blender/intern/cycles/kernel/geom/geom_curve.h

/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

CCL_NAMESPACE_BEGIN

/* Curve Primitive
 *
 * Curve primitive for rendering hair and fur. These can be render as flat
 * ribbons or curves with actual thickness. The curve can also be rendered as
 * line segments rather than curves for better performance.
 */

#ifdef __HAIR__

/* Reading attributes on various curve elements */

ccl_device float curve_attribute_float(KernelGlobals *kg, const ShaderData *sd, const AttributeDescriptor desc, float *dx, float *dy)
{
	if(desc.element == ATTR_ELEMENT_CURVE) {
#ifdef __RAY_DIFFERENTIALS__
		if(dx) *dx = 0.0f;
		if(dy) *dy = 0.0f;
#endif

		return kernel_tex_fetch(__attributes_float, desc.offset + sd->prim);
	}
	else if(desc.element == ATTR_ELEMENT_CURVE_KEY || desc.element == ATTR_ELEMENT_CURVE_KEY_MOTION) {
		float4 curvedata = kernel_tex_fetch(__curves, sd->prim);
		int k0 = __float_as_int(curvedata.x) + PRIMITIVE_UNPACK_SEGMENT(sd->type);
		int k1 = k0 + 1;

		float f0 = kernel_tex_fetch(__attributes_float, desc.offset + k0);
		float f1 = kernel_tex_fetch(__attributes_float, desc.offset + k1);

#ifdef __RAY_DIFFERENTIALS__
		if(dx) *dx = sd->du.dx*(f1 - f0);
		if(dy) *dy = 0.0f;
#endif

		return (1.0f - sd->u)*f0 + sd->u*f1;
	}
	else {
#ifdef __RAY_DIFFERENTIALS__
		if(dx) *dx = 0.0f;
		if(dy) *dy = 0.0f;
#endif

		return 0.0f;
	}
}

ccl_device float3 curve_attribute_float3(KernelGlobals *kg, const ShaderData *sd, const AttributeDescriptor desc, float3 *dx, float3 *dy)
{
	if(desc.element == ATTR_ELEMENT_CURVE) {
		/* idea: we can't derive any useful differentials here, but for tiled
		 * mipmap image caching it would be useful to avoid reading the highest
		 * detail level always. maybe a derivative based on the hair density
		 * could be computed somehow? */
#ifdef __RAY_DIFFERENTIALS__
		if(dx) *dx = make_float3(0.0f, 0.0f, 0.0f);
		if(dy) *dy = make_float3(0.0f, 0.0f, 0.0f);
#endif

		return float4_to_float3(kernel_tex_fetch(__attributes_float3, desc.offset + sd->prim));
	}
	else if(desc.element == ATTR_ELEMENT_CURVE_KEY || desc.element == ATTR_ELEMENT_CURVE_KEY_MOTION) {
		float4 curvedata = kernel_tex_fetch(__curves, sd->prim);
		int k0 = __float_as_int(curvedata.x) + PRIMITIVE_UNPACK_SEGMENT(sd->type);
		int k1 = k0 + 1;

		float3 f0 = float4_to_float3(kernel_tex_fetch(__attributes_float3, desc.offset + k0));
		float3 f1 = float4_to_float3(kernel_tex_fetch(__attributes_float3, desc.offset + k1));

#ifdef __RAY_DIFFERENTIALS__
		if(dx) *dx = sd->du.dx*(f1 - f0);
		if(dy) *dy = make_float3(0.0f, 0.0f, 0.0f);
#endif

		return (1.0f - sd->u)*f0 + sd->u*f1;
	}
	else {
#ifdef __RAY_DIFFERENTIALS__
		if(dx) *dx = make_float3(0.0f, 0.0f, 0.0f);
		if(dy) *dy = make_float3(0.0f, 0.0f, 0.0f);
#endif

		return make_float3(0.0f, 0.0f, 0.0f);
	}
}

/* Curve thickness */

ccl_device float curve_thickness(KernelGlobals *kg, ShaderData *sd)
{
	float r = 0.0f;

