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COGL 0.9.2 Reference Manual | ![]() |
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Top | Description |
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);
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.
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()
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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;
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A 4x4 transformation matrix |
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
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The address of a 4x4 matrix to store the result in |
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A 4x4 transformation matrix |
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A 4x4 transformation matrix |
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.
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A 4x4 transformation matrix |
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The angle you want to rotate in degrees |
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X component of your rotation vector |
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Y component of your rotation vector |
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Z component of your rotation vector |
void cogl_matrix_translate (CoglMatrix *matrix, float x, float y, float z);
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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.
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A 4x4 transformation matrix |
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The X scale factor |
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The Y scale factor |
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The Z scale factor |
void cogl_matrix_init_from_array (CoglMatrix *matrix, const float *array);
This initialises matrix
with the contents of array
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A 4x4 transformation matrix |
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A linear array of 16 floats (column-major order) |
const float * cogl_matrix_get_array (const CoglMatrix *matrix);
This casts a CoglMatrix to a float array which can be directly passed to OpenGL.
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A 4x4 transformation matrix |
Returns : |