XCEngine/engine/src/Rendering/RenderSceneExtractor.cpp

#include "Rendering/RenderSceneExtractor.h"

#include "Components/CameraComponent.h"
#include "Components/GameObject.h"
#include "Components/LightComponent.h"
#include "Rendering/RenderSceneUtility.h"
#include "Scene/Scene.h"

#include <algorithm>

namespace XCEngine {
namespace Rendering {

namespace {

bool IsUsableCamera(const Components::CameraComponent* camera) {
    return camera != nullptr &&
           camera->IsEnabled() &&
           camera->GetGameObject() != nullptr &&
           camera->GetGameObject()->IsActiveInHierarchy();
}

RenderLightType ToRenderLightType(Components::LightType lightType) {
    switch (lightType) {
        case Components::LightType::Directional:
            return RenderLightType::Directional;
        case Components::LightType::Point:
            return RenderLightType::Point;
        case Components::LightType::Spot:
            return RenderLightType::Spot;
    }

    return RenderLightType::Point;
}

RenderDirectionalLightData BuildDirectionalLightData(
    const Components::LightComponent& light) {
    RenderDirectionalLightData lightData;
    lightData.enabled = true;
    lightData.castsShadows = light.GetCastsShadows();
    lightData.intensity = light.GetIntensity();
    lightData.color = light.GetColor();
    lightData.direction = BuildRenderLightDirection(light);
    return lightData;
}

RenderAdditionalLightData BuildAdditionalLightData(
    const Components::LightComponent& light) {
    RenderAdditionalLightData lightData;
    lightData.type = ToRenderLightType(light.GetLightType());
    lightData.enabled = true;
    lightData.castsShadows = light.GetCastsShadows();
    lightData.color = light.GetColor();
    lightData.intensity = light.GetIntensity();

    switch (light.GetLightType()) {
        case Components::LightType::Directional:
            lightData.direction = BuildRenderLightDirection(light);
            break;
        case Components::LightType::Point:
            lightData.position = light.transform().GetPosition();
            lightData.range = light.GetRange();
            break;
        case Components::LightType::Spot:
            lightData.position = light.transform().GetPosition();
            lightData.direction = BuildRenderLightDirection(light);
            lightData.range = light.GetRange();
            lightData.spotAngle = light.GetSpotAngle();
            break;
    }

    return lightData;
}

float ComputeAdditionalLightInfluence(
    const Components::LightComponent& light,
    const Math::Vector3& cameraPosition) {
    if (light.GetIntensity() <= Math::EPSILON) {
        return 0.0f;
    }

    if (light.GetLightType() == Components::LightType::Directional) {
        return light.GetIntensity();
    }

    const float range = std::max(light.GetRange(), 0.001f);
    const float rangeSq = range * range;
    const Math::Vector3 lightPosition = light.transform().GetPosition();
    const float distanceSq = (lightPosition - cameraPosition).SqrMagnitude();
    if (distanceSq >= rangeSq) {
        return 0.0f;
    }

    return light.GetIntensity() / std::max(distanceSq, Math::EPSILON);
}

uint32_t GetAdditionalLightGroupRank(const Components::LightComponent& light) {
    return light.GetLightType() == Components::LightType::Directional ? 0u : 1u;
}

uint32_t GetAdditionalLightTypeRank(const Components::LightComponent& light) {
    switch (light.GetLightType()) {
        case Components::LightType::Directional:
            return 0u;
        case Components::LightType::Point:
            return 1u;
        case Components::LightType::Spot:
            return 2u;
    }

    return 3u;
}

bool CompareVisibleItems(const VisibleRenderItem& lhs, const VisibleRenderItem& rhs) {
    return CompareVisibleRenderItemsStable(lhs, rhs);
}

} // namespace

RenderSceneData RenderSceneExtractor::Extract(
    const Components::Scene& scene,
    Components::CameraComponent* overrideCamera,
    uint32_t viewportWidth,
    uint32_t viewportHeight) const {
    RenderSceneData sceneData;
    sceneData.camera = SelectCamera(scene, overrideCamera);
    if (sceneData.camera == nullptr) {
        return sceneData;
    }

    sceneData.cameraData = BuildRenderCameraData(*sceneData.camera, viewportWidth, viewportHeight);
    const Math::Vector3 cameraPosition = sceneData.cameraData.worldPosition;
    const uint32_t cullingMask = sceneData.camera->GetCullingMask();

    const std::vector<Components::GameObject*> rootGameObjects = scene.GetRootGameObjects();
    for (Components::GameObject* rootGameObject : rootGameObjects) {
        ExtractVisibleItems(rootGameObject, cameraPosition, cullingMask, sceneData.visibleItems);
    }

    std::stable_sort(
        sceneData.visibleItems.begin(),
        sceneData.visibleItems.end(),
        CompareVisibleItems);
    ExtractLighting(scene, cameraPosition, cullingMask, sceneData.lighting);

    return sceneData;
}

RenderSceneData RenderSceneExtractor::ExtractForCamera(
    const Components::Scene& scene,
    Components::CameraComponent& camera,
    uint32_t viewportWidth,
    uint32_t viewportHeight) const {
    RenderSceneData sceneData;
    if (!IsUsableCamera(&camera)) {
        return sceneData;
    }

    sceneData.camera = &camera;
    sceneData.cameraData = BuildRenderCameraData(camera, viewportWidth, viewportHeight);
    const Math::Vector3 cameraPosition = sceneData.cameraData.worldPosition;
    const uint32_t cullingMask = camera.GetCullingMask();

    const std::vector<Components::GameObject*> rootGameObjects = scene.GetRootGameObjects();
    for (Components::GameObject* rootGameObject : rootGameObjects) {
        ExtractVisibleItems(rootGameObject, cameraPosition, cullingMask, sceneData.visibleItems);
    }

    std::stable_sort(
        sceneData.visibleItems.begin(),
        sceneData.visibleItems.end(),
        CompareVisibleItems);
    ExtractLighting(scene, cameraPosition, cullingMask, sceneData.lighting);

    return sceneData;
}

Components::CameraComponent* RenderSceneExtractor::SelectCamera(
    const Components::Scene& scene,
    Components::CameraComponent* overrideCamera) const {
    if (IsUsableCamera(overrideCamera)) {
        return overrideCamera;
    }

    const std::vector<Components::CameraComponent*> cameras = scene.FindObjectsOfType<Components::CameraComponent>();

    Components::CameraComponent* primaryCamera = nullptr;
    for (Components::CameraComponent* camera : cameras) {
        if (!IsUsableCamera(camera)) {
            continue;
        }

        if (camera->IsPrimary()) {
            if (primaryCamera == nullptr || camera->GetDepth() > primaryCamera->GetDepth()) {
                primaryCamera = camera;
            }
        }
    }

    if (primaryCamera != nullptr) {
        return primaryCamera;
    }

    for (Components::CameraComponent* camera : cameras) {
        if (IsUsableCamera(camera)) {
            return camera;
        }
    }

    return nullptr;
}

void RenderSceneExtractor::ExtractLighting(
    const Components::Scene& scene,
    const Math::Vector3& cameraPosition,
    uint32_t cullingMask,
    RenderLightingData& lightingData) const {
    lightingData = {};

    const std::vector<Components::LightComponent*> lights =
        scene.FindObjectsOfType<Components::LightComponent>();

    Components::LightComponent* mainDirectionalLight =
        FindMainDirectionalLight(scene, cullingMask);
    if (mainDirectionalLight != nullptr) {
        lightingData.mainDirectionalLight = BuildDirectionalLightData(*mainDirectionalLight);
    }

    struct AdditionalLightCandidate {
        RenderAdditionalLightData data = {};
        float influence = 0.0f;
        uint32_t groupRank = 0u;
        uint32_t typeRank = 0u;
        Components::GameObject::ID gameObjectId = Components::GameObject::INVALID_ID;
    };

    std::vector<AdditionalLightCandidate> candidates;
    candidates.reserve(lights.size());
    for (Components::LightComponent* light : lights) {
        if (light == nullptr ||
            !IsLightVisibleForCullingMask(*light, cullingMask) ||
            light == mainDirectionalLight) {
            continue;
        }

        AdditionalLightCandidate candidate;
        candidate.data = BuildAdditionalLightData(*light);
        candidate.influence = ComputeAdditionalLightInfluence(*light, cameraPosition);
        candidate.groupRank = GetAdditionalLightGroupRank(*light);
        candidate.typeRank = GetAdditionalLightTypeRank(*light);
        candidate.gameObjectId = light->GetGameObject() != nullptr
            ? light->GetGameObject()->GetID()
            : Components::GameObject::INVALID_ID;
        candidates.push_back(candidate);
    }

    std::sort(
        candidates.begin(),
        candidates.end(),
        [](const AdditionalLightCandidate& lhs, const AdditionalLightCandidate& rhs) {
            if (lhs.groupRank != rhs.groupRank) {
                return lhs.groupRank < rhs.groupRank;
            }

            if (lhs.influence != rhs.influence) {
                return lhs.influence > rhs.influence;
            }

            if (lhs.typeRank != rhs.typeRank) {
                return lhs.typeRank < rhs.typeRank;
            }

            return lhs.gameObjectId < rhs.gameObjectId;
        });

    const uint32_t additionalLightCount = static_cast<uint32_t>(
        std::min(candidates.size(), static_cast<size_t>(RenderLightingData::kMaxAdditionalLightCount)));
    lightingData.additionalLightCount = additionalLightCount;
    for (uint32_t index = 0; index < additionalLightCount; ++index) {
        lightingData.additionalLights[index] = candidates[index].data;
    }
}

void RenderSceneExtractor::ExtractVisibleItems(
    Components::GameObject* gameObject,
    const Math::Vector3& cameraPosition,
    uint32_t cullingMask,
    std::vector<VisibleRenderItem>& visibleItems) const {
    if (gameObject == nullptr || !gameObject->IsActiveInHierarchy()) {
        return;
    }

    const uint32_t gameObjectLayerMask = 1u << gameObject->GetLayer();
    const bool isVisibleInCameraMask = (cullingMask & gameObjectLayerMask) != 0;

    if (isVisibleInCameraMask) {
        AppendRenderItemsForGameObject(*gameObject, cameraPosition, visibleItems);
    }

    for (Components::GameObject* child : gameObject->GetChildren()) {
        ExtractVisibleItems(child, cameraPosition, cullingMask, visibleItems);
    }
}

} // namespace Rendering
} // namespace XCEngine