Due to performance issues drawing thousands of similar triangles (with different attributes), I would like to draw all of these using a single call to drawElements. But in order to draw each triangle with their respective attributes (ex: world location, color, orientation) I believe i need to send an array buffer to my vertex shader, where the array is a list of all the triangle attributes.
If this approach is indeed the standard way to do it, then i am delighted to know i have the theory correct. I just need to know how to send an array buffer to the shader. Note that currently i know how to send a multiple attributes and uniforms (though they are not contiguous in memory, which is what im looking for).
If not, i'd appreciate it if a resident expert can point me in the right direction.
I have a related question because I am having trouble actually implementing a VBO.
How to include model matrix to a VBO?
You do have the theory correct, let me just clear a few things...
You can only "send vertex array" to the vertex shader via pointers using attributes so this part of the code stays pretty much the same. What you do seem to be looking for are 2 optimisations, putting the whole buffer on the GPU and using interleaved vertex data.
To put the whole buffer on the GPU you need to use VBOs as already mentioned in the comment. By doing that you create a raw buffer on the GPU to which you can put any data you want and even modify them in runtime if needed. In your case that would be vertex data. To use non interleaved data you would probably create a buffer for each, position, colour, orientation...
To use interleaved data you need to put them into the buffer sequentially, if possible it is best to create a data structure that holds all the vertex data (of a single vertex, not the whole array) and send those to the buffer (a simple primitive array will work as well). A C example of such structure:
typedef union {
struct {
float x,y,z; //position
float r,g,b,a; //color
float ox,oy,oz; //orientation
};
struct {
float position[3];
float color[4];
float orientation[3];
};
}Vertex;
What you need to do then is set the correct pointers when using this data. In the VBO you start with NULL (0) and that would represent the position in this case, to set colour you would have to then use ((float *)NULL)+3 or use some conveniences such as offsetof(Vertex, color) in C. With that you also need to set the stride, that would be the size of the Vertex structure so you could use sizeof(Vertex) or hardcoded sizeof(float)*(3+4+3).
After this all you need to watch for is correct buffer binding/unbinding while rest of your code should be exactly the same.
Related
You can set multiple vertex buffers with IASetVertexBuffers,
but there is no plural version of IASetIndexBuffer.
What is the point of creating (non-interleaved) multiple vertex buffer datas if you wont be able to refer them with individual index buffers
(assume i have a struct called vector3 with 3 floats x,y,z)
let say i have a model of human with 250.000 vertices and 1.000.000 triangles;
i will create a vertex buffer with size of 250.000 * sizeof(vector3)
for vertex LOCATIONS and also,
i will create another vertex buffer with size of 1.000.000 * 3 *
sizeof(vector3) for vertex NORMALS (and propably another for diffuse
texture)
i can set these vertex buffers like:
ID3D11Buffer* vbs[2] = { meshHandle->VertexBuffer_Position, meshHandle->VertexBuffer_Normal };
uint strides[] = { Vector3f_size, Vector3f_size };
uint offsets[] = { 0, 0 };
ImmediateContext->IASetVertexBuffers(0, 2, vbs, strides, offsets);
how can i set seperated index buffers for these vertex datas if IASetIndexBuffer only supports 1 index buffer
and also (i know there are techniques for decals like creating extra triangles from the original model but)
let say i want to render a small texture like a SCAR on this human model's face (let say forehead), and this scar will only spread through 4 triangles,
is it possible creating a uv buffer (with only 4 triangles) and creating 3 different index buffers for locations, normals and UVs for only 4 triangles but using the same original vertex buffers (same data from full human model). i dont want to create tonnes of uv data which will never be rendered beside characters forehead (and i dont want to re-use, re-create vertex position datas for this secondary texture layers (decals))
EDIT:
i realized i didnt properly ask a question, so my question is:
did i misunderstand non-interleaved model structure (is it being used
for some other reason instead having non-aligned vertex components)?
or am i approaching non-interleaved structure wrong (is there a way
defining multiple non-aligned vertex buffers and drawing them with
only one index buffer)?
The reason you can't have more than on Index buffer bound at a time is because you need to specify a Fixed number of primitives when you make a call to DrawIndexed.
So in your example, if you have one index buffer with 3000 primitives and another with 12000 primitives, the pipeline would have no idea how to match the first set to the second set.
If is generally normal that some vertex data (mostly position) eventually requires to be duplicated across your vertex buffer, since your buffers requires to be the same size.
Index buffer works as a "lookup table", so your data across vertex buffers need to be consistent.
Non interleaved model structure has many advantages:
First using separate buffers can lead to better performances if you need to draw the models several times and some draws do not require attributes.
For example, when you render a shadow map, you will need to access only positions, so in interleaved mode, you still need to bind a large data structure and access elements in a non contiguous way (Input Assembler does that). In case of non interleaved data, Position will be contiguous in memory so fetch will be much faster.
Also non interleaved allows to more easily do some processing on some attributes, it is common nowadays to perform some displacement or skinning in a compute shader, so in that case you can also easily create another Position+Normal buffer, perform your skinning on those and attach them in the pipeline once processed (And you can keep UV buffer intact).
If you want to draw non aligned Vertex buffers, you could use Structured Buffers instead (and use SV_VertexID and some custom lookup tables in your shader code).
