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app: fix gimp_transform_matrix_generic() 

When the resulting matrix transforms all input points behind the
camera, negate the matrix, instead of failing, which results in a
matrix that transforms the input points to the corresponding points
in front of the camera.  This avoids rejecting certain valid
transforms as invalid, in the generic transform tools (unified,
perspective, and handle transform).

Make the number of input and output points explicit in the
function's signature, and add comments.
This commit is contained in:
Ell 2018-01-31 09:58:31 -05:00
parent 536c65afa0
commit 17ec3d130e
2 changed files with 54 additions and 10 deletions
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60
app/core/gimp-transform-utils.c
View File

@ -424,19 +424,30 @@ mod_gauss (gdouble matrix[],
return TRUE;
}
/* multiplies 'matrix' by the matrix that transforms a set of 4 'input_points'
* to corresponding 'output_points', if such matrix exists, and is valid (i.e.,
* keeps the output points in front of the camera).
*
* returns TRUE if successful.
*/
gboolean
gimp_transform_matrix_generic (GimpMatrix3 *matrix,
const GimpVector2 *input_points,
const GimpVector2 *output_points)
const GimpVector2 input_points[4],
const GimpVector2 output_points[4])
{
GimpMatrix3 trafo;
gdouble coeff[8 * 9];
gboolean negative;
gint i;
g_return_val_if_fail (matrix != NULL, FALSE);
g_return_val_if_fail (input_points != NULL, FALSE);
g_return_val_if_fail (output_points != NULL, FALSE);
/* find the matrix that transforms 'input_points' to 'output_points', whose
* (3, 3) coeffcient is 1, by solving a system of linear equations whose
* solution is the remaining 8 coefficients.
*/
for (i = 0; i < 4; i++)
{
coeff[i * 9 + 0] = input_points[i].x;
@ -460,23 +471,56 @@ gimp_transform_matrix_generic (GimpMatrix3 *matrix,
coeff[(i + 4) * 9 + 8] = output_points[i].y;
}
/* if there is no solution, bail */
if (! mod_gauss (coeff, (gdouble *) trafo.coeff, 8))
return FALSE;
trafo.coeff[2][2] = 1.0;
gimp_matrix3_mult (&trafo, matrix);
/* make sure that none of the input points maps to a point at infinity, and
* that all output points are on the same side of the camera.
*/
for (i = 0; i < 4; i++)
{
gdouble w = matrix->coeff[2][0] * input_points[i].x +
matrix->coeff[2][1] * input_points[i].y +
matrix->coeff[2][2];
gdouble w;
gboolean neg;
if (w <= EPSILON)
w = trafo.coeff[2][0] * input_points[i].x +
trafo.coeff[2][1] * input_points[i].y +
trafo.coeff[2][2];
if (fabs (w) <= EPSILON)
return FALSE;
neg = (w < 0.0);
if (i == 0)
negative = neg;
else if (neg != negative)
return FALSE;
}
/* if the output points are all behind the camera, negate the matrix, which
* would map the input points to the corresponding points in front of the
* camera.
*/
if (negative)
{
gint r;
gint c;
for (r = 0; r < 3; r++)
{
for (c = 0; c < 3; c++)
{
trafo.coeff[r][c] = -trafo.coeff[r][c];
}
}
}
/* append the transformation to 'matrix' */
gimp_matrix3_mult (&trafo, matrix);
return TRUE;
}

4
app/core/gimp-transform-utils.h
View File

@ -89,8 +89,8 @@ void gimp_transform_matrix_perspective (GimpMatrix3 *matrix,
gdouble t_x4,
gdouble t_y4);
gboolean gimp_transform_matrix_generic (GimpMatrix3 *matrix,
const GimpVector2 *input_points,
const GimpVector2 *output_points);
const GimpVector2 input_points[4],
const GimpVector2 output_points[4]);
gboolean gimp_transform_polygon_is_convex (gdouble x1,
gdouble y1,