Compute ray direction

Hi all,

I need to compute primary ray direction in fragment shader. I do this like that :

  • compute the 4 ndc cornners of near plane
    vec3 hg = (invV*vec4(-1, 1,-1,1)).xyz;
    vec3 bg = (invV*vec4(-1,-1,-1,1)).xyz;
    vec3 hd = (invV*vec4( 1, 1,-1,1)).xyz;
    vec3 bd = (invV*vec4( 1,-1,-1,1)).xyz;

  • put uv between [-1,1]
    vec2 uv = 0.5*(vec2(-1)+2*texCoord.xy);

  • compute the position of a pixel on near plane

 vec3 pt = mix(mix(bg,bd,texCoord.x),mix(hg,hd,texCoord.x),texCoord.y);

  • at last compute the ray direction

    vec3 dir  = normalize(;
    vec3 orig =;

Am i right?

You can do it simpler :

vec3 pt = (invV*vec4(uv,-1,1)).xyz;