Matrices

Matrices — Fuctions for initializing and manipulating 4x4 matrices.

Synopsis

                    CoglMatrix;
void                cogl_matrix_init_identity           (CoglMatrix *matrix);
void                cogl_matrix_multiply                (CoglMatrix *result,
                                                         const CoglMatrix *a,
                                                         const CoglMatrix *b);
void                cogl_matrix_rotate                  (CoglMatrix *matrix,
                                                         float angle,
                                                         float x,
                                                         float y,
                                                         float z);
void                cogl_matrix_translate               (CoglMatrix *matrix,
                                                         float x,
                                                         float y,
                                                         float z);
void                cogl_matrix_scale                   (CoglMatrix *matrix,
                                                         float sx,
                                                         float sy,
                                                         float sz);
void                cogl_matrix_init_from_array         (CoglMatrix *matrix,
                                                         const float *array);
const float *       cogl_matrix_get_array               (const CoglMatrix *matrix);

Description

Matrices are used in Cogl to describe affine model-view transforms, texture transforms, and projective transforms. This exposes a utility API that can be used for direct manipulation of these matrices.

Details

CoglMatrix

typedef struct {
    /* column 0 */
    float xx;
    float yx;
    float zx;
    float wx;

    /* column 1 */
    float xy;
    float yy;
    float zy;
    float wy;

    /* column 2 */
    float xz;
    float yz;
    float zz;
    float wz;

    /* column 3 */
    float xw;
    float yw;
    float zw;
    float ww;
} CoglMatrix;

A CoglMatrix holds a 4x4 transform matrix. This is a single precision, column-major matrix which means it is compatible with what OpenGL expects.

A CoglMatrix can represent transforms such as, rotations, scaling, translation, sheering, and linear projections. You can combine these transforms by multiplying multiple matrices in the order you want them applied.

The transformation of a vertex (x, y, z, w) by a CoglMatrix is given by:

x_new = xx * x + xy * y + xz * z + xw * w
y_new = yx * x + yy * y + yz * z + yw * w
z_new = zx * x + zy * y + zz * z + zw * w
w_new = wx * x + wy * y + wz * z + ww * w

Where w is normally 1

Note: You must consider the members of the CoglMatrix structure read only, and all matrix modifications must be done via the cogl_matrix API. This allows Cogl to annotate the matrices internally. Violation of this will give undefined results. If you need to initialize a matrix with a constant other than the identity matrix you can use cogl_matrix_init_from_array().


cogl_matrix_init_identity ()

void                cogl_matrix_init_identity           (CoglMatrix *matrix);

Resets matrix to the identity matrix:

.xx=1; .xy=0; .xz=0; .xw=0;
.yx=0; .yy=1; .yz=0; .yw=0;
.zx=0; .zy=0; .zz=1; .zw=0;
.wx=0; .wy=0; .wz=0; .ww=1;

matrix :

A 4x4 transformation matrix

cogl_matrix_multiply ()

void                cogl_matrix_multiply                (CoglMatrix *result,
                                                         const CoglMatrix *a,
                                                         const CoglMatrix *b);

This function multiples the two supplied matricies together and stores the result in result

result :

The address of a 4x4 matrix to store the result in

a :

A 4x4 transformation matrix

b :

A 4x4 transformation matrix

cogl_matrix_rotate ()

void                cogl_matrix_rotate                  (CoglMatrix *matrix,
                                                         float angle,
                                                         float x,
                                                         float y,
                                                         float z);

This function multiples your matrix with a rotation matrix that applies a rotation of angle degrees around the specified 3D vector.

matrix :

A 4x4 transformation matrix

angle :

The angle you want to rotate in degrees

x :

X component of your rotation vector

y :

Y component of your rotation vector

z :

Z component of your rotation vector

cogl_matrix_translate ()

void                cogl_matrix_translate               (CoglMatrix *matrix,
                                                         float x,
                                                         float y,
                                                         float z);

matrix :

x :

y :

z :


cogl_matrix_scale ()

void                cogl_matrix_scale                   (CoglMatrix *matrix,
                                                         float sx,
                                                         float sy,
                                                         float sz);

This function multiples your matrix with a transform matrix that scales along the X, Y and Z axis.

matrix :

A 4x4 transformation matrix

sx :

The X scale factor

sy :

The Y scale factor

sz :

The Z scale factor

cogl_matrix_init_from_array ()

void                cogl_matrix_init_from_array         (CoglMatrix *matrix,
                                                         const float *array);

This initialises matrix with the contents of array

matrix :

A 4x4 transformation matrix

array :

A linear array of 16 floats (column-major order)

cogl_matrix_get_array ()

const float *       cogl_matrix_get_array               (const CoglMatrix *matrix);

This casts a CoglMatrix to a float array which can be directly passed to OpenGL.

matrix :

A 4x4 transformation matrix

Returns :