c++ - OpenGL程序纹理着色器解释

Question

我对 OpenGL 相当陌生，我想为木材制作一个很酷的程序纹理，可以在我的 OpenGL 项目中使用。我不知道从哪里开始，所以我试图在网上查找一些关于它的东西。我找到了片段和顶点着色器的代码片段，我开始处理一些 obj 文件。

遗憾的是，我不太明白代码中的某些函数的用途，并想问，是否有人可以解释为什么需要这些 mode289 函数。我了解了 snoise 函数的用途，但大部分代码真的很难理解。

如果您能告诉我理解代码，那将非常有帮助。

此外，我想问一下，哪些值负责纹理的亮度，以及如何将 mtl 文件合并到着色器中。我设法让一个 obj 文件工作，但从来不需要 mtl。帧着色器

#version 440 core
precision highp float;
precision highp int;

uniform vec3 color1;
uniform vec3 color2;
uniform float frequency;
uniform float noiseScale;
uniform float ringScale;
uniform float contrast;
uniform float time;

in vec3 vs_normal;
in vec2 vUv;
in vec3 vs_position;

out vec4 finalTexture;

vec3 mod289(vec3 x) {
    return x - floor(x * (1.0 / 289.0)) * 289.0;
}

vec4 mod289(vec4 x) {
    return x - floor(x * (1.0 / 289.0)) * 289.0;
}

vec4 permute(vec4 x) {
    return mod289(((x*34.0)+1.0)*x);
}

vec4 taylorInvSqrt(vec4 r) {
    return 1.79284291400159 - 0.85373472095314 * r;
}

float snoise(vec3 v) {
    const vec2  C = vec2(1.0/6.0, 1.0/3.0) ;
    const vec4  D = vec4(0.0, 0.5, 1.0, 2.0);

    // First corner
    vec3 i  = floor(v + dot(v, C.yyy) );
    vec3 x0 =   v - i + dot(i, C.xxx) ;

    // Other corners
    vec3 g = step(x0.yzx, x0.xyz);
    vec3 l = 1.0 - g;
    vec3 i1 = min( g.xyz, l.zxy );
    vec3 i2 = max( g.xyz, l.zxy );

    //   x0 = x0 - 0.0 + 0.0 * C.xxx;
    //   x1 = x0 - i1  + 1.0 * C.xxx;
    //   x2 = x0 - i2  + 2.0 * C.xxx;
    //   x3 = x0 - 1.0 + 3.0 * C.xxx;
    vec3 x1 = x0 - i1 + C.xxx;
    vec3 x2 = x0 - i2 + C.yyy; // 2.0*C.x = 1/3 = C.y
    vec3 x3 = x0 - D.yyy;      // -1.0+3.0*C.x = -0.5 = -D.y

    // Permutations
    i = mod289(i);
    vec4 p = permute( permute( permute(
                    i.z + vec4(0.0, i1.z, i2.z, 1.0 ))
                + i.y + vec4(0.0, i1.y, i2.y, 1.0 ))
            + i.x + vec4(0.0, i1.x, i2.x, 1.0 ));

    // Gradients: 7x7 points over a square, mapped onto an octahedron.
    // The ring size 17*17 = 289 is close to a multiple of 49 (49*6 = 294)
    float n_ = 0.142857142857; // 1.0/7.0
    vec3  ns = n_ * D.wyz - D.xzx;

    vec4 j = p - 49.0 * floor(p * ns.z * ns.z);  //  mod(p,7*7)

    vec4 x_ = floor(j * ns.z);
    vec4 y_ = floor(j - 7.0 * x_ );    // mod(j,N)

    vec4 x = x_ *ns.x + ns.yyyy;
    vec4 y = y_ *ns.x + ns.yyyy;
    vec4 h = 1.0 - abs(x) - abs(y);

    vec4 b0 = vec4( x.xy, y.xy );
    vec4 b1 = vec4( x.zw, y.zw );

    vec4 s0 = floor(b0)*2.0 + 1.0;
    vec4 s1 = floor(b1)*2.0 + 1.0;
    vec4 sh = -step(h, vec4(0.0));

    vec4 a0 = b0.xzyw + s0.xzyw*sh.xxyy ;
    vec4 a1 = b1.xzyw + s1.xzyw*sh.zzww ;

    vec3 p0 = vec3(a0.xy,h.x);
    vec3 p1 = vec3(a0.zw,h.y);
    vec3 p2 = vec3(a1.xy,h.z);
    vec3 p3 = vec3(a1.zw,h.w);

    // Normalise gradients
    vec4 norm = taylorInvSqrt(vec4(dot(p0,p0), dot(p1,p1), dot(p2, p2), dot(p3,p3)));
    p0 *= norm.x;
    p1 *= norm.y;
    p2 *= norm.z;
    p3 *= norm.w;

    // Mix final noise value
    vec4 m = max(0.6 - vec4(dot(x0,x0), dot(x1,x1), dot(x2,x2), dot(x3,x3)), 0.0);
    m = m * m;
    return 42.0 * dot( m*m, vec4( dot(p0,x0), dot(p1,x1),
                dot(p2,x2), dot(p3,x3) ) );
}

void main() {
    //texture change on movement
    //float n = snoise(vs_position);
   
   //texture fixed on movement
    float n = snoise( vec3(vs_position.x,-0.68,vs_position.z) );
    
    float ring = fract( frequency * vs_position.z + noiseScale * n );
    ring *= contrast * ( 1.0 - ring );
    
    // Adjust ring smoothness and shape, and add some noise
    float lerp = pow( ring, ringScale ) + n;
    vec3 base = mix( color1, color2, lerp);
    finalTexture = vec4( base, 1.0 );
}

顶点着色器

#version 440

precision highp float;
precision highp int;

layout (location = 0) in vec3 vertex_position;
layout (location = 1) in vec2 uv;
layout (location = 2) in vec2 uv2;
layout (location = 3) in vec3 vertex_normal;

out vec3 vs_position;
out vec3 vs_normal;
out vec2 vUv;

uniform mat4 ModelMatrix;
uniform mat4 ViewMatrix;
uniform mat4 ProjectionMatrix;

void main() {

    vUv = uv;
    vs_position = vec4(ModelMatrix * vec4(vertex_position, 1.f)).xyz;
    vs_normal = mat3(ModelMatrix) * vertex_normal;
    
    gl_Position = ProjectionMatrix * ViewMatrix * ModelMatrix * vec4(vertex_position, 1.f);

}

遗憾的是，应该解释的 URL 不再起作用：http: //blog.2pha.com/demos/threejs/shaders/wood_grain.html

渲染对象的图像：

标签： c++openglglslshaderprocedural-generation