Skyward Sword Brush shader. Accurately emulates what's done with TEVs in a shader. Does NOT include the blurring pass.

ss-fs.glsl

#version 300 es
precision highp float;

in vec2 UV;
out vec4 out_color;
uniform float ratio, time;
uniform sampler2D texture0;

const float PI_3 = 1.0471975512;

void main(void) {
    
    float v = 0.004f;
    vec2 d = vec2(v / ratio, v);

    #define hexa(k) vec2(cos(PI_3 * k), sin(PI_3 * k))
    vec2 deltas[6] = vec2[6](
	hexa(0.), hexa(1.), hexa(2.), 
        hexa(3.), hexa(4.), hexa(5.) 
    );
    #undef hexa

    vec2 xy = vec2(UV.x, 1.0f - UV.y);
    vec4 col = texture(texture0,  xy);

    for (int i = 0; i < 6; ++i) {
        vec4 col2 = texture(texture0,  xy + deltas[i] * d);
        vec4 t = max(sign(col2 - col), 0.);
        col += (col2 - col) * t;
    }

    col.a = 1.0;
    out_color = col;
}

This is basically a screen space filter that looks for the maximum rgb components among 6 nears samples.
Contrary to popular belief, there is no Depth of Field. The effect is just turned off for samples that are near the camera, but the brush strokes don't get bigger the furthest a sample is.

The 0.004f isn't the exact value used by the game, but close enough to not make a visible difference.
The game does that in two passes, plus another pass where it applies a blur filter. Which is just downsampling and upscaling.