How to draw outside sprites boundaries with Unity's shaders?

Question

I'm learning how to make shader in Unity and I have a question about shaders applied on sprites.

I made a shader which modifies a sprite to create a distortion effect:

But, as you can see on the picture linked above, my sprite is cut on the boundaries of the sprite.

Is there any way to avoid this cut and draw the missing part ?

My shader :

Shader "Shader101/testShader"
{
    Properties
    {
        _MainTex( "Texture", 2D ) = "white" {}
        _DisplaceTex( "Displacement Texture", 2D ) = "white" {}
        _Power("Power", Range(-0.4, 0.4)) = 0
    }

    SubShader
    {
        Tags
        {
            "Queue" = "Transparent"
        }

        Pass
        {
            Blend SrcAlpha OneMinusSrcAlpha

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float4 vertex : SV_POSITION;
                float2 uv : TEXCOORD0;
            };

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = mul( UNITY_MATRIX_MVP, v.vertex);
                o.uv = v.uv;
                return o;
            }

            sampler2D _MainTex;
            sampler2D _DisplaceTex;
            float _Power;

            fixed4 frag (v2f i) : SV_Target
            {
                float2 distuv = float2( 0, i.uv.y + _Time.x * 2 );

                float2 wave = tex2D( _DisplaceTex, distuv * 5  ).xy;
                wave = (( wave * 2 ) - 1) * _Power - 0.25;

                float4 color = tex2D( _MainTex, i.uv + float2(wave.y, 0) );
                return color;
            }
            ENDCG
        }
    }
}

Sorry for my poor english :|

Thank you

Answer 1

Take a look at your scene view with shaded wireframe mode on.

Here you should see that your shader does not change the vertex position, but only changes the rendered pixel colors in the fragment shader. Therefore it can not draw outside of the mesh.

The easiest way to fix it would be to modify the sprite texture with more transparent areas around your cat. (In Photoshop > Image > Canvas Size ...)