Read 0 outside image (instead of clamp-to-edge)

[haesleinhuepf]

We should be able to read pixels outside the image as 0 . Problem: This is not officially defined by the opencl standard. Furthermore, a code section relevant for this is commented out. I think I remember that this didn't work on specific hardware:

pyclesperanto_prototype/pyclesperanto_prototype/_tier0/preamble.cl

Line 36 in efb38e9

if (true) { // if (CLK_ADDRESS_CLAMP_TO_EDGE & sampler) {

Anyway, it would be great to have some specific kernels read 0 outside the image.

[StRigaud]

I think this should be an Issue for the kernel repo and be addressed in the preamble / OpenCL management, with possible an option defined at runtime.

Right now, the border effect correspond to the nearest mode ( aaaa | abcd | dddd ).