Given a set of Faces with each face containing the number of vertices and a pointer to a vertex in a vector std::Vector, i want to iterate over all faces and use glDrawElements to draw each face:
Edit: I just noticed i forgot to activate the vertex_array
for(std::vector<Face>::iterator it = faces.begin();it != faces.end();++it) {
const Face &f = *it;
std::Vector<GLint> indices;
std::Vector<GLfloat> positions;
for(int i=0;i<f.vcount;++i){
const Vertex &v = vertices[f.vertices[i]];
positions.push_back(v.x);
positions.push_back(v.y);
positions.push_back(v.z);
indices.push_back(f.vertices[i]);
}
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3,GL_FLOAT,3*sizeof(GL_FLOAT),&positions[0]);
glDrawElements(GL_POLYGON,indices.size(),GL_UNSIGNED_INT,&indices[0]);
glDisableClientState(GL_VERTEX_ARRAY);
positions.clear();
indices.clear();
}
But apparently this does not work correctly and there is nothing displayed.
Edit: Enabling the GL_VERTEX_ARRAY draws something on the screen but not the model i tried to create. So there seems to be something wrong with the addressing.
Your index array doesn't make sense. The indices glDrawElements will use just refer to the vertex arrays you have set up - and you are setting up a new array for each separate polygon.
This means that
indices.push_back(f.vertices[i]);
should be conceptually just
indices.push_back(i);
which in the end means that you could skip the indices completely and just use
glDrawArrays(GL_POLYGON,0,f.vcount);
Note that what you are doing here is a very inefficent way to render the ojects. You would be much better if you would use a single draw call for the whole object. You could do that by manually triangulating the polygons into triangles as a pre-processing step.
Related
So, I need the way to render multiple objects(not instances) using one draw call. Actually I know how to do this, just to place data into single vbo/ibo and render, using glDrawElements.
The question is: what is efficient way to update uniform data without setting it up for every single object, using glUniform...?
How can I setup one buffer containing all uniform data of dozens of objects, include MVP matrices, bind it and perform render using single draw call?
I tried to use UBOs, but it's not what I need at all.
For rendering instances we just place uniform data, including matrices, at another VBO and set up attribute divisor using glVertexAttribDivisor, but it only works for instances.
Is there a way to do that I want in OpenGL? If not, what can I do to overcome overheads of setting uniform data for dozens of objects?
For example like this:
{
// setting up VBO
glGenBuffers(1, &vbo);
glBindBuffer(vbo);
glBufferData(..., data_size);
// setup buffer
for(int i = 0; i < objects_num; i++)
glBufferSubData(...offset, size, &(objects[i]));
// the same for IBO
.........
// when setup some buffer, that will store all uniforms, for every object
.........
glDrawElements(...);
}
Thanks in advance for helping.
If you're ok with requiring OpenGL 4.3 or higher, I believe you can render this with a single draw call using glMultiDrawElementsIndirect(). This allows you to essentially make multiple draw calls with a single API call. Each sub-call is defined by values in a struct of the form:
typedef struct {
GLuint count;
GLuint instanceCount;
GLuint firstIndex;
GLuint baseVertex;
GLuint baseInstance;
} DrawElementsIndirectCommand;
Since you do not want to draw multiple instances of the same vertices, you use 1 for the instanceCount in each draw call. The key idea is that you can still use instancing by specifying a different baseInstance value for each one. So each object will have a different gl_InstanceID value, and you can use instanced attributes for the values (matrices, etc) that you want to vary per object.
