I am not a very experienced Qt C++ Programmer, but unfortunately I have to create a 3D Cube containing 8x8x8 points.
I already found the Qt tutorial to create a simple cube, but I am completely lost on how to make it hollow and draw the 512point matrix within the cube. Furthermore the goal is to change the color of specific points within this matrix.
Anybody know how to proceed?
Thank you in advance!
https://github.com/peteristhegreat/circles-in-a-cube
Check out the awesome example I put together!
Basically I took the Grabber example and did some modifications to it.
http://doc.qt.io/qt-5/examples-widgets-opengl.html
http://doc.qt.digia.com/qt-quick3d-snapshot/qt3d-examples.html
http://doc.qt.digia.com/qt-5.2/qtopengl-grabber-example.html
It looks like you could modify this one to something similar.
http://doc.qt.io/qt-5/qtopengl-hellogl2-example.html
The core features of what is going on, is holding on to information about the individual spheres and modifying them when you need to.
To hold the pointers to sphere objects, I used two different lists.
One is a straight forward QList, and the other is a 3D Vector. The 3D QVector allows you to access a sphere pointer with spheresInSpace[x][y][z], where x,y,z are any integer between 0-7.
To change the colors of the spheres, I change the reflectance values.
Hope that helps.
Related
I'm still trying to density control (grade) meshes in CGAL. Specifically tet-meshing a polygon surface (or multiple surface manifolds) that I simply load as OFF files. I can also load lists of selected faces or face nodes too.
But I can't seem to get to first base on this with the polygon tet-mesher. All I want to do is assign and enforce a mesh density/size at selected faces in the OFF file.
I CAN get some kinds of mesh density working by inserting 1-D features with volumetric data meshing, but for CAD and 3D printing purposes it has to be computed from an STL-like triangular surface manifold, so volume-based meshing is not do-able.
Is what I'm trying to do even possible in CGAL? It feels to me like it must be, and I'm just missing something obvious.
I really hope someone can help here. FYI i'm mostly working with the Mesh3 example using v4.14.
Thanks very much.
Look at the Mesh_facet_criteria and in particular this constructor where SizingField is where you can control the size. For locating the point wrt a face, you can use the AABB-tree function closest_point_and_primitive().
Is there a way of visualising isolines in 3D space (x, y and z)?
I am basically trying to show the flow of some points based off the velocities of these points and the example on the VTK website only does this in 2D (http://www.vtk.org/Wiki/VTK/Examples/Cxx/Visualization/LabelContours) and I don't know how to adapt this. I have tried replacing the plane variable with a 3D glyph but I am getting a lot of errors and nothing appears in the render window
I am not sure if what you want is an isoline. Because an isoline is defined on a scalar field, which means one attribute at each point. Since you are talking about velocity of points, it seems to me you are dealing with a vector field. In that case, you should not create an isoline, but a streamline instead. Take a look at this example, it might help you.
the vtkContourFilter class works for both 2D and 3D. there is an example here.
Okay, i understand that voxels are just basically a volumetric version of a pixel.
After that, I have no idea what to even look for.
Googling doesn't show any tutorials, I can't find a book on it anywhere, I can't find anything even having to do with the basic idea of what a voxel really is.
I know much of the C++ library, and have the basics of OpenGL down.
Can someone point me in the right direction?
EDIT: I guess I'm just confused on how to implement them? Sorry for being a pain, it's just that I can't really find anything that I can easily correlate to... I think I was imagining a voxel being relevant to a vector in which you can actually store data.
a voxel can be represented as ANY 3D shape? For example, say I wanted the shape to be a cylinder. Is this possible, or do they have to link like cubes?
Minecraft is a good example of using voxels. In Minecraft each voxel is a cube.
To see a C++ example you can look at the Minecraft clone Minetest-c55. This is open source so you can read all of the source code to see how its done.
Being cubes is not a requirement of voxels. They could be pyramids or any other shape that can fit together.
I suspect that you are looking for information on Volume Rendering techniques (since you mention voxels and OpenGL). You can find plenty of simple rendering code in C++, and more advanced OpenGL shaders as well with a little searching on that term.
In the simplest possible implementation, a voxel space is just a 3 dimensional Array. For solids you could use a single bit per voxel: 1 == filled and 0 == empty. You use implicit formulas to make shapes, e.g. A sphere is all the voxels within a radius from the center voxel.
Voxels are not really compatible with polygon-based 3d rendering, but they are widely used in image analysis, medical imaging, computer vision...
Let's Make a Voxel Engine on Google Sites might help one to get started creating a voxel based engine:
https://sites.google.com/site/letsmakeavoxelengine/
In addition to that there are presentations of the results on Youtube worth checking:
http://www.youtube.com/watch?v=nH_bHqury9Q&list=PL3899B2CEE4CD4687
Typically a voxel is a position in some 3D space that has a volume (analogous to the area that a pixel contains.
Just like in an image, where a pixel contains some scalar value (grayscale) or vector of values (like in a color image where the vector is either the red, green, and blue components, or hue, saturation, and value components) the entries for a voxel can have some scale or vector of values.
