heat visor?

have anyone any idea for a thermal visor?
i found this shader effect but i don’t know how to use it

uniform sampler2D sceneTex;
uniform float vx_offset;
void main()
  vec2 uv = gl_TexCoord[0].xy;

  vec3 tc = vec3(1.0, 0.0, 0.0);
  if (uv.x < (vx_offset-0.005))
    vec3 pixcol = texture2D(sceneTex, uv).rgb;
    vec3 colors[3];
    colors[0] = vec3(0.,0.,1.);
    colors[1] = vec3(1.,1.,0.);
    colors[2] = vec3(1.,0.,0.);
    float lum = dot(vec3(0.30, 0.59, 0.11), pixcol.rgb);
    int ix = (lum < 0.5)? 0:1;
    tc = mix(colors[ix],colors[ix+1],(lum-float(ix)*0.5)/0.5);
  else if (uv.x>=(vx_offset+0.005))
    tc = texture2D(sceneTex, uv).rgb;
	gl_FragColor = vec4(tc, 1.0);

Looks like that’s supposed to be used as a postprocessing shader. Render the main scene into a buffer instead of into the main window, create a fullscreen card on render2d, apply the rendered texture to it, and this shader (along with a simple vertex shader).