UE4 LOD Screen Size

UE4 LOD Screen Size

Screen Size 直白翻译就是屏幕大小，在UE4中常用于控制LOD的加载。

计算屏幕大小

/**
 * Computes the screen size of a given sphere bounds in the given view.
 * The screen size is the projected diameter of the bounding sphere of the model. 
 * i.e. 0.5 means half the screen's maximum dimension.
 * @param BoundsOrigin - Origin of the bounds in world space
 * @param SphereRadius - Radius of the sphere to use to calculate screen coverage
 * @param ViewOrigin - The origin of the view to calculate the display factor for
 * @param ProjMatrix - The projection matrix used to scale screen size bounds
 * @return float - The screen size calculated
 */
float ComputeBoundsScreenSize(const FVector4& BoundsOrigin, const float SphereRadius, const FVector4& ViewOrigin, const FMatrix& ProjMatrix)
{
    
    
	const float Dist = FVector::Dist(BoundsOrigin, ViewOrigin);

	// Get projection multiple accounting for view scaling.
	const float ScreenMultiple = FMath::Max(0.5f * ProjMatrix.M[0][0], 0.5f * ProjMatrix.M[1][1]);

	// Calculate screen-space projected radius
	const float ScreenRadius = ScreenMultiple * SphereRadius / FMath::Max(1.0f, Dist);

	// For clarity, we end up comparing the diameter
	return ScreenRadius * 2.0f;
}

测试场景

参考

1. UE4 投影矩阵
2. UE4 模型简化