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<head> <meta charset=utf-8> <title>跳跳球</title> <script> //box var box_x=0; var box_y=0; var box_width=300; var box_height=300; //注意:定位球采用球的中心 var ball_x=10; var ball_y=10; var ball_radius=10; var ball_vx=5; var ball_vy=3; var box_bound_left=box_x+ball_radius; var box_bound_right=box_x+box_width-ball_radius; var box_bound_top=box_y+ball_radius; var box_bound_bottom=box_y+box_height-ball_radius; //ball //context var ctx; function init() { ctx=document.getElementById('canvas').getContext('2d'); ctx.lineWidth=ball_radius; ctx.fillStyle="rgb(200,0,50)"; move_ball(); setInterval(move_ball,100);//note } function move_ball() { ctx.clearRect(box_x,box_y,box_width,box_height); move_and_check(); ctx.beginPath(); ctx.arc(ball_x,ball_y,ball_radius,0,Math.PI*2,true); ctx.fill(); ctx.strokeRect(box_x,box_y,box_width,box_height); } function move_and_check() { var cur_ball_x=ball_x+ball_vx; var cur_ball_y=ball_y+ball_vy; if(cur_ball_x<box_bound_left) { ball_vx=-ball_vx; cur_ball_x=box_bound_left; } if(cur_ball_x>box_bound_right) { ball_vx=-ball_vx; cur_ball_x=box_bound_right; } if(cur_ball_y<box_bound_top) { ball_vy=-ball_vy; cur_ball_y=box_bound_top; } if(cur_ball_y>box_bound_bottom) { ball_vy=-ball_vy; cur_ball_y=box_bound_bottom; } ball_x=cur_ball_x; ball_y=cur_ball_y; } </script> </head> <body onLoad="init()"> <canvas id="canvas" width="400" height="400"/> </body> </html> |