Question

Other questions close to this topic don’t seem to help me understand it very much. I’m just starting programming using Visual Studio and Direct2D and I’m having trouble understanding how to make two “eyes,” which are ellipses inside of ellipses, follow my mouse.

Inside of the function void MainWindow::CalculateLayout() I’m using

    const float radius3=radius/4;
    const float radius3_2=radius/5;
    const float x3=x-100;
    const float y3=y-150;
    ellipse3 = D2D1::Ellipse(D2D1::Point2F(x3, y3), radius3, radius3_2);
        //left eye

    const float radius4=radius/4;
    const float radius4_2=radius/5;
    const float x4=x+100;
    const float y4=y-150;
    ellipse4 = D2D1::Ellipse(D2D1::Point2F(x4, y4), radius4, radius4_2);
        //right eye

    const float radius5=radius/8;
    const float radius5_2=radius5/2;
    const float x5=x-100;
    const float y5=y-150;
    ellipse5 = D2D1::Ellipse(D2D1::Point2F(x5, y5), radius5, radius5_2);    
    // left eyeball

    const float radius6=radius/8;
    const float radius6_2=radius6/2;
    const float x6=x+100;
    const float y6=y-150;
    ellipse6 = D2D1::Ellipse(D2D1::Point2F(x6, y6), radius6, radius6_2);    
    // right eyeball

to set up where the eyes and eyeballs are. I think that something along the line of this should be used to control where the mouse is. I am trying to do this from a blank project, not from a form. Is the solution to simply replace const float x5=x-100 with the X value of MouseMove?

Answer 1

You need to replace the definition of x5, but you need to do it with a formula which will bound it to stay within the eyeball.

Your formula will look something like this:

// compute the angle from the eyes to the mouse
angle = arctan( (mouseY - y) / (mouseX - x) );
// x-100 and y-150 are assumed to be the origins (center) of the eyeball
// eyeballRadius should be the radius of the eyeball, or slightly smaller (so the eyes do not extend outside of it)
x5 = (x-100) + cos(angle) * eyeballRadius;
y5 = (y-150) + sin(angle) * eyeballRadius;

Hope this helps.

To get the cross-eyed effect when the cursor is very near, you should have each eyeball compute its own angle, for example the left’s would be leftAngle = arctan( (mouseY - (y-150)) / (mouseX - (x-100)) )