Possible optimization of 8 if-else branches?

[prisma atlas]

Is there a better way to write and possibly optimize this?

// a and b are objects with a shape attribute which is an enum value
// the shape enum value is either a circle or polygon

if (a->shape == CIRCLE && b->shape == CIRCLE)
    collide_circle_x_circle(a, b);

else if (a->shape == CIRCLE && b->shape == POLYGON)
    collide_polygon_x_circle(b, a);

else if (a->shape == POLYGON && b->shape == CIRCLE)
    collide_polygon_x_circle(a, b);

else if (a->shape == POLYGON && b->shape == POLYGON)
    collide_polygon_x_polygon(a, b);

// these last 4 if-else branches are controlled if collision happened
if (collision) {
    if (a->shape == CIRCLE && b->shape == CIRCLE)
        contact_circle_x_circle(a, b);

    else if (a->shape == CIRCLE && b->shape == POLYGON)
        contact_polygon_x_circle(b, a);

    else if (a->shape == POLYGON && b->shape == CIRCLE)
        contact_polygon_x_circle(a, b);

    else if (a->shape == POLYGON && b->shape == POLYGON)
        contact_polygon_x_polygon(a, b);

[wooden vapor]

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[polar bronze]

You can use nested if

if(a->shape==CIRCLE)
{
    if(b->shape==CIRCLE)
        collide_circle_x_circle(a,b);
    else if(b->shape==POLYGON)
        collide_polygon_x_circle(b,a);
}

[fringe veldt]

switch

[wooden vapor]

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