Pixel-Composer/shaders/sh_invert/sh_invert.fsh

//
// Simple passthrough fragment shader
//
varying vec2 v_vTexcoord;
varying vec4 v_vColour;

void main() {
	vec4 c = texture2D( gm_BaseTexture, v_vTexcoord );
    gl_FragColor = vec4(1. - c.rgb, c.a);
}