Messages

1

Graphics / Re: Comet tail

« on: July 11, 2015, 03:33:02 pm »

Thank you for your replies.

I decided using VertexArray and the tail works perfectly. I even tried fading it by iterating through all vertices and changing their alpha values calculated from quadratic function (to make it smooth). It looks nice.

Should I somehow dispose of faded vertices? Because they are faded, but they still exist in memory and are drawn each frame.

2

Graphics / Re: Comet tail

« on: July 09, 2015, 02:09:42 pm »

If you want the tail to be contiguous and stay behind you could simply draw a line between each of the points denoting the previous positions.

You mean storing coordinates each frame and appending it to VertexArray?

EDIT: Well, it really works fine, only now I can't alter line thickness

3

Graphics / Comet tail

« on: July 09, 2015, 01:40:53 pm »

I'm writing a game in which moving objects leave tails behind themselves, like comets. Objects can be moved either by player input or mathematical function (e.g. on sinusoid).

I couldn't find a good way to perform this so I tried the simplest one - creating CircleShape in regular intervals in objects' positions. And it worked, because of simplicity, but later on it became a performance bottleneck. It's snappy and the tails sometimes break -pics.

How to do it properly? Thor particles?

4

Graphics / Pixel Perfect Collision Image Problem.

« on: November 06, 2014, 11:55:10 pm »

Hi.
I'm writing a code, which performs pixel perfect collision check.
It creates sf::Rect which is rectangle of collision.
Then it transforms its coordinates to sprites' local (referring it to 0,0 points of both sprites).
Then I can use those coordinates to choose pixels in sf::Image entities which are created from the same texture as sprites (it has to be sf::Image because spirtes don't have getPixel method) and check their alpha channels.

And it works perfectly fine until i try to scale my sprites in main loop. Then coordinates in sprite don't match coordinates in image, because one of them is scaled.

How do I manage this? Should I somehow scale sprite back to it's original size at the beginning of function?

(click to show/hide)

bool PixelPerfect(MyClass A, MyClass B)
// MyClass::getGlobalBounds(); just means the same as MyClass::sprite::getGlobalBounds();
// MyClass::GetImg(); returns a reference to static sf::Image variable in class (loaded at the beginning of app)
{
        if( A.getGlobalBounds().intersects(B.getGlobalBounds()) )       //if sprites intersect, do pixel perfect test
        {
                int RectLeft   = static_cast<int> ( max(A.getGlobalBounds().left , B.getGlobalBounds().left) );
                int RectRight  = static_cast<int> ( min(A.getGlobalBounds().left + A.getGlobalBounds().width , B.getGlobalBounds().left + B.getGlobalBounds().width) );
                int RectBottom = static_cast<int> ( min(A.getGlobalBounds().height + A.getGlobalBounds().top , B.getGlobalBounds().height + B.getGlobalBounds().top) );
                int RectTop    = static_cast<int> ( max(A.getGlobalBounds().top , B.getGlobalBounds().top) );

                sf::IntRect Rect(RectLeft,                                      //collision rectangle
                                                RectTop,
                                                RectRight - RectLeft,
                                                RectBottom - RectTop);         

                int LocalLeftA = RectLeft - static_cast<int> (A.sprite.getPosition().x);        //local coordinates of Rect (referring to A and B),
                int LocalTopA  = RectTop  - static_cast<int> (A.sprite.getPosition().y);        //they will be used to refer to pixel positions in sf::Image
                int LocalLeftB = RectLeft - static_cast<int> (B.sprite.getPosition().x);        //as they are the same (if not scaled)
                int LocalTopB  = RectTop  - static_cast<int> (B.sprite.getPosition().y);

                for(int i=0; i<Rect.width; i++)
                {
                        for(int j=0; j<Rect.height; j++)
                        {
                                if (A.GetImg().getPixel(i+LocalLeftA , j+LocalTopA).a > 0 && B.GetImg().getPixel(i+LocalLeftB , j+LocalTopB).a > 0)
                                {
                                        return 1;  //pixel intersection
                                }
                        }
                }
                return 0; //only bounding boxes intersection, no pixel
        }
        else return 0; //no bounding boxes intersection
}