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cell: use an approximation in compute_lambda_2d() to avoid sqrt

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Though, the logf() call still needs attention.
This commit is contained in:
Brian Paul 2008-10-17 09:09:57 -06:00
parent 9fa8671c73
commit 81724da4f6
1 changed files with 12 additions and 2 deletions
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14
src/gallium/drivers/cell/spu/spu_texture.c
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@ -414,7 +414,7 @@ sample_texture_2d_bilinear_int(vector float s, vector float t,
/**
* Compute level of detail factor from texcoords.
*/
static float
static INLINE float
compute_lambda_2d(uint unit, vector float s, vector float t)
{
uint baseLevel = 0;
@ -424,11 +424,21 @@ compute_lambda_2d(uint unit, vector float s, vector float t)
float dsdy = width * (spu_extract(s, 2) - spu_extract(s, 0));
float dtdx = height * (spu_extract(t, 1) - spu_extract(t, 0));
float dtdy = height * (spu_extract(t, 2) - spu_extract(t, 0));
#if 0
/* ideal value */
float x = dsdx * dsdx + dtdx * dtdx;
float y = dsdy * dsdy + dtdy * dtdy;
float rho = x > y ? x : y;
rho = sqrtf(rho);
float lambda = logf(rho) * 1.442695f;
#else
/* approximation */
dsdx = fabsf(dsdx);
dsdy = fabsf(dsdy);
dtdx = fabsf(dtdx);
dtdy = fabsf(dtdy);
float rho = (dsdx + dsdy + dtdx + dtdy) * 0.5;
#endif
float lambda = logf(rho) * 1.442695f; /* compute logbase2(rho) */
return lambda;
}