HTML5 simulates flat throwing motion (simulating the flat throwing motion process of a small ball)_html5 tutorial skills

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<script> <br>//box <br>var box_x=0; <br>var box_y=0; <br>var box_width=300; <br>var box_height=300; <br>//ball <br>var ball_x=10; <br>var ball_y=10; =10; <br>var ball_vx=10; <br>var ball_vy=0; <br>//constant <br>var g=10;//note <br>var rate=0.9; <br>//bound <br>var bound_left=box_x ball_radius; <br>var bound_right=box_x box_width-ball_radius; <br>var bound_top=box_y ball_radius; <br>var bound_bottom=box_y box_height-ball_radius; <br>//context <br>var ctx; <br>function init() <br>{ <br>ctx=document.getElementById('canvas').getContext('2d'); <br>ctx.lineWidth=ball_radius; <br>ctx.fillStyle= "rgb(200,0,50)"; <br>move_ball(); <br>setInterval(move_ball,100); <br>} <br>function move_ball() <br>{ <br>ctx.clearRect( box_x,box_y,box_width,box_height); <br>move_and_check(); <br>ctx.beginPath(); <br>ctx.arc(ball_x,ball_y,ball_radius,0,Math.PI*2,true); <br>ctx.fill(); <br>ctx.strokeRect(box_x,box_y,box_width,box_height); <br>} <br>function move_and_check() <br>{ <br>var cur_ball_x=ball_x ball_vx; <br>var temp=ball_vy; <br>ball_vy=ball_vy g; <br>var cur_ball_y=ball_y ball_vy g/2; <br>if(cur_ball_x<bound_left) <br />{ <br />cur_ball_x=bound_left; <br />ball_vx =-ball_vx*0.9; <br />ball_vy=ball_vy*0.9; <br />} <br />if(cur_ball_x>bound_right) <br>{ <br>cur_ball_x=bound_right; <br>ball_vx=-ball_vx*0.9; <br>ball_vy=ball_vy*0.9; <br>} <br>if(cur_ball_y<bound_top) <br />{ <br />cur_ball_y=bound_top; <br />ball_vy=-ball_vy*0.9; <br />ball_vx=ball_vx*0.9 ; <br />} <br />if(cur_ball_y>bound_bottom) <br>{ <br>cur_ball_y=bound_bottom; <br>ball_vy=-ball_vy*0.9; <br>ball_vx=ball_vx*0.9; <br>} <br>ball_x=cur_ball_x; <br>ball_y=cur_ball_y; <br>} <br></script>