How to draw points efficiently - c++

Question

My program receives PCL pointcloud and plot each point one by one using:
glBegin(GL_POINTS);
glVertex3f(point.x, point.y, point].z);
glEnd();
It works but due to the large number of points the program is pretty slow. Is there a more efficient way to do this?

Answer 1

Jam all the points into a big VBO when the point-cloud changes & draw 'em all in one go using a single glDrawArrays() call. That way OpenGL can shift all the vertex data to GPU once instead of you spoon-feeding the driver geometry one glVertex() at a time every frame.
Heck, even vertex arrays will buy you a huge speed-up by avoiding hundreds of thousands of function-calls into the GL driver.
EDIT: Comparison:
10 million random points, using vertex buffer objects:
Vertex arrays:
Display lists:
And using immediate-mode:
Code (hit 'n' to cycle between drawing methods):
// http://glew.sourceforge.net/
#include <GL/glew.h>
// http://freeglut.sourceforge.net/
#include <GL/freeglut.h>
// http://glm.g-truc.net/
#include <glm/glm.hpp>
#include <glm/gtc/random.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <vector>
#include <sstream>
#include <chrono>
#include <cstddef>
struct Vertex
{
glm::vec4 pos;
glm::vec4 color;
};
std::vector< Vertex > verts;
GLuint vbo = 0;
GLuint dlist = 0;
void init()
{
// init geometry
for( size_t i = 0; i < 10000000; i++ )
{
Vertex vert;
vert.pos = glm::vec4( glm::linearRand( glm::vec3( -1.0f, -1.0f, -1.0f ), glm::vec3( 1.0f, 1.0f, 1.0f ) ), 1.0f );
vert.color = glm::vec4( glm::linearRand( glm::vec3( 0.00f, 0.0f, 0.0f ), glm::vec3( 1.0f, 1.0f, 1.0f ) ), 1.0f );
verts.push_back( vert );
}
// create display list
dlist = glGenLists( 1 );
glNewList( dlist, GL_COMPILE );
glBegin( GL_POINTS );
for( size_t i = 0; i < verts.size(); ++i )
{
glColor4fv( glm::value_ptr( verts[i].color) );
glVertex4fv( glm::value_ptr( verts[i].pos) );
}
glEnd();
glEndList();
// create VBO
glGenBuffers( 1, &vbo );
glBindBuffer( GL_ARRAY_BUFFER, vbo );
glBufferData( GL_ARRAY_BUFFER, sizeof( Vertex ) * verts.size(), verts.data(), GL_STATIC_DRAW );
}
unsigned int method = 0;
void keyboard( unsigned char key, int x, int y )
{
if( 'n' == key )
{
method++;
if( method > 3 ) method = 0;
}
}
void display()
{
// timekeeping
static std::chrono::steady_clock::time_point prv = std::chrono::steady_clock::now();
std::chrono::steady_clock::time_point cur = std::chrono::steady_clock::now();
const float dt = std::chrono::duration< float >( cur - prv ).count();
prv = cur;
glClearColor( 0, 0, 0, 1 );
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
double w = glutGet( GLUT_WINDOW_WIDTH );
double h = glutGet( GLUT_WINDOW_HEIGHT );
gluPerspective( 60.0, w / h, 0.1, 10.0 );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
gluLookAt( 2, 2, 2, 0, 0, 0, 0, 0, 1 );
static float angle = 0.0f;
angle += dt * 6.0f;
glRotatef( angle, 0, 0, 1 );
// render
switch( method )
{
case 0:
// VBO
glBindBuffer( GL_ARRAY_BUFFER, vbo );
glEnableClientState( GL_VERTEX_ARRAY );
glEnableClientState( GL_COLOR_ARRAY );
glVertexPointer( 4, GL_FLOAT, sizeof( Vertex ), (void*)offsetof( Vertex, pos ) );
glColorPointer( 4, GL_FLOAT, sizeof( Vertex ), (void*)offsetof( Vertex, color ) );
glDrawArrays( GL_POINTS, 0, verts.size() );
glDisableClientState( GL_VERTEX_ARRAY );
glDisableClientState( GL_COLOR_ARRAY );
glBindBuffer( GL_ARRAY_BUFFER, 0 );
break;
case 1:
// vertex array
glEnableClientState( GL_VERTEX_ARRAY );
glEnableClientState( GL_COLOR_ARRAY );
glVertexPointer( 4, GL_FLOAT, sizeof( Vertex ), &verts[0].pos );
glColorPointer( 4, GL_FLOAT, sizeof( Vertex ), &verts[0].color );
glDrawArrays( GL_POINTS, 0, verts.size() );
glDisableClientState( GL_VERTEX_ARRAY );
glDisableClientState( GL_COLOR_ARRAY );
break;
case 2:
// display list
glCallList( dlist );
break;
case 3:
// immediate mode
glBegin( GL_POINTS );
for( size_t i = 0; i < verts.size(); ++i )
{
glColor4fv( glm::value_ptr( verts[i].color) );
glVertex4fv( glm::value_ptr( verts[i].pos) );
}
glEnd();
break;
}
// info/frame time output
std::stringstream msg;
msg << "Using ";
switch( method )
{
case 0: msg << "vertex buffer object"; break;
case 1: msg << "vertex array"; break;
case 2: msg << "display list"; break;
case 3: msg << "immediate mode"; break;
}
msg << std::endl;
msg << "Frame time: " << (dt * 1000.0f) << " ms";
glColor3ub( 255, 255, 0 );
glWindowPos2i( 10, 25 );
glutBitmapString( GLUT_BITMAP_9_BY_15, (unsigned const char*)( msg.str().c_str() ) );
glutSwapBuffers();
}
int main(int argc, char **argv)
{
glutInit( &argc, argv );
glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE );
glutInitWindowSize( 600, 600 );
glutCreateWindow( "GLUT" );
glewInit();
init();
glutDisplayFunc( display );
glutKeyboardFunc( keyboard );
glutIdleFunc( display );
glutMainLoop();
return 0;
}

Answer 2

Yes definitely, the code you are showing is from a quite old version of OpenGL.
In more recent versions you can pack your data together and send it to the GPU in one call. The code becomes a little bit more complex but it is worth it.
I suggest you to look at this website : https://learnopengl.com/
It gathers everything you need to start using modern opengl.
Hope it helped.