OpenGL ES (iPhone) Touch Picking

Question

Looking to do classic OpenGL mouse picking in ES. I\'d prefer not to use third party libs, GLU ports and OpenGL name stacks, etc, are out. This pretty much leaves inverse

Answer 1

I managed to fix it:

-(void)view2WorldPoint:(CGPoint)point :(GLfloat*)worldPoint {
    // this is the inverse translation of the modelview
    GLfloat width = (GLfloat)backingWidth;
    GLfloat height = (GLfloat)backingHeight;

    float clickX = point.x;
    float clickY = point.y;
    float clickZ = 0.0f;

    NSLog(@"click point : x = %f, y = %f, z = %f", clickX, clickY, clickZ);

    //  NSLog(@"Me : x = %f, y = %f, z = %f", a[0], a[1], a[2]);
    //  NSLog(@"Dev : x = %f, y = %f, z = %f", squareX, squareY, squareZ);

    //viewport -> normalized device coord -> clip
    GLfloat n[] = {
        2 * clickX / width - 1,
        2 * (480-clickY) / height - 1,
        2 * clickZ - 1,
        1
    };
    //  NSLog(@"Obj : x = %f, y = %f, z = %f", rect.origin.x, rect.origin.y, -0.5);
    //  NSLog(@"N : x = %f, y = %f, z = %f", n[0], n[1], n[2]); 

    //I'm a viewing volume symmetric projection matrix
    //  GLfloat P[] = {
    //      near / right, 0, 0, 0,
    //      0, near / top, 0, 0,
    //      0, 0, -(far + near) / (far - near), (-2 * far * near) / (far - near),
    //      0, 0, -1, 0
    //  };
    GLfloat P[16];
    glGetFloatv(GL_PROJECTION_MATRIX, P);
    //  [self dumpMatrix:P :@"P"];

    GLfloat Pminus1[] = {
        1/P[0], 0, 0, 0,
        0, 1/P[5], 0, 0,
        0, 0, 0, 1/P[11],
        0, 0, 1/P[14], -(P[10]/ (P[11]*P[14]))
    };

    //  [self dumpMatrix:Pminus1 :@"P-1"];

    //clip -> view
    GLfloat v[] = {
        (Pminus1[0] * n[0]) + (Pminus1[1] * n[1]) + (Pminus1[2]  * n[2]) + (Pminus1[3] * n[3]),
        (Pminus1[4] * n[0]) + (Pminus1[5] * n[1]) + (Pminus1[6]  * n[2]) + (Pminus1[7] * n[3]),
        (Pminus1[8] * n[0]) + (Pminus1[9] * n[1]) + (Pminus1[10] * n[2]) + (Pminus1[11] * n[3]),
        (Pminus1[12] * n[0]) + (Pminus1[13] * n[1]) + (Pminus1[14] * n[2]) + (Pminus1[15] * n[3])
    };

    //  NSLog(@"v = [%f, %f, %f, %f]", v[0], v[1], v[2], v[3]);


    //  [self dumpMatrix:mv :@"mv"];

    //view -> world
    GLfloat Rt[] = {
        mv[0], mv[4], -mv[8],
        mv[1], mv[5], -mv[9],
        -mv[2], -mv[6], mv[10]
    };

    //  NSLog(@"Rt0 = [%f, %f, %f]", Rt[0], Rt[1], Rt[2]);
    //  NSLog(@"Rt1 = [%f, %f, %f]", Rt[3], Rt[4], Rt[5]);
    //  NSLog(@"Rt2 = [%f, %f, %f]", Rt[6], Rt[7], Rt[8]);

    GLfloat tPrime[] = {
        Rt[0] * mv[12] + Rt[1] * mv[13] + Rt[2] * mv[14],
        Rt[3] * mv[12] + Rt[4] * mv[13] + Rt[5] * mv[14],
        Rt[6] * mv[12] + Rt[7] * mv[13] + Rt[8] * mv[14]
    };

    //  NSLog(@"tPrime = [%f, %f, %f]", tPrime[0], tPrime[1], tPrime[2]);

    GLfloat Mminus1[] = {
        Rt[0], Rt[1], Rt[2], -(tPrime[0]),
        Rt[3], Rt[4], Rt[5], -(tPrime[1]),
        Rt[6], Rt[7], Rt[8], -(tPrime[2]),
        0, 0, 0, 1
    };

    //point in world space
    GLfloat w[] = {
        Mminus1[0] * v[0] + Mminus1[1] * v[1] + Mminus1[2] * v[2] + Mminus1[3] * v[3],
        Mminus1[4] * v[0] + Mminus1[5] * v[1] + Mminus1[6] * v[2] + Mminus1[7] * v[3],
        Mminus1[8] * v[0] + Mminus1[9] * v[1] + Mminus1[10] * v[2] + Mminus1[11] * v[3],
        Mminus1[12] * v[0] + Mminus1[13] * v[1] + Mminus1[14] * v[2] + Mminus1[15] * v[3]
    };
    NSLog(@"W : x = %f, y = %f, z = %f", w[0], w[1], w[2]);
    worldPoint[0] = w[0];
    worldPoint[1] = w[1];
    worldPoint[2] = w[2];
}