SYNOPSIS

#include <agar/core.h>
#include <agar/gui.h>

DESCRIPTION

The Agar AG_Units interface implements unit conversion. The AG_Unit structure is defined as follows:

typedef struct ag_unit {
	char *key;
	char *abbr;
	char *name;
	double divider;
	double (*func)(double, int mode);
} AG_Unit;

The key member is a unique identifier for this unit. abbr is an abbreviated symbol, and name is the full name of the unit.

The linear conversion factor is specified in divider. For non-linear conversions, func can be defined instead (the first argument to the function is the value to convert; if mode is 1, the function make the reverse conversion).

A set of standard conversion unit groups are defined in gui/units.c in the Agar sources. The standard groups are summarized below.

GENERAL

agPercentageUnits	Value in percentile
agFrequencyUnits	Units of frequency
agTimeUnits	Units of time

LENGTHS & ANGLES

agLengthUnits	Units of length/distance
agAngleUnits	Units of angular measurement
agVideoUnits	Units of video pixel resolution
agAreaUnits	Units of area
agVolumeUnits	Units of volume
agSpeedUnits	Units of velocity

PHYSICAL

agMassUnits	Units of weight
agPressureUnits	Units of pressure and stress (general)
agVacuumUnits	Units of pressure (low pressures)
agThermalConductivityUnits	Units of thermal conductivity
agThermalExpansionUnits	Units of thermal expansion
agDensityUnits	Units of density
agLightUnits	Units of light intensity
agSubstanceAmountUnits	Units of substance amount (moles)

THERMODYNAMICS

agPowerUnits	Units of power
agTemperatureUnits	Units of temperature
agEnergyPerSubstanceAmountUnits	Units of energy per substance amount
agMolarHeatCapacityUnits	Units of molar heat capacity

ELECTRICAL

agEMFUnits	Units of electromotive force / voltage
agCurrentUnits	Units of electrical current
agResistanceUnits	Units of electrical resistance
agResistanceTC1Units	Units of first-order temperature coefficients
agResistanceTC2Units	Units of second-order temperature coefficients
agResistivityUnits	Units of resistivity of a material
agCapacitanceUnits	Units of electrical capacitance
agInductanceUnits	Units of electrical inductance

INTERFACE

const AG_Unit * AG_FindUnit (const char *key)

const AG_Unit * AG_BestUnit (const AG_Unit *unit_group, double n)

char * AG_UnitFormat (double n, const AG_Unit unit_group[])

const char * AG_UnitAbbr (const AG_Unit *unit)

double AG_Unit2Base (double n, const AG_Unit *unit)

double AG_Base2Unit (double n, const AG_Unit *unit)

double AG_Unit2Unit (double n, const AG_Unit *unit_from, const AG_Unit *unit_to)

The AG_FindUnit() function searches the unit database for a unit matching the given key, and returns a pointer to the unit on success or NULL if none was found.

The AG_BestUnit() function returns the unit expected to yield the least number of non-significant figures when formatting the given number n. AG_UnitFormat() formats the given number n using the best unit in unit_group.

AG_UnitAbbr() returns the abbreviation string associated with the given unit.

The AG_Unit2Base() function converts from n in specified units to the equivalent number of base units. AG_Base2Unit() converts n base units to the equivalent number of specified units.

EXAMPLES

One widget which uses this interface is AG_Numerical(3), which accepts unit arguments. The following code fragment creates a widget for editing a length value given in meters:

float length = 1.234;
AG_Numerical *num;
num = AG_NumericalNewFlt(parent, 0, "m", "Length: ", &length)

The following code fragment prints the equivalent milliseconds for a given n number of seconds:

printf("%f seconds = %f milliseconds", n,
    AG_Base2Unit(n, AG_FindUnit("ms")));

The following code fragment prints the equivalent of 27 degrees Celsius, in kilo Kelvins:

const AG_Unit *degC = AG_FindUnit("degC");
const AG_Unit *kk = AG_FindUnit("kk");

printf("27C = %fkk", AG_Unit2Unit(27.0, degC, kk));

This code fragment displays the value of r using the resistance unit most suitable to its magnitude.

printf("Resistance = %s", AG_UnitFormat(r, agResistanceUnits));

Also see tests/unitconv.c in the Agar source distribution.

HISTORY

The AG_Units facility first appeared in Agar 1.0.