So if you currently have a rendering loop:
for (int k = 0; k < objectCount; ++k) {
// set uniforms for object k.
glDrawElements(GL_TRIANGLES, object[k].indexCount,
GL_UNSIGNED_INT, object[k].indexOffset * sizeof(GLuint));
}
you would instead fill an array of the struct defined above with the arguments:
DrawElementsIndirectCommand cmds[objectCount];
for (int k = 0; k < objectCount; ++k) {
cmds[k].count = object[k].indexCount;
cmds[k].instanceCount = 1;
cmds[k].firstIndex = object[k].indexOffset;
cmds[k].baseVertex = 0;
cmds[k].baseInstance = k;
}
// Rest of setup.
glMultiDrawElementsIndirect(GL_TRIANGLES, GL_UNSIGNED_INT, 0, objectCount, 0);
I didn't provide code for the full setup above. The key steps include:
Drop the cmds array into a buffer, and bind it as GL_DRAW_INDIRECT_BUFFER.
Store the per-object values in a VBO. Set up the corresponding vertex attributes, which includes specifying them as instanced with glVertexAttribDivisor(1).
Set up the per-vertex attributes as usual.
Set up the index buffer as usual.
For this to work, the indices for all the objects will have to be in the same index buffer, and the values for each attribute will have to be in the same VBO across all objects.
This question already has answers here:
What is the proper way to modify OpenGL vertex buffer?
(3 answers)
Closed 2 years ago.
I've got a training app written in winapi
So, I've got GL initialized there and I've got node-based system, that can be described by couple of classes
class mesh
{
GLuint vbo_index; //this is for having unique vbo
float *vertex_array;
float *normal_array;
unsigned int vertex_count;
etc.. //all those mesh things.
....
}
class node
{
bool is_mesh; //the node may or may not represent a mesh
mesh * mesh_ptr; //if it does then this pointer is a valid address
}
I've also got 2 global variables for keeping record of renderable mesh..
mesh **mesh_table;
unsigned int mesh_count;
Right now I'm experimenting on 2 objects. So I create 2 nodes of type mesh::cube with customizable number of x y and z segments. Expected behaviour of my app is let the user click between 2 of the nodes CUBE0, CUBE1 and show their customizable attributes - segments x, segments y, segments z. The user tweaks both objecs' parameters and they are being rendered out on top of each other in wireframe mode, so we can see the changing in their topology in real time.
When the node is being created for the first time, if the node type is mesh, then the mesh object is generated and it's mesh_ptr is written into the mesh_table and mesh_count increments. After that my opengl window class creates a unique vertex buffer object for the new mesh and stores it's index in the mesh_ptr.vbo_index
void window_glview::add_mesh_to_GPU(mesh* mesh_data)
{
glGenBuffers(1,&mesh_data->vbo_index);
glBindBuffer(GL_ARRAY_BUFFER ,mesh_data->vbo_index);
glBufferData(GL_ARRAY_BUFFER ,mesh_data->vertex_count*3*4,mesh_data->vertex_array,GL_DYNAMIC_DRAW);
glVertexAttribPointer(5,3,GL_FLOAT,GL_FALSE,0,NULL);//set vertex attrib (0)
glEnableVertexAttribArray(5);
}
After that the user is able to tweak the parameters and each time the parameter value changes the object's mesh information is being re-evaluated based on the new parameter values, while still being the same mesh instance, after that VBO data is being updated by
void window_glview::update_vbo(mesh *_mesh)
{
glBindBuffer(GL_ARRAY_BUFFER,_mesh->vbo_vertex);
glBufferData(GL_ARRAY_BUFFER,_mesh->vertex_count*12,_mesh->vertex_array,GL_DYNAMIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER,0);
}
and the whole scene redrawn by
for (unsigned short i=0;i<mesh_count;i++)
draw_mesh(mesh_table[i],GL_QUADS,false);
SwapBuffers(hDC);
The function for a single mesh is
bool window_glview::draw_mesh(mesh* mesh_data,unsigned int GL_DRAW_METHOD,bool indices)
{
glUseProgram(id_program);
glBindBuffer(GL_ARRAY_BUFFER,mesh_data->vbo_index);
GLuint id_matrix_loc = glGetUniformLocation(id_program, "in_Matrix");
glUniformMatrix4fv(id_matrix_loc,1,GL_TRUE,cam.matrixResult.get());
GLuint id_color_loc=glGetUniformLocation(id_program,"uColor");
glPolygonMode( GL_FRONT_AND_BACK, GL_LINE );
glUniform3f(id_color_loc,mesh_color[0],mesh_color[1],mesh_color[2]);
glDrawArrays(GL_DRAW_METHOD,0,mesh_data->vertex_count);
glBindBuffer(GL_ARRAY_BUFFER,0);
glUseProgram(0);
return true;
}
The problem is that only the last object in stack is being drawn that way, and the other object's points are all in 0 0 0, so in the viewport it's rendered one cube with proper parameters and one cube just as a DOT
QUESTION: Where did I go wrong?
