Ultimately, objects are always drawn in the screen by setting pixels into it. Plotting a point by setting a pixel is entirely reasonable, and can be indeed done directly, in realtime, for several millions of points. I just tested the C program below, compiled with gcc without optimizations, and it gives about 80 fps for three million points (on my 6 year-old thinkpad). My point: CPUs are ridiculously fast, and you
can indeed do a lot of large-scale data visualization without need to meddle with the GPU.
#define FPS 80
void plot_points(
float *o, // output raster array (w*h)
int w, // width of raster
int h, // height of raster
float *x, // input point coordinates (2*n)
int n // number of input points
)
{
// initialize the output raster
for (int i = 0; i < 2*w*h; i++)
o[i] = 0;
// accumulate the points that fall inside the raster
for (int i = 0; i < n; i++)
{
int p = x[2*i+0];
int q = x[2*i+1];
if (p >= 0 && p < w && q >= 0 && q < h)
o[w*q+p] += 1;
}
}
#include <stdlib.h>
int main(void)
{
int w = 1000;
int h = 1000;
int n = 3000000;
float *x = malloc(2*n*sizeof*x);
float *o = malloc(w*h*sizeof*o);
for (int i = 0; i < 2*n; i++)
x[i] = 1000*(rand()/(1.0+RAND_MAX));
for (int i = 0; i < FPS ; i++)
plot_points(o, w, h, x, n);
return 0;
}
// NOTE: if this program runs in less than 1 second, it means that it
// is faster than "FPS"
