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The x y parameters definition

I'm trying to understand the mapping kernel in Renderscript.

A sample mapping kernel looks like this

uchar4 RS_KERNEL invert(uchar4 in, uint32_t x, uint32_t y) {
uchar4 out = in;
out.r = 255 - in.r;
out.g = 255 - in.g;
out.b = 255 - in.b;
return out;
}

However, there is not much clarity regarding what the x, y parameters refer to ( whether x points to height or width of the given pixel in a bitmap)

enter image description here

The official documentation only says so much about x, y

A mapping kernel function or a reduction kernel accumulator function may access the coordinates of the current execution using the special arguments x, y, and z, which must be of type int or uint32_t. These arguments are optional.

This is critical information as interchanging and accessing can lead to out of bounds error. If you have worked on it, please give your insights on this.

Solution

  • The x and y (and z, if using a 3D allocation) are the width and height (and depth for 3D). This means that the in parameter of your kernel function corresponds to the data in your allocation at the point x, y.