You have a fundamental misunderstanding of what glBindBuffer(GL_ARRAY_BUFFER,mesh_data->vbo_vertex); does.
That sets the bound array buffer, which is actually only used by a handful of commands (mostly glVertexAttrib{I|L}Pointer (...)), binding the buffer itself is not going to do anything useful.
What you need to do is something along the lines of this:
bool window_glview::draw_mesh(mesh* mesh_data,unsigned int GL_DRAW_METHOD,bool indices)
{
glUseProgram(id_program);
//
// Setup Vertex Pointers in addition to binding a VBO
//
glBindBuffer(GL_ARRAY_BUFFER,mesh_data->vbo_vertex);
glVertexAttribPointer(5,3,GL_FLOAT,GL_FALSE,0,NULL);//set vertex attrib (0)
glEnableVertexAttribArray(5);
GLuint id_matrix_loc = glGetUniformLocation(id_program, "in_Matrix");
glUniformMatrix4fv(id_matrix_loc,1,GL_TRUE,cam.matrixResult.get());
GLuint id_color_loc=glGetUniformLocation(id_program,"uColor");
glPolygonMode( GL_FRONT_AND_BACK, GL_LINE );
glUniform3f(id_color_loc,mesh_color[0],mesh_color[1],mesh_color[2]);
glDrawArrays(GL_DRAW_METHOD,0,mesh_data->vertex_count);
glBindBuffer(GL_ARRAY_BUFFER,0);
glUseProgram(0);
return true;
}
Now, if you really want to make this simple and be able to do this just by changing a single object binding, I would suggest you look into Vertex Array Objects. They will persistently store the vertex pointer state.
in your draw glBindBuffer(GL_ARRAY_BUFFER,mesh_data->vbo_index); doesn't actually do anything; the information about the vertex attribute is not bound to the buffer at all. it is set in the glVertexAttribPointer(5,3,GL_FLOAT,GL_FALSE,0,NULL); call which gets overwritten each time a new mesh is uploaded.
either create and use a VAO or move that call from add_mesh_to_GPU to draw_mesh:
for the VAO you would do:
void window_glview::add_mesh_to_GPU(mesh* mesh_data)
{
glGenVertexArrays(1, &mesh_data->vao_index);//new GLInt field
glBindVertexArray(mesh_data->vao_index);
glGenBuffers(1,&mesh_data->vbo_index);
glBindBuffer(GL_ARRAY_BUFFER ,mesh_data->vbo_index);
glBufferData(GL_ARRAY_BUFFER ,mesh_data->vertex_count*3*4,mesh_data->vertex_array,GL_DYNAMIC_DRAW);
glVertexAttribPointer(5,3,GL_FLOAT,GL_FALSE,0,NULL);//set vertex attrib (0)
glEnableVertexAttribArray(5);
glBindVertexArray(0);
}
bool window_glview::draw_mesh(mesh* mesh_data,unsigned int GL_DRAW_METHOD,bool indices)
{
glBindVertexArray(mesh_data->vao_index);
glUseProgram(id_program);
GLuint id_matrix_loc = glGetUniformLocation(id_program, "in_Matrix");
glUniformMatrix4fv(id_matrix_loc,1,GL_TRUE,cam.matrixResult.get());
GLuint id_color_loc=glGetUniformLocation(id_program,"uColor");
glPolygonMode( GL_FRONT_AND_BACK, GL_LINE );
glUniform3f(id_color_loc,mesh_color[0],mesh_color[1],mesh_color[2]);
glDrawArrays(GL_DRAW_METHOD,0,mesh_data->vertex_count);
glUseProgram(0);
glBindVertexArray(0);
return true;
}
I have an array of Vertex Array Objects, that each contain a VBO reference, and and array of matrices, of the same size, such as:
unsigned int vaoArray[128];
matrix_t matrixArray[128];
rather than
for (i = 0; i < 128; i++)
{
glBindVertexArray(vaoArray[i]);
glUniformMatrix4fv(U_MVP_MATRIX_SLOT, 1, GL_FALSE, &matrixArray[i]);
glDrawArrays(BGL_TRIANGLE_FAN, 0, 4);
}
Is there a way I can push the entire array of VAOs and matrices to the GPU at once? Maybe using the instancing extension somehow?
