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widget: Fix gtk_widget_pick() on 3d-transformed widgets

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Picking is done by drawing a line along the parent's z axis and picking
at the intersection with the child's z=0 plane.

However, the previous code was casting a ray along the child's z axis.

This patch actually transforms the line to pick into the target's
coordinate system and then computes the corrrect intersection with the
z=0 plane.

Using graphene_point3d_interpolate() to compute the final intersection
point is a bit of abuse of that function, but I found no better way in
Graphene to achieve the same thing.
This commit is contained in:
Benjamin Otte 2019-03-03 19:40:32 +01:00
parent 8ceff21497
commit bed4c68041
1 changed files with 12 additions and 5 deletions
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17
gtk/gtkwidget.c
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@ -822,13 +822,20 @@ gtk_widget_real_pick (GtkWidget *widget,
GtkWidgetPrivate *priv = gtk_widget_get_instance_private (child);
graphene_matrix_t inv;
GtkWidget *picked;
graphene_point_t p;
graphene_point3d_t p0, p1, res;
graphene_matrix_inverse (&priv->transform, &inv);
graphene_point_init (&p, x, y);
graphene_matrix_transform_point (&inv, &p, &p);
if (!graphene_matrix_inverse (&priv->transform, &inv))
continue;
graphene_point3d_init (&p0, x, y, 0);
graphene_point3d_init (&p1, x, y, 1);
graphene_matrix_transform_point3d (&inv, &p0, &p0);
graphene_matrix_transform_point3d (&inv, &p1, &p1);
if (fabs (p0.z - p1.z) < 1.f / 4096)
continue;
picked = gtk_widget_pick (child, p.x, p.y);
graphene_point3d_interpolate (&p0, &p1, p0.z / (p0.z - p1.z), &res);
picked = gtk_widget_pick (child, res.x, res.y);
if (picked)
return picked;
}