XCEngine/engine/src/Rendering/RenderSceneExtractor.cpp

#include "Rendering/RenderSceneExtractor.h"

#include "Components/CameraComponent.h"
#include "Components/GameObject.h"
#include "Components/LightComponent.h"
#include "Rendering/RenderMaterialUtility.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();
}

bool IsUsableLight(const Components::LightComponent* light) {
    return light != nullptr &&
           light->IsEnabled() &&
           light->GetGameObject() != nullptr &&
           light->GetGameObject()->IsActiveInHierarchy();
}

bool CompareVisibleItems(const VisibleRenderItem& lhs, const VisibleRenderItem& rhs) {
    if (lhs.renderQueue != rhs.renderQueue) {
        return lhs.renderQueue < rhs.renderQueue;
    }

    const bool isTransparentQueue = IsTransparentRenderQueue(lhs.renderQueue);
    if (lhs.cameraDistanceSq != rhs.cameraDistanceSq) {
        return isTransparentQueue
            ? lhs.cameraDistanceSq > rhs.cameraDistanceSq
            : lhs.cameraDistanceSq < rhs.cameraDistanceSq;
    }

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

    return lhs.sectionIndex < rhs.sectionIndex;
}

} // 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, 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, 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,
    RenderLightingData& lightingData) const {
    const std::vector<Components::LightComponent*> lights =
        scene.FindObjectsOfType<Components::LightComponent>();

    Components::LightComponent* mainDirectionalLight = nullptr;
    for (Components::LightComponent* light : lights) {
        if (!IsUsableLight(light) ||
            light->GetLightType() != Components::LightType::Directional) {
            continue;
        }

        if (mainDirectionalLight == nullptr ||
            light->GetIntensity() > mainDirectionalLight->GetIntensity()) {
            mainDirectionalLight = light;
        }
    }

    if (mainDirectionalLight == nullptr) {
        lightingData = {};
        return;
    }

    RenderDirectionalLightData lightData;
    lightData.enabled = true;
    lightData.castsShadows = mainDirectionalLight->GetCastsShadows();
    lightData.intensity = mainDirectionalLight->GetIntensity();
    lightData.color = mainDirectionalLight->GetColor();

    Math::Vector3 direction = mainDirectionalLight->transform().GetForward() * -1.0f;
    if (direction.SqrMagnitude() <= Math::EPSILON) {
        direction = Math::Vector3::Back();
    } else {
        direction = direction.Normalized();
    }
    lightData.direction = direction;

    lightingData.mainDirectionalLight = lightData;
}

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