Display transformation matrix functions

The display transformation matrix specifies an affine transformation that should be applied to video frames for correct presentation. More...

Functions
double	av_display_rotation_get (const int32_t matrix[9])
	Extract the rotation component of the transformation matrix. More...
void	av_display_rotation_set (int32_t matrix[9], double angle)
	Initialize a transformation matrix describing a pure clockwise rotation by the specified angle (in degrees). More...
void	av_display_matrix_flip (int32_t matrix[9], int hflip, int vflip)
	Flip the input matrix horizontally and/or vertically. More...

Detailed Description

The display transformation matrix specifies an affine transformation that should be applied to video frames for correct presentation.

It is compatible with the matrices stored in the ISO/IEC 14496-12 container format.

The data is a 3x3 matrix represented as a 9-element array:

                               | a b u |
(a, b, u, c, d, v, x, y, w) -> | c d v |
                               | x y w |

All numbers are stored in native endianness, as 16.16 fixed-point values, except for u, v and w, which are stored as 2.30 fixed-point values.

The transformation maps a point (p, q) in the source (pre-transformation) frame to the point (p', q') in the destination (post-transformation) frame as follows:

            | a b u |
(p, q, 1) . | c d v | = z * (p', q', 1)
            | x y w |

The transformation can also be more explicitly written in components as follows:

p' = (a * p + c * q + x) / z;
q' = (b * p + d * q + y) / z;
z  =  u * p + v * q + w

Function Documentation

av_display_rotation_get()

double av_display_rotation_get

(

const int32_t

matrix[9]

)

Extract the rotation component of the transformation matrix.

Parameters

matrix

the transformation matrix

Returns

the angle (in degrees) by which the transformation rotates the frame counterclockwise. The angle will be in range [-180.0, 180.0], or NaN if the matrix is singular.

Note

floating point numbers are inherently inexact, so callers are recommended to round the return value to nearest integer before use.

av_display_rotation_set()

void av_display_rotation_set	(	int32_t	matrix[9],
		double	angle
	)

Initialize a transformation matrix describing a pure clockwise rotation by the specified angle (in degrees).

Parameters

matrix	an allocated transformation matrix (will be fully overwritten by this function)
angle	rotation angle in degrees.

av_display_matrix_flip()

void av_display_matrix_flip	(	int32_t	matrix[9],
		int	hflip,
		int	vflip
	)

Flip the input matrix horizontally and/or vertically.

Parameters

matrix	an allocated transformation matrix
hflip	whether the matrix should be flipped horizontally
vflip	whether the matrix should be flipped vertically