Proof of concept spatial interpolation filter working on VisPy ImageVisual

color.py

_interpolation_template = """
    #include "misc/spatial-filters.frag"
    vec4 texture_lookup_filtered(vec2 texcoord) {
        if(texcoord.x < 0.0 || texcoord.x > 1.0 ||
        texcoord.y < 0.0 || texcoord.y > 1.0) {
            discard;
        }
        return %s($texture, $shape, texcoord);
    }"""

_texture_lookup = """
    vec4 texture_lookup(vec2 texcoord) {
        if(texcoord.x < 0.0 || texcoord.x > 1.0 ||
        texcoord.y < 0.0 || texcoord.y > 1.0) {
            discard;
        }
        return texture2D($texture, texcoord);
    }"""

class Interpolation(object):
    def __init__(self, interpolation='nearest'):
        self.shader = Function("""
        """)

        # load interpolation kernel
        self._kernel, self._interpolation_names = load_spatial_filters()
        # create interpolation shader functions for available
        # interpolations
        fun = [Function(_interpolation_template % n)
               for n in self._interpolation_names]
        self._interpolation_names = [n.lower()
                                     for n in self._interpolation_names]

        self._interpolation_fun = dict(zip(self._interpolation_names, fun))
        self.interpolation_filters = self._interpolation_names

        # overwrite "nearest" and "bilinear" spatial-filters
        # with  "hardware" interpolation _data_lookup_fn
        self._interpolation_fun['nearest'] = Function(_texture_lookup)
        self._interpolation_fun['bilinear'] = Function(_texture_lookup)

        # create interpolation kernel Texture2D, using 'r16f'
        # as discussed in issue #1017
        self._kerneltex = Texture2D(self._kernel, interpolation='nearest',
                                    internalformat='r16f')

        if interpolation not in self._interpolation_names:
            raise ValueError("interpolation must be one of %s" %
                             ', '.join(self._interpolation_names))

        self._interpolation = interpolation

        # check texture interpolation
        if self._interpolation == 'bilinear':
            texture_interpolation = 'linear'
        else:
            texture_interpolation = 'nearest'

        self._attvis = None

    def _attach(self, visual):
        self._attvis = visual
        self._build_interpolation(visual)

    @property
    def interpolation(self):
        return self._interpolation

    @interpolation.setter
    def interpolation(self, i):
        if i not in self._interpolation_names:
            raise ValueError("interpolation must be one of %s" % ', '.join(self._interpolation_names))
        #if self.interpolation != i:
        self._interpolation = i
        self._build_interpolation(self._attvis)
        print(i)
            #self._need_interpolation_update = True
            #self.update()

    @property
    def interpolation_functions(self):
        return self._interpolation_names

    def _build_interpolation(self, visual):
        """Rebuild the _data_lookup_fn using different interpolations within
        the shader
        """
        interpolation = self._interpolation
        visual._data_lookup_fn = self._interpolation_fun[interpolation]
        visual.shared_program.frag['get_data'] = visual._data_lookup_fn

        # only 'Bilinear' uses 'linear' texture interpolation
        if interpolation == 'bilinear':
            texture_interpolation = 'linear'
        else:
            # 'Nearest' (and also 'Bilinear') doesn't use spatial_filters.frag
            # so u_kernel and shape setting is skipped
            texture_interpolation = 'nearest'
            if interpolation != 'nearest':
                visual.shared_program['u_kernel'] = self._kerneltex
                visual._data_lookup_fn['shape'] = visual._data.shape[:2][::-1]

        if visual._texture.interpolation != texture_interpolation:
            visual._texture.interpolation = texture_interpolation

        visual._data_lookup_fn['texture'] = visual._texture
        visual.update()