AnotherFoxGuy/polyvox
1
0
Fork 0
Code Issues Pull Requests Activity

Added missing files.

Browse Source
This commit is contained in:
David Williams 2010-08-21 13:13:39 +00:00
parent 6d58348297
commit 5adabf624a
3 changed files with 167 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
documentation/index.rst
View File

@ -4,10 +4,11 @@ Welcome to PolyVox's documentation!
Contents:
.. toctree::
:maxdepth: 1
:maxdepth: 2
install
basicexample
principles
tutorial1
Indices and tables

3
documentation/principles.rst Normal file
View File

@ -0,0 +1,3 @@
**********************
Principles of PolyVox
**********************

161
documentation/tutorial1.rst Normal file
View File

@ -0,0 +1,161 @@
**********************
Tutorial 1 - Basic use
**********************
Introduction
============
This tutorial covers the basic use of the PolyVox API. After reading this tutorial you should have a good idea how to create a PolyVox volume and fill it with data, extract a triangle mesh representing the surface, and render the result. This tutorial assumes you are already familiar with the basic concepts behind PolyVox (see the :doc:`principles of polyvox <principles>` document if not), and are reasonably confident with 3D graphics and C++. It also assumes you have already got PolyVox installed on your system, if this is not the case then please consult :doc:`installation guide <install>`.
The code samples and text in this tutorial correspond directly to the basic OpenGL example. This example uses the Qt toolkit for window and input handling, and for providing an OpenGL context to render into. In this tutorial we will omit code which performs these tasks and will instead focus on on the PolyVox code. You can consult the `Qt documentation <http://doc.qt.nokia.com/latest/>`_ if you want more information about these other aspects of the system.
Creating a volume
=================
*Mention required headers*
The most fundamental construct when working with PolyVox is that of the volume. This is represented by the :polyvox:`Volume` class and stores a 3D grid of voxels. Our basic example application creates a volume with the following line of code:
.. code-block:: c++
Volume<MaterialDensityPair44> volData(64, 64, 64);
As can be seen, the Volume class is templated upon the voxel type. This means it is straight forward to create a volume of integers, floats, or a custom voxel type (see the :polyvox:`Volume documentation <PolyVox::Volume>` for more details). In this particular case we have created a volume in which each voxel is an instance of :polyvox:`MaterialDensityPair44`. Each instance of MaterialDensityPair44 holds both a material and a density and uses four bits of data for each. This means that both the material and the density have a range of 0-15, and each voxel requires one byte of storage. For more information about materials and densities please consult the :doc:`principles of polyvox <principles>` document.
Each voxel is initialised using its default constructor, which in the case of MaterialDensityPair44 will mean that both the material and the density are set to zero. This corresponds to a volume full of empty space because the density of each voxel is below the threshold.
Next, we set some of the voxels in the volume to be 'solid' in order to create a large sphere in the centre of the volume. We do this with the following function call:
.. code-block:: c++
createSphereInVolume(volData, 30, 1);
Note that this function is part of the basic OpenGL example (rather than being part of the PolyVox library) and is implemented as follows:
.. code-block:: c++
void createSphereInVolume(Volume<MaterialDensityPair44>& volData, float fRadius)
{
//This vector hold the position of the center of the volume
Vector3DFloat v3dVolCenter(volData.getWidth() / 2, volData.getHeight() / 2, volData.getDepth() / 2);
//This three-level for loop iterates over every voxel in the volume
for (int z = 0; z < volData.getWidth(); z++)
{
for (int y = 0; y < volData.getHeight(); y++)
{
for (int x = 0; x < volData.getDepth(); x++)
{
//Store our current position as a vector...
Vector3DFloat v3dCurrentPos(x,y,z);
//And compute how far the current position is from the center of the volume
float fDistToCenter = (v3dCurrentPos - v3dVolCenter).length();
//If the current voxel is less than 'radius' units from the center then we make it solid.
if(fDistToCenter <= fRadius)
{
//Our new density value
uint8_t uDensity = MaterialDensityPair44::getMaxDensity();
//Get the old voxel
MaterialDensityPair44 voxel = volData.getVoxelAt(x,y,z);
//Modify the density
voxel.setDensity(uDensity);
//Wrte the voxel value into the volume
volData.setVoxelAt(x, y, z, voxel);
}
}
}
}
}
This function takes as input the Volume in which we want to create the sphere, and also a radius specifying how large we want the sphere to be. In our case we have specified a radius of 30 voxels, which will fit nicely inside our Volume of dimensions 64x64x64.
Because this is a simple example function it always places the sphere at the center of the volume. It computes this centre by halving the dimensions of the volume as given by the functions Volume::getWidth(), Volume::getHeight() and Volume::getDepth(). The resulting position is stored using a Vector3DFloat. This simply a typedef from our templatised Vector class, meaning that other sizes and storage types are available if you need them.
