cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   Mitch Lindgren
   Member

   Hi all,
   In my game I have decided to use a number of simple, un-textured particle systems for various effects. Because the particle systems included with Cocos2D necessarily have some overhead due to the fact that they're meant to be textured, I've written my own particle system for these effects to gain some extra speed. It's very similar to the original Cocos2D particle systems, but without the ability to render textures and some of the more complex attributes.

   It's working pretty well, but I'm having an odd problem. All of particles are being rendered on screen at twice the x/y values they're supposed to be rendered at. So for instance, if a particle is positioned at (160, 240) - the center of the screen - it will be rendered at (320, 480) - the top right. I can't for the life of me figure out why this is occurring. I've checked with GDB and confirmed that the particles do indeed have the correct x/y values, but somehow when I pass them to OpenGL they get messed up.

   My assumption is that the array I use to store the particle positions is getting bit-shifted to the left somehow. However, I can't find anything in my code that would cause this. I'm pretty much lost.

   Here's the code: http://pastie.org/610543

   Thanks for any help you can provide. Also, while it's not done yet, but please feel free to use it if you think it would help in your project.

   Posted 2 years ago #
2. 

   yarri
   Member

   Hi, your types and stride on the glVertexPointer() call on line #180 don't look right. Try using type GLfloat* instead of CGPoint* for positions perhaps?

   --yarri

   Posted 2 years ago #
3. 

   Mitch Lindgren
   Member

   I thought something like that could be a problem, but check out this function from Cocos2D's drawingPrimitives.m:

   void drawPoints( CGPoint *points, unsigned int numberOfPoints )
   {
   glVertexPointer(2, GL_FLOAT, 0, points);
   glEnableClientState(GL_VERTEX_ARRAY);

   glDrawArrays(GL_POINTS, 0, numberOfPoints);

   glDisableClientState(GL_VERTEX_ARRAY);
   }

   That one works fine, and uses the same data types. However, if I pass my points to the function, they're still drawn at twice their x/y values. The regular particle systems also use CGPoints, although for some reason they use an alias for them - ccVertexf or something.

   Edit: Just to try it out anyway, I created a test struct which used GLfloats instead of regular floats and replaced my CGPoints with it. No change.

   Edit 2: Feeling pretty stupid. I guess because the drawing is performed inside a CocosNode draw selector, the coordinates have to be in node space, not world space. I thought that because I was making direct OpenGL calls this would not be the case, but I guess I was wrong. Problem solved!

   For now I'm removing the code because I realized it has some memory management bugs. I will post it again ASAP in case anyone might find it useful.

   Posted 2 years ago #

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