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I'm working with Unity shaders for the first time and I have a problem with making a shader that will draw only some part of a texture. The code below works on mac standalone build, but not on iOS device. How can I fix that?

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
        }
    }
}

Thanks!

Sebastian
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1 Answers1

0

In mobile devices, it is advised not to use clip / discard methods as it is a very expensive operation.

I have updated the fragment shader part without the clip/discard method. Here, instead of clipping, make the portions you don't want to display in transparent color, and for the rest of the portion, render as is.

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) ;
Shadow
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