static void
set_clip_planes (CoglFramebuffer *framebuffer,
CoglMatrixEntry *modelview_entry,
float x_1,
float y_1,
float x_2,
float y_2)
{
CoglMatrix modelview_matrix;
CoglMatrixStack *projection_stack =
_cogl_framebuffer_get_projection_stack (framebuffer);
CoglMatrix projection_matrix;
CoglMatrix modelview_projection;
float signed_area;
float vertex_tl[4] = { x_1, y_1, 0, 1.0 };
float vertex_tr[4] = { x_2, y_1, 0, 1.0 };
float vertex_bl[4] = { x_1, y_2, 0, 1.0 };
float vertex_br[4] = { x_2, y_2, 0, 1.0 };
cogl_matrix_stack_get (projection_stack, &projection_matrix);
cogl_matrix_entry_get (modelview_entry, &modelview_matrix);
cogl_matrix_multiply (&modelview_projection,
&projection_matrix,
&modelview_matrix);
project_vertex (&modelview_projection, vertex_tl);
project_vertex (&modelview_projection, vertex_tr);
project_vertex (&modelview_projection, vertex_bl);
project_vertex (&modelview_projection, vertex_br);
/* Calculate the signed area of the polygon formed by the four
vertices so that we can know its orientation */
signed_area = (vertex_tl[0] * (vertex_tr[1] - vertex_bl[1])
+ vertex_tr[0] * (vertex_br[1] - vertex_tl[1])
+ vertex_br[0] * (vertex_bl[1] - vertex_tr[1])
+ vertex_bl[0] * (vertex_tl[1] - vertex_br[1]));
/* Set the clip planes to form lines between all of the vertices
using the same orientation as we calculated */
if (signed_area > 0.0f)
{
/* counter-clockwise */
set_clip_plane (framebuffer, GL_CLIP_PLANE0, vertex_tl, vertex_bl);
set_clip_plane (framebuffer, GL_CLIP_PLANE1, vertex_bl, vertex_br);
set_clip_plane (framebuffer, GL_CLIP_PLANE2, vertex_br, vertex_tr);
set_clip_plane (framebuffer, GL_CLIP_PLANE3, vertex_tr, vertex_tl);
}
else
{
/* clockwise */
set_clip_plane (framebuffer, GL_CLIP_PLANE0, vertex_tl, vertex_tr);
set_clip_plane (framebuffer, GL_CLIP_PLANE1, vertex_tr, vertex_br);
set_clip_plane (framebuffer, GL_CLIP_PLANE2, vertex_br, vertex_bl);
set_clip_plane (framebuffer, GL_CLIP_PLANE3, vertex_bl, vertex_tl);
}
}
CoglBool
cogl_matrix_stack_get_inverse (CoglMatrixStack *stack,
CoglMatrix *inverse)
{
CoglMatrix matrix;
CoglMatrix *internal = cogl_matrix_stack_get (stack, &matrix);
if (internal)
return cogl_matrix_get_inverse (internal, inverse);
else
return cogl_matrix_get_inverse (&matrix, inverse);
}
