IOS – OpenGL ES 图像哈哈镜效果 GPUImageStretchDistortionFilter

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//@Author:猿说编程
//@Blog(个人博客地址): www.codersrc.com
//@File:IOS – OpenGL ES 图像哈哈镜效果 GPUImageStretchDistortionFilter
//@Time:2022/06/02 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 kGPUImageStretchDistortionFragmentShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;

 uniform highp vec2 center;

 void main()
 {
     highp vec2 normCoord = 2.0 * textureCoordinate - 1.0;
     highp vec2 normCenter = 2.0 * center - 1.0;

     normCoord -= normCenter;
     mediump vec2 s = sign(normCoord);
     normCoord = abs(normCoord);
     normCoord = 0.5 * normCoord + 0.5 * smoothstep(0.25, 0.5, normCoord) * normCoord;
     normCoord = s * normCoord;

     normCoord += normCenter;

     mediump vec2 textureCoordinateToUse = normCoord / 2.0 + 0.5;


     gl_FragColor = texture2D(inputImageTexture, textureCoordinateToUse );

 }
);
#else
NSString *const kGPUImageStretchDistortionFragmentShaderString = SHADER_STRING
(
 varying vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;

 uniform vec2 center;

 void main()
 {
     vec2 normCoord = 2.0 * textureCoordinate - 1.0;
     vec2 normCenter = 2.0 * center - 1.0;

     normCoord -= normCenter;
     vec2 s = sign(normCoord);
     normCoord = abs(normCoord);
     normCoord = 0.5 * normCoord + 0.5 * smoothstep(0.25, 0.5, normCoord) * normCoord;
     normCoord = s * normCoord;

     normCoord += normCenter;

     vec2 textureCoordinateToUse = normCoord / 2.0 + 0.5;

     gl_FragColor = texture2D(inputImageTexture, textureCoordinateToUse);
 }
);
#endif