iphone - Using GPUImage, how would I split image into 4 and apply different filters to all 4 corners and recombine? -

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i want similar gpu logo, different filter on each corner.

gpu logo

so far have managed achieve image size half of original. here simplification of code:

_croptopleft = [[gpuimagecropfilter alloc]                  initwithcropregion:cgrectmake(0.0, 0.0, 0.5, 0.5)];  cgaffinetransform toplefttransform = cgaffinetransformmaketranslation(-1, -1); toplefttransform = cgaffinetransformscale(toplefttransform, 0.5, 0.5); _transformtl = [[gpuimagetransformfilter alloc] init]; _transformtl.affinetransform = toplefttransform;   // set pipeline: image -> crop -> transform  //   don't apply effects corners now,  //   try recreate original image  [imagesource addtarget:_croptopleft]; [_croptopleft addtarget:_transformtl];   // same other corners... tr, bl & br    // recombine // can apply 2 inputs blend filter, combine using 3 filteres // blend filteres `gpuimagenormalblendfilter` instances  [_transformtl addtarget:_blendfiltertop]; [_transformtr addtarget:_blendfiltertop]; [_transformbl addtarget:_blendfilterbottom]; [_transformbr addtarget:_blendfilterbottom];  [_blendfiltertop addtarget:_blendfilterall]; [_blendfilterbottom addtarget:_blendfilterall];  [_blendfilterall addtarget:_mygpuimageview];

the issue when corner of image cropped, canvas size halved.

i believe half size used through pipeline.

my work around half corner again transform, results in 1/2 resolution output image.

i think easiest solution is, instead of messing of crops , transforms, create shader set alpha 0 on entire image except quadrant applying filter to.

your filter chain this...

for each quadrant:
apply effect filter -> apply set alpha filter -> on blend previous pass


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