IOS – OpenGL ES 图像马赛克圆点 GPUImagePolkaDotFilter-猿说编程

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零基础 OpenGL (ES) 学习路线推荐 : OpenGL (ES) 学习目录 >> OpenGL ES 基础

零基础 OpenGL (ES) 学习路线推荐 : OpenGL (ES) 学习目录 >> OpenGL ES 转场

零基础 OpenGL (ES) 学习路线推荐 : OpenGL (ES) 学习目录 >> OpenGL ES 特效

零基础 OpenGL (ES) 学习路线推荐 : OpenGL (ES) 学习目录 >> OpenGL ES 函数

零基础 OpenGL (ES) 学习路线推荐 : OpenGL (ES) 学习目录 >> OpenGL ES GPUImage 使用

零基础 OpenGL (ES) 学习路线推荐 : OpenGL (ES) 学习目录 >> OpenGL ES GLSL 编程

一.简介

GPUImage 共 125 个滤镜, 分为四类

1、Color adjustments : 31 filters , 颜色处理相关
2、Image processing : 40 filters , 图像处理相关.
3、Blending modes : 29 filters , 混合模式相关.
4、Visual effects : 25 filters , 视觉效果相关.

GPUImagePolkaDotFilter 属于 GPUImage 图像视觉效果相关，用来处理图像图像马赛克圆点效果。shader 源码如下：

/******************************************************************************************/
//@Author:猿说编程
//@Blog(个人博客地址): www.codersrc.com
//@File:IOS – OpenGL ES 图像马赛克圆点
//@Time:2022/06/11 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！
/******************************************************************************************/

#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImagePolkaDotFragmentShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;
 
 uniform sampler2D inputImageTexture;
 
 uniform highp float fractionalWidthOfPixel;
 uniform highp float aspectRatio;
 uniform highp float dotScaling;
 
 void main()
 {
     highp vec2 sampleDivisor = vec2(fractionalWidthOfPixel, fractionalWidthOfPixel / aspectRatio);
     
     highp vec2 samplePos = textureCoordinate - mod(textureCoordinate, sampleDivisor) + 0.5 * sampleDivisor;
     highp vec2 textureCoordinateToUse = vec2(textureCoordinate.x, (textureCoordinate.y * aspectRatio + 0.5 - 0.5 * aspectRatio));
     highp vec2 adjustedSamplePos = vec2(samplePos.x, (samplePos.y * aspectRatio + 0.5 - 0.5 * aspectRatio));
     highp float distanceFromSamplePoint = distance(adjustedSamplePos, textureCoordinateToUse);
     lowp float checkForPresenceWithinDot = step(distanceFromSamplePoint, (fractionalWidthOfPixel * 0.5) * dotScaling);

     lowp vec4 inputColor = texture2D(inputImageTexture, samplePos);
     
     gl_FragColor = vec4(inputColor.rgb * checkForPresenceWithinDot, inputColor.a);
 }
);
#else
NSString *const kGPUImagePolkaDotFragmentShaderString = SHADER_STRING
(
 varying vec2 textureCoordinate;
 
 uniform sampler2D inputImageTexture;
 
 uniform float fractionalWidthOfPixel;
 uniform float aspectRatio;
 uniform float dotScaling;
 
 void main()
 {
     vec2 sampleDivisor = vec2(fractionalWidthOfPixel, fractionalWidthOfPixel / aspectRatio);
     
     vec2 samplePos = textureCoordinate - mod(textureCoordinate, sampleDivisor) + 0.5 * sampleDivisor;
     vec2 textureCoordinateToUse = vec2(textureCoordinate.x, (textureCoordinate.y * aspectRatio + 0.5 - 0.5 * aspectRatio));
     vec2 adjustedSamplePos = vec2(samplePos.x, (samplePos.y * aspectRatio + 0.5 - 0.5 * aspectRatio));
     float distanceFromSamplePoint = distance(adjustedSamplePos, textureCoordinateToUse);
     float checkForPresenceWithinDot = step(distanceFromSamplePoint, (fractionalWidthOfPixel * 0.5) * dotScaling);
     
     vec4 inputColor = texture2D(inputImageTexture, samplePos);

     gl_FragColor = vec4(inputColor.rgb * checkForPresenceWithinDot, inputColor.a);
 }
);
#endif