Frag Coord experiments

On hamburg (Fedora, GTS450) the original version of this appeared as a constant green/brown colour.

On Nexus 7/Nightly, it appeared as horizontal stripes - the bits that used gl_FragCoord's fractional part to compute the colour were black => the fractional part is 0.0.

The fragment shader had a hack to use a value that was floor(gl_FragCoord) + vec2(0.5, 0.5), and then behaviour was consistent.

However the mod/float/mult/div/etc maths that is used to generate a pseudorandom number is giving different results :-(

External references:

Debug messages will appear here