lens_distortion.frag

uniform sampler2D bgl_RenderedTexture;

const vec4 kappa = vec4(1.0,1.7,0.7,15.0);

uniform float screen_width;
uniform float screen_height;

const float scaleFactor = 0.85;

const vec2 leftCenter = vec2(0.25, 0.5);
const vec2 rightCenter = vec2(0.75, 0.5);

// Scales input texture coordinates for distortion.
vec2 hmdWarp(vec2 LensCenter, vec2 texCoord, vec2 Scale, vec2 ScaleIn)
{
    vec2 theta = (texCoord - LensCenter) * ScaleIn;
    float rSq = theta.x * theta.x + theta.y * theta.y;
    vec2 rvector = theta * (kappa.x + kappa.y*rSq + kappa.z*rSq*rSq + kappa.w*rSq*rSq*rSq);
    vec2 tc = LensCenter + Scale * rvector;
    return tc;
}

bool validate(vec2 tc, int left_eye)
{
    //keep within bounds of texture
    if ((left_eye == 1 && (tc.x < 0.0 || tc.x > 0.5)) ||
        (left_eye == 0 && (tc.x < 0.5 || tc.x > 1.0)) ||
        tc.y < 0.0 || tc.y > 1.0)
    {
        return false;
    }
    return true;
}

void main()
{
    vec2 screen = vec2(screen_width, screen_height);

    float as = float(screen.x / 2.0) / float(screen.y);
    vec2 Scale = vec2(0.5, as);
    vec2 ScaleIn = vec2(2.0 * scaleFactor, 1.0 / as * scaleFactor);

    vec2 texCoord = gl_TexCoord[0].st;

    vec2 tc = vec2(0);
    vec4 color = vec4(0);

    if (texCoord.x < 0.5)
    {
        tc = hmdWarp(leftCenter, texCoord, Scale, ScaleIn );
        color = texture2D(bgl_RenderedTexture, tc);
        if (!validate(tc, 1))
            color = vec4(0);
    }
    else
    {
        tc = hmdWarp(rightCenter, texCoord, Scale, ScaleIn);
        color = texture2D(bgl_RenderedTexture, tc);
        if (!validate(tc, 0))
            color = vec4(0);
    }
    gl_FragColor = color;
}