL 4.5

I'm just about to put the feature freezes on NGL 4.5 and this blog post is going to highlight the many changes from version 4.0 which many of you may have used in last years assignments.

The Big Picture
Perhaps the biggest change in the whole library is the conversion OpenGL 3.2 core profile only.  This design decision was made for a number of reason, primarily for speed and compatibility across platforms, but also so I can teach the very latest versions of OpenGL and CGI techniques. The only major issue you may encounter with this change is that only Mac OSX Lion is now supported.

The main reason for this decision was so we could use GLSL 150 which is only available under mac using Lion and also makes it easier to port all the code base to OpenGL ES ( there is an iPhone port of NGL which will be released soon). If you don't wish to upgrade to Lion then you will have to use the legacy version or develop under another platform.

This also means that all immediate mode OpenGL has gone, (under Lion they are not present as it uses two different libraries for GL2.0 and GL3.2 see here ) so it means you can no longer use functions like glBegin, glVertex, glRotate, glTranslate, glScale etc. It also means that the whole OpenGL lighting and Material subsystem has also gone and we need to use shaders to do everything. I've already mentioned some of these things in previous posts.

It has now also been tested to work with boost 1.4.7 and the Windows version seems to be a lot more stable (but will still be the last version to be developed as I hardly ever use windows)

Changes
The following list shows the major changes to NGL from 4.0 to 4.5

1. ngl::Clip class has been removed as the student version of Houdini no longer support ASCII clip export, this has been replaced with the NCCAPointBake system and eventually Alembic support will be added
2. ngl::ShaderManager has been replaced with ngl::ShaderLib, this is mainly a name change after some healthy in class discussions with Ian about class naming. Also all calls to the shader subsystem no longer need the name of the shader passed as a parameter. It is assumed that the currently active shader is the one to set parameters for.
3. ngl::VBOPrimitives has been replaced with ngl::VAOPrimitives, the class is effectively the same, however we now use Vertex Array Objects to store our primitives, this also has advantages for porting to OpenGL ES 2.0 
4. ngl::VertexArrayObject class was added in 4.0 but is now used internally to create all geometry required in any of the classes. This has made the removal of any immediate mode OpenGL much easier.
5. ADDLARGEMODELS define has been added to the NGL.pro file, if defined it will add 4 new primitives to the VAOPrimitives class these are the NCCA Troll, Stanford Bunny, Buddha and Dragon. These models are very large and should only be enabled if required. The image below shows them in action on the iPhone 4s

New Classes

The following new classes have been added, some are to help with GLSL compatibility and some because of the changes to core profile required it.

1. ngl::Mat3x3 a simple 3x3 matrix class which can be created from the ngl::Matrix class. This is generally used to calculate the normal matrix for GLSL shaders and lighting calculations.
2. ngl::Vec3 is a simple container for a GLSL vec3 type, it is basically a subset of the ngl::Vector class and is used internally for passing vertices etc to the GLSL
3. ngl::Vec2 is a simple container for a GLSL vec2 type and works similarly to above.
4. ngl::Text this class is described in detail here but is needed as we can no longer use the Qt renderText method as it relies on immediate mode OpenGL

Demo Programs

I'm currently in the process of converting the demo programs to work on the new Version of NGL and this is taking a little time as there are quite a lot of changes in the way the shaders work and this does take some time.

The following videos talk through how the SimpleNGL demo works

Text Rendering using OpenGL 3.2

I've been working on porting the ngl:: library to be completely OpenGL core profile 3.2. One of the main issues I've had is the rendering of text. In the last version I used the QGLWidget::renderText method, however this is not available when using core profile OpenGL and also has a habit of crashing when using certain modern OpenGL elements.

To overcome this problem I have designed and implemented my own OpenGL text renderer and the following post will explain the process / design of this and my approach.  The approach I use follows the standard methods used in other packages and the following survey gives a good overview of these. My main concern with the design was that it only uses Fonts from Qt and that it works with OpenGL 3.2 core profile and above.

