void sod_img_set_pixel(sod_img input, int x, int y, int c, float val);
Add a constant value to a pixel at the given location. This value must be set between 0..1 such as 0.7.
The x-coordinate, in logical units, of the pixel to be set.
The y-coordinate, in logical units, of the pixel to be set.
The constant value to be added at the target location.
None. If the coordinate is out-of-range then this function is a no-op.