How to Implement GPUImageMaskFilter using GPUImage

Question

I need to Cut from the Full Image using the mask and created the masked Image.

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Answer 1

You don't need a mask filter but an alpha mask blend.

I implemented one here like this:

// GPUImage shader strings
NSString * const kNBUAlphaMaskShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;
 varying highp vec2 textureCoordinate2;

 uniform sampler2D inputImageTexture;
 uniform sampler2D inputImageTexture2;

 void main()
 {
     lowp vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
     lowp vec4 textureColor2 = texture2D(inputImageTexture2, textureCoordinate2);

     gl_FragColor = vec4(textureColor.xyz, textureColor2.a);
 }
 );

Simply keeps the colors from one image and the alpha channel of the second one.

Then create a GPUImageTwoInputFilter:

GPUImageTwoInputFilter * alphaMask = [[GPUImageTwoInputFilter alloc] initWithFragmentShaderFromString:kNBUAlphaMaskShaderString];

I'm not sure if a similar blend filter has been added to GPUImage since.

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Just checked again to see if there's a built-in blend that does it, and there isn't. But the blend filter I used as inspiration is still there (GPUImageAlphaBlendFilter). It merges two images using the alpha mask to mix them. The filter mentioned above doesn't require a second "empty" image.