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-rw-r--r--src/mesa/pipe/softpipe/sp_headers.h2
-rw-r--r--src/mesa/pipe/softpipe/sp_prim_setup.c22
2 files changed, 15 insertions, 9 deletions
diff --git a/src/mesa/pipe/softpipe/sp_headers.h b/src/mesa/pipe/softpipe/sp_headers.h
index 82f03ec078..cd2dc984c5 100644
--- a/src/mesa/pipe/softpipe/sp_headers.h
+++ b/src/mesa/pipe/softpipe/sp_headers.h
@@ -74,7 +74,7 @@ struct quad_header {
GLint x0;
GLint y0;
GLuint mask;
- GLuint facing; /**< Front or back facing? */
+ GLuint facing; /**< Front (0) or back (1) facing? */
struct {
GLfloat color[4][QUAD_SIZE]; /* rrrr, gggg, bbbb, aaaa */
diff --git a/src/mesa/pipe/softpipe/sp_prim_setup.c b/src/mesa/pipe/softpipe/sp_prim_setup.c
index 8e43f5d04d..332113979c 100644
--- a/src/mesa/pipe/softpipe/sp_prim_setup.c
+++ b/src/mesa/pipe/softpipe/sp_prim_setup.c
@@ -279,26 +279,32 @@ static GLboolean setup_sort_vertices( struct setup_stage *setup,
setup->etop.dx = setup->vmax->data[0][0] - setup->vmid->data[0][0];
setup->etop.dy = setup->vmax->data[0][1] - setup->vmid->data[0][1];
- /* xxx: may need to adjust this sign according to the if-tree
- * above:
+ /*
+ * Compute triangle's area. Use 1/area to compute partial
+ * derivatives of attributes later.
*
- * XXX: this is like 'det', but calculated from screen coords??
+ * The area will be the same as prim->det, but the sign may be
+ * different depending on how the vertices get sorted above.
+ *
+ * To determine whether the primitive is front or back facing we
+ * use the prim->det value because its sign is correct.
*/
{
const GLfloat area = (setup->emaj.dx * setup->ebot.dy -
setup->ebot.dx * setup->emaj.dy);
setup->oneoverarea = 1.0 / area;
+ /*
+ _mesa_printf("%s one-over-area %f area %f det %f\n",
+ __FUNCTION__, setup->oneoverarea, area, prim->det );
+ */
}
- /* XXX need to know if this is a front or back-facing triangle:
+ /* We need to know if this is a front or back-facing triangle for:
* - the GLSL gl_FrontFacing fragment attribute (bool)
* - two-sided stencil test
*/
- setup->quad.facing = 0;
-
- _mesa_printf("%s one-over-area %f\n", __FUNCTION__, setup->oneoverarea );
-
+ setup->quad.facing = (prim->det > 0.0) ^ (setup->softpipe->setup.front_winding == PIPE_WINDING_CW);
return GL_TRUE;
}