# FreeType-2.2.1 API Reference

# Computations

## Synopsis

| FT_MulDiv |  | FT_Matrix_Invert |  | FT_Tan
| FT_MulFix |  | FT_Angle |  | FT_Atan2
| FT_DivFix |  | FT_ANGLE_PI |  | FT_Angle_Diff
| FT_RoundFix |  | FT_ANGLE_2PI |  | FT_Vector_Unit
| FT_CeilFix |  | FT_ANGLE_PI2 |  | FT_Vector_Rotate
| FT_FloorFix |  | FT_ANGLE_PI4 |  | FT_Vector_Length
| FT_Vector_Transform |  | FT_Sin |  | FT_Vector_Polarize
| FT_Matrix_Multiply |  | FT_Cos |  | FT_Vector_From_Polar

This section contains various functions used to perform computations on 16.16 fixed-float numbers or 2d vectors.

#### FT_MulDiv
      FT_EXPORT( FT_Long )
      FT_MulDiv( FT_Long  a,
                 FT_Long  b,
                 FT_Long  c );
A very simple function used to perform the computation ‘(a*b)/c’ with maximal accuracy (it uses a 64-bit intermediate integer whenever necessary). This function isn't necessarily as fast as some processor specific operations, but is at least completely portable.
input
a | The first multiplier.
b | The second multiplier.
c | The divisor.
return
The result of ‘(a*b)/c’. This function never traps when trying to divide by zero; it simply returns ‘MaxInt’ or ‘MinInt’ depending on the signs of ‘a’ and ‘b’.

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#### FT_MulFix
      FT_EXPORT( FT_Long )
      FT_MulFix( FT_Long  a,
                 FT_Long  b );
A very simple function used to perform the computation ‘(a*b)/0x10000’ with maximal accuracy. Most of the time this is used to multiply a given value by a 16.16 fixed float factor.
input
a | The first multiplier.
b | The second multiplier. Use a 16.16 factor here whenever possible (see note below).
return
The result of ‘(a*b)/0x10000’.
note
This function has been optimized for the case where the absolute value of ‘a’ is less than 2048, and ‘b’ is a 16.16 scaling factor. As this happens mainly when scaling from notional units to fractional pixels in FreeType, it resulted in noticeable speed improvements between versions 2.x and 1.x. As a conclusion, always try to place a 16.16 factor as the second argument of this function; this can make a great difference.

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#### FT_DivFix
      FT_EXPORT( FT_Long )
      FT_DivFix( FT_Long  a,
                 FT_Long  b );
A very simple function used to perform the computation ‘(a*0x10000)/b’ with maximal accuracy. Most of the time, this is used to divide a given value by a 16.16 fixed float factor.
input
a | The first multiplier.
b | The second multiplier. Use a 16.16 factor here whenever possible (see note below).
return
The result of ‘(a*0x10000)/b’.
note
The optimization for FT_DivFix() is simple: If (a << 16) fits in 32 bits, then the division is computed directly. Otherwise, we use a specialized version of FT_MulDiv.

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#### FT_RoundFix
      FT_EXPORT( FT_Fixed )
      FT_RoundFix( FT_Fixed  a );
A very simple function used to round a 16.16 fixed number.
input
a | The number to be rounded.
return
The result of ‘(a + 0x8000) & -0x10000’.

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#### FT_CeilFix
      FT_EXPORT( FT_Fixed )
      FT_CeilFix( FT_Fixed  a );
A very simple function used to compute the ceiling function of a 16.16 fixed number.
input
a | The number for which the ceiling function is to be computed.
return
The result of ‘(a + 0x10000 - 1) & -0x10000’.

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#### FT_FloorFix
      FT_EXPORT( FT_Fixed )
      FT_FloorFix( FT_Fixed  a );
A very simple function used to compute the floor function of a 16.16 fixed number.
input
a | The number for which the floor function is to be computed.
return
The result of ‘a & -0x10000’.

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#### FT_Vector_Transform
      FT_EXPORT( void )
      FT_Vector_Transform( FT_Vector*        vec,
                           const FT_Matrix*  matrix );
Transform a single vector through a 2x2 matrix.
inout
vector | The target vector to transform.
input
matrix | A pointer to the source 2x2 matrix.
note
The result is undefined if either ‘vector’ or ‘matrix’ is invalid.

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#### FT_Matrix_Multiply
      FT_EXPORT( void )
      FT_Matrix_Multiply( const FT_Matrix*  a,
                          FT_Matrix*  b );
Performs the matrix operation ‘b = a*b’.
input
a | A pointer to matrix ‘a’.
inout
b | A pointer to matrix ‘b’.
note
The result is undefined if either ‘a’ or ‘b’ is zero.