Initial Process
The usual process of text rendering is to create a billboard for each character in the text string and apply a texture to that quad for the given character. The image below shows a basic set of billboards and a (not to scale) set of text glyphs

The process we need to follow to create the text to render is as follows

1. Load a font and generate all the characters required
2. Generate OpenGL textures for each individual character
3. Generate billboards for each glyph depending upon the char height and width
4. Store this data for later text rendering

As the design of this system evolved It was decided to foce the user of the fonts to decide in advance the size and emphasis of the the font.  This was done so the texture / billboard generation only happens once at the start of the program, however once this is done any text can be rendered using this font set. This makes any programs using the text much quicker as the data is effectively cached as OpenGL textures / Vertex Array Objects

Loading the Font

The initial design decision was to create a single texture image containing all the visible ASCII characters, however this was soon dropped as there are issues with the ways that fonts are constructed to have different kerning values. So for the final design an individual image / texture is created for each font, with the character calculated to be at an origin of (0,0) Top left of the screen. Using this we will need to then calculate the height of the font once and for each character generated store the width of the different text types. 

As we are using Qt we can use the QFont class and the QFontMetrics class to gather all of this information. For each class the initial design was to store the following :-

struct FontChar
{
    int width; /// @brief the width of the font
    GLuint textureID; /// @brief the texture id of the font billboard
    ngl::VertexArrayObject *vao; /// a vao for the font
};

This class stores the individual width of each character's glyph gathered from the method QFontMetric::width() as well as the id for a generated texture and a pointer to a vertex array object which will contain the Vertices and UV data for the billboard.

The following code shows the basic process of generating each of the font textures.

  // so first we grab the font metric of the font being used
  QFontMetrics metric(_f);
  // this allows us to get the height which should be the same for all
  // fonts of the same class as this is the total glyph height
  float fontHeight=metric.height();

  // loop for all basic keyboard chars we will use space to ~
  // should really change this to unicode at some stage
  const static char startChar=' ';
  const static char endChar='~';
  // Most OpenGL cards need textures to be in powers of 2 (128x512 1024X1024 etc etc) so
  // to be safe we will conform to this and calculate the nearest power of 2 for the glyph height
  // we will do the same for each width of the font below
  int heightPow2=nearestPowerOfTwo(fontHeight);

  // we are now going to create a texture / billboard for each font
  // they will be the same height but will possibly have different widths
  for(char c=startChar; c<=endChar; ++c)
  {
    QChar ch(c);
    FontChar fc;
    // get the width of the font and calculate the ^2 size
    int width=metric.width(c);
    int widthPow2=nearestPowerOfTwo(width);
    // now we set the texture co-ords for our quad it is a simple
    // triangle billboard with tex-cords as shown
    //  s0/t0  ---- s1,t0
    //         |\ |
    //         | \|
    //  s0,t1  ---- s1,t1
    // each quad will have the same s0 and the range s0-s1 == 0.0 -> 1.0
    ngl::Real s0=0.0;
    // we now need to scale the tex cord to it ranges from 0-1 based on the coverage
    // of the glyph and not the power of 2 texture size. This will ensure that kerns
    // / ligatures match
    ngl::Real s1=width*1.0/widthPow2;
    // t0 will always be the same
    ngl::Real t0=0.0;
    // this will scale the height so we only get coverage of the glyph as above
    ngl::Real t1=metric.height()*-1.0/heightPow2;
    // we need to store the font width for later drawing
    fc.width=width;
    // now we will create a QImage to store the texture, basically we are going to draw
    // into the qimage then save this in OpenGL format and load as a texture.
    // This is relativly quick but should be done as early as possible for max performance when drawing
    QImage finalImage(nearestPowerOfTwo(width),nearestPowerOfTwo(fontHeight),QImage::Format_ARGB32);
    // set the background for transparent so we can avoid any areas which don't have text in them
    finalImage.fill(Qt::transparent);
    // we now use the QPainter class to draw into the image and create our billboards
    QPainter painter;
    painter.begin(&finalImage);
    // try and use high quality text rendering (works well on the mac not as good on linux)
    painter.setRenderHints(QPainter::HighQualityAntialiasing
                   | QPainter::TextAntialiasing);
    // set the font to draw with
    painter.setFont(_f);
    // we set the glyph to be drawn in black the shader will override the actual colour later
    // see TextShader.h in src/shaders/
    painter.setPen(Qt::black);
    // finally we draw the text to the Image
    painter.drawText(0, metric.ascent(), QString(c));
    painter.end();

First we need to create a QImage to render the character to a glyph. As most OpenGL implementations required power of 2 textures we also need to round our image size to the nearest power of two. To do this I found a handy function here which is called with the image width and height to make sure we get the correct texture sizes.

Next we set the texture fill to be Qt::transparent and the image pen colour to be Qt::black. As the actual text rendering is done by a special shader this value is unimportant, what we are actually after is the alpha  values in the image which are used to indicate the "coverage" of the text (more of this later).
After this is done we use the QPainter class to render the text into our QImage.