A couple natural examples of volumetric images that contains voxels are 3D medical imagines such as CT, MRI, 3D ultrasound etc.
Mathematically speaking a 3D image is a function from some voxel space to some set of numbers.
look for voxlap or try this http://www.html5code.com/gallery/voxel-rain/ or write your own code. Yes, a voxel can be reduced to a 3d coordinate (which can be implied by it's position in the file structure) and a graphical representation which can be anything (cube, sphere, picture, color ...). Just like a pixel is a 2D coordinate with a color index.
You only need to parse your file and render the corresponding voxels. Sadly, there is no 'right' file format although voxlaps file formats seem pretty neat.
good luck
I'm trying to draw a 2D silhouette of an island/land of sort in C++ with OpenGL. It is just a simple island that looks something like the one here
I tried ways like drawing polygons, fill the colour black and then hard-code tons of vertex points to get the shape of the island and also to keep the edges look rough like the one in the example. But I feel that this really isn't the best way to do this because the number of vertices is just too many. It is also very difficult to tweak because it's not like I'm in Photoshop where I could just pull/add/change the points visually.
Are there any better and more clever way to draw a 2D island silhouette to get the mountain-like edges? As for the overall shape of the island, is my naive way to plant tons of points to form the polygon shape the only way?
I have just started on OpenGL and will be grateful for any suggestions. Thanks!
There are many ways to go about this here are two simple ones;
Easy way: As said in the comments, create the island in an image editor (with alpha) and draw as a quad/tris with blending enabled.
Harder way: Import a vector graphic (vector meaning points making a shape) and draw as polygons. This could get complicated for a newbie if using an existing format. Also, not as efficient as method 1, but can have a much nicer visual effect especially if you plan on zooming/scaling.
In the end it is entirely up to you how you want to implement it, but the first method is straight-forward and easy, I recommend that for a newbie (be sure to come back to it later and try method 2 though ;) ).
From My last question: Marching Cube Question
However, i am still unclear as in:
how to create imaginary cube/voxel to check if a vertex is below the isosurface?
how do i know which vertex is below the isosurface?
how does each cube/voxel determines which cubeindex/surface to use?
how draw surface using the data in triTable?
Let's say i have a point cloud data of an apple.
how do i proceed?
can anybody that are familiar with Marching Cube help me?
i only know C++ and opengl.(c is a little bit out of my hand)
First of all, the isosurface can be represented in two ways. One way is to have the isovalue and per-point scalars as a dataset from an external source. That's how MRI scans work. The second approach is to make an implicit function F() which takes a point/vertex as its parameter and returns a new scalar. Consider this function:
float computeScalar(const Vector3<float>& v)
{
return std::sqrt(v.x*v.x + v.y*v.y + v.z*v.z);
}
Which would compute the distance from the point and to the origin for every point in your scalar field. If the isovalue is the radius, you just figured a way to represent a sphere.
This is because |v| <= R is true for all points inside a sphere, or which lives on its interior. Just figure out which vertices are inside the sphere and which ones are on the outside. You want to use the less or greater-than operators because a volume divides the space in two. When you know which points in your cube are classified as inside and outside, you also know which edges the isosurface intersects. You can end up with everything from no triangles to five triangles. The position of the mesh vertices can be computed by interpolating across the intersected edges to find the actual intersection point.
If you want to represent say an apple with scalar fields, you would either need to get the source data set to plug in to your application, or use a pretty complex implicit function. I recommend getting simple geometric primitives like spheres and tori to work first, and then expand from there.
1) It depends on yoru implementation. You'll need to have a data structure where you can lookup the values at each corner (vertex) of the voxel or cube. This can be a 3d image (ie: an 3D texture in OpenGL), or it can be a customized array data structure, or any other format you wish.
2) You need to check the vertices of the cube. There are different optimizations on this, but in general, start with the first corner, and just check the values of all 8 corners of the cube.
3) Most (fast) algorithms create a bitmask to use as a lookup table into a static array of options. There are only so many possible options for this.
4) Once you've made the triangles from the triTable, you can use OpenGL to render them.
Let's say i have a point cloud data of an apple. how do i proceed?
This isn't going to work with marching cubes. Marching cubes requires voxel data, so you'd need to use some algorithm to put the point cloud of data into a cubic volume. Gaussian Splatting is an option here.
Normally, if you are working from a point cloud, and want to see the surface, you should look at surface reconstruction algorithms instead of marching cubes.
If you want to learn more, I'd highly recommend reading some books on visualization techniques. A good one is from the Kitware folks - The Visualization Toolkit.
You might want to take a look at VTK. It has a C++ implementation of Marching Cubes, and is fully open sourced.
As requested, here is some sample code implementing the Marching Cubes algorithm (using JavaScript/Three.js for the graphics):
http://stemkoski.github.com/Three.js/Marching-Cubes.html
For more details on the theory, you should check out the article at
http://paulbourke.net/geometry/polygonise/