gui/src/camera_path.cu

/*
 * SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 * SPDX-License-Identifier: Apache-2.0
 *
 * 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.
 */

/** @file   camera_path.cpp
 *  @author Thomas Müller & Alex Evans, NVIDIA
 */

#include <neural-graphics-primitives/camera_path.h>
#include <neural-graphics-primitives/common.h>
#include <neural-graphics-primitives/json_binding.h>

#ifdef NGP_GUI
#	include <imgui/imgui.h>
#	include <imguizmo/ImGuizmo.h>
#endif

#include <fstream>
#include <json/json.hpp>

using namespace nlohmann;

namespace ngp {

CameraKeyframe lerp(const CameraKeyframe& p0, const CameraKeyframe& p1, float t, float t0, float t1) {
	t = (t - t0) / (t1 - t0);
	quat R1 = p1.R;

	// take the short path
	if (dot(R1, p0.R) < 0.0f) {
		R1 = -R1;
	}

	return {
		normalize(slerp(p0.R, R1, t)),
		p0.T + (p1.T - p0.T) * t,
		p0.fov + (p1.fov - p0.fov) * t,
		p0.timestamp + (p1.timestamp - p0.timestamp) * t,
	};
}

CameraKeyframe normalize(const CameraKeyframe& p0) {
	CameraKeyframe result = p0;
	result.R = normalize(result.R);
	return result;
}

CameraKeyframe spline_cm(float t, const CameraKeyframe& p0, const CameraKeyframe& p1, const CameraKeyframe& p2, const CameraKeyframe& p3) {
	CameraKeyframe q0 = lerp(p0, p1, t, -1.f, 0.f);
	CameraKeyframe q1 = lerp(p1, p2, t, 0.f, 1.f);
	CameraKeyframe q2 = lerp(p2, p3, t, 1.f, 2.f);
	CameraKeyframe r0 = lerp(q0, q1, t, -1.f, 1.f);
	CameraKeyframe r1 = lerp(q1, q2, t, 0.f, 2.f);
	return lerp(r0, r1, t, 0.f, 1.f);
}

CameraKeyframe spline_cubic(float t, const CameraKeyframe& p0, const CameraKeyframe& p1, const CameraKeyframe& p2, const CameraKeyframe& p3) {
	float tt = t * t;
	float ttt = t * t * t;
	float a = (1 - t) * (1 - t) * (1 - t) * (1.f / 6.f);
	float b = (3.f * ttt - 6.f * tt + 4.f) * (1.f / 6.f);
	float c = (-3.f * ttt + 3.f * tt + 3.f * t + 1.f) * (1.f / 6.f);
	float d = ttt * (1.f / 6.f);
	return normalize(p0 * a + p1 * b + p2 * c + p3 * d);
}

CameraKeyframe spline_quadratic(float t, const CameraKeyframe& p0, const CameraKeyframe& p1, const CameraKeyframe& p2) {
	float tt = t * t;
	float a = (1 - t) * (1 - t) * 0.5f;
	float b = (-2.f * tt + 2.f * t + 1.f) * 0.5f;
	float c = tt * 0.5f;
	return normalize(p0 * a + p1 * b + p2 * c);
}

CameraKeyframe spline_linear(float t, const CameraKeyframe& p0, const CameraKeyframe& p1) { return normalize(p0 * (1.0f - t) + p1 * t); }

void to_json(json& j, const CameraKeyframe& p) {
	j = json{
		{"R",         p.R        },
		{"T",         p.T        },
		{"fov",       p.fov      },
		{"timestamp", p.timestamp},
	};
}

bool load_relative_to_first = false; // set to true when using a camera path that is aligned with the first training image, such that it is
                                     // invariant to changes in the space of the training data

void from_json(bool is_first, const json& j, CameraKeyframe& p, const CameraKeyframe& first, const mat4x3& ref) {
	if (is_first && load_relative_to_first) {
		p.from_m(ref);
	} else {
		p.R = j.at("R");
		p.T = j.at("T");

		if (load_relative_to_first) {
			mat4 ref4 = {ref};
			mat4 first4 = {first.m()};
			mat4 p4 = {p.m()};
			p.from_m(mat4x3(ref4 * inverse(first4) * p4));
		}
	}
	j.at("fov").get_to(p.fov);
	if (j.contains("timestamp")) {
		j.at("timestamp").get_to(p.timestamp);
	} else {
		p.timestamp = 0.f;
	}
}

void CameraPath::save(const fs::path& path) {
	json j = {
		{"loop",             loop              },
		{"time",             play_time         },
		{"path",             keyframes         },
		{"duration_seconds", duration_seconds()},
		{"spline_order",     spline_order      },
	};
	std::ofstream f(native_string(path));
	f << j;
}

void CameraPath::load(const fs::path& path, const mat4x3& first_xform) {
	std::ifstream f{native_string(path)};
	if (!f) {
		throw std::runtime_error{fmt::format("Camera path {} does not exist.", path.str())};
	}

	json j;
	f >> j;

	CameraKeyframe first;

	keyframes.clear();
	if (j.contains("loop")) {
		loop = j["loop"];
	}
	if (j.contains("time")) {
		play_time = j["time"];
	}
	if (j.contains("path")) {
		for (auto& el : j["path"]) {
			CameraKeyframe p;
			bool is_first = keyframes.empty();
			from_json(is_first, el, p, first, first_xform);
			if (is_first) {
				first = p;
			}
			keyframes.push_back(p);
		}
	}

	spline_order = j.value("spline_order", 3);
	sanitize_keyframes();

	play_time = 0.0f;

	if (keyframes.size() >= 16) {
		keyframe_subsampling = keyframes.size() - 1;
		editing_kernel_type = EEditingKernel::Gaussian;
	}
}

void CameraPath::add_camera(const mat4x3& camera, float fov, float timestamp) {
	int n = std::max(0, int(keyframes.size()) - 1);
	int i = (int)ceil(play_time * (float)n + 0.001f);
	if (i > keyframes.size()) {
		i = keyframes.size();
	}
	if (i < 0) {
		i = 0;
	}
	keyframes.insert(keyframes.begin() + i, CameraKeyframe(camera, fov, timestamp));
	update_cam_from_path = false;
	play_time = get_playtime(i);

	sanitize_keyframes();
}

float editing_kernel(float x, EEditingKernel kernel) {
	x = kernel == EEditingKernel::Gaussian ? x : clamp(x, -1.0f, 1.0f);
	switch (kernel) {
		case EEditingKernel::Gaussian: return expf(-2.0f * x * x);
		case EEditingKernel::Quartic: return (1.0f - x * x) * (1.0f - x * x);
		case EEditingKernel::Hat: return 1.0f - fabsf(x);
		case EEditingKernel::Box: return x > -1.0f && x < 1.0f ? 1.0f : 0.0f;
		case EEditingKernel::None: return fabs(x) < 0.0001f ? 1.0f : 0.0f;
		default: throw std::runtime_error{"Unknown editing kernel"};
	}
}

#ifdef NGP_GUI
int CameraPath::imgui(char path_filename_buf[1024], float frame_milliseconds, const mat4x3& camera, float fov, const mat4x3& first_xform) {
	int n = std::max(0, int(keyframes.size()) - 1);
	int read = 0; // 1=smooth, 2=hard

	ImGui::InputText("##PathFile", path_filename_buf, 1024);
	ImGui::SameLine();
	static std::string camera_path_load_error_string = "";

	if (rendering) {
		ImGui::BeginDisabled();
	}

	if (ImGui::Button("Load")) {
		try {
			load(path_filename_buf, first_xform);
		} catch (const std::exception& e) {
			ImGui::OpenPopup("Camera path load error");
			camera_path_load_error_string = std::string{"Failed to load camera path: "} + e.what();
		}
	}

	if (rendering) {
		ImGui::EndDisabled();
	}

	if (ImGui::BeginPopupModal("Camera path load error", NULL, ImGuiWindowFlags_AlwaysAutoResize)) {
		ImGui::Text("%s", camera_path_load_error_string.c_str());
		if (ImGui::Button("OK", ImVec2(120, 0))) {
			ImGui::CloseCurrentPopup();
		}
		ImGui::EndPopup();
	}

	if (!keyframes.empty()) {
		ImGui::SameLine();
		if (ImGui::Button("Save")) {
			save(path_filename_buf);
		}
	}

	if (rendering) {
		ImGui::BeginDisabled();
	}

	if (ImGui::Button("Add from cam")) {
		const float duration = duration_seconds();
		add_camera(camera, fov, 0.0f);
		make_keyframe_timestamps_equidistant(duration);
		read = 2;
	}

	auto p = get_pos(play_time);

