A few pixels inside

Member

Posts: 131
Joined: 2010.08

Post: #1

Aug 10, 2010 — 08:00 PM

These are pieces of code for drawing a circle and doing collision detection with the view's edges. Why are the left and right collision edges a few pixels inside the view?

Code:

    size = [self bounds].size;

    viewAspect = size.width / size.height;

glOrtho(0.0, viewAspect, 0.0, 1.0, -1.0, 1.0);

Code:

    GLint i;

    GLfloat cosine, sine, PI;

    PI = 3.14159265;

    glTranslatef(ballX, ballY, 0.0f);

    glBegin(GL_POLYGON);

    {

        for(i=0;i<100;i++)

        {

            cosine=cos(i*2*PI/100.0);

            sine=sin(i*2*PI/100.0);

            glVertex2f(RADIUS*cosine, RADIUS*sine);

        }

    }

    glEnd();

Code:

    if (((ballX + ballSpeedX) - viewAspect*RADIUS_FRACTION) < 0.0)

    {

        penetration = 0.0f - ((ballX + ballSpeedX) - viewAspect*RADIUS_FRACTION);

        ballX += penetration * 2.0f;

        ballSpeedX = -ballSpeedX;

    }

    if (((ballX + ballSpeedX) + viewAspect*RADIUS_FRACTION) > viewAspect)

    {

        penetration = ((ballX + ballSpeedX) + viewAspect*RADIUS_FRACTION) - viewAspect;

        ballX -= penetration * 2.0f;

        ballSpeedX = -ballSpeedX;

    }

    if (((ballY + ballSpeedY) - RADIUS_FRACTION) < 0.0)

    {

        penetration = 0.0f - ((ballY + ballSpeedY) - RADIUS_FRACTION);

        ballY += penetration * 2.0f;

        ballSpeedY = -ballSpeedY;

    }

    if (((ballY + ballSpeedY) + RADIUS_FRACTION) > 1.0)

    {

        penetration = ((ballY + ballSpeedY) + RADIUS_FRACTION) - 1.0;

        ballY -= penetration * 2.0f;

        ballSpeedY = -ballSpeedY;

    }

    ballY += ballSpeedY;

    ballX += ballSpeedX;

Miglu

Member

Posts: 131
Joined: 2010.08

Post: #2

Aug 12, 2010 — 02:46 PM

It seems that no-one who has looked at this question can answer it. Is any OpenGL expert on these forums willing to look at the entire project, if that makes it easier, so that I would send it.

McSpider

Apprentice

Posts: 16
Joined: 2010.02

Post: #3

Aug 12, 2010 — 07:03 PM

I'm no pro but wouldn't this work?
You would of course need a viewWidth variable.

Code:

ballY += ballSpeedY;

            ballX += ballSpeedX;

    if ((ballX - RADIUS) < 0.0)

    {

    penetration = 0.0 - (ballX - RADIUS);

        ballX += penetration * 2.0f;

        ballSpeedX = -ballSpeedX;

    }

    if ((ballX + RADIUS) > viewWidth)

    {

    penetration = (ballX + RADIUS) - viewWidth;

        ballX -= penetration * 2.0f;

        ballSpeedX = -ballSpeedX;

    }

    if ((ballY - RADIUS) < 0.0)

    {

        penetration = 0.0f - (ballY - RADIUS);

        ballY += penetration * 2.0f;

        ballSpeedY = -ballSpeedY;

    }

    if ((ballY + RADIUS) > 1.0)

    {

        penetration = (ballY + RADIUS) - 1.0;

        ballY -= penetration * 2.0f;

        ballSpeedY = -ballSpeedY;

    }

And I don't really get why your doing:
((ballX - viewAspect*RADIUS) < 0.0)
Could you explain your logic behind that if statement?

Miglu

Member

Posts: 131
Joined: 2010.08

Post: #4

Aug 12, 2010 — 07:41 PM

I improved the third piece of code, but forgot to update the post until now. However, the edges are still a few pixels inside the view.

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