IOS – OpenGL ES 图像球形折射 GPUImageSphereRefractionFilter

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//@Author:猿说编程
//@Blog(个人博客地址): www.codersrc.com
//@File:IOS – OpenGL ES 图像球形折射 GPUImageSphereRefractionFilter
//@Time:2022/06/03 06:30
//@Motto:不积跬步无以至千里，不积小流无以成江海，程序人生的精彩需要坚持不懈地积累！
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#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageSphereRefractionFragmentShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;

 uniform highp vec2 center;
 uniform highp float radius;
 uniform highp float aspectRatio;
 uniform highp float refractiveIndex;

 void main()
 {
     highp vec2 textureCoordinateToUse = vec2(textureCoordinate.x, (textureCoordinate.y * aspectRatio + 0.5 - 0.5 * aspectRatio));
     highp float distanceFromCenter = distance(center, textureCoordinateToUse);
     lowp float checkForPresenceWithinSphere = step(distanceFromCenter, radius);

     distanceFromCenter = distanceFromCenter / radius;

     highp float normalizedDepth = radius * sqrt(1.0 - distanceFromCenter * distanceFromCenter);
     highp vec3 sphereNormal = normalize(vec3(textureCoordinateToUse - center, normalizedDepth));

     highp vec3 refractedVector = refract(vec3(0.0, 0.0, -1.0), sphereNormal, refractiveIndex);

     gl_FragColor = texture2D(inputImageTexture, (refractedVector.xy + 1.0) * 0.5) * checkForPresenceWithinSphere;
 }
);
#else
NSString *const kGPUImageSphereRefractionFragmentShaderString = SHADER_STRING
(
 varying vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;

 uniform vec2 center;
 uniform float radius;
 uniform float aspectRatio;
 uniform float refractiveIndex;

 void main()
 {
     vec2 textureCoordinateToUse = vec2(textureCoordinate.x, (textureCoordinate.y * aspectRatio + 0.5 - 0.5 * aspectRatio));
     float distanceFromCenter = distance(center, textureCoordinateToUse);
     float checkForPresenceWithinSphere = step(distanceFromCenter, radius);

     distanceFromCenter = distanceFromCenter / radius;

     float normalizedDepth = radius * sqrt(1.0 - distanceFromCenter * distanceFromCenter);
     vec3 sphereNormal = normalize(vec3(textureCoordinateToUse - center, normalizedDepth));

     vec3 refractedVector = refract(vec3(0.0, 0.0, -1.0), sphereNormal, refractiveIndex);

     gl_FragColor = texture2D(inputImageTexture, (refractedVector.xy + 1.0) * 0.5) * checkForPresenceWithinSphere;
 }
);
#endif