High framerate drawing stream of RGB frames on Raspberry framebuffer (https://www.raspberrypi.org/forums/viewtopic.php?f=43&t=264109)

rgb2fb.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <time.h>

#include <unistd.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
#include <sys/ioctl.h>

int align_up(int x, int y)  { return ((x-1)|((1<<y)-1))+1; }

#include <time.h>
long prev_us = 0, delta_us = 0, base_sec = 0;
#define _  {long a=prev_us;struct timespec t;clock_gettime(CLOCK_REALTIME,&t);\
  if (!base_sec) { base_sec = t.tv_sec; }\
  prev_us=1000000*(t.tv_sec-base_sec)+t.tv_nsec/1000; delta_us = prev_us - a;}
#define __ _ fprintf(stderr, "%ld\n", delta_us);
#define ___(n, blk) for(int i=0; i<n; ++i) { blk }

void FillArea32(char *buf, unsigned nStride3, unsigned *fbp, unsigned lStride,
		int xres, int yres, int x1, int y1, int x2, int y2, int cmask)
{
  fbp += (y1 * lStride + x1);

  for(int y = y1; y < y2; y++, fbp += lStride, buf += nStride3 - 3 * (x2 - x1))
  {
    if (y < 0)     { buf += nStride3; continue; }
    if (y >= yres) { break; }

    char *p = (char*)fbp;
    for(int x = x1; x < x2; x++, p+=4)
    {
      if ((x < 0) || (x >= xres)) { buf += 3; continue; }

      p[2] = cmask & 0x04 ? *buf++ : (buf++,0);
      p[1] = cmask & 0x02 ? *buf++ : (buf++,0);
      p[0] = cmask & 0x01 ? *buf++ : (buf++,0);
      p[3] = 0;
    }
  }
}

int main(int argc, char *argv[])
{
  unsigned width, height, nStride, nSliceHeight, nLen, cmask;
  char *buf;

  int fbfd = 0;
  struct fb_var_screeninfo vinfo;
  struct fb_fix_screeninfo finfo;
  unsigned *fbp = NULL;

  assert((argc+1)/2==2 || !"Format: rgb2fb width height [dmask]");

// memory mapped framebuffer
  assert(-1 != (fbfd = open("/dev/fb0", O_RDWR)));

  assert(ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) != -1);
  assert(ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) != -1);
  assert(vinfo.xoffset == 0);
  assert(vinfo.yoffset == 0);
  assert(vinfo.bits_per_pixel == 32);

  fbp = mmap(0, finfo.smem_len, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
  assert(fbp != (void*)-1);

  for(volatile unsigned *p = fbp; p < fbp + finfo.smem_len/4; ++p)
    *p = *p;

  msync(fbp, finfo.smem_len, MS_SYNC);

// init rgb stdin related variables
  width  = atoi(argv[1]); nStride      = align_up(width,  5);
  height = atoi(argv[2]); nSliceHeight = align_up(height, 4);

  nLen = nStride * nSliceHeight * 3;

  assert( (buf = malloc(nLen)) );

  cmask  = (argc == 3) ? 'F' : argv[3][0];
  cmask -= (cmask > '9') ? '7' : '0';

// take rgb frames from stdin and display on framebuffer
//
  fread(buf, nLen, 1, stdin);
_ // do not profile 1st fread
  while (!feof(stdin))
  {
__  int colmask[4] = {0x07, 0x01, 0x02, 0x04};

_   for(int i=3; i>=0; --i)
      if (cmask & (1<<i))
      {
	int x = vinfo.xres / 2 - (1 - i%2) * width;
	int y = vinfo.yres / 2 - (1 - i/2) * height;

        FillArea32(buf, nStride * 3, fbp, finfo.line_length/4,
          vinfo.xres, vinfo.yres, x, y, x + width, y + height, colmask[i]);
      }

    if (cmask == 0)
    {
      int x = (vinfo.xres - width) / 2;
      int y = (vinfo.yres - height) / 2;

      FillArea32(buf, nStride * 3, fbp, finfo.line_length/4,
        vinfo.xres, vinfo.yres, x, y, x + width, y + height, 0x07);
    }
__
    msync(fbp, finfo.smem_len, MS_SYNC);
_
    int ret = fread(buf, nLen, 1, stdin);
    assert(feof(stdin) || (1 == ret));
  }
  free(buf);
  munmap(fbp, finfo.smem_len);
  close(fbfd);

  return 0;
}