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Member Since 19 Aug 2012
Offline Last Active Aug 11 2015 11:49 AM

Topics I've Started

Issues with BulletPhysics & OpenGL

02 February 2015 - 01:40 PM

Dear community,

I'm currently programming a 3D game in pure C++ with OpenGL, GLM, ASSIMP, SFML & BulletPhysics. smile.png

But now, I'm at a point, where I'm done with it, 'cause I couldn't get the problem or find something on the internet, which can lead into the direction of a fix. huh.png 
I've got a problem with updating my meshs model matrix with the world matrix, getting from the btMotionState of a btRigidBody, to render it via shader. unsure.png


The shader computes the vertex location like

gl_Position = projection_mat4 * view_mat4 * model_mat4 * vec4(position, 1.0);

Where projection is computed by glm::perspective(...), view by glm::lookAt(...) and model by the physics system, see below. smile.png



So far, I'm creating the whole physics world in a class called "PhysicsManager".
It's a test and so it creates the whole bullet physics system like that:

m_broadphase = new btDbvtBroadphase();
m_collisionConfiguration = new btDefaultCollisionConfiguration();
m_dispatcher = new btCollisionDispatcher(m_collisionConfiguration);


m_solver = new btSequentialImpulseConstraintSolver();
m_dynamicsWorld = new btDiscreteDynamicsWorld(m_dispatcher, m_broadphase, m_solver, m_collisionConfiguration);
m_dynamicsWorld->setGravity(btVector3(0.0f, -9.81f, 0.0f));

// Floor
m_groundShape = new btStaticPlaneShape(btVector3(0, 1, 0), 1);
m_groundMotionState = new btDefaultMotionState(btTransform(btQuaternion(0, 0, 0, 1), btVector3(0, 0, -1)));
btRigidBody::btRigidBodyConstructionInfo groundRigidBodyCI(0, m_groundMotionState, m_groundShape, btVector3(0, 0, 0));
m_groundRigidBody = new btRigidBody(groundRigidBodyCI);


// Model as a sphere in BulletPhysics
m_fallShape = new btSphereShape(1);
m_fallMotionState = new btDefaultMotionState(btTransform(btQuaternion(0, 0, 0, 1), btVector3(8, 50, 8)));
btScalar mass = 2;
btVector3 fallInertia(0, 0, 0);
m_fallShape->calculateLocalInertia(mass, fallInertia);
btRigidBody::btRigidBodyConstructionInfo fallRigidBodyCI(mass, m_fallMotionState, m_fallShape, fallInertia);
m_fallRigidBody = new btRigidBody(fallRigidBodyCI);


// GLDebugDrawer from the demos of the Bullet 3.X github page
glDebugDrawer = GLDebugDrawer();
glDebugDrawer.setDebugMode(btIDebugDraw::DBG_DrawAabb | btIDebugDraw::DBG_DrawWireframe | btIDebugDraw::DBG_DrawConstraints | btIDebugDraw::DBG_DrawConstraintLimits | btIDebugDraw::DBG_DrawNormals);

And I'm updating the world each frame with 

m_dynamicsWorld->stepSimulation(1.0f / 60.0f, 10);

After that, I'm updating the meshs model matrix with

btTransform trans;

where "m_model" is a glm::mat4 initialised as "m_model = glm::mat4()". smile.png



Then rendering is done via

glBindTexture(GL_TEXTURE_2D, mesh->tex);

GLuint uniform_model = glGetUniformLocation(p_shader, "model");

glUniformMatrix4fv(uniform_model, 1, GL_FALSE, glm::value_ptr(p_objects->at(i).m_model));
glDrawArrays(GL_TRIANGLES, 0, mesh->size);

glBindTexture(GL_TEXTURE_2D, 0);

So I bind all the stuff of the 3D mesh, draw it and unbind it.



Problem is:

Why is my rendering not aligned with the physically computed bounding boxes?
(I mean not perfectly aligned like origin/center of mass but not anywhere near the collision box?)

Can anyone give me a hint or something like that?


Here's a picture of what I mean:





Help with calculate skinned models loaded with Assimp

30 September 2014 - 01:36 PM

Hey dudes.


I'm using C++ with SFML + OpenGL (+ GLM) + Assimp and I'm currently working on an animation system for my first 3D game project and I'm struggling with bone animated 3D meshs and the Assimp library since a few weeks.

Since threads to this theme are rare on the internet, I decided to ask you guys. ^^

First of all, I wanted to say, that I can load and display static models with textures assigned properly. smile.png 
Although the shaders for rendering to a different framebuffer and for post processing are working fine.
But I can't get some animation working flawlessly due to the fact, that I didn't understand some things in order to complete this task. ohmy.png

So, my main question is (which is moreover the main problem): How do I get one specific keyframe of the bones and get their transformations/rotations/scaling ?

