GNOME.org

Transformations

Transformations — Manipulating the current transformation matrix

Synopsis

void                cairo_translate                     (cairo_t *cr,
                                                         double tx,
                                                         double ty);
void                cairo_scale                         (cairo_t *cr,
                                                         double sx,
                                                         double sy);
void                cairo_rotate                        (cairo_t *cr,
                                                         double angle);
void                cairo_transform                     (cairo_t *cr,
                                                         const cairo_matrix_t *matrix);
void                cairo_set_matrix                    (cairo_t *cr,
                                                         const cairo_matrix_t *matrix);
void                cairo_get_matrix                    (cairo_t *cr,
                                                         cairo_matrix_t *matrix);
void                cairo_identity_matrix               (cairo_t *cr);
void                cairo_user_to_device                (cairo_t *cr,
                                                         double *x,
                                                         double *y);
void                cairo_user_to_device_distance       (cairo_t *cr,
                                                         double *dx,
                                                         double *dy);
void                cairo_device_to_user                (cairo_t *cr,
                                                         double *x,
                                                         double *y);
void                cairo_device_to_user_distance       (cairo_t *cr,
                                                         double *dx,
                                                         double *dy);

Description

The current transformation matrix, ctm, is a two-dimensional affine transformation that maps all coordinates and other drawing instruments from the user space into the surface's canonical coordinate system, also known as the device space.

Details

cairo_translate ()

void                cairo_translate                     (cairo_t *cr,
                                                         double tx,
                                                         double ty);

Modifies the current transformation matrix (CTM) by translating the user-space origin by (tx, ty). This offset is interpreted as a user-space coordinate according to the CTM in place before the new call to cairo_translate(). In other words, the translation of the user-space origin takes place after any existing transformation.

cr :

 a cairo context

tx :

 amount to translate in the X direction

ty :

 amount to translate in the Y direction

cairo_scale ()

void                cairo_scale                         (cairo_t *cr,
                                                         double sx,
                                                         double sy);

Modifies the current transformation matrix (CTM) by scaling the X and Y user-space axes by sx and sy respectively. The scaling of the axes takes place after any existing transformation of user space.

cr :

 a cairo context

sx :

 scale factor for the X dimension

sy :

 scale factor for the Y dimension

cairo_rotate ()

void                cairo_rotate                        (cairo_t *cr,
                                                         double angle);

Modifies the current transformation matrix (CTM) by rotating the user-space axes by angle radians. The rotation of the axes takes places after any existing transformation of user space. The rotation direction for positive angles is from the positive X axis toward the positive Y axis.

cr :

 a cairo context

angle :

 angle (in radians) by which the user-space axes will be rotated

cairo_transform ()

void                cairo_transform                     (cairo_t *cr,
                                                         const cairo_matrix_t *matrix);

Modifies the current transformation matrix (CTM) by applying matrix as an additional transformation. The new transformation of user space takes place after any existing transformation.

cr :

 a cairo context

matrix :

 a transformation to be applied to the user-space axes

cairo_set_matrix ()

void                cairo_set_matrix                    (cairo_t *cr,
                                                         const cairo_matrix_t *matrix);

Modifies the current transformation matrix (CTM) by setting it equal to matrix.

cr :

 a cairo context

matrix :

 a transformation matrix from user space to device space

cairo_get_matrix ()

void                cairo_get_matrix                    (cairo_t *cr,
                                                         cairo_matrix_t *matrix);

Stores the current transformation matrix (CTM) into matrix.

cr :

 a cairo context

matrix :

 return value for the matrix

cairo_identity_matrix ()

void                cairo_identity_matrix               (cairo_t *cr);

Resets the current transformation matrix (CTM) by setting it equal to the identity matrix. That is, the user-space and device-space axes will be aligned and one user-space unit will transform to one device-space unit.

cr :

 a cairo context

cairo_user_to_device ()

void                cairo_user_to_device                (cairo_t *cr,
                                                         double *x,
                                                         double *y);

Transform a coordinate from user space to device space by multiplying the given point by the current transformation matrix (CTM).

cr :

 a cairo context

x :

 X value of coordinate (in/out parameter)

y :

 Y value of coordinate (in/out parameter)

cairo_user_to_device_distance ()

void                cairo_user_to_device_distance       (cairo_t *cr,
                                                         double *dx,
                                                         double *dy);

Transform a distance vector from user space to device space. This function is similar to cairo_user_to_device() except that the translation components of the CTM will be ignored when transforming (dx,dy).

cr :

 a cairo context

dx :

 X component of a distance vector (in/out parameter)

dy :

 Y component of a distance vector (in/out parameter)

cairo_device_to_user ()

void                cairo_device_to_user                (cairo_t *cr,
                                                         double *x,
                                                         double *y);

Transform a coordinate from device space to user space by multiplying the given point by the inverse of the current transformation matrix (CTM).

cr :

 a cairo

x :

 X value of coordinate (in/out parameter)

y :

 Y value of coordinate (in/out parameter)

cairo_device_to_user_distance ()

void                cairo_device_to_user_distance       (cairo_t *cr,
                                                         double *dx,
                                                         double *dy);

Transform a distance vector from device space to user space. This function is similar to cairo_device_to_user() except that the translation components of the inverse CTM will be ignored when transforming (dx,dy).

cr :

 a cairo context

dx :

 X component of a distance vector (in/out parameter)

dy :

 Y component of a distance vector (in/out parameter)

See Also

cairo_matrix_t