I am building index and vertex buffers from OpenMesh structures which I will feed into my rendering engine. Here I iterate my elements (not shown) and create VertexHandles for each of my points and then add the face.
std::vector<Mesh::VertexHandle> vhandles;
for (... 3 triangle points) {
vhandles.push_back(mesh.add_vertex(Mesh::Point(
point->px, point->py, point->pz)));
}
mesh.add_face(face_vhandles);
The vertex buffer for a Point appears below and I copy the vhandles data into this struct, then build an array of these to feed to the graphics engine.
struct Point
{
float px, py, pz; // positions
float nx, ny, nz; // normals
float cx, cy, cz; // diffuse
}
When I build the vhandles vector above, I did not add an index/id to the VertexHandle.
I need to somewheres store and have access to the id of the point with the VertexHandle iteself. Where would I store that? I've not yet found a field for this purpose within the source of a VertexHandle, but seems like something that would be needed.
Although I'm still just getting familiar with OpenMesh, it seems to me like a bad practice to access any element by their index because these are internal indices that will be rearranged upon garbage collection. OpenMesh provides iterators and circulators to iterate over its elements. If you need random access, you can always store the handles associated to whatever index you want in a container. Also, there are the vertex_handle(), face_handle(), edge_handle() functions which give you mesh elements by their internal indices.
I was just trying to learn how VBOs and IBOs work in WEBGL.
Here is my understanding:
IBOs help reduce the amount of info passed down to the GPU . So we have a VBO and then we create an IBO with its indices pointing to the VBO. I had a doubt as to how WEBGL knows the IBO <--> VBO mapping . In case of a single VBO/IBO , I thought as GL was a state machine it sees the last ARRAY_BUFFER it is bound to and then uses that buffer as the IBO target .Below is a case with multiple VBOs(position buffer and color buffer) as given below:
gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, cubeVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexColorBuffer);
gl.vertexAttribPointer(shaderProgram.vertexColorAttribute, cubeVertexColorBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
setMatrixUniforms();
gl.drawElements(gl.TRIANGLES, cubeVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0);
In the above code(which works - i took it from a tutorial), we have two VBOs and one IBO (cubeVertexIndexBuffer) , what i don't understand is how WEBGL knows the indices of the IBO point to the position buffer and not the color buffer(though the color buffer is the last bound ARRAY_BUFFER).
Please let me know as to what I am missing here....
The GL_ELEMENT_ARRAY_BUFFER binding has nothing to do with the GL_ARRAY_BUFFER binding, each binding is used by a different set of commands. This is why people should not learn OpenGL using multiple VBOs in the beginning, interleaved VBOs avoid this sort of confusion. I will attempt to clear up your confusion below.
The GL_ARRAY_BUFFER binding is used for commands like glVertexAttribPointer (...). The GL_ELEMENT_ARRAY_BUFFER binding, on the other hand, by glDrawElements (...).
The indices in the IBO point to neither of the element arrays per-se. What they point to
are the glVertexAttribPointer (...)s you setup while you had a GL_ARRAY_BUFFER bound.
In case it was not already obvious, you cannot have more than one buffer object of the same type bound at any given time. When you set your attrib pointers and you are not using interleaved arrays you have to change the bound VBO. Thus, glDrawElements (...) could not care less which VBO is bound, it only cares about the vertex attrib pointers that you setup and the bound element array. Those pointers are relative to whatever VBO was bound when you set them up, but after the pointer is setup the state of the binding is no longer relevant.
The statefulness in OpenGL is awful. If you want to work with any of the buffers, you almost always need two calls: One to tell OpenGL which buffer you want to use and a second (and third and more) that operate on the buffer. The ambiguous buffer names make the whole thing more confusing. So, let us quickly clear up some things:
As explained here, binding to gl.ARRAY_BUFFER (or GL_ARRAY_BUFFER) indicates that the specified buffer is a VBO.
gl.ELEMENT_ARRAY_BUFFER (or GL_ELEMENT_ARRAY_BUFFER) indicates an IBO (that link is worth checking out). An IBO represents one complete surface. It is a list of indices to all vertices that this surface is made of. The IBO needs to be bound to gl.ELEMENT_ARRAY_BUFFER before a draw call because that's how the pipeline knows which vertices are where.
Since you sometimes need multiple attributes per vertex that you might (for some reason) want to store in separate buffers, you can use a single IBO to index into multiple VBOs.
Finally, (and I think, here is your confusion), the vertexAttribPointer tells the shader to look up the given attribute of given type in the given relative offset in the VBO that is bound when vertexAttribPointer is called. This way, the pipeline can get each attribute once it has the right vertex index, which it reads from the IBO. In your case, vertexAttribPointer says that the vertexPositionAttribute comes from the cubeVertexPositionBuffer, and color from your color buffer. In order to avoid calling vertexAttribPointer before every draw call, you can instead use a VAO to cache that information.
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.
I was sending vertex arrays (of 32 bit floats) to the GPU every time I wanted to draw them, but this wasn't efficient, so I switched to Vertex Buffer Objects to cache my vertex arrays in the GPU.
It's working, but I was wondering if there's a way to determine the size of a given VBO later on without going back to the original vertex arrays? Here's the process I'm struggling with:
I have a vertex array of, for example, six 32 bit floats.
I send my vertex array to the GPU via OpenGL-ES where it's stored in a VBO - to which I retain a handle.
My vertex array is redundant at this point so I delete it.
Later on I use the handle to make OpenGL-ES draw something, but at this point I'd also like to know how to determine the size of the vertex array that was originally used to create the VBO. I now have just the VBO handle - can I re-determine somehow that I'd stored six 32 bit floats in this VBO?
I'm probably missing something really obvious.
Thanks for any suggestions!
Doh! Just found it:
int nBufferSize = 0;
glGetBufferParameteriv(GL_ARRAY_BUFFER, GL_BUFFER_SIZE, &nBufferSize);
int originalVertexArraySize = ( nBufferSize / sizeof(float) );