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Transformations

Transformations — Manipulating the current transformation matrix

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.

Functions

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.

Parameters

cr

a cairo context

 

tx

amount to translate in the X direction

 

ty

amount to translate in the Y direction

 

Since: 1.0


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.

Parameters

cr

a cairo context

 

sx

scale factor for the X dimension

 

sy

scale factor for the Y dimension

 

Since: 1.0


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.

Parameters

cr

a cairo context

 

angle

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

 

Since: 1.0


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.

Parameters

cr

a cairo context

 

matrix

a transformation to be applied to the user-space axes

 

Since: 1.0


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 .

Parameters

cr

a cairo context

 

matrix

a transformation matrix from user space to device space

 

Since: 1.0


cairo_get_matrix ()

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

Stores the current transformation matrix (CTM) into matrix .

Parameters

cr

a cairo context

 

matrix

return value for the matrix

 

Since: 1.0


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.

Parameters

cr

a cairo context

 

Since: 1.0


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).

Parameters

cr

a cairo context

 

x

X value of coordinate (in/out parameter)

 

y

Y value of coordinate (in/out parameter)

 

Since: 1.0


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 ).

Parameters

cr

a cairo context

 

dx

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

 

dy

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

 

Since: 1.0


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).

Parameters

cr

a cairo

 

x

X value of coordinate (in/out parameter)

 

y

Y value of coordinate (in/out parameter)

 

Since: 1.0


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 ).

Parameters

cr

a cairo context

 

dx

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

 

dy

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

 

Since: 1.0

Types and Values

See Also

cairo_matrix_t

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