	if(sd->type & PRIMITIVE_ALL_CURVE) {
		float4 curvedata = kernel_tex_fetch(__curves, sd->prim);
		int k0 = __float_as_int(curvedata.x) + PRIMITIVE_UNPACK_SEGMENT(sd->type);
		int k1 = k0 + 1;

		float4 P_curve[2];

		if(sd->type & PRIMITIVE_CURVE) {
			P_curve[0]= kernel_tex_fetch(__curve_keys, k0);
			P_curve[1]= kernel_tex_fetch(__curve_keys, k1);
		}
		else {
			motion_curve_keys(kg, sd->object, sd->prim, sd->time, k0, k1, P_curve);
		}

		r = (P_curve[1].w - P_curve[0].w) * sd->u + P_curve[0].w;
	}

	return r*2.0f;
}

/* Curve location for motion pass, linear interpolation between keys and
 * ignoring radius because we do the same for the motion keys */

ccl_device float3 curve_motion_center_location(KernelGlobals *kg, ShaderData *sd)
{
	float4 curvedata = kernel_tex_fetch(__curves, sd->prim);
	int k0 = __float_as_int(curvedata.x) + PRIMITIVE_UNPACK_SEGMENT(sd->type);
	int k1 = k0 + 1;

	float4 P_curve[2];

	P_curve[0]= kernel_tex_fetch(__curve_keys, k0);
	P_curve[1]= kernel_tex_fetch(__curve_keys, k1);

	return float4_to_float3(P_curve[1]) * sd->u + float4_to_float3(P_curve[0]) * (1.0f - sd->u);
}

/* Curve tangent normal */

ccl_device float3 curve_tangent_normal(KernelGlobals *kg, ShaderData *sd)
{
	float3 tgN = make_float3(0.0f,0.0f,0.0f);

	if(sd->type & PRIMITIVE_ALL_CURVE) {

		tgN = -(-sd->I - sd->dPdu * (dot(sd->dPdu,-sd->I) / len_squared(sd->dPdu)));
		tgN = normalize(tgN);

		/* need to find suitable scaled gd for corrected normal */
#if 0
		tgN = normalize(tgN - gd * sd->dPdu);
#endif
	}

	return tgN;
}

/* Curve bounds utility function */

ccl_device_inline void curvebounds(float *lower, float *upper, float *extremta, float *extrema, float *extremtb, float *extremb, float p0, float p1, float p2, float p3)
{
	float halfdiscroot = (p2 * p2 - 3 * p3 * p1);
	float ta = -1.0f;
	float tb = -1.0f;

	*extremta = -1.0f;
	*extremtb = -1.0f;
	*upper = p0;
	*lower = (p0 + p1) + (p2 + p3);
	*extrema = *upper;
	*extremb = *lower;

	if(*lower >= *upper) {
		*upper = *lower;
		*lower = p0;
	}

	if(halfdiscroot >= 0) {
		float inv3p3 = (1.0f/3.0f)/p3;
		halfdiscroot = sqrtf(halfdiscroot);
		ta = (-p2 - halfdiscroot) * inv3p3;
		tb = (-p2 + halfdiscroot) * inv3p3;
	}

	float t2;
	float t3;

	if(ta > 0.0f && ta < 1.0f) {
		t2 = ta * ta;
		t3 = t2 * ta;
		*extremta = ta;
		*extrema = p3 * t3 + p2 * t2 + p1 * ta + p0;

		*upper = fmaxf(*extrema, *upper);
		*lower = fminf(*extrema, *lower);
	}

	if(tb > 0.0f && tb < 1.0f) {
		t2 = tb * tb;
		t3 = t2 * tb;
		*extremtb = tb;
		*extremb = p3 * t3 + p2 * t2 + p1 * tb + p0;

		*upper = fmaxf(*extremb, *upper);
		*lower = fminf(*extremb, *lower);
	}
}

#endif  /* __HAIR__ */

CCL_NAMESPACE_END