Is it possible to add a compound shape when using Physijs's addWheel function (in conjunction with Vehicle), as you cannot use wheelparent.geometry which does not include the children's geometry? The geometries of the children use indexed buffer geometries, and I tried using merge to no avail (this question refers).
I guess that's a no, it cannot be done. What I did was create my own function to merge all the vertices, correctly indexed, then uses the new geometry to create a new wheel shape.
Related
I'm working with Vulkan since a few weeks. I have a question about the data structure of a model:
I'm using Assimp for loading fbx and dae files. The loaded model then usually contains several nodes (RootNode and their ChildNodes).
Should I keep this structure on non-rigged models? Or could I transform all the meshes (or rather their vertices) into world space at the first loading by multiplying with the offset matrix of the node (and then delete the node structure in my program)? Because I've never seen that someone transform a node (and their meshes) after loading, if the model isn't rigged.
Or is there any other reason why I should keep this structure?
Assimp also offers the flag aiProcess_PreTransformVertices to flatten the transformation hierarchy. You can also do it manually, of course, by using the aiNode::mTransformation matrices and multiplying them in the right order.
A potential problem with these approaches (especially with the flag) can be that the material properties of sub-meshes can get lost. Assimp doesn't care if sub-meshes have different material properties and just merges them, s.t. the material properties can get lost for a certain sub-mesh. This also applies to other properties like sub-mesh names. If sub-meshes get merged, only one (arbitrarily chosen?) sub-mesh name remains.
I.e. you'll want to prevent flattening the node hierarchy if you would like to use specific properties (names, material properties) of sub-meshes.
If your concern is only w.r.t. transforming them to world space: If you are never going to do something with the nodes in object space (like, e.g., transforming a sub-node in relation to a parent node), then I don't see a reason to not transform them into world space.
Threejs has a parameter called renderOrder for objects, which allows threejs to sort them if the sortObjects = false for the renderer. Before sorting threejs divides the objects into two bins (a transparency and opaque bin). Each bin the objects are sorted. The opaque gets rendered first and there after the transparency.
If you set sortObjects to false then you are relying on the depthbuffer.
My question is there a way I can manually sort the objects? I would like to have all my objects in one bin since I am sorting from back to front and do not need two bins (which in my case messes things up). I do not use the depthbuffer.
Say you have one 'body' geometry (from OBJ file) and several different 'lens' geometries, of different sizes, that can be 'mounted' on the body object.
How is the mount information best represented (I am thinking the data models for body and lens would need offset data representing the respective mount points)?
In THREE.js, for a chosen lens/body pair would a Group be used to 'put together' the two pieces?
New to THREE.js (sorry). . .
That sounds like a good approach.
I have two varchar columns with wkt value (a polygon and a point). I want to know if there are a polygon that contains some point using Oracle.
I'm using sdo_contains command, but don't work. According the documentation, the polygon should be indexed. Can anyone help me how to get around this problem?
I don't want to create a geometry column. I can't change the table structure or add a column.
SDO_CONTAINS is a spatial operator function and does indeed require an index (or rather, an indexed geometry column).
For arbitrary in-memory geometry objects, you can use SDO_GEOM.RELATE with the CONTAINS or INSIDE mask.
https://docs.oracle.com/cd/B19306_01/appdev.102/b14255/sdo_objgeom.htm#BGHCDIDG
I am working on a small game using webgl. Within this game I have some kind of forest which consists out of many (100+) tree objects. Because I only have a few different tree models, I rotate and scale these models in a different way before I display them.
At the moment I loop over all trees to display them:
for (var tree in trees) {
tree.display();
}
While the display() method of tree looks like:
display : function() { // tree
this.treeModel.setRotation(this.rotation);
this.treeModel.setScale(this.scale);
this.treeModel.setPosition(this.position);
this.treeModel.display();
}
Many tree objects share the same treeModel object, so I have to set rotation/scale/position of the model everytime before I display it. The rotation/scale/position values are different for every tree.
