Hierarchy textures

So, it's been a while. I was so busy at SIGGRAPH that I never had the time to share anything.

In this post, I'm showing you some of the last textures I've been working on. These are build as a hierarchy. We use again our variation of the Voronoi diagram to create weird shapes. But this time, instead of using simply one level, we introduce many levels.

On the first level, again, the Voronoi cells are computed and once we know in which cell we are, if that cell has a sub-level, we can then continue the visit in the structure into that sub-level. Each level has can have a small or big influence on the final color of the pixel.

So, here's some outputs:

One of the first output made. It has two cells on the first level. One is the circle-like shape in the middle and then the rest. In the "rest", there's a sub level with a simple small division of the plane in two.

Exactly as the previous one, but here, there's a sub-level in the circle-like shape. As you can see, the fact that there's a new sub-level only affects the part where that sub-level is.

The actual first output that I got with the hierarchy.

In the next images, I start playing with colors inside the cells. Naturally, all of these images where made from random point distribution.

In these images, I simply played with the hierarchy. Each cell has a random chance to get a sub-level and so on. Until a maximal depth was reached. In some of them, I played also with the feature that at each level, you can influence the final color by accumulating a value.

Finally, there's two big step to do before we consider that project finished. First, we want to investigate various patterns. So, how can we do a particular shape for a cell. For this part, we don't need the hierarchy because we know it works. When we are able to control properly the patterns, we will be able to used them at various level.

Second, we want to be more dynamic for the color. Right now, each cell use a function f:[0;1]->[0;1] to control its value that will influence all the other levels. But those functions are a bit static. I can add more, but it will never be enough. So we turn to use something like the shaders in OpenGL. Literally, each cell could have its own function (coded in CUDA-C) and that function would be used to control the contribution of that cell and its sub-level to the final color of the pixel.

SIGGRAPH

This week, I will be at SIGGRAPH in Vancouver. I will try to share some of the stuff I will see on the blog. I hope to be able to talk about the last stuffs in procedural texturing and rendering.

Red and Cyan Stereoscopy

Here's a small entry for any of you who has a pair of 3D glasses (the ones with a red and cyan lens) and are interested in creating a 3D environment with OpenGL.

I'm not giving a lot of detail, for this post, I assume that you're familiar with OpenGL. At least the basic. If you're not, you can follow the tutorials on NeHe Productions. Here, I'm more interested with the general strategy because there's more than one way to do this. In this example, I present an approach that makes everything you see coming out of the screen. The screen itself would be the farthest object in the scene.

Consider that you have a function called draw_scene() where all the geometry and the computation is done, except the initialization to render the scene like clearing the depth buffer or glFlush();.

So here's the approach to render your scene:

Step 1:

glColorMask is a function that control which color you want to modify. So calling it with the four parameters set to true will allow to write on the red, green, blue and alpha value of each pixel concerned.

glColorMask(true, true, true, true);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 

If you use the stencil buffer, or any other buffers, add them as parameter in glClear.

Step 2:

Now, we want to draw what the left eye (red lens) will see. Imagine that the variables position, look_at and up are a structure such as:

struct coordinate
{
  float x, y, z;
};

describing two locations in space (position and look_at) and a vector (up).
Here we use gluLookAt to create a matrix used to setup the point of view on the scene. But other functions or methods exist to create the initial viewpoint.

glColorMask(true, false, false, true);
glLoadIdentity();
gluLookAt(position.x, position.y, position.z, look_at.x, look_at.y, look_at.z, up.x, up.y, up.z);
draw_scene();

At this point, half of the drawing is done.

Step 3:

For the right eye, we need first to move a little bit the point of view to simulate the distance between our eyes. Let the variable eye_distance be that distance. The piece of code is very similar to the code in the previous step.

glColorMask(false, false, true, true);
glLoadIdentity();
glTranslatef(-eye_distance, 0.0f, 0.0f);
gluLookAt(position.x, position.y, position.z, look_at.x, look_at.y, look_at.z, up.x, up.y, up.z);
draw_scene();

First, we switch the mask to accept only the blue. But why the "-eye_distance" ? Remember that I want everything to go out of the screen. This mean that the same object that we see with the right eye needs to be to the left of the copy of that object that we see with our left eye.

To understand this phenomenon. Put I finger in front of you and close your right eye. Then switch to your left eye. You can observe that your finger seems to be moving to the left. And the closer you put your finger, the larger the distance is. It's this effect that allow your eyes, when they focus on the same object, to determine the distance.

Another proof of this, take the example at the bottom. Look at the image first with you glasses and see how closer it is to you than the screen. Then clique on the image to have the larger version. You will see that the object looks even closer. And this is because the distance between the red and blue version is larger and your eyes make you think the object is closer.

Step 4:

Compile (debug if necessary) and enjoy your work.

Bonus step:

Let say that you have a background that is suppose to be far far away, like the sky. Your eyes shouldn't see the difference because it should be right on the screen. So, to save time, you should draw it before both eyes with the red and blue color activated. This way, you draw this part only once.

Here's the kind of images you should have: