# SYNOPSIS

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

# DESCRIPTION

The Agar
SK class implements a general-purpose 2D "sketching" engine with dimensioning
and geometrical constraint solving.
Sketches define a set of elements and a set of relations between those
elements.

Elements are organized in a tree (the same structure is used to described group and leaf nodes). Each element in the graph is associated with a transformation matrix. The major sketch elements are points, lines and arcs, but other types can be added through a class registration interface.

Relations represent geometric constraints affecting points, lines, circles, segments and arcs. The following constraints are implemented:

The SK_View(3) widget is commonly used to display and edit SK objects.

Elements are organized in a tree (the same structure is used to described group and leaf nodes). Each element in the graph is associated with a transformation matrix. The major sketch elements are points, lines and arcs, but other types can be added through a class registration interface.

Relations represent geometric constraints affecting points, lines, circles, segments and arcs. The following constraints are implemented:

- Parallelism
- Incidence
- Perpendicularity
- Tangency
- Concentricity
- Colinearity
- Explicit distance
- Explicit angle

The SK_View(3) widget is commonly used to display and edit SK objects.

# INHERITANCE HIERARCHY

AG_Object(3)-> SK.

# INITIALIZATION

The SK_New() function allocates, initializes, and attaches a SK object.

# NODE MANIPULATION

**void**SK_RegisterClass (SK_NodeOps *ops)

**void**SK_NodeInit (void *node, const SK_NodeOps *ops, Uint flags)

**void ***SK_NodeAdd (void *pnode, const SK_NodeOps *ops, Uint flags)

**void**SK_NodeAttach (void *pnode, void *node)

**void**SK_NodeDetach (void *pnode, void *node)

The SK_RegisterClass() function registers a new node class, described by the given

**SK_NodeOps**structure.

The SK_NodeInit() function initializes the given

**SK_Node**structure. It is usually invoked from node constructor functions.

`ops`points to the

**SK_NodeOps**structure which contains class information. The

`flags`argument should be 0. The SK_NodeAdd() variant also allocates, initializes and attaches the node to a parent node.

The SK_NodeAttach() and SK_NodeDetach() functions attach/detach a node to/from a given parent.

# NODE TRANSFORMATIONS

These functions multiply a node's transformation matrix

`T`with a translation, scaling or rotation matrix. They are only aliases for**M_Matrix*** functions, except that they accept a pointer to a node instead of a matrix.**void**SK_Translatev (SK_Node *node, M_Vector3 v)

**void**SK_Translate2 (SK_Node *node, M_Real x, M_Real y)

**void**SK_Scalev (SK_Node *node, M_Vector3 v)

**void**SK_Rotatev (SK_Node *node, M_Real theta, M_Vector3 axis)

**void**SK_Rotatevd (SK_Node *node, M_Real degrees, M_Vector3 axis)

**void**SK_GetNodeTransform (void *node, M_Matrix44 *T)

The SK_Translate*() functions multiply

`T`by a 2D translation matrix.

The SK_Scalev() function multiplies

`T`by a 2D scaling matrix.

SK_Rotate*() multiply

`T`by a 2D rotation matrix. Angles are given in radians, except for SK_Rotate*d() variants which accept angular arguments in degrees.

SK_Rotatev() generates a rotation of

`theta`radians around

`axis`. The SK_Rotate*() variants with the "d" suffix accept angles in degrees instead of radians.

The SK_GetNodeTransform() function returns a matrix which is the product of the transformation matrices of the given node and all of its parents.

# SEE ALSO

# HISTORY

The
SK engine first appeared in
Agar 1.6.0.