Next, the function uses a three-level 'for' loop to iterate over each voxel in the volume. For each voxel it computes the distance from the voxel to the centre of the volume. If this distance is less than or equal to the specified radius then the voxel form part of the sphere and is made solid. During surface extraction, the voxel will be considered solid if it's density is set to any value greater than its threshold, which can be obtained by calling MaterialDensityPair44::::getThreshold(). In our case we simply set it to the largest possible value by calling MaterialDensityPair44::getMaxDensity().
Extracting the surface
======================
Now that we have built our volume we need to convert it into a triangle mesh for rendering. This process is performed by the SurfaceExtractor class. An instance of the SurfaceExtractor is created as follows:
.. code-block:: c++
SurfaceExtractor<MaterialDensityPair44> surfaceExtractor(volData);
Again, note thiat this class is templatised on the voxel type. It also takes a reference to the Volume on which the surface extraction will be performed.
The actual extraction happens in the SurfaceExtractor::extractSurfaceForRegion() function. This function needs to be told which Region of the Volume the extraction should be performed on (in more advanced application this is useful for extracting only those parts of the volume which have been modified since the last extraction), but for our purposes the Volume class provides a convienient Volume::getEnclosingRegion() function which returns a Region representing the whole volume.
.. code-block:: c++
shared_ptr<SurfaceMesh> surface = surfaceExtractor.extractSurfaceForRegion(volData.getEnclosingRegion());
The result is a SurfaceMesh object, which basically contains an index and vertex buffer representing the desired triangle mesh. This is returned via a shared_ptr, meaning it will automatically be deleted once there are no remaining references to it.
Rendering the surface
=====================
Rendering the surface with OpenGL is handled by the OpenGLWidget class. Again, this is not part of PolyVox, it is simply an example based on Qt and OpenGL which demonstrates how rendering can be performed. Within this class there are mainly two functions which are of interest - the OpenGLWidget::setSurfaceMeshToRender() function which constructs OpenGL buffers from our SurfaceMesh and the OpenGLWidget::paintGL() function which is called each frame to perform the rendering.
The OpenGLWidget::setSurfaceMeshToRender() function is impemented as follows:
.. code-block:: c++
void OpenGLWidget::setSurfaceMeshToRender(const PolyVox::SurfaceMesh& surfaceMesh)
{
//Convienient access to the vertices and indices
const vector<uint32_t>& vecIndices = surfaceMesh.getIndices();
const vector<SurfaceVertex>& vecVertices = surfaceMesh.getVertices();
//Build an OpenGL index buffer
glGenBuffers(1, &indexBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
const GLvoid* pIndices = static_cast<const GLvoid*>(&(vecIndices[0]));
glBufferData(GL_ELEMENT_ARRAY_BUFFER, vecIndices.size() * sizeof(uint32_t), pIndices, GL_STATIC_DRAW);
//Build an OpenGL vertex buffer
glGenBuffers(1, &vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
const GLvoid* pVertices = static_cast<const GLvoid*>(&(vecVertices[0]));
glBufferData(GL_ARRAY_BUFFER, vecVertices.size() * sizeof(SurfaceVertex), pVertices, GL_STATIC_DRAW);
m_uBeginIndex = 0;
m_uEndIndex = vecIndices.size();
}
We begin by obtaining direct access to the index and vertex buffer in the SurfaceMesh class in order to make the following code slightly cleaner. Both the SurfaceMesh::getIndices() and SurfaceMesh::getVertices() functions return an std::vector containing the relevant data.
The OpenGL functions which are called to construct the index and vertex buffer are best explained by the OpenGL documentation. In both cases we are making an exact copy of the data stored in the SurfaceMesh.
The begin and end indices are used in the OpenGLWidget::paintGL() to control what part of the index buffer is actually rendered. For this simple example we will the whole buffer from '0' to 'vecIndices.size()'.
With the OpenGL index and vertex buffers set up, we can now look at the code which is called each frame to render them:
.. code-block:: c++
void OpenGLWidget::paintGL()
{
//Clear the screen
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//Set up the viewing transformation
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f,0.0f,-100.0f); //Centre volume and move back
glRotatef(m_xRotation, 1.0f, 0.0f, 0.0f);
glRotatef(m_yRotation, 0.0f, 1.0f, 0.0f);
glTranslatef(-32.0f,-32.0f,-32.0f); //Centre volume and move back
//Bind the index buffer
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
//Bind the vertex buffer
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glVertexPointer(3, GL_FLOAT, sizeof(SurfaceVertex), 0);
glNormalPointer(GL_FLOAT, sizeof(SurfaceVertex), (GLvoid*)12);
glDrawRangeElements(GL_TRIANGLES, m_uBeginIndex, m_uEndIndex-1, m_uEndIndex - m_uBeginIndex, GL_UNSIGNED_INT, 0);
}
Again, the explanation of this code is best left to the OpenGL documentation. Note that is is called automatically by Qt each time the display needs to be updated.