My thoughts are:

  1. Load the vertex bone data, so each vertex know, by what bone it is how much influenced (done! biggrin.png )
  2. Each frame:
    - Get the time, since the animation started (done! smile.png)
    - Look up the "nearest" time stamp in the keyframe list (I didn't want to interpolate yet, just keyframe after keyframe for now )
    - Calculate all transformations per bone for this specific keyframe in a 4x4 matrix
    - Update transformation matrices in the shader (maybe done, can't test it... biggrin.png)

1. is done properly and I stuck with 2. since a few weeks now.
The problem is, so far I can define it, how can I look up one keyframe for each bone in Assimps "aiScene" and how do I calculate the per bone transformations? unsure.png 

Does anybody have good tips on this or something like that? blink.png 

Good evening,

Perlin Noise gives too small values?

04 August 2014 - 03:12 PM



Today I've implemented a perlin noise algorithm with extra methods like pertubation and eroding to create a terrain. smile.png

I found the code for it here: Click me smile.png


After the "addPerlinNoise()" method, you can see 3 reference pictures on that page (in the middle), build with the frequencies 1.0f, 4.0f and 1.0f + 8.0f (without perturb or sth like that, just plain noise).


If I use a frequency of 4.0f, this is my output (plain noise): https://imgur.com/7OElD3n


And when I use 64.0f as my frequency, I get this: https://imgur.com/dqA04N6


Can you help me to achieve something like the reference pictures with the reference frequencies (1.0f, 4.0f, 1.0f + 8.0f)?

I only understand a little behind the maths of it, so I can't really do something to fix it. sad.png


The code on the linked site is in C#, mine is in C++.


The only things, which are different between my code and the code on the site is the following part:

void PerlinGenerator::initGradients()
	//Type of random number distribution
	std::uniform_real_distribution<float> dist(0.0f, 1.0f);  //(min, max)

	//Mersenne Twister: Good quality random number generator
	std::mt19937 rng;
	//Initialize with non-deterministic seeds

	for (int i = 0; i < gradientTableSize; i++)
		float z = 1.0f - 2.0f * dist(rng);
		float r = (float)sqrt(1.0f - z * z);
		float theta = 2 * (float)M_PI * dist(rng);
		gradients[i * 3] = r * cos(theta);
		gradients[i * 3 + 1] = r * sin(theta);
		gradients[i * 3 + 2] = z;

Can it be the random double, which is used for the computing?


For the rendering I determine the vertex coordinates for a VBO like this and render it with glDrawElements(...) :

void Terrain::createVBO()
	// Create vertex data
	float *vertices = new float[3 * heightMap->size * heightMap->size];
	float blockSize = 16.0f;
	int vertex = 0;

	for (int y = 0; y < heightMap->size; y++) {
		for (int x = 0; x < heightMap->size; x++) {
			vertices[vertex++] = x * blockSize;
			vertices[vertex++] = y * blockSize;
			vertices[vertex++] = heightMap->heights[y][x] * blockSize;

	// Create index data

	// Create VAO

	// Create VBO

	// Create EBO

	// Handle vertex attributes in shader prog

Hopefully you can help me, thanks,


glAlphaFunc in gl20 ? or How do I enable alpha in gl20 ?

04 November 2012 - 03:23 PM

Hey guys.

I'm currently coding a little game with the libGdx library and I wanted to have a slight fade in/fade out effect if the screen changes (e.g. from MainMenu into the game).
After some time, I've got the idea, that I draw a black filled rectangle over the whole screen with an increasing alpha value. At the point where the alpha value is 0.0f (so, the whole screen is black) I change the screen to my game, where at this point my alpha value is getting bigger (so it will be transparent more and more).

So I implemented something like this:

// init
Gdx.gl.glEnable( GL10.GL_ALPHA_TEST );
// [...]
// render
Gdx.gl10.glAlphaFunc( GL10.GL_GREATER, 0 );
// render my quad

While having my project setting up with LwjglApplicationConfig.useGL20 = false; it will work very well.
But enabling gl20, it won't start, saying that there is a problem with GL10.GL_ALPHA_TEST
So I searched if gl20 have something like that... but now it's 30 minutes later and I don't have any solution.

Could you help?
What I have to enable in gl20 ( and setting up) to use alpha like in gl10 ?


Problem with width and height of quads

06 September 2012 - 10:56 AM

Hello dudes,

I've got a little problem, but maybe I am only too silly to solve it. unsure.pngbiggrin.png

I've got a window (1280x720) and a perspective from 0.01f till 1000.0f.
So, when I will render a normal quad with the width and height of the whole screen, I don't know where the vertices of the quad must be.
I try with (-1/-1), (-1/1), (1/-1), (1/1) and for each z-Axis coordinate 1 (I'm rendering with trianglestrips!), but then it is way too big! dry.png

So my question is, how I could know the true coordinates of each vertex for rendering a quad which is as big as the screen? wacko.png
Are there any mathematical tricks or something like that? mellow.png