Sprite disappear shader - unity3d

Question

i am working on Unity 2D platform game.
i am using a shader i found here, but when i flip my sprite (scale -1),
the sprite disappeared, i have little understand in shader coding,
And i didn't found any help on Google, can any one help fixing the shader?.
here is the shader:
Properties {
[PerRendererData] _MainTex ("Main texture", 2D) = "white" {}
_DissolveTex ("Dissolution texture", 2D) = "gray" {}
_Threshold ("Threshold", Range(0., 1.01)) = 0.
}
SubShader {
Tags { "Queue"="Transparent" }
Blend SrcAlpha OneMinusSrcAlpha
Pass {
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
struct v2f {
float4 pos : SV_POSITION;
float2 uv : TEXCOORD0;
};
sampler2D _MainTex;
v2f vert(appdata_base v) {
v2f o;
o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
o.uv = v.texcoord;
return o;
}
sampler2D _DissolveTex;
float _Threshold;
fixed4 frag(v2f i) : SV_Target {
float4 c = tex2D(_MainTex, i.uv);
float val = tex2D(_DissolveTex, i.uv).r;
c.a *= step(_Threshold, val);
return c;
}
ENDCG
}
}

Answer 1

The sprite is rendered as a rectangle with two triangle of positive index order: clockwise.
You can change the Shading Mode to Shaded Wireframe to inspect that.
And if you flip the sprite (scale -1), the two triangles of the sprite will become counterclockwise. And, counterclockwise triangles will not be rendered by GPU. That's why your sprite disappeared. See also what is a clockwise face in openGL.
If you want to see your sprite even when it is flipped, you can
create two sprites with the same texture: a normal one and a flipped one:
MySprite
|--Normal
|--Flipped (scaled -1)
Then, scale MySprite GameObject to -1 instead.
Turn off backface culling in your shader.
Just add Cull Off to the subshader. See also this.
SubShader {
Tags { "Queue"="Transparent" }
Blend SrcAlpha OneMinusSrcAlpha
Pass {
Cull Off
...