I can't combine them all in one VAO/VBO, because the combination can change (this is drawing text, with each character having its own VAO/VBO combo).
And yes, I realize this all involves using ES 2.0 extensions. That's OK.
BTW, All of the VAOs for each character are identical except for the VBO id, if that helps.
I'm working for the first time on a 3D project (actually, I'm programming a Bullet Physics integration in a Quartz Composer plug-in), and as I try to optimize my rendering method, I began to use glDrawElements instead of the direct access to vertices by glVertex3d...
I'm very surprised by the result. I didn't check if it is actually quicker, but I tried on this very simple scene below. And, from my point of view, the rendering is really better in immediate mode.
The "draw elements" method keep showing the edges of the triangles and a very ugly shadow on the cube.
I would really appreciate some information on this difference, and may be a way to keep quality with glDrawElements. I'm aware that it could really be a mistake of mines...
Immediate mode
DrawElements
The vertices, indices and normals are computed the same way in the two method. Here are the 2 codes.
Immediate mode
glBegin (GL_TRIANGLES);
int si=36;
for (int i=0;i<si;i+=3)
{
const btVector3& v1 = verticesArray[indicesArray[i]];;
const btVector3& v2 = verticesArray[indicesArray[i+1]];
const btVector3& v3 = verticesArray[indicesArray[i+2]];
btVector3 normal = (v1-v3).cross(v1-v2);
normal.normalize ();
glNormal3f(-normal.getX(),-normal.getY(),-normal.getZ());
glVertex3f (v1.x(), v1.y(), v1.z());
glVertex3f (v2.x(), v2.y(), v2.z());
glVertex3f (v3.x(), v3.y(), v3.z());
}
glEnd();
glDrawElements
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glNormalPointer(GL_FLOAT, sizeof(btVector3), &(normalsArray[0].getX()));
glVertexPointer(3, GL_FLOAT, sizeof(btVector3), &(verticesArray[0].getX()));
glDrawElements(GL_TRIANGLES, indicesCount, GL_UNSIGNED_BYTE, indicesArray);
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
Thank you.
