Unity3D - a shader that will crop texture on an iOS device

Question

This is the first time I have been working with Unity shaders, and I have a problem creating a shader that will draw only part of the texture. The code below works with a stand-alone build of Mac, but not on an iOS device. How can i fix this?

Shader "Sprite/ClipArea"
{
    Properties
    {
        _MainTex ("Base (RGB), Alpha (A)", 2D) = "white" {}
        _Length ("Length", Range(0.0, 1.0)) = 1.0
        _Width ("Width", Range(0.0, 1.0)) = 1.0
     }

    SubShader
    {
        LOD 200

        Tags
        {
            "Queue" = "Transparent"
            "IgnoreProjector" = "True"
            "RenderType" = "Transparent"
        }

        Pass
        {
            Cull Off
            Lighting Off
            ZWrite Off
            Offset -1, -1
            Fog { Mode Off }
            ColorMask RGB
            Blend SrcAlpha OneMinusSrcAlpha

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float _Length;
            float _Width;

            struct appdata_t
            {
                float4 vertex : POSITION;
                float2 texcoord : TEXCOORD0;
            };

            struct v2f
            {
                float4 vertex : POSITION;
                float2 texcoord : TEXCOORD0;
            };

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

            half4 frag (v2f IN) : COLOR
            {
                if ((IN.texcoord.x<0) || (IN.texcoord.x>_Width) || (IN.texcoord.y<0) || (IN.texcoord.y>_Length))
                {
                    clip(-1);
                }
                return tex2D(_MainTex, IN.texcoord);
            }
            ENDCG
        }
    }
}

Thank!

Answer 1

On mobile devices, it is recommended that you do not use clip / reset methods, as this is a very expensive operation.

I updated the fragment shader part without the clip / discard method. Here, instead of clipping, make parts that you do not want to display in a transparent color, and for the rest, render as they are.

if ((IN.texcoord.x<0) || (IN.texcoord.x>_Width) || (IN.texcoord.y<0) || (IN.texcoord.y>_Length))
{
    half4 colorTransparent = half4(0,0,0,0) ;
    return colorTransparent ;
}
else
    return tex2D(_MainTex, IN.texcoord) ;