How to write SPI data with registers in esp32?

I'm trying to modify esp32-nesemu project to use it with 18-bit color of ILI9486. While loop sends bmp line in every iteration,

while(1) {
   xQueueReceive(vidQueue, &bmp, portMAX_DELAY);
   ili9341_write_frame(x, y, DEFAULT_WIDTH, DEFAULT_HEIGHT, (const uint8_t **)bmp->line);
}

but this code is ok for rgb565 (16-bit color), if I compile it for ILI9486 I will get grayscale bmps.

I found another code of TFT-eSPI library, where 16-bit color code is converted to 18-bit:

// Split out the colours
uint32_t r = (color & 0xF800)>>8;
uint32_t g = (color & 0x07E0)<<5;
uint32_t b = (color & 0x001F)<<19;

// Concatenate 4 pixels into three 32 bit blocks
uint32_t r0 = r<<24 | b | g | r;
uint32_t r1 = r0>>8 | g<<16;
uint32_t r2 = r1>>8 | b<<8;

Using SPI registers I'm able to write 16 x 4 bytes in time. esp32-nesemu offers to write one horizontal line in time putting all pixels in array

while (x<width) {
   for (i=0; i<16; i++) {
      if(data == NULL){
         temp[i] = 0;
         x += 2;
         continue;
      }
      x1 = myPalette[(unsigned char)(data[y][x])]; x++;
      y1 = myPalette[(unsigned char)(data[y][x])]; x++;
      temp[i] = U16x2toU32(x1,y1);
   }
   while (READ_PERI_REG(SPI_CMD_REG(SPI_NUM))&SPI_USR);
   for (i=0; i<16; i++) {
      WRITE_PERI_REG((SPI_W0_REG(SPI_NUM) + (i << 2)), temp[i]);
   }
   SET_PERI_REG_MASK(SPI_CMD_REG(SPI_NUM), SPI_USR);
}

if I convert temp[i] to 18-bit color before writing I'll get true colors, but my pixels will be mixed. How do I modify this code to write pixels to display using SPI registers?