EDIT
Here is the code for the vertices / indices / normals
GLubyte indicesArray[] = {
0,1,2,
3,2,1,
4,0,6,
6,0,2,
5,1,4,
4,1,0,
7,3,1,
7,1,5,
5,4,7,
7,4,6,
7,2,3,
7,6,2 };
btVector3 verticesArray[] = {
btVector3(halfExtent[0], halfExtent[1], halfExtent[2]),
btVector3(-halfExtent[0], halfExtent[1], halfExtent[2]),
btVector3(halfExtent[0], -halfExtent[1], halfExtent[2]),
btVector3(-halfExtent[0], -halfExtent[1], halfExtent[2]),
btVector3(halfExtent[0], halfExtent[1], -halfExtent[2]),
btVector3(-halfExtent[0], halfExtent[1], -halfExtent[2]),
btVector3(halfExtent[0], -halfExtent[1], -halfExtent[2]),
btVector3(-halfExtent[0], -halfExtent[1], -halfExtent[2])
};
indicesCount = sizeof(indicesArray);
verticesCount = sizeof(verticesArray);
btVector3 normalsArray[verticesCount];
int j = 0;
for (int i = 0; i < verticesCount * 3; i += 3)
{
const btVector3& v1 = verticesArray[indicesArray[i]];;
const btVector3& v2 = verticesArray[indicesArray[i+1]];
const btVector3& v3 = verticesArray[indicesArray[i+2]];
btVector3 normal = (v1-v3).cross(v1-v2);
normal.normalize ();
normalsArray[j] = btVector3(-normal.getX(), -normal.getY(), -normal.getZ());
j++;
}
You can (and will) achieve the exact same results with immediate mode and vertex array based rendering. Your images suggest that you got your normals wrong. As you did not include the code with which you create your arrays, I can only guess what might be wrong. One thing I could imagine: you are using one normal per triangle, so in the normal array, you have to repeat that normal for each vertex.
You should be aware that a vertex in the GL is not just the position (which you specify via glVertex in immediate mode), but the set of all attributes like position, normals, texcoords and so on. So if you have a mesh where an end point is part of different triangles, this is only one vertex if all attributes are shared, not just the position. In your case, the normals are per triangle, so you will need different vertices (sharing position with some other vertices, but using a different normal) per triangle.
I began to use glDrawElements
Good!
instead of the direct access to vertices by glVertex3d...
There's nothing "direct" about immediate mode. In fact it's as far away from the GPU as you can get (on modern GPU architectures).
I'm very surprised by the result. I didn't check if it is actually quicker, but I tried on this very simple scene below. And, from my point of view, the rendering is really better with the direct access method.
Actually its several orders of magnitudes slower. Each and every glVertex call causes the overhead of a context switch. Also a GPU needs larger batches of data to work efficiently, so glVertex calls first fill a buffer created ad-hoc.
Your immediate code segment must be actually understand as following
glNormal3f(-normal.getX(),-normal.getY(),-normal.getZ());
glVertex3f (v1.x(), v1.y(), v1.z());
// implicit copy of the glNormal supplied above
glVertex3f (v2.x(), v2.y(), v2.z());
// implicit copy of the glNormal supplied above
glVertex3f (v3.x(), v3.y(), v3.z());
The reason for that is, that a vertex is not just a position, but the whole combination of its attributes. And when working with vertex arrays you must supply the full attribute vector to form a valid vertex.
My goal was to color the vertexes according to their order
EDIT: long time goal: access to preceding and following vertexes to simulate gravity behavior
i've used following code
#version 120
#extension GL_EXT_geometry_shader4 : enable
void main( void ) {
for( int i = 0 ; i < gl_VerticesIn ; i++ ) {
gl_FrontColor = vec4(float(i)/float(gl_VerticesIn),0.0,0.0,1.0);
gl_Position = gl_PositionIn[i];
EmitVertex();
}
}
but all vertexes are drawn black, it seem that i is always evaluated as 0, am i missing something or doing it wrong?
EDIT: figured the meta-problem out: how to feed all me model geometry into single geometry shader call, so the mainloop iterates over all the vertexes, not for every triangle.
You don't let a single geometry shader invocation iterate over all your vertexes, it is called for every original primitive (point, line, triangle, ...).
The solution is much easier: In the vertex shader (that is actually called for every vertex) you can read the special variable gl_VertexID, which contains the vertex's index. That index is either just a counter incremented for every vertex (if using glDrawArrays) and reset by every draw call, or the index from the index array (if using glDrawElements).
EDIT: Regarding the long time goal. Not directly but you might use a texture buffer for that. This basically enables you to get direct linear array-access to a buffer object (in your case the vertex buffer) which you can then just index with this vertex index. But there might also be other ways to accomplish that, which may suffice for another question.