How to use 2D drivers

Here are demos using 2D drivers:

• https://www.youtube.com/watch?v=suswjbpR1HU
• https://www.youtube.com/watch?v=JFmCin3EJIs

The first video is a scaling test (source coming soon), and the second video is a demo of moving a lot of sprites around at once.

• https://github.com/librerpi/lk-overlay/blob/master/app/grid/grid.c

In this file, gfx_create_surface() will create a bitmap image in ram.

Lines 18-29:

  for (int x=0; x< width; x++) {
    for (int y=0; y < height; y++) {
      uint color = 0x00000000;
      if (true) {
        if (y % grid == 0) color |= 0xffff0000;
        if (y % grid == 1) color |= 0xffff0000;
        if (x % grid == 0) color |= 0xff0000ff;
        if (x % grid == 1) color |= 0xff0000ff;
      }
      gfx_putpixel(gfx_grid, x, y, color);
    }
  }

Those lines will render a grid into it (there's also the ability to load tga image files).

Lines 31-35:

  grid_layer = malloc(sizeof(hvs_layer));
  mk_unity_layer(grid_layer, gfx_grid, 60, 100, 100);
  grid_layer->name = "grid";
  grid_layer->w = 100;
  grid_layer->h = 300;

Those lines will create a sprite description.

Lines 37-40:

  mutex_acquire(&channels[channel].lock);
  hvs_dlist_add(channel, grid_layer);
  hvs_update_dlist(channel);
  mutex_release(&channels[channel].lock);
}

Those lines will make that sprite visible, and will schedule a pageflip on the next vsync.

Line 53:

    hvs_wait_vsync(channel);

will wait for vsync to happen.

Lines 55-72:

    {
      if (grow_w && (grid_layer->w >= 300)) grow_w = false;
      if (!grow_w && (grid_layer->w <= 5)) grow_w = true;

      int delta = 1;
      if (!grow_w) delta = -1;

      grid_layer->w += delta;
    }
    {
      if (grow_h && (grid_layer->h >= 300)) grow_h = false;
      if (!grow_h && (grid_layer->h <= 5)) grow_h = true;

      int delta = 1;
      if (!grow_h) delta = -1;

      grid_layer->h += delta;
    }

These lines change the sprite size.

And finally, line 75:

    hvs_update_dlist(channel);

This line schedules another pageflip on vsync.

With all that code, and some GPIO reading, you can make a 2D demo or game, and this basically uses 0% of the cpu, instead, it uses the gpu, and has absolutely no screen tearing.