Mesh.GetUVDistributionMetric

Объявление

public float GetUVDistributionMetric(int uvSetIndex);

Параметры

uvSetIndex

UV задайте индекс, для которого будет возвращена метрика распределения UV. 0 за первый.

Возвращает

float Средняя площадь треугольника / площадь УФ.

Описание

Метрику распределения UV можно использовать для расчета желаемого уровня MIP-карты на основе положения камеры.

В примере кода показано, как это значение можно использовать с некоторыми свойствами камеры для расчета требуемого уровня MIP-карты.


using UnityEngine;

public class MyMipmapClass : MonoBehaviour
{
    private Vector3 m_CameraPosition;
    private float m_CameraEyeToScreenDistanceSquared;

    private float m_MeshUVDistributionMetric;
    private float m_TexelCount;
    private Texture2D m_Texture;

    public void SetView(Vector3 cameraPosition, float cameraHalfAngle, float screenHalfHeight, float aspectRatio)
    {
        m_CameraPosition = cameraPosition;
        m_CameraEyeToScreenDistanceSquared = Mathf.Pow(screenHalfHeight / Mathf.Tan(cameraHalfAngle), 2.0f);

        // Switch to using the horizontal dimension if larger
        if (aspectRatio > 1.0f)    // Width is larger than height
            m_CameraEyeToScreenDistanceSquared *= aspectRatio;
    }

    public void SetView(Camera camera)
    {
        float cameraHA = Mathf.Deg2Rad * camera.fieldOfView * 0.5f;
        float screenHH = (float)camera.pixelHeight * 0.5f;
        SetView(camera.transform.position, cameraHA, screenHH, camera.aspect);
    }

    private int CalculateMipmapLevel(Bounds bounds, float uvDistributionMetric, float texelCount)
    {
        // based on  http://web.cse.ohio-state.edu/~crawfis.3/cse781/Readings/MipMapLevels-Blog.html
        // screenArea = worldArea * (ScreenPixels/(D*tan(FOV)))^2
        // mip = 0.5 * log2 (uvArea / screenArea)
        float dSq = bounds.SqrDistance(m_CameraPosition);
        if (dSq < 1e-06)
            return 0;

        // uvDistributionMetric is the average of triangle area / uv area (a ratio from world space triangle area to normalised uv area)
        // - triangle area is in world space
        // - uv area is in normalised units (0->1 rather than 0->texture size)

        // m_CameraEyeToScreenDistanceSquared / dSq is the ratio of screen area to world space area

        float v = (texelCount * dSq) / (uvDistributionMetric * m_CameraEyeToScreenDistanceSquared);
        float desiredMipLevel = 0.5f * Mathf.Log(v, 2);

        return (int)desiredMipLevel;
    }

    // Pick the larger two scales of the 3 components and multiply together
    float GetLargestAreaScale(float x, float y, float z)
    {
        if (x > y)
        {
            if (y > z)
                return x * y;
            else
                return x * z;
        }
        else // x <= y
        {
            if (x < z)
                return y * z;
            else
                return x * y;
        }
    }

    public void Start()
    {
        Mesh mesh = GetComponent<MeshFilter>().sharedMesh;
        m_MeshUVDistributionMetric = mesh.GetUVDistributionMetric(0);

        // If the mesh has a transform scale or uvscale it would need to be applied here

        // Transform scale:
        // Use two scale values as we need an 'area' scale.
        // Use the two largest component to usa a more conservative selection and pick the higher resolution mip
        m_MeshUVDistributionMetric *= GetLargestAreaScale(transform.lossyScale.x, transform.lossyScale.y, transform.lossyScale.z);

        // To determine uv scale for a material use Material.GetTextureScale
        // If there is a uv scale to apply then divide the m_MeshUVDistributionMetric by (uvScale.x * uvScale.y)

        m_TexelCount = m_Texture.width * m_Texture.height;
    }

    public void Update()
    {
        SetView(Camera.main);

        m_Texture.requestedMipmapLevel = CalculateMipmapLevel(GetComponent<Renderer>().bounds, m_MeshUVDistributionMetric, m_TexelCount);
    }
}

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