梯度运算算法梯度算法的shader处理方法及实现的方法(2)

深入源代码，查看GPUImageSharpenFilter的具体实现

@interface GPUImageSharpenFilter : GPUImageFilter

GPUImageSharpenFilter比较简单，直接继承自GPUImageFilter，并且只有一个GLProgram。

if (!(self = [super initWithVertexShaderFromString:kGPUImageSharpenVertexShaderString fragmentShaderFromString:kGPUImageSharpenFragmentShaderString]))
{
    return nil;
}
...

初始化过程还需要调用父类的初始化接口并传入着色器。

NSString *const kGPUImageSharpenVertexShaderString = SHADER_STRING
(
 attribute ve position;
 attribute ve inputTextureCoordinate;
 
 uniform float imageWidthFactor; 
 uniform float imageHeightFactor; 
 uniform float sharpness;
 
 varying vec2 textureCoordinate;
 varying vec2 leftTextureCoordinate;
 varying vec2 rightTextureCoordinate; 
 varying vec2 topTextureCoordinate;
 varying vec2 bottomTextureCoordinate;
 
 varying float centerMultiplier;
 varying float edgeMultiplier;
 
 void main()
 {
     gl_Position = position;
     
     vec2 widthStep = vec2(imageWidthFactor, 0.0);
     vec2 heightStep = vec2(0.0, imageHeightFactor);
     
     textureCoordinate = inputTextureCoordinate.xy;
     leftTextureCoordinate = inputTextureCoordinate.xy - widthStep;
     rightTextureCoordinate = inputTextureCoordinate.xy + widthStep;
     topTextureCoordinate = inputTextureCoordinate.xy + heightStep;     
     bottomTextureCoordinate = inputTextureCoordinate.xy - heightStep;
     
     centerMultiplier = 1.0 + 4.0 * sharpness;
     edgeMultiplier = sharpness;
 }
);

相同的技术，将相邻坐标的计算放在顶点着色器中。

NSString *const kGPUImageSharpenFragmentShaderString = SHADER_STRING
(
 precision highp float;
 
 varying highp vec2 textureCoordinate;
 varying highp vec2 leftTextureCoordinate;
 varying highp vec2 rightTextureCoordinate; 
 varying highp vec2 topTextureCoordinate;
 varying highp vec2 bottomTextureCoordinate;
 
 varying highp float centerMultiplier;
 varying highp float edgeMultiplier;
 uniform sampler2D inputImageTexture;
 
 void main()
 {
     mediump vec3 textureColor = texture2D(inputImageTexture, textureCoordinate).rgb;
     mediump vec3 leftTextureColor = texture2D(inputImageTexture, leftTextureCoordinate).rgb;
     mediump vec3 rightTextureColor = texture2D(inputImageTexture, rightTextureCoordinate).rgb;
     mediump vec3 topTextureColor = texture2D(inputImageTexture, topTextureCoordinate).rgb;
     mediump vec3 bottomTextureColor = texture2D(inputImageTexture, bottomTextureCoordinate).rgb;
     gl_FragColor = ve((textureColor * centerMultiplier - (leftTextureColor * edgeMultiplier + rightTextureColor * edgeMultiplier + topTextureColor * edgeMultiplier + bottomTextureColor * edgeMultiplier)), texture2D(inputImageTexture, bottomTextureCoordinate).w);
 }
);

片段着色器分别获取顶部，底部，左侧和右侧的像素值，并根据模板系数计算乘积。可以注意到，这里的模板系数实际上不是固定的，而是根据外部设置的清晰度动态调整的，因此可以针对不同的图片和不同的需求设置不同的锐化强度。在上面的跑步效果图中设置的锐度值为1. 0，可以设置不同的强度值，甚至可以使用不同的锐化模板。

作者简介：Bill，每天都是Ptu iOS工程师

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