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#### FT_Matrix_Invert
      FT_EXPORT( FT_Error )
      FT_Matrix_Invert( FT_Matrix*  matrix );
Inverts a 2x2 matrix. Returns an error if it can't be inverted.
inout
matrix | A pointer to the target matrix. Remains untouched in case of error.
return
FreeType error code. 0 means success.

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#### FT_Angle
      typedef FT_Fixed  FT_Angle;
This type is used to model angle values in FreeType. Note that the angle is a 16.16 fixed float value expressed in degrees.

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#### FT_ANGLE_PI
    #define FT_ANGLE_PI  ( 180L << 16 )
The angle pi expressed in FT_Angle units.

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#### FT_ANGLE_2PI
    #define FT_ANGLE_2PI  ( FT_ANGLE_PI * 2 )
The angle 2*pi expressed in FT_Angle units.

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#### FT_ANGLE_PI2
    #define FT_ANGLE_PI2  ( FT_ANGLE_PI / 2 )
The angle pi/2 expressed in FT_Angle units.

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#### FT_ANGLE_PI4
    #define FT_ANGLE_PI4  ( FT_ANGLE_PI / 4 )
The angle pi/4 expressed in FT_Angle units.

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#### FT_Sin
      FT_EXPORT( FT_Fixed )
      FT_Sin( FT_Angle  angle );
Return the sinus of a given angle in fixed point format.
input
angle | The input angle.
return
The sinus value.
note
If you need both the sinus and cosinus for a given angle, use the function FT_Vector_Unit.

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#### FT_Cos
      FT_EXPORT( FT_Fixed )
      FT_Cos( FT_Angle  angle );
Return the cosinus of a given angle in fixed point format.
input
angle | The input angle.
return
The cosinus value.
note
If you need both the sinus and cosinus for a given angle, use the function FT_Vector_Unit.

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#### FT_Tan
      FT_EXPORT( FT_Fixed )
      FT_Tan( FT_Angle  angle );
Return the tangent of a given angle in fixed point format.
input
angle | The input angle.
return
The tangent value.

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#### FT_Atan2
      FT_EXPORT( FT_Angle )
      FT_Atan2( FT_Fixed  x,
                FT_Fixed  y );
Return the arc-tangent corresponding to a given vector (x,y) in the 2d plane.
input
x | The horizontal vector coordinate.
y | The vertical vector coordinate.
return
The arc-tangent value (i.e. angle).

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#### FT_Angle_Diff
      FT_EXPORT( FT_Angle )
      FT_Angle_Diff( FT_Angle  angle1,
                     FT_Angle  angle2 );
Return the difference between two angles. The result is always constrained to the ]-PI..PI] interval.
input
angle1 | First angle.
angle2 | Second angle.
return
Contrainted value of ‘value2-value1’.

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#### FT_Vector_Unit
      FT_EXPORT( void )
      FT_Vector_Unit( FT_Vector*  vec,
                      FT_Angle    angle );
Return the unit vector corresponding to a given angle. After the call, the value of ‘vec.x’ will be ‘sin(angle)’, and the value of ‘vec.y’ will be ‘cos(angle)’. This function is useful to retrieve both the sinus and cosinus of a given angle quickly.
output
vec | The address of target vector.
input
angle | The address of angle.

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#### FT_Vector_Rotate
      FT_EXPORT( void )
      FT_Vector_Rotate( FT_Vector*  vec,
                        FT_Angle    angle );
Rotate a vector by a given angle.
inout
vec | The address of target vector.
input
angle | The address of angle.

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#### FT_Vector_Length
      FT_EXPORT( FT_Fixed )
      FT_Vector_Length( FT_Vector*  vec );
Return the length of a given vector.
input
vec | The address of target vector.
return
The vector length, expressed in the same units that the original vector coordinates.

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#### FT_Vector_Polarize
      FT_EXPORT( void )
      FT_Vector_Polarize( FT_Vector*  vec,
                          FT_Fixed   *length,
                          FT_Angle   *angle );
Compute both the length and angle of a given vector.
input
vec | The address of source vector.
output
length | The vector length.
angle | The vector angle.

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#### FT_Vector_From_Polar
      FT_EXPORT( void )
      FT_Vector_From_Polar( FT_Vector*  vec,
                            FT_Fixed    length,
                            FT_Angle    angle );
Compute vector coordinates from a length and angle.
output
vec | The address of source vector.
input
length | The vector length.
angle | The vector angle.

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