	if (!keyframes.empty()) {
		ImGui::SameLine();
		if (ImGui::Button("Split")) {
			update_cam_from_path = false;
			int i = clamp(p.kfidx + 1, 0, (int)keyframes.size());
			const float duration = duration_seconds();
			keyframes.insert(keyframes.begin() + i, eval_camera_path(play_time));
			make_keyframe_timestamps_equidistant(duration);
			play_time = get_playtime(i);
			read = 2;
		}
		ImGui::SameLine();

		int i = p.kfidx;
		if (!loop) {
			i += (int)round(p.t);
		}

		if (ImGui::Button("|<")) {
			play_time = 0.f;
			read = 2;
		}
		ImGui::SameLine();
		if (ImGui::Button("<")) {
			play_time = n ? (get_playtime(i - 1) + 0.0001f) : 0.f;
			read = 2;
		}
		ImGui::SameLine();
		if (ImGui::Button(update_cam_from_path ? "Stop" : "Read")) {
			update_cam_from_path = !update_cam_from_path;
			read = 2;
		}
		ImGui::SameLine();
		if (ImGui::Button(">")) {
			play_time = n ? (get_playtime(i + 1) + 0.0001f) : 1.0f;
			read = 2;
		}
		ImGui::SameLine();
		if (ImGui::Button(">|")) {
			play_time = 1.0f;
			read = 2;
		}
		ImGui::SameLine();
		if (ImGui::Button("Dup")) {
			update_cam_from_path = false;
			const float duration = duration_seconds();
			keyframes.insert(keyframes.begin() + i, keyframes[i]);
			make_keyframe_timestamps_equidistant(duration);
			play_time = get_playtime(i);
			read = 2;
		}
		ImGui::SameLine();
		if (ImGui::Button("Del")) {
			update_cam_from_path = false;
			const float duration = duration_seconds();
			keyframes.erase(keyframes.begin() + i);
			make_keyframe_timestamps_equidistant(duration);
			play_time = get_playtime(i - 1);
			read = 2;
		}
		ImGui::SameLine();
		if (ImGui::Button("Set")) {
			keyframes[i] = CameraKeyframe(camera, fov, keyframes[i].timestamp);
			read = 2;
			if (n) {
				play_time = get_playtime(i);
			}
		}

		if (ImGui::RadioButton("Translate", m_gizmo_op == ImGuizmo::TRANSLATE)) {
			m_gizmo_op = ImGuizmo::TRANSLATE;
		}
		ImGui::SameLine();
		if (ImGui::RadioButton("Rotate", m_gizmo_op == ImGuizmo::ROTATE)) {
			m_gizmo_op = ImGuizmo::ROTATE;
		}
		ImGui::SameLine();
		if (ImGui::RadioButton("Local", m_gizmo_mode == ImGuizmo::LOCAL)) {
			m_gizmo_mode = ImGuizmo::LOCAL;
		}
		ImGui::SameLine();
		if (ImGui::RadioButton("World", m_gizmo_mode == ImGuizmo::WORLD)) {
			m_gizmo_mode = ImGuizmo::WORLD;
		}
		ImGui::SameLine();
		ImGui::Checkbox("Loop path", &loop);

		if (ImGui::Button("Start") && !keyframes.empty()) {
			auto_play_speed = 0.0f;
			play_time = 0.0f;
			read = 2;
		}
		ImGui::SameLine();
		if (ImGui::Button("Rev") && !keyframes.empty()) {
			auto_play_speed = -1.0f / duration_seconds();
		}
		ImGui::SameLine();
		if (ImGui::Button(auto_play_speed != 0 ? "Pause" : "Play") && !keyframes.empty()) {
			auto_play_speed = auto_play_speed == 0.0f ? (1.0f / duration_seconds()) : 0.0f;
		}
		ImGui::SameLine();
		if (ImGui::Button("End") && !keyframes.empty()) {
			auto_play_speed = 0.0f;
			play_time = 1.0f;
			read = 2;
		}

