SFML community forums

Help => Graphics => Topic started by: Overlord on October 03, 2011, 11:14:14 pm

Title: Making sprite go in circles
Post by: Overlord on October 03, 2011, 11:14:14 pm

I used trigonometric cicrcle to make ball sprite move on a circular path. It does, only thing is that the path is always moving and changing radius. Don't know if it is a float rounding error or my computer going mad, or probably a semantic error. I'd be grateful if someone took a look at code and helped my find the error.
Sry if code isn't readable. I commented only logic parts.

Code: [Select]



#include <SFML\Graphics.hpp>
#include <cmath>

int main()
{
    sf::VideoMode VMode(800, 600, 32);
    sf::RenderWindow Window(VMode, "Test");

    sf::Texture Ball;
    if (!Ball.LoadFromFile("ball.png"))
        return 1;

    double speed = 1;//constants and start values
    long double angle = 90;
    const double rad = 57.2957795;
    double ang = 0;

    sf::Sprite ball(Ball);
    ball.SetPosition(400,300);
    ball.SetScale(0.1,0.1);




    sf::Event Event;
    while (Window.IsOpened())
    {


        while (Window.PollEvent(Event))
        {
            if (Event.Type == sf::Event::Closed)
            {
                Window.Close();
                break;
            }

        }
        if (angle > 360)//if angle exceeds 360
                angle -= 360;//reset it
            angle += speed * Window.GetFrameTime();//angle in degrees
            ang = angle/rad;//angle in radians

        ball.Move(std::sin(ang),std::cos(ang));//move on a circular path
        Window.Clear(sf::Color(255,0,0));
        Window.Draw(ball);
        Window.Display();
    }

    return 0;
}


Title: Making sprite go in circles
Post by: sbroadfoot90 on October 03, 2011, 11:26:36 pm

You need to use

Code: [Select]

ball.SetPosition(radius*std::sin(ang), radius*std::cos(ang));

Set radius to something because moving on a circle radius 1 wont look that interesting for you.

Also, stylistically, you have two variables named angle and ang, both storing the same data but one is in radians, one in degrees, and the names don't reflect this at all, when your project gets bigger how are you going to remember to change one when the other changes, and how are you going to remember which is which?

Title: Making sprite go in circles
Post by: Overlord on October 04, 2011, 02:38:23 pm

Found the problem. It isn't graphic package. Window.GetFrameTime() returns 1 or 0. Tried with Clock class, but still the same problem. Anyone know a fix for it?

Title: Making sprite go in circles
Post by: Laurent on October 04, 2011, 02:50:25 pm

Quote

Window.GetFrameTime() returns 1 or 0

In recent SFML 2, it returns an integer number of milliseconds.

Title: Making sprite go in circles
Post by: Overlord on October 04, 2011, 02:55:41 pm

:lol: I used old revision with new docs. Back to cmake and compiling. Sry for wasting your time :lol:

Title: Making sprite go in circles
Post by: sbroadfoot90 on October 04, 2011, 11:35:44 pm

Quote

Code: [Select]

       ball.Move(std::sin(ang),std::cos(ang));

You still have the maths wrong though. The Move(x2, y2) function will move it from it's current position (x, y) to (x + x2, y + y2).

What I've found is that this will draw a circle, but the radius will depend on the frame rate.

See high framerate http://grab.by/b0lK
See low framerate  http://grab.by/b0lL

If the frame rate is variable enough, then it won't even draw a circle see http://grab.by/b0lI.

If you want it to move along a fixed circle at a fixed rate, use the code I posted in my first reply