matrix: Add cogl_matrix_look_at

Similar to the widely used gluLookAt API, this adds a CoglMatrix utility
for setting up a view transform in terms of positioning a camera/eye
position that points to a given object position aligned to a given
world-up vector.

Reviewed-by: Neil Roberts <neil@linux.intel.com>
This commit is contained in:
Robert Bragg 2011-07-09 02:43:17 +01:00
parent 3a2f94045e
commit f37d9bbb4d
3 changed files with 119 additions and 0 deletions

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@ -2051,3 +2051,65 @@ cogl_matrix_is_identity (const CoglMatrix *matrix)
else else
return memcmp (matrix, identity, sizeof (float) * 16) == 0; return memcmp (matrix, identity, sizeof (float) * 16) == 0;
} }
void
cogl_matrix_look_at (CoglMatrix *matrix,
float eye_position_x,
float eye_position_y,
float eye_position_z,
float object_x,
float object_y,
float object_z,
float world_up_x,
float world_up_y,
float world_up_z)
{
CoglMatrix tmp;
CoglVector3 forward;
CoglVector3 side;
CoglVector3 up;
/* Get a unit viewing direction vector */
cogl_vector3_init (&forward,
object_x - eye_position_x,
object_y - eye_position_y,
object_z - eye_position_z);
cogl_vector3_normalize (&forward);
cogl_vector3_init (&up, world_up_x, world_up_y, world_up_z);
/* Take the sideways direction as being perpendicular to the viewing
* direction and the word up vector. */
cogl_vector3_cross_product (&side, &forward, &up);
cogl_vector3_normalize (&side);
/* Now we have unit sideways and forward-direction vectors calculate
* a new mutually perpendicular up vector. */
cogl_vector3_cross_product (&up, &side, &forward);
tmp.xx = side.x;
tmp.yx = side.y;
tmp.zx = side.z;
tmp.wx = 0;
tmp.xy = up.x;
tmp.yy = up.y;
tmp.zy = up.z;
tmp.wy = 0;
tmp.xz = -forward.x;
tmp.yz = -forward.y;
tmp.zz = -forward.z;
tmp.wz = 0;
tmp.xw = 0;
tmp.yw = 0;
tmp.zw = 0;
tmp.ww = 1;
cogl_matrix_translate (&tmp, -eye_position_x, -eye_position_y, -eye_position_z);
tmp.flags = (MAT_FLAG_GENERAL_3D | MAT_DIRTY_TYPE | MAT_DIRTY_INVERSE);
cogl_matrix_multiply (matrix, matrix, &tmp);
}

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@ -193,6 +193,62 @@ cogl_matrix_scale (CoglMatrix *matrix,
float sy, float sy,
float sz); float sz);
#define cogl_matrix_look_at cogl_matrix_look_at_EXP
/**
* cogl_matrix_look_at:
* @matrix: A 4x4 transformation matrix
* @eye_position_x: The X coordinate to look from
* @eye_position_y: The Y coordinate to look from
* @eye_position_z: The Z coordinate to look from
* @object_x: The X coordinate of the object to look at
* @object_y: The Y coordinate of the object to look at
* @object_z: The Z coordinate of the object to look at
* @world_up_x: The X component of the world's up direction vector
* @world_up_y: The Y component of the world's up direction vector
* @world_up_z: The Z component of the world's up direction vector
*
* Applies a view transform @matrix that positions the camera at
* the coordinate (@eye_position_x, @eye_position_y, @eye_position_z)
* looking towards an object at the coordinate (@object_x, @object_y,
* @object_z). The top of the camera is aligned to the given world up
* vector, which is normally simply (0, 1, 0) to map up to the
* positive direction of the y axis.
*
* Because there is a lot of missleading documentation online for
* gluLookAt regarding the up vector we want to try and be a bit
* clearer here.
*
* The up vector should simply be relative to your world coordinates
* and does not need to change as you move the eye and object
* positions. Many online sources may claim that the up vector needs
* to be perpendicular to the vector between the eye and object
* position (partly because the man page is somewhat missleading) but
* that is not necessary for this function.
*
* <note>You should never look directly along the world-up
* vector.</note>
*
* <note>It is assumed you are using a typical projection matrix where
* your origin maps to the center of your viewport.</note>
*
* <note>Almost always when you use this function it should be the first
* transform applied to a new modelview transform</note>
*
* Since: 1.8
* Stability: unstable
*/
void
cogl_matrix_look_at (CoglMatrix *matrix,
float eye_position_x,
float eye_position_y,
float eye_position_z,
float object_x,
float object_y,
float object_z,
float world_up_x,
float world_up_y,
float world_up_z);
/** /**
* cogl_matrix_frustum: * cogl_matrix_frustum:
* @matrix: A 4x4 transformation matrix * @matrix: A 4x4 transformation matrix

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@ -424,6 +424,7 @@ cogl_matrix_free
cogl_matrix_frustum cogl_matrix_frustum
cogl_matrix_ortho cogl_matrix_ortho
cogl_matrix_perspective cogl_matrix_perspective
cogl_matrix_look_at
cogl_matrix_multiply cogl_matrix_multiply
cogl_matrix_rotate cogl_matrix_rotate
cogl_matrix_translate cogl_matrix_translate