Develop Reference

Physics-based/Polynomial Animation with Box2d (Java)

I'm creating a 2d game using the Java version of Box2d.
I know that the engine is generally paired with a separate library to handle animation, but I'm looking for something simple, with a more rustic feel, so I'm considering handling the animation from scratch.
The animation I am trying to create is something for the collision of two objects.
I'm using openGl to handle the graphics, and I pretty much have everything set up with the fps and rendering, it's just a matter of tweaking the frames to make it look smooth.
I tried bliting images of some things that I drew myself and it looked atrocious. I think the main problem is that the animation frame images are not linked to the physics forces and so they don't blend well.
What I want to try next is a sort 'spark effect' using a small number of pixels that sort of resemble 'dust' exploding off of the colliding images. If you've ever played dxball, you may recall a similar effect when the ball collided with the paddle at high speed.
As you can see in the above image, the principles are fairly simple. I figure by creating a set of small bodies with fixtures, I can use the box2d engine to produce this effect. I already have code that grabs the point of collision for all bodies, and am familiar enough with parabolic functions that I pretty sure I can create the force direction.
I'm just not sure if there is a better way of doing this, or how to apply a polynomial function to a body like in the image.
Does anybody know how to achieve this functionality with box2d? Any built in methods or documentation that would be helpful?
As a point of reference, the following snippet of code demonstrates the drawing of a small, red box on all of the collision points.
for(Vec2 point : listener.worldmanifold.points){
glPushMatrix();
newpos = point.mul(30);
glTranslatef(newpos.x, newpos.y, 0);
glColor3f(1,0,0);
glRectf(-2, -2, 2, 2);
glPopMatrix();
}

Opengl multiple glDrawArrays calls

I have a Problem with vertex array objects in opengl (java, lwjgl).
The Program itself works, i have an object, can move around it.
The draw call is simple:
Gl11.glDrawArrays(drawmode, 0, 4);
In the shader i have one uniform for the model, (called model ^^).
Now i tried the following: (pseudo code)
update the model
draw
update the model
draw again
This doesn't work. why? I know there is instancing, but that isn't my aim here. I just want to draw 2 things with 2 draw calls. But i only see the first one.. does anyone have an idea?
** Edit **
I hate it. I hate this principe... Again and again I forget to flip the buffer before using it in opengl. Now again. That was the point... the first time i flipped it the second time not... I can't get it into my brain to flip this buffers -.-

Third Person Perspective Camera with Opengl

I want to implement a TPP Camera for my project, but something is not working + i don't know if i use the right concept.
Should I rotate the whole scene model-view matrices except my main model, which will be centered on the screen or rotate the lookAt camera?
Other thing is how to make the model move in given direction after rotating? (I think moving the whole scene makes it easier?) + how to add collision detection to it?

Collision detection is nothing to do with openGL you use you game state variables to work that out you can manage it in the same loop as the game where you do user input and display.
You should use a LookAtMatrix for the third person camera you will have the eye component behind the player and the at somewhere infront. Persective can be implemented by using a perspective matrix.
So the matrix multiplication will look like.
PerspectiveMatrix * LookAtMatrix * worldSpacePosition
Here is a good answer from gamedev explaining a lookatmatrix, most OpenGL / Computer Graphics books will also cover this.
Are you working with the new or old pipeline model?

JOGL - open GL - keeping part of the world stationary while moving the rest

I'm kind of new to JOGL, and I am working on a game. I have a rocket, stars in the background, and planets. I want the rocket to remain stationary at the bottom of the screen, the GO button to be pressed, and then planets start coming down for the rocket to avoid.
I keep ending up with hitting go, the planets coming down (via translation), and the rocket also going down. I know Why this is happened with the camera moving, so the whole world is moving. I've been trying to use the pushMatrix and popMatrix, but haven't had any luck.
i.e.
if (goButtonPressed)
{
//gl.glTranslatef(0.0f,0.3f,0f); // this line just keeps the whole thing still
drawRocket(gl); // I was trying to 'undo' the translation
gl.glPushMatrix();
gl.glMatrixMode(GL.GL_PROJECTION);
gl.glTranslatef(0.0f, -0.3f, 0f);
gl.glPopMatrix();
}
Is what I am trying to do possible in opengl? Am I making it too difficult?

Instead of relying on the projection matrix to hold the state of your rockets' positions, how about storing this information in your own code and then passing absolute coordinates to JOGL? Then updating the position of an object can be done with a more obvious bit of code like rocket.y += dy;.
As a small aside, the projection matrix is not intended to be used for spatial transformations. Use GL_MODELVIEW instead to avoid subtle problems down the road.

Not exactly an answer to your question, but you should look at JMonkeyEngine if you want to make a game with opengl in Java.
http://jmonkeyengine.com/
The thing you are trying to do is certainly possible with opengl and fairly easy to do with JMonkeyEngine. They have plenty of tutorials and such on their site.

OpenGL: Create a sky box?

I'm new to OpenGL. I'm using JOGL.
I would like to create a sky for my world that I can texture with clouds or stars. I'm not sure what the best way to do this is. My first instinct is to make a really big sphere with quadric orientation GLU_INSIDE, and texture that. Is there a better way?

A skybox is a pretty good way to go. You'll want to use a cube map for this. Basically, you render a cube around the camera and map a texture onto the inside of each face of the cube. I believe OpenGL may include this in its fixed function pipeline, but in case you're taking the shader approach (fixed function is deprecated anyway), you'll want to use cube map samplers (samplerCUBE in Cg, not sure about GLSL). When drawing the cube map, you also want to remove translation from the modelview matrix but keep the rotation (this causes the skybox to "follow" the camera but allows you to look around at different parts of the sky).
The best thing to do is actually draw the cube map after drawing all opaque objects. This may seem strange because by default the sky will block other objects, but you use the following trick (if using shaders) to avoid this: when writing the final output position in the vertex shader, instead of writing out .xyzw, write .xyww. This will force the sky to the far plane which causes it to be behind everything. The advantage to this is that there is absolutely 0 overdraw!

Yes.
Making a really big sphere has two major problems. First, you may encounter problems with clipping. The sky may disappear if it is outside of your far clipping distance. Additionally, objects that enter your sky box from a distance will visually pass through a very solid wall. Second, you are wasting a lot of polygons(and a lot of pain) for a very simple effect.
Most people actually use a small cube(Hence the name "Sky box"). You need to render the cube in the pre-pass with depth testing turned off. Thus, all objects will render on top of the cube regardless of their actual distance to you. Just make sure that the length of a side is greater than twice your near clipping distance, and you should be fine.

Spheres are nice to handle as they easily avoid distortions, corners etc. , which may be visible in some situations. Another possibility is a cylinder.
For a really high quality sky you can make a sky lighting simulation, setting the sphere colors depending on the time (=> sun position!) and direction, and add some clouds as 3D objects between the sky sphere and the view position.