The display method of treeModel does all the gl stuff:
display : function() { // treeModel
// bind texture
// set uniforms for projection/modelview matrix based on rotation/scale/position
// bind buffers
// drawArrays
}
All tree models use the same shader but can use different textures.
Because a single tree model consists only out of a few triangles I want to combine all trees into one VBO and display the whole forest with one drawArrays() call.
Some assumptions to make talking about numbers easier:
There are 250 trees to display
There are 5 different tree models
Every tree model has 50 triangles
Questions I have:
At the moment I have 5 buffers that are 50 * 3 * 8 (position + normal + texCoord) * floatSize bytes large. When i want to display all trees with one vbo i would have a buffer with 250 * 50 * 3 * 8 * floatSize byte size. I think I can't use an index buffer because I have different position values for every tree (computed out of the position value of the tree model and the tree position/scale/rotation). Is this correct or is there still a way I can use index buffers to reduce the buffer size at least a bit? Maybe there are other ways to optimize this?
How to handle different textures of the tree models? I can bind all textures to different texture units but how can I decide within the shader which texture should be used for the fragment that is currently displayed?
When I want to add a new tree (or any other kind of object) to this buffer at runtime: Do I have to create a new buffer and copy the content? I think new values can't be added by using glMapBuffer. Is this correct?
Index element buffers can only reach over attributes that are equal to or below 65535 in length, so you need to use drawArrays instead. It's usually not a big loss.
You can add trees to the end of the buffers using GL.bufferSubData.
If your textures are in reasonable sized (like 128x128 or 256x256), you can probably merge them into one big texture and handle the whole thing with the UV-coords. If not, you can add another attribute saying what texture the vertex belongs to and have a condition in the vertex shader, alternatively an array of sampler2Ds (not sure it works, never tried it). Remember that conditions in shaders are pretty slow.
If you decide to stick to your current solution, make sure to sort the trees so the once using the same textures are rendered after each other - keeping state switching down is essential, always.
A few thoughts:
Once you plant a tree in your world, do you ever modify it? Will it animate at all? Or is it just static geometry? If it's truly static, you could always build a single buffer with several copies of each tree. As you append trees, first apply (in Javascript) that instance's world transform to the vertices. If using triangle strips, you can link trees together using degenerate polygons.
You could roll your own pseudo-instanced drawing:
Encode an instance ID in the array buffer. Just set this to the same value for all vertices that are part of the same tree instance. I seem to recall that you can't have non-floaty vertex attributes in ES GLSL (maybe that's a Chrome limitation), so you will need to bring it in as a float but use it as an int. Since it's coming in as a float, you will have to deal with the fact that it's interpolated across your triangle, and so the value will have minor fluctuations - but simply rounding to the nearest integer fixes that right up.
Use a separate texture (which I will call the data texture) to encode all the per-instance information. In your vertex shader, look at the instance ID of the current vertex and use that to compute a texture coordinate in the data texture. Pull out whatever you need to transform the current vertex, and apply it. I think this is called a "dependent texture read", which is generally frowned upon because it can cause performance issues, but it might help you batch your geometry, which can help solve performance issues. If you're interested, you'll have to try it and see what happens.
Hope for an extension to support real instanced drawing.
Your current approach isn't so bad. I'd say: Stick with it until you hit some wall.
50 triangles is already a reasonable batch size for a single drawElements/drawArrays call. It's not optimal, but also not so bad. So for every tree change the paramters like location, texture and maybe shape through uniforms. Then do a draw call for each tree. Also a total of 250 drawElements calls isn't so bad either.
So I'd use one single VBO that contains all the used tree geometry variants. I'd actually split up the trees into building blocks, so that I could recombine them for added variety. And for each tree set appropriate offsets into the VBO before calling drawArrays or drawElements.
Also don't forget that you can do a very cheap field of view culling of each tree.