Position of the vertex not filled in Android?

Hi,

I wrote this simple shader. It is supposed to display disqus on top of a texture: center and radius are input values.
My problem is that is works nicely on my laptop. But strangely on my android. It displays either MainTex or the color of the disqus (on the whole material).
Playing around with values, I'm under the impression that i.vertex in my code is (0 0 0).

Any idea?
Thanks a lot,
Michaël

Shader"Unlit/simpleUnlit2"
{
Properties
{
_MainTex ("Texture", 2D) = "white" {}
_CentrePoint1 ("Centre1", Vector) = (0, 0, 0, 0)
_CentrePoint2 ("Centre2", Vector) = (0, 0, 0, 0)
_rayon ("rayon", Float) = 0.5
_luminosity ("luminosity", Float) = 1
_Color1 ("Color1", Color) = (0.3, 0.4, 0.7, 1.0)
_Color2 ("Color2", Color) = (0.6, 0.2, 0.7, 1.0)
}
SubShader
{
Tags { "RenderType"="Opaque" }
LOD 100

Pass
{
CGPROGRAM
#pragmavertexvert
#pragmafragmentfragalpha


#include "UnityCG.cginc"

struct appdata
{
float4vertex : POSITION;
float2 uv : TEXCOORD0;
};

struct v2f
{
float2 uv : TEXCOORD0;
float4vertex : SV_POSITION;
};

sampler2D _MainTex;
float4 _MainTex_ST;
float4 _CentrePoint1;
float4 _CentrePoint2;
float _rayon;
float _luminosity;
float4 _Color1;
float4 _Color2;

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

float4 frag (v2f i) : SV_Target
{
//samplethe texture
float4 col = tex2D(_MainTex, i.uv);

float curDistance1 = float(distance(_CentrePoint1.xyz, i.vertex));
float curDistance2 = float(distance(_CentrePoint2.xyz, i.vertex));
int a1= int(max(float(0),sign(_rayon-curDistance1)));
int a2= int(max(float(0),sign(_rayon-curDistance2)));
inta=abs(a1-a2);

float4 c1=_Color1.rgba*a1;
c1.a=a1;
float4 c2=_Color2.rgba*a2;
c2.a=a2;
float4 cF;
//floatisHidden=float(abs(a1-a2));
//floatisTransparent=1-isHidden;
float isHidden=a1;
float isTransparent=1-isHidden;
cF.rgb=isHidden*(c1+c2)+col.rgb*isTransparent*_luminosity;
col.rgb=cF.rgb;
col.a = 1;

return col;
}
ENDCG
}
}
}

 

OpenGL ES (used in most mobile devices) doesn't support reading screen position in pixel shader. You have to compute it in vertex shader and pass it over. There's a built in function for that - ComputeScreenPos.
1) make room in your input structure

Code (CSharp):

1. float4 screenPos : TEXCOORD1;

2) compute screen position in vertex shader

Code (CSharp):

1. o.screenPos = ComputeScreenPos(v.vertex);

3) divide by w in pixel shader and use it instead of i.vertex

Code (CSharp):

1. float2 screenPos = i.screenPos.xy / i.screenPos.w;

 

THANK YOU, Michal. I was almost dancing when I saw it working