Programming Forums > Application Development > C++

Konnor · Dec 7th, 2005, 6:40 PM

I'd like to have a ball trail implemented in my openGL game (round circles of decreasing size behind the ship when it is moving).

The code I'm using to draw a cirlce is as follows

(Toggle Plain Text)

glBegin(GL_POLYGON);
    glColor3f(0.0, 1.0, 0.0);
    for(int i=0; i<360; i+=5)
    {
          float xcoord = Xtri + 2 * cos(i*(PI/180));
          float ycoord = Ytri + 2 * sin(i*(PI/180));
          glVertex2f(xcoord, ycoord);
    }
glEnd();

the 'Xtri' and 'Ytri' represent The position the circle is drawn and is constantly updated.

I can visualise it in my head but I cant get it down on paper. I (think) i need to store the old co-ordinates for the ball in an array (an array each for X and Y). What might the code for this look like? how can I shift the old co-ordinates through an array of say length 5, filling it will different old values? (the current X and Y values are being updated all the time when the user presses the arrow keys to move the ship round the screen).

Once I have the old values I can duplicate the code above and draw more circles behind the ship and smaller to give the trail effect.

Many thanks,

Ooble · Dec 8th, 2005, 11:21 AM

I would personally use a queue. You can implement one yourself, or use the standard library's one (std::queue). When you're adding a new ring, enqueue a coordinate, and when you're removing one, dequeue it.

Dec 7th, 2005, 6:40 PM	#1
Konnor Newbie Join Date: Aug 2005 Posts: 23 Rep Power: 0	Implementing a ball trail I'd like to have a ball trail implemented in my openGL game (round circles of decreasing size behind the ship when it is moving). The code I'm using to draw a cirlce is as follows (Toggle Plain Text) glBegin(GL_POLYGON); glColor3f(0.0, 1.0, 0.0); for(int i=0; i<360; i+=5) { float xcoord = Xtri + 2 * cos(i(PI/180)); float ycoord = Ytri + 2 sin(i(PI/180)); glVertex2f(xcoord, ycoord); } glEnd(); glBegin(GL_POLYGON); glColor3f(0.0, 1.0, 0.0); for(int i=0; i<360; i+=5) { float xcoord = Xtri + 2 cos(i(PI/180)); float ycoord = Ytri + 2 sin(i*(PI/180)); glVertex2f(xcoord, ycoord); } glEnd(); the 'Xtri' and 'Ytri' represent The position the circle is drawn and is constantly updated. I can visualise it in my head but I cant get it down on paper. I (think) i need to store the old co-ordinates for the ball in an array (an array each for X and Y). What might the code for this look like? how can I shift the old co-ordinates through an array of say length 5, filling it will different old values? (the current X and Y values are being updated all the time when the user presses the arrow keys to move the ship round the screen). Once I have the old values I can duplicate the code above and draw more circles behind the ship and smaller to give the trail effect. Many thanks,

Dec 8th, 2005, 11:21 AM	#2
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	I would personally use a queue. You can implement one yourself, or use the standard library's one (std::queue). When you're adding a new ring, enqueue a coordinate, and when you're removing one, dequeue it. __________________ Me :: You :: Them

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Programming Forums > Application Development > C++

Implementing a ball trail