		ImGui::SliderFloat("Playback speed", &auto_play_speed, -1.0f, 1.0f);
		if (auto_play_speed != 0.0f) {
			float prev = play_time;
			play_time = clamp(play_time + auto_play_speed * (frame_milliseconds / 1000.f), 0.0f, 1.0f);

			if (play_time != prev) {
				read = 1;
			}
		}

		if (ImGui::SliderFloat("Camera path time", &play_time, 0.0f, 1.0f)) {
			read = 1;
		}
		ImGui::Text("Current keyframe %d/%d:", i, n + 1);

		if (ImGui::SliderFloat("Field of view", &keyframes[i].fov, 0.0f, 120.0f)) {
			read = 2;
		}
		if (ImGui::Button("Apply to all keyframes")) {
			for (auto& k : keyframes) {
				k.fov = keyframes[i].fov;
			}
		}


		if (ImGui::TreeNodeEx("Batch keyframe editing")) {
			ImGui::Combo("Editing kernel", (int*)&editing_kernel_type, EditingKernelStr);
			ImGui::SliderFloat(
				"Editing kernel radius", &editing_kernel_radius, 0.001f, 10.0f, "%.4f", ImGuiSliderFlags_Logarithmic | ImGuiSliderFlags_NoRoundToFormat
			);

			ImGui::TreePop();
		}

		if (ImGui::TreeNodeEx("Advanced camera path settings")) {
			ImGui::SliderInt("Spline order", &spline_order, 0, 3);
			ImGui::SliderInt("Keyframe subsampling", &keyframe_subsampling, 1, max((int)keyframes.size() - 1, 1));
			ImGui::TreePop();
		}
	}

	if (rendering) {
		ImGui::EndDisabled();
	}

	return keyframes.empty() ? 0 : read;
}

bool debug_project(const mat4& proj, vec3 p, ImVec2& o) {
	vec4 ph{p.x, p.y, p.z, 1.0f};
	vec4 pa = proj * ph;
	if (pa.w <= 0.f) {
		return false;
	}

	o.x = pa.x / pa.w;
	o.y = pa.y / pa.w;
	return true;
}

void add_debug_line(ImDrawList* list, const mat4& proj, vec3 a, vec3 b, uint32_t col, float thickness) {
	ImVec2 aa, bb;
	if (debug_project(proj, a, aa) && debug_project(proj, b, bb)) {
		list->AddLine(aa, bb, col, thickness * 2.0f);
	}
}

void visualize_cube(ImDrawList* list, const mat4& world2proj, const vec3& a, const vec3& b, const mat3& render_aabb_to_local) {
	mat3 m = transpose(render_aabb_to_local);
	add_debug_line(list, world2proj, m * vec3{a.x, a.y, a.z}, m * vec3{a.x, a.y, b.z}, 0xffff4040); // Z
	add_debug_line(list, world2proj, m * vec3{b.x, a.y, a.z}, m * vec3{b.x, a.y, b.z}, 0xffffffff);
	add_debug_line(list, world2proj, m * vec3{a.x, b.y, a.z}, m * vec3{a.x, b.y, b.z}, 0xffffffff);
	add_debug_line(list, world2proj, m * vec3{b.x, b.y, a.z}, m * vec3{b.x, b.y, b.z}, 0xffffffff);

	add_debug_line(list, world2proj, m * vec3{a.x, a.y, a.z}, m * vec3{b.x, a.y, a.z}, 0xff4040ff); // X
	add_debug_line(list, world2proj, m * vec3{a.x, b.y, a.z}, m * vec3{b.x, b.y, a.z}, 0xffffffff);
	add_debug_line(list, world2proj, m * vec3{a.x, a.y, b.z}, m * vec3{b.x, a.y, b.z}, 0xffffffff);
	add_debug_line(list, world2proj, m * vec3{a.x, b.y, b.z}, m * vec3{b.x, b.y, b.z}, 0xffffffff);

	add_debug_line(list, world2proj, m * vec3{a.x, a.y, a.z}, m * vec3{a.x, b.y, a.z}, 0xff40ff40); // Y
	add_debug_line(list, world2proj, m * vec3{b.x, a.y, a.z}, m * vec3{b.x, b.y, a.z}, 0xffffffff);
	add_debug_line(list, world2proj, m * vec3{a.x, a.y, b.z}, m * vec3{a.x, b.y, b.z}, 0xffffffff);
	add_debug_line(list, world2proj, m * vec3{b.x, a.y, b.z}, m * vec3{b.x, b.y, b.z}, 0xffffffff);
}

