man SoCalculator (3): General purpose calculator for floats and 3D float vectors.

SYNOPSIS

#include <Inventor/engines/SoCalculator.h>

Inherits SoEngine.

Public Member Functions

virtual SoType getTypeId (void) const

virtual const SoFieldData * getFieldData (void) const

virtual const SoEngineOutputData * getOutputData (void) const

SoCalculator (void)

Static Public Member Functions

static SoType getClassTypeId (void)

static void * createInstance (void)

static void initClass (void)

Public Attributes

SoMFFloat a

SoMFFloat b

SoMFFloat c

SoMFFloat d

SoMFFloat e

SoMFFloat f

SoMFFloat g

SoMFFloat h

SoMFVec3f A

SoMFVec3f B

SoMFVec3f C

SoMFVec3f D

SoMFVec3f E

SoMFVec3f F

SoMFVec3f G

SoMFVec3f H

SoMFString expression

SoEngineOutput oa

SoEngineOutput ob

SoEngineOutput oc

SoEngineOutput od

SoEngineOutput oA

SoEngineOutput oB

SoEngineOutput oC

SoEngineOutput oD

Protected Member Functions

virtual ~SoCalculator (void)

virtual void inputChanged (SoField *which)

Static Protected Member Functions

static const SoFieldData ** getInputDataPtr (void)

static const SoEngineOutputData ** getOutputDataPtr (void)

Detailed Description

General purpose calculator for floats and 3D float vectors.

The SoCalculator uses the values from the input fields (which are either single floating point values or vectors) as variables in the free-form engine expressions and places the results on the output fields.

The engine has sixteen input fields; eight scalar inputs (a, b, c, d, e, f g, and h), and eight vector inputs (A, B, C, D, E, F, G, and H).

There are eight output fields; four scalar outputs (oa, ob, oc, and od), and four vector outputs (oA, oB, oC, and oD).

The expression syntax is quite similar to C/C++, with a very limited set of keywords and functions.

An example:

  oa = a * (0.5 + b) / c

Will multiply the value in a with the value in b plus 0.5, divide that result with c, and place the result in oa. Since this is an engine, the expression will only be evaluated when someone attempts to read the value in oa, not every time an input in changed.

All inputs are multi-fields, and if there are several values in an input, the expression will be evaluated once for every input field value, and the output will create as many values as there are input field values.

If there is more than one input field, and the input fields do not have the same number of values, the engine will create as many output values as the input field with the biggest number of values. When the index get out of bounds for some other input field, the last field value will be used.

Vector expressions are similar to scalar expression. An example:

  oA = A + vec3f(1.0, 0.0, 0.0) * B

Will take the vector in A, add the value in B multiplied with (1,0,0), and place the result in oA.

In addition to regular arithmetics, the SoCalculator syntax also includes some functions.

Scalar functions:

cos(x) - cosine function (x in radians)
sin(x) - sinus function
tan(x) - tangent function
acos(x) - arc cosine function
asin(x) - arc sinus function
atan(x) - arc tangent function
atan2(y, x) - arc tangent function of two variables (y, x).
cosh(x) - hyperbolic cosine function
sinh(x) - hyperbolic sinus function
tanh(x) - hyperbolic tangent function
sqrt(x) - square root function
pow(x,y) - x raised to the power of y
exp(x) - e to the power of x
log(x) - natural logarithm of x
log10() - base-10 logarithm of x
ceil(x) - rounds x upwards to the nearest integer
floor(x) - rounds x downwards to the nearest integer
fabs(x) - absolute value
fmod(x, y) - remainder of dividing x by y
rand(x) - pseudo-random value between 0 and 1

Vector functions:

cross(x, y) - cross product of x and y
dot(x,y) - dot product of x and y (returns scalar value)
length(x) - length of x (returns scalar value)
normalize(x) - returns normalized version of x
x[y] - access components in x (y should be a scalar value in the range [0,2])

There are also some named constants that can be used:

MAXFLOAT
MINFLOAT
M_E
M_LOG2E
M_LOG10E
M_LN2
M_PI
M_SQRT2 - sqrt(2)
M_SQRT1_2 - sqrt(1/2)

The only control flow available is the ? operator. An example:

  oa = (a > b) ? (a * 0.5) : (b * c)

(The parentheses are not necessary, they're there just to make the example easier to read)

In addition to the standard comparators (<, >, <=, >=, ==, !=), you can also use && (AND) and || (OR) to combine expression, and the unary ! (NOT) operator.

