OpenGL ES 2.0/3.0 中的虹彩效果。替换黑色区域

Question

我正在尝试对对象应用彩虹色效果。为此，我使用了以下着色器：

顶点着色器：

#version 300 es 
uniform mat4 u_mvpMatrix; 
uniform mat4 u_mvMatrix; 
uniform mat4 u_vMatrix;

in vec4 a_position; 
in vec2 a_textureCoordinates; 
in vec3 a_normal; 

out vec2 v_textureCoordinates; 
out float v_CosViewAngle;
out float v_LightIntensity;

void main() {
    // transform normal orientation into eye space
    vec3 modelViewNormal = mat3(u_mvMatrix) * a_normal;
    vec3 modelViewVertex = vec3(u_mvMatrix * a_position);
    mediump vec3 eyeDirection = normalize(-modelViewVertex);

    vec3 lightVector = normalize(lightPosition - modelViewVertex);
    lightVector = mat3(u_vMatrix) * lightVector;

    v_LightIntensity = max(dot(lightVector, modelViewNormal), 0.0);
    v_CosViewAngle = max(dot(eyeDirection, modelViewNormal), 0.1);
    ...
}

片段着色器：

#version 300 es
precision lowp float;

in vec2 v_textureCoordinates; 
in float v_CosViewAngle;
in float v_LightIntensity;
out vec4 outColor;
uniform sampler2D s_texture;

// wave numbers for the iridescence effect: k = 2.0 * pi / wavelength (nm).
const mediump float PI = 3.141592654;
const mediump vec3 rgbK = 2.0 * PI * vec3(1.0/475.0, 1.0/510.0, 1.0/650.0);
const mediump float iridescence = 4.4;
const mediump float minThickness = 80.0;
const mediump float maxVariation = 50.0;

void main() {
    float thickness = texture(s_texture, v_textureCoordinates).r 
        * maxVariation + minThickness; // or texture2D() - in OpenGL ES 2.0
    float delta = (thickness / v_LightIntensity) + (thickness / v_CosViewAngle);
    lowp vec3 color = cos(delta * rgbK) * iridescence * v_LightIntensity;
    vec4 resultColor = vec4(color, 1.0);
    outColor = resultColor;
}

结果：

问题：如何用普通贴图替换黑色区域？换句话说，要有一个共同的纹理而不是黑色。

注：我试id为：

vec4 resultColor = texture(s_texture, v_textureCoordinates) * (vec4(color, 1.0) + 0.5);

等等：

if (color == vec3(0.0, 0.0, 0.0)) { // if black color
    resultColor = texture(s_texture, v_textureCoordinates);
} else {
    resultColor = texture(s_texture, v_textureCoordinates) * (vec4(color, 1.0) + 0.5);
}

但这并没有解决问题。

提前致谢！

着色器的代码部分取自 PVRShamanGUI。

更新： 根据 Rabbid76 的回答，我也使用了 delta，但只是为了检查波长（以 nm 为单位）：

...
if (delta > 1700.0 || delta < 370.0) { 
    resultColor = texture(s_texture, v_textureCoordinates) * v_commonLight;
} else {
    resultColor = vec4(color, 1.0);
}
outColor = resultColor;

结果：

Answer 1

颜色不是全黑，颜色通道的值不完全是0.0。计算平均颜色（灰度）和mix依赖于灰度的颜色和纹理颜色：

vec4  texturColor = texture(s_texture, v_textureCoordinates);
float gray_scale  = (color.r + color.g + color.b) / 3.0;  
resultColor = mix(texturColor, color, gray_scale);

另一种可能性是根据 delta 的值混合颜色：

vec4 texturColor = texture(s_texture, v_textureCoordinates);
resultColor = mix(texturColor, color, delta);

OpenGL ES 2.0/3.0 中的虹彩效果。替换黑色区域

Iridescence effect in OpenGL ES 2.0/3.0. Replacing the black area

shader

android

opengl-es

glsl

opengl-es-3.0