This stage is all Qt specific, as long as you have a Font library which allows you to save the glyphs into and image format and gather the font metrics it should be easy to port to other libraries.

Generating the Billboards
Now we have the font dimensions and the glyph as a QImage we can generate both the billboard and the  OpenGL textures.

To generate the textures we use the following code

 // now we create the OpenGL texture ID and bind to make it active
    glGenTextures(1, &fc.textureID);
    glBindTexture(GL_TEXTURE_2D, fc.textureID);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    // QImage has a method to convert itself to a format suitable for OpenGL
    // we call this and then load to OpenGL
    finalImage = QGLWidget::convertToGLFormat(finalImage);
    // the image in in RGBA format and unsigned byte load it ready for later
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, finalImage.width(), finalImage.height(),
       0, GL_RGBA, GL_UNSIGNED_BYTE, finalImage.bits());

The image above show the original sketch for the Billboard as two triangles, with the UV cords and the sequence of generation. The ngl library has a simple class for storing this kind of data called the VertexArrayObject all we have to do is pass the data to the class and then use it to draw. The following code does this.

 // this structure is used by the VAO to store the data to be uploaded
    // for drawing the quad
    struct textVertData
    {
    ngl::Real x;
    ngl::Real y;
    ngl::Real u;
    ngl::Real v;
    };
    // we are creating a billboard with two triangles so we only need the
    // 6 verts, (could use index and save some space but shouldn't be too much of an
    // issue
    textVertData d[6];
    // load values for triangle 1
    d[0].x=0;
    d[0].y=0;
    d[0].u=s0;
    d[0].v=t0;

    d[1].x=fc.width;
    d[1].y=0;
    d[1].u=s1;
    d[1].v=t0;

    d[2].x=0;
    d[2].y=fontHeight;
    d[2].u=s0;
    d[2].v=t1;
    // load values for triangle two
    d[3].x=0;
    d[3].y=0+fontHeight;
    d[3].u=s0;
    d[3].v=t1;


    d[4].x=fc.width;
    d[4].y=0;
    d[4].u=s1;
    d[4].v=t0;


    d[5].x=fc.width;
    d[5].y=fontHeight;
    d[5].u=s1;
    d[5].v=t1;


    // now we create a VAO to store the data
    ngl::VertexArrayObject *vao=ngl::VertexArrayObject::createVOA(GL_TRIANGLES);
    // bind it so we can set values
    vao->bind();
    // set the vertex data (2 for x,y 2 for u,v)
    vao->setData(6*sizeof(textVertData),d[0].x);
    // now we set the attribute pointer to be 0 (as this matches vertIn in our shader)
    vao->setVertexAttributePointer(0,2,GL_FLOAT,sizeof(textVertData),0);
    // We can now create another set of data (which will be added to the VAO)
    // in this case the UV co-ords
    // now we set this as the 2nd attribute pointer (1) to match inUV in the shader
    vao->setVertexAttributePointer(1,2,GL_FLOAT,sizeof(textVertData),2);
    // say how many indecis to be rendered
    vao->setNumIndices(6);

    // now unbind
    vao->unbind();
    // store the vao pointer for later use in the draw method
    fc.vao=vao;
    // finally add the element to the map, this must be the last
    // thing we do
    m_characters[c]=fc;
  }

Text rendering 
To render the text we need to convert from screen space (where top left is 0,0) to OpenGL NDC space, effectively we need to create an Orthographic project for our billboard to place it on the correct place.

The following diagrams show the initial designs for this.

As each of the billboards is initially calculated with the top right at (0,0) this transformation can be simplified. The following vertex shader is used to position the billboard vertices.

#version 150 
in vec2 inVert; 
in vec2 inUV; 
out vec2 vertUV; 
uniform vec3 textColour; 
uniform float scaleX; 
uniform float scaleY; 
uniform float xpos;  
uniform float ypos; 

void main() 
{ 
 vertUV=inUV; 
 gl_Position=vec4( ((xpos+inVert.x)*scaleX)-1.0,((ypos+inVert.y)*scaleY)+1.0,0.0,1.0);
}

This shader is passed the scaleX and scaleY values from the Text class these values are calculated in the method setScreenSize as shown below.

 
void Text::setScreenSize(
                          int _w,
                          int _h
                        )
{

  float scaleX=2.0/_w;
  float scaleY=-2.0/_h;
  // in shader we do the following code to transform from
  // x,y to NDC
  // gl_Position=vec4( ((xpos+inVert.x)*scaleX)-1,((ypos+inVert.y)*scaleY)+1.0,0.0,1.0); "
  // so all we need to do is calculate the scale above and pass to shader every time the
  // screen dimensions change
  ngl::ShaderLib *shader=ngl::ShaderLib::instance();
  (*shader)["nglTextShader"]->use();

  shader->setShaderParam1f("scaleX",scaleX);
  shader->setShaderParam1f("scaleY",scaleY);
}

This method must be called every time the screen changes size so the x,y position of the font are correctly calculated.

The xpos / ypos uniforms are the x,y co-ordinates of the current text to be rendered and the actual billboard vertices are passed to the shader as the inVert attribute. This is shown in the renderText method below.

void Text::renderText(
                      float _x,
                      float _y,
                      const QString &text
                     ) const
{
  // make sure we are in texture unit 0 as this is what the
  // shader expects
  glActiveTexture(0);
  // grab an instance of the shader manager
  ngl::ShaderLib *shader=ngl::ShaderLib::instance();
  // use the built in text rendering shader
  (*shader)["nglTextShader"]->use();
  // the y pos will always be the same so set it once for each
  // string we are rendering
  shader->setShaderParam1f("ypos",_y);
  // now enable blending and disable depth sorting so the font renders
  // correctly
  glEnable(GL_BLEND);
  glDisable(GL_DEPTH_TEST);
  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
  // now loop for each of the char and draw our billboard
  unsigned int textLength=text.length();

  for (unsigned int i = 0; i < textLength; ++i)
  {
    // set the shader x position this will change each time
    // we render a glyph by the width of the char
    shader->setShaderParam1f("xpos",_x);
    // so find the FontChar data for our current char
    FontChar f = m_characters[text[i].toAscii()];
    // bind the pre-generated texture
    glBindTexture(GL_TEXTURE_2D, f.textureID);
    // bind the vao
    f.vao->bind();
    // draw
    f.vao->draw();
    // now unbind the vao
    f.vao->unbind();
    // finally move to the next glyph x position by incrementing
    // by the width of the char just drawn
    _x+=f.width;

  }
  // finally disable the blend and re-enable depth sort
  glDisable(GL_BLEND);
  glEnable(GL_DEPTH_TEST);

}

Before we can render the text we need to enable the OpenGL alpha blending and we use the SRC_ALPHA, ONE_MINUS_SRC_ALPHA so the text will be rendered over the top of any other geometry. I also disable depth sorting so if the text is rendered last it should always appear over any geometry.

Text Colour
To set the text colour we use the fragment shader below.

#version 150 

uniform sampler2D tex; 
in vec2 vertUV; 
out vec4 fragColour; 
uniform vec3 textColour; 

void main() 
{ 
  vec4 text=texture(tex,vertUV.st); 
  fragColour.rgb=textColour.rgb; 
  fragColour.a=text.a; 
}

This shader is quite simple, it takes the input texture (the glyph) and grabs the alpha channel (which we can think of as the coverage of the ink). We then set the rest of the colour to be the user defined current colour and this will get rendered to the screen as shown in the following screen shot

Future Work

As an initial proof of concept / working version this works quite well. It is reasonably fast and most fonts I have tried seem to work ok (including Comic Sans!)

The next tests / optimisations are to determine if we have any billboards of the same size and only store ones we need. This should same VAO space and make things a little more efficient.

Update 

I've actually added code to do the billboard optimisation, all it needed was

QHash <int,vertexarrayobject * > widthVAO;
 ......
// see if we have a Billboard of this width already
if (!widthVAO.contains(width))
{
      // do the billboard vao creation
}
else
{
  fc.vao=widthVAO[width];
}

For Times font we now only create 15 Billboards, for Arial 16 unique billboards, for Courier only one as it's a mono spaced font.

Now for Unicode support!

Installing Ubuntu with Virtual Box

Term has started and a number of students have been asking about installing the version of Ubuntu we use in the labs on their home machines. There are many ways of doing this and my preferred way is to delete windows and only use Ubuntu, however most students don't want to do this as they want windows for gaming etc.

The simplest solution to run a basic linux box suitable for basic programming / exercises needed in the first year of our courses is to use Oracle (Sun) Virtual box and install a basic linux system.

Getting Started
First we need to download a couple of packages. The first is the virtual box host software which can be found here and a linux iso ready to install. For the current university build we are using Ubuntu 10.4 LTS which can be found here and we are using the 64 bit version.

The following videos show the install process and how to proceed.
Part 1

Part 2

Part 3

Part 4