Eevee: Update LTC code

Main change are:
- the fresnel LUT is separated from the main GGX LUT.
- LUTs use sqrt(1.0 - NV) as roughness remapping. Improving precision and
  removes needs for acos().
- LTC LUT is normalized by matrix middle component. Improving precision.

source/blender/draw/engines/eevee/eevee_materials.c

@@ -441,7 +441,7 @@ static void eevee_init_noise_texture(void)
 
 static void eevee_init_util_texture(void)
 {
-	const int layers = 3 + 16;
+	const int layers = 4 + 16;
 	float (*texels)[4] = MEM_mallocN(sizeof(float[4]) * 64 * 64 * layers, "utils texels");
 	float (*texels_layer)[4] = texels;
 
@@ -450,12 +450,12 @@ static void eevee_init_util_texture(void)
 	texels_layer += 64 * 64;
 
 	/* Copy bsdf_split_sum_ggx into 2nd layer red and green channels.
-	   Copy ltc_mag_ggx into 2nd layer blue channel. */
+	   Copy ltc_mag_ggx into 2nd layer blue and alpha channel. */
 	for (int i = 0; i < 64 * 64; i++) {
 		texels_layer[i][0] = bsdf_split_sum_ggx[i * 2 + 0];
 		texels_layer[i][1] = bsdf_split_sum_ggx[i * 2 + 1];
-		texels_layer[i][2] = ltc_mag_ggx[i];
-		texels_layer[i][3] = ltc_disk_integral[i];
+		texels_layer[i][2] = ltc_mag_ggx[i * 2 + 0];
+		texels_layer[i][3] = ltc_mag_ggx[i * 2 + 1];
 	}
 	texels_layer += 64 * 64;
 
@@ -468,13 +468,22 @@ static void eevee_init_util_texture(void)
 	}
 	texels_layer += 64 * 64;
 
-	/* Copy Refraction GGX LUT in layer 4 - 20 */
+	/* Copy ltc_disk_integral in 4th layer  */
+	for (int i = 0; i < 64 * 64; i++) {
+		texels_layer[i][0] = ltc_disk_integral[i];
+		texels_layer[i][1] = 0.0; /* UNUSED */
+		texels_layer[i][2] = 0.0; /* UNUSED */
+		texels_layer[i][3] = 0.0; /* UNUSED */
+	}
+	texels_layer += 64 * 64;
+
+	/* Copy Refraction GGX LUT in layer 5 - 21 */
 	for (int j = 0; j < 16; ++j) {
 		for (int i = 0; i < 64 * 64; i++) {
 			texels_layer[i][0] = btdf_split_sum_ggx[j * 2][i];
-			texels_layer[i][1] = btdf_split_sum_ggx[j * 2][i];
-			texels_layer[i][2] = btdf_split_sum_ggx[j * 2][i];
-			texels_layer[i][3] = btdf_split_sum_ggx[j * 2][i];
+			texels_layer[i][1] = 0.0; /* UNUSED */
+			texels_layer[i][2] = 0.0; /* UNUSED */
+			texels_layer[i][3] = 0.0; /* UNUSED */
 		}
 		texels_layer += 64 * 64;
 	}