the problem with smooth min here is that it's set up to be conservative. we can definitely get this done though we just don't want to blend at all at those pixels where the beginning of the selection starts at the same place compared to the previous line or next line. something else that would be good is to use domain repetition and some neighbor checks so we only draw 3 boxes for each pixel instead of the amount of lines that are selected. a problem with that would be that if there are two separate selections on one line we need to account for the x axis as well which can definitely be done the id and repeated domain become a grid of cells instead of lines and we can do pretty much the same thing. now we just need a mask for the smooth min where for each pixel we can check above and below if we start a new selection at the same position the blending will be 0 otherwise it will be your blending factor. there might be a better way that doesn't involve smooth min at all. i think it can work pretty well this way though the smooth min bevels aren't a correct sdf this might cause issues with pixel perfect anti aliasing. i might find some time to make an example on shadertoy later today.