void visualize_camera(ImDrawList* list, const mat4& world2proj, const mat4x3& xform, float aspect, uint32_t col, float thickness) {
	const float axis_size = 0.025f;
	const vec3* xforms = (const vec3*)&xform;
	vec3 pos = xforms[3];
	add_debug_line(list, world2proj, pos, pos + axis_size * xforms[0], 0xff4040ff, thickness);
	add_debug_line(list, world2proj, pos, pos + axis_size * xforms[1], 0xff40ff40, thickness);
	add_debug_line(list, world2proj, pos, pos + axis_size * xforms[2], 0xffff4040, thickness);
	float xs = axis_size * aspect;
	float ys = axis_size;
	float zs = axis_size * 2.0f * aspect;
	vec3 a = pos + xs * xforms[0] + ys * xforms[1] + zs * xforms[2];
	vec3 b = pos - xs * xforms[0] + ys * xforms[1] + zs * xforms[2];
	vec3 c = pos - xs * xforms[0] - ys * xforms[1] + zs * xforms[2];
	vec3 d = pos + xs * xforms[0] - ys * xforms[1] + zs * xforms[2];
	add_debug_line(list, world2proj, pos, a, col, thickness);
	add_debug_line(list, world2proj, pos, b, col, thickness);
	add_debug_line(list, world2proj, pos, c, col, thickness);
	add_debug_line(list, world2proj, pos, d, col, thickness);
	add_debug_line(list, world2proj, a, b, col, thickness);
	add_debug_line(list, world2proj, b, c, col, thickness);
	add_debug_line(list, world2proj, c, d, col, thickness);
	add_debug_line(list, world2proj, d, a, col, thickness);
}

bool CameraPath::has_valid_timestamps() const {
	float prev_timestamp = 0.0f;
	for (size_t i = 0; i < keyframes.size(); ++i) {
		if (!(keyframes[i].timestamp > prev_timestamp)) {
			return false;
		}

		prev_timestamp = keyframes[i].timestamp;
	}

	return true;
}

void CameraPath::make_keyframe_timestamps_equidistant(const float duration_seconds) {
	const float sanitized_duration = duration_seconds > 0.0f ? duration_seconds : default_duration_seconds;
	for (size_t i = 0; i < keyframes.size(); ++i) {
		keyframes[i].timestamp = sanitized_duration * (i + 1) / (float)keyframes.size();
	}
}

void CameraPath::sanitize_keyframes() {
	if (has_valid_timestamps()) {
		return;
	}

	// Timestamps are invalid. Best effort is to equally space all frames. Default to 3 seconds duration.
	make_keyframe_timestamps_equidistant(default_duration_seconds);
}

float CameraPath::duration_seconds() const {
	if (keyframes.empty()) {
		return 0.0f;
	}

	return keyframes.back().timestamp;
}

void CameraPath::set_duration_seconds(const float duration) {
	const float old_duration = duration_seconds();
	if (!(old_duration > 0.0f)) {
		make_keyframe_timestamps_equidistant(duration);
		return;
	}

	const float multiplier = duration / old_duration;
	for (auto& kf : keyframes) {
		kf.timestamp *= multiplier;
	}
}

CameraPath::Pos CameraPath::get_pos(float playtime) {
	if (keyframes.empty()) {
		return {-1, 0.0f};
	} else if (keyframes.size() == 1) {
		return {0, playtime};
	}

	const float duration = loop ? keyframes.back().timestamp : keyframes[keyframes.size() - 2].timestamp;
	playtime *= duration;

	CameraKeyframe dummy;
	dummy.timestamp = playtime;

	// Binary search to obtain relevant keyframe in O(log(n_keyframes)) time
	auto it = std::upper_bound(keyframes.begin(), keyframes.end(), dummy, [](const auto& a, const auto& b) {
		return a.timestamp < b.timestamp;
	});

	int i = clamp((int)std::distance(keyframes.begin(), it), 0, (int)keyframes.size() - (loop ? 1 : 2));
	float prev_timestamp = i == 0 ? 0.0f : keyframes[i - 1].timestamp;

	return {
		i,
		(playtime - prev_timestamp) / (keyframes[i].timestamp - prev_timestamp),
	};
}

bool CameraPath::imgui_viz(
	ImDrawList* list,
	mat4& view2proj,
	mat4& world2proj,
	mat4& world2view,
	vec2 focal,
	float aspect,
	float znear,
	float zfar
) {
	bool changed = false;
	// float flx = focal.x;
	float fly = focal.y;
	mat4 view2proj_guizmo = transpose(
		mat4{
			fly * 2.0f / aspect,
			0.0f,
			0.0f,
			0.0f,
			0.0f,
			-fly * 2.0f,
			0.0f,
			0.0f,
			0.0f,
			0.0f,
			(zfar + znear) / (zfar - znear),
			-(2.0f * zfar * znear) / (zfar - znear),
			0.0f,
			0.0f,
			1.0f,
			0.0f,
		}
	);

	if (!update_cam_from_path && !keyframes.empty()) {
		auto p = get_pos(play_time);
		int cur_cam_i = p.kfidx;
		if (!loop) {
			cur_cam_i += (int)round(p.t);
		}

		vec3 prevp;
		for (int i = 0; i < keyframes.size(); i += max(min(keyframe_subsampling, (int)keyframes.size() - 1 - i), 1)) {
			visualize_camera(list, world2proj, keyframes[i].m(), aspect, (i == cur_cam_i) ? 0xff80c0ff : 0x8080c0ff);
			vec3 p = keyframes[i].T;
			if (i && keyframe_subsampling == 1) {
				add_debug_line(list, world2proj, prevp, p, 0xccffc040);
			}
			prevp = p;
		}

		ImGuiIO& io = ImGui::GetIO();
		mat4 matrix = keyframes[cur_cam_i].m();
		ImGuizmo::SetRect(0, 0, io.DisplaySize.x, io.DisplaySize.y);
		if (ImGuizmo::Manipulate(
				(const float*)&world2view,
				(const float*)&view2proj_guizmo,
				(ImGuizmo::OPERATION)m_gizmo_op,
				(ImGuizmo::MODE)m_gizmo_mode,
				(float*)&matrix,
				NULL,
				NULL
			)) {
			// Find overlapping keypoints...
			int i0 = cur_cam_i;
			while (i0 > 0 && keyframes[cur_cam_i].same_pos_as(keyframes[i0 - 1])) {
				i0--;
			}
			int i1 = cur_cam_i;
			while (i1 < keyframes.size() - 1 && keyframes[cur_cam_i].same_pos_as(keyframes[i1 + 1])) {
				i1++;
			}

			vec3 tdiff = matrix[3].xyz() - keyframes[cur_cam_i].T;
			mat3 rdiff = mat_log(mat3(matrix) * inverse(to_mat3(normalize(keyframes[cur_cam_i].R))));

			for (int i = 0; i < keyframes.size(); ++i) {
				float x = (get_playtime(i) - get_playtime(cur_cam_i)) / editing_kernel_radius;
				float w = editing_kernel(x, editing_kernel_type);

				keyframes[i].T += w * tdiff;
				keyframes[i].R = quat(mat_exp(w * rdiff) * to_mat3(normalize(keyframes[i].R)));
			}

			// ...and ensure overlapping keypoints were edited exactly in tandem
			for (int i = i0; i <= i1; ++i) {
				keyframes[i].T = keyframes[cur_cam_i].T;
				keyframes[i].R = keyframes[cur_cam_i].R;
			}

			changed = true;
		}

		visualize_camera(list, world2proj, eval_camera_path(play_time).m(), aspect, 0xff80ff80);

		float dt = 0.001f;
		float total_length = 0.0f;
		for (float t = 0.0f;; t += dt) {
			if (t > 1.0f) {
				t = 1.0f;
			}
			vec3 p = eval_camera_path(t).T;
			if (t) {
				total_length += distance(prevp, p);
			}
			prevp = p;
			if (t >= 1.0f) {
				break;
			}
		}

		dt = 0.001f / total_length;
		static const uint32_t N_DASH_STEPS = 10;
		uint32_t i = 0;
		for (float t = 0.0f;; t += dt, ++i) {
			if (t > 1.0f) {
				t = 1.0f;
			}
			vec3 p = eval_camera_path(t).T;
			if (t && (i / N_DASH_STEPS) % 2 == 0) {
				float thickness = 1.0f;
				if (editing_kernel_type != EEditingKernel::None) {
					float x = (t + dt / 2.0f - get_playtime(cur_cam_i)) / editing_kernel_radius;
					thickness += 4.0f * editing_kernel(x, editing_kernel_type);
				}

				add_debug_line(list, world2proj, prevp, p, 0xff80c0ff, thickness);
			}

			prevp = p;
			if (t >= 1.0f) {
				break;
			}
		}

	}

	return changed;
}
#endif // NGP_GUI

} // namespace ngp