Comment: Add a wall on the canvas by dragging the mouse, and control the polygon to move up, down, left and right through the direction keys. If you encounter a wall, you cannot move forward. Below is an introduction to the problems that need to be solved and the specific implementation code. Interested friends can learn it.
Game renderingsAdd a wall on the canvas by dragging the mouse, and use the arrow keys to control the polygon to move up, down, left and right. If you encounter a wall, you cannot move forward.
Issues that need to be solved
Detection of mouse press, mouse drag, mouse release event
Drawing of polygons
Painting of walls
Collision detection between polygons and walls (essentially, it is the judgment of intersection between circles and line segments)
MYCode:
<html>
<head>
<title>Maze</title>
<script>
var canvas_width = 900;
var canvas_height = 350;
var ctx;
var canvas;
var everything = [];
var cur_wall;
var wall_width;
var wall_style = "rgb(200,0,200)";
var walls = [];
var in_motion = false;
var unit = 10;
function Token(sx, sy, rad, style_string, n)
{
this.sx = sx;
this.sy = sy;
this.rad = rad;
this.draw = draw_token;
this.n = n;
this.angle = (2 * Math.PI) / n;
this.move = move_token;
this.fill_style = style_string;
}
function draw_token()//Draw regular n-side
{
ctx.fill_style = this.fill_style;
ctx.beginPath();
var i;
var rad = this.rad;
ctx.moveTo(this.sx + rad * Math.cos(-0.5 * this.angle), this.sy + rad * Math.sin(-0.5 * this.angle));
for (i = 1; i < this.n; i++)
ctx.lineTo(this.sx + rad * Math.cos((i - 0.5) * this.angle), this.sy + rad * Math.sin((i - 0.5) * this.angle));
ctx.fill();
}
function move_token(dx, dy)
{
this.sx += dx;
this.sy += dy;
var i;
var wall;
for (i = 0; i < walls.length; i++)
{
wall = walls[i];
if (intersect(wall.sx, wall.sy, wall.fx, wall.fy, this.sx, this.sy, this.rad))
{
this.sx -= dx;
this.sy -= dy;
break;
}
}
}
function Wall(sx, sy, fx, fy, width, styleString)
{
this.sx = sx;
this.sy = sy;
this.fx = fx;
this.fy = fy;
this.width = width;
this.draw = draw_line;
this.strokeStyle = styleString;
}
function draw_line()
{
ctx.lineWidth = this.width;
ctx.strokeStye = this.strokeStyle;
ctx.beginPath();
ctx.moveTo(this.sx, this.sy);
ctx.lineTo(this.fx, this.fy);
ctx.stