Noise Algorithm Problem (GLES)

[sanchiski]

I am struggling to get the next simple algorithm working in the Samsung Galaxy SIII



float rand(vec2 co)
{
return fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453);
}

....
vec3 color = texture2D(u_texture, v_texcoord);
gl_FragColor.rgb = color + vec3(rand(gl_FragCoord.xy + time / 1000.0));
....


The code generates perfectly the expected noise in Samsung Galaxy S1 and Google Nexus S. But it fails completely in the new smartphone which uses ARM's Mali-400/MP4.

Anyone can spot anything wrong with this algorithm? Or maybe understand why could it fail?

[mbentrup]

Mali fragment programs use a 16-bit float type by default (with 10 bits mantissa), so that the argument to fract probably will not have enough precision to store any fractional digits.

[ZbuffeR]

Is it possible to access to more precision with this phone ?

[sanchiski]

So I tried to put high precision by prefixing the float with highp. And I've got the next compiler error:

"High precision not supported, instead compiling high precision as medium precision"

If this then a precision issue? and if so, what alternatives to I have?