可以从纹理生成法线贴图吗？

Question

如果我有纹理,那么可以为这个纹理生成法线贴图,那么它可以用于凹凸贴图吗？

或者通常如何制作法线贴图？

Answer 1

是.好吧,有点.可以从高度图准确地制作法线贴图.一般来说,你也可以通过常规纹理,并获得不错的结果.请记住,还有其他方法可以制作法线贴图,例如采用高分辨率模型,使其分辨率较低,然后进行光线投射,以查看低分辨率模型模拟较高分辨率模型的正常情况.

对于高度贴图到法线贴图,您可以使用Sobel算子.此运算符可以在x方向上运行,告诉您正常的x分量,然后是y方向,告诉您y分量.您可以计算z,1.0 / strength其中强度是法线贴图的重点或"深度".然后,取出x,y和z,将它们放入一个向量中,对其进行标准化,然后你就可以正常了.将其编码到像素中即可完成.

这是一些较旧的不完整代码,用于演示:

// pretend types, something like this
struct pixel
{
    uint8_t red;
    uint8_t green;
    uint8_t blue;
};

struct vector3d; // a 3-vector with doubles
struct texture; // a 2d array of pixels

// determine intensity of pixel, from 0 - 1
const double intensity(const pixel& pPixel)
{
    const double r = static_cast<double>(pPixel.red);
    const double g = static_cast<double>(pPixel.green);
    const double b = static_cast<double>(pPixel.blue);

    const double average = (r + g + b) / 3.0;

    return average / 255.0;
}

const int clamp(int pX, int pMax)
{
    if (pX > pMax)
    {
        return pMax;
    }
    else if (pX < 0)
    {
        return 0;
    }
    else
    {
        return pX;
    }
}

// transform -1 - 1 to 0 - 255
const uint8_t map_component(double pX)
{
    return (pX + 1.0) * (255.0 / 2.0);
}

texture normal_from_height(const texture& pTexture, double pStrength = 2.0)
{
    // assume square texture, not necessarily true in real code
    texture result(pTexture.size(), pTexture.size());

    const int textureSize = static_cast<int>(pTexture.size());
    for (size_t row = 0; row < textureSize; ++row)
    {
        for (size_t column = 0; column < textureSize; ++column)
        {
            // surrounding pixels
            const pixel topLeft = pTexture(clamp(row - 1, textureSize), clamp(column - 1, textureSize));
            const pixel top = pTexture(clamp(row - 1, textureSize), clamp(column, textureSize));
            const pixel topRight = pTexture(clamp(row - 1, textureSize), clamp(column + 1, textureSize));
            const pixel right = pTexture(clamp(row, textureSize), clamp(column + 1, textureSize));
            const pixel bottomRight = pTexture(clamp(row + 1, textureSize), clamp(column + 1, textureSize));
            const pixel bottom = pTexture(clamp(row + 1, textureSize), clamp(column, textureSize));
            const pixel bottomLeft = pTexture(clamp(row + 1, textureSize), clamp(column - 1, textureSize));
            const pixel left = pTexture(clamp(row, textureSize), clamp(column - 1, textureSize));

            // their intensities
            const double tl = intensity(topLeft);
            const double t = intensity(top);
            const double tr = intensity(topRight);
            const double r = intensity(right);
            const double br = intensity(bottomRight);
            const double b = intensity(bottom);
            const double bl = intensity(bottomLeft);
            const double l = intensity(left);

            // sobel filter
            const double dX = (tr + 2.0 * r + br) - (tl + 2.0 * l + bl);
            const double dY = (bl + 2.0 * b + br) - (tl + 2.0 * t + tr);
            const double dZ = 1.0 / pStrength;

            math::vector3d v(dX, dY, dZ);
            v.normalize();

            // convert to rgb
            result(row, column) = pixel(map_component(v.x), map_component(v.y), map_component(v.z));
        }
    }

    return result;
}