To make the bird fall, we'll use this function:
function make_bird_slow_and_fall() {
if (bird.velocity_y < max_fall_speed) {
bird.velocity_y = bird.velocity_y + acceleration;
}
if (bird.y > myCanvas.height - bird.MyImg.height) {
// gone off bottom
bird.velocity_y = 0;
game_mode = 'over';
}
}
It simply says
if the bird has not yet reached it's maximum fall speed, then
increase it's downward velocity by the amount of acceleration we've selected.
If the bird's y-position is past the bottom of the canvas, then set the velocity back to zero, and we'll set a variable called game_mode to 'over', which will come in handy elsewhere.
Have a good look at the function and be sure you understand how it achieves its goal.
We're going to call this function from our main Do_a_Frame renderer.