One final thing worth mentioning is the temporary variables. There exists sixteen temporary variables that can be used in expressions. ta, tb, tc, td, te, tf, tg, and th are scalar variables, and tA, tB, tC, tD, tE, tF, tG, and tH are vector variables. They are usually used when you have more than one expression that should be evaluated in order.

An example with three expressions:

  ta = a * b; tb = c + d; tc = e - f
  tA = vec3f(ta, tb, tc) + A
  oA = tA * B

The example just shows how temporary variables can be used to make your expressions easier to read. Please note that it's possible to have several statements in one expression. You just separate them with semicolons.

Here is a simple example of how an SoCalculator engine may be used in an .iv file:

  DEF mycamera PerspectiveCamera {
    orientation 1 0 0 1.57
  }
  DEF headlight DirectionalLight {
    intensity 0.8
    direction 0 0 1
  }
  Separator {
    # Render a cube not affected by lighting
    LightModel { model BASE_COLOR }
    BaseColor { rgb = Calculator {
                        a = USE headlight . intensity
                        expression [ 'oA = vec3f( a, a, a)' ]
                      } . oA }
    Cube {}
  }

In the example, the color of the Cube is a function of the intensity of the DirectionalLight, even though the Cube is rendered without lighting because of the BASE_COLOR LightModel.

Constructor & Destructor Documentation

SoCalculator::SoCalculator (void)

Constructor.

SoCalculator::~SoCalculator (void) [protected], [virtual]

Destructor.

Member Function Documentation

SoType SoCalculator::getClassTypeId (void) [static]

This static method returns the SoType object associated with objects of this class.

Reimplemented from SoEngine.

SoType SoCalculator::getTypeId (void) const [virtual]

Returns the type identification of an object derived from a class inheriting SoBase. This is used for run-time type checking and 'downward' casting.

Usage example:

  void foo(SoNode * node)
  {
    if (node->getTypeId() == SoFile::getClassTypeId()) {
      SoFile * filenode = (SoFile *)node;  // safe downward cast, knows the type
    }
  }

For application programmers wanting to extend the library with new nodes, engines, nodekits, draggers or others: this method needs to be overridden in all subclasses. This is typically done as part of setting up the full type system for extension classes, which is usually accomplished by using the pre-defined macros available through for instance Inventor/nodes/SoSubNode.h (SO_NODE_INIT_CLASS and SO_NODE_CONSTRUCTOR for node classes), Inventor/engines/SoSubEngine.h (for engine classes) and so on.

For more information on writing Coin extensions, see the class documentation of the toplevel superclasses for the various class groups.

Implements SoBase.

const SoFieldData ** SoCalculator::getInputDataPtr (void) [static], [protected]

Returns the SoFieldData class which holds information about inputs in this engine.

Reimplemented from SoEngine.

const SoEngineOutputData ** SoCalculator::getOutputDataPtr (void) [static], [protected]

Returns the SoEngineOutputData class which holds information about the outputs in this engine.

Reimplemented from SoEngine.

const SoFieldData * SoCalculator::getFieldData (void) const [virtual]

Returns a pointer to the class-wide field data storage object for this instance. If no fields are present, returns NULL.

Reimplemented from SoFieldContainer.

const SoEngineOutputData * SoCalculator::getOutputData (void) const [virtual]

This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.

Implements SoEngine.

void SoCalculator::initClass (void) [static]

Sets up initialization for data common to all instances of this class, like submitting necessary information to the Coin type system.

Reimplemented from SoEngine.

void SoCalculator::inputChanged (SoField *which) [protected], [virtual]

Called when an input is changed. The default method does nothing, but subclasses may override this method to do The Right Thing when a specific field is changed.

Reimplemented from SoEngine.