如何在Renderscript中获得位图分配的相邻像素？

Question

I want to perform an image processing operation that needs neighboring pixels, but I'm not sure how to access them from an allocation. Most kernels I have seen operate on a single pixel, update it, and then return it. Is there a way I can access the neighbors of (x, y) in the method below.

uchar4 __attribute__((kernel)) invert(uchar4 in, uint32_t x, uint32_t y) {

  uchar4 neighbor = allocation[x+1][y]; // How do I do this in renderscript?
  uchar4 otherNeighbor = allocation[x-1][y]; 
  ...
}

Answer 1

The standard input/output allocations that get implicitly connected are harder to access for neighboring pixels, but you can get to them by just creating a global variable of type rs_allocation.

rs_allocation input;
uchar4 __attribute__((kernel)) invert(uchar4 in, uint32_t x, uint32_t y) {

uchar4 neighbor = rsGetElementAt_uchar4(input, x+1, y);
uchar4 otherNeighbor = rsGetElementAt_uchar4(input, x-1, y);
...
}

In Java, before you call forEach on your kernel, you just need to do:

myScript.set_input(myInputAllocation);
myScript.forEach_invert(myInputAllocation, myOutputAllocation);

Answer 2

You can, do this:

...
uchar4 neighbor = rsGetElementAt(in, x + 1, y);
uchar4 otherNeighbor = rsGetElementAt(in, x - 1, y);
...