Shader precision on Android device

Archived Forums Questions & Answers
1

Hi,

I’m using a shader to interlace the image of two cameras. The left camera is displayed in the odd rows, the right camera is displayed in the even rows.

It works fine on PC, but on an Android tablet, it only works for HALF the screen, then the interlacing becomes weird and faulty.

I think this is a floating point precision issue. How can I get rid of it?

Pass {
		ZTest Always
		Cull Off
		ZWrite Off
		Fog {
			Mode off
		}
		CGPROGRAM
		#pragma vertex vert_img
		#pragma fragment frag
		#pragma fragmentoption ARB_precision_hint_nicest 
		#include "UnityCG.cginc"
		
		uniform float _Weave_X; //columns, here 1920
		uniform float _Weave_Y; //rows, here 1200
		uniform sampler2D	_LeftTex;
		uniform sampler2D	_RightTex;

		float4 frag( v2f_img IN ) : COLOR0 {
			float3 left = tex2D( _LeftTex, IN.uv ).rgb;		// Sample scene texture
			float3 right = tex2D( _RightTex, IN.uv ).rgb;	// Sample scene texture
			
			int x = fmod(floor( IN.uv.x*_Weave_X) + floor(IN.uv.y*_Weave_Y),2);      //checks if even or odd					
			return float4( lerp( left, right, x ), 0.0 );                                //interpolated between even and odd pixels
		}
		ENDCG
	}

Thanks in advance!

2

It seems I solved the problem.

I modified UnityCG.cginc by adding a custom Modulo function:

float mod(float x, float y){
     return x-y*floor(x/y);
}

and now it works on the Android tablet as well.