culling.h

#pragma once
 
#include <glm/glm.hpp>
#include <glm/gtc/constants.hpp>
 
#include "core/math/bounds.h"
#include "core/math/frustum.h"
 
namespace Vkm::Engine {

struct VisibilityContext {
    Math::Frustum frustum;
    glm::vec3     cameraPosition;  
    glm::mat4     view;
 
    float minPixels;              
    float maxDistance;            
    float maxDistanceSquared;
    float screenSizeThresholdSq;  
    float lodDistanceScale = 1.0f;

    bool perspective = true;
};

namespace Culling {

inline bool isNearEnough(const Math::AABB& bounds, const VisibilityContext& context) {
    if (context.maxDistance <= 0.0f) return true;
 
    const glm::vec3 delta = bounds.center() - context.cameraPosition;
    return glm::dot(delta, delta) <= context.maxDistanceSquared;
}

inline bool isLargeEnough(const Math::AABB& bounds, const VisibilityContext& context) {
    if (context.minPixels <= 0.0f || !context.perspective) return true;
 
    const glm::vec3 worldHalfExtent = bounds.halfExtent();
    const float     worldRadiusSq   = glm::dot(worldHalfExtent, worldHalfExtent);
 
    const glm::vec3 viewCenter = glm::vec3(context.view * glm::vec4(bounds.center(), 1.0f));
    const float     depth      = -viewCenter.z;
    if (depth <= glm::epsilon<float>()) return true;
 
    return worldRadiusSq >= context.screenSizeThresholdSq * (depth * depth);
}
 
} // namespace Culling
 
} // namespace Vkm::Engine