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llvmpipe: avoid overflow in triangle culling

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Avoid multiplying fixed-point values.  Calculate triangle area in
floating point use that for culling.

Lift area calculations up a level as we are already doing this in the
triangle_both() case.

Would like to share the calculated area with attribute interpolation,
but the way the code is structured makes this difficult.
This commit is contained in:
Keith Whitwell 2010-10-08 17:06:05 +01:00
parent ad6730fadb
commit 29d6a1483d
1 changed files with 38 additions and 39 deletions
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77
src/gallium/drivers/llvmpipe/lp_setup_tri.c
View file

@ -228,7 +228,6 @@ do_triangle_ccw(struct lp_setup_context *setup,
struct lp_rast_triangle *tri;
int x[3];
int y[3];
int area;
struct u_rect bbox;
unsigned tri_bytes;
int i;
@ -312,21 +311,8 @@ do_triangle_ccw(struct lp_setup_context *setup,
tri->plane[1].dcdx = y[1] - y[2];
tri->plane[2].dcdx = y[2] - y[0];
area = (tri->plane[0].dcdy * tri->plane[2].dcdx -
tri->plane[2].dcdy * tri->plane[0].dcdx);
LP_COUNT(nr_tris);
/* Cull non-ccw and zero-sized triangles.
*
* XXX: subject to overflow??
*/
if (area <= 0) {
lp_scene_putback_data( scene, tri_bytes );
LP_COUNT(nr_culled_tris);
return TRUE;
}
/* Setup parameter interpolants:
*/
lp_setup_tri_coef( setup, &tri->inputs, v0, v1, v2, frontfacing );
@ -635,23 +621,36 @@ fail:
/**
* Draw triangle if it's CW, cull otherwise.
* Try to draw the triangle, restart the scene on failure.
*/
static void triangle_cw( struct lp_setup_context *setup,
const float (*v0)[4],
const float (*v1)[4],
const float (*v2)[4] )
static void retry_triangle_ccw( struct lp_setup_context *setup,
const float (*v0)[4],
const float (*v1)[4],
const float (*v2)[4],
boolean front)
{
if (!do_triangle_ccw( setup, v1, v0, v2, !setup->ccw_is_frontface ))
if (!do_triangle_ccw( setup, v0, v1, v2, front ))
{
if (!lp_setup_flush_and_restart(setup))
return;
if (!do_triangle_ccw( setup, v1, v0, v2, !setup->ccw_is_frontface ))
if (!do_triangle_ccw( setup, v0, v1, v2, front ))
return;
}
}
static INLINE float
calc_area(const float (*v0)[4],
const float (*v1)[4],
const float (*v2)[4])
{
float dx01 = v0[0][0] - v1[0][0];
float dy01 = v0[0][1] - v1[0][1];
float dx20 = v2[0][0] - v0[0][0];
float dy20 = v2[0][1] - v0[0][1];
return dx01 * dy20 - dx20 * dy01;
}
/**
* Draw triangle if it's CW, cull otherwise.
@ -661,17 +660,23 @@ static void triangle_cw( struct lp_setup_context *setup,
const float (*v1)[4],
const float (*v2)[4] )
{
if (!do_triangle_ccw( setup, v0, v1, v2, setup->ccw_is_frontface ))
{
if (!lp_setup_flush_and_restart(setup))
return;
float area = calc_area(v0, v1, v2);
if (!do_triangle_ccw( setup, v0, v1, v2, setup->ccw_is_frontface ))
return;
}
if (area < 0.0f)
retry_triangle_ccw(setup, v0, v2, v1, !setup->ccw_is_frontface);
}
static void triangle_ccw( struct lp_setup_context *setup,
const float (*v0)[4],
const float (*v1)[4],
const float (*v2)[4])
{
float area = calc_area(v0, v1, v2);
if (area > 0.0f)
retry_triangle_ccw(setup, v0, v1, v2, setup->ccw_is_frontface);
}
/**
* Draw triangle whether it's CW or CCW.
@ -681,18 +686,12 @@ static void triangle_both( struct lp_setup_context *setup,
const float (*v1)[4],
const float (*v2)[4] )
{
/* edge vectors e = v0 - v2, f = v1 - v2 */
const float ex = v0[0][0] - v2[0][0];
const float ey = v0[0][1] - v2[0][1];
const float fx = v1[0][0] - v2[0][0];
const float fy = v1[0][1] - v2[0][1];
float area = calc_area(v0, v1, v2);
/* det = cross(e,f).z */
const float det = ex * fy - ey * fx;
if (det < 0.0f)
triangle_ccw( setup, v0, v1, v2 );
else if (det > 0.0f)
triangle_cw( setup, v0, v1, v2 );
if (area > 0.0f)
retry_triangle_ccw( setup, v0, v1, v2, setup->ccw_is_frontface );
else if (area < 0.0f)
retry_triangle_ccw( setup, v0, v2, v1, !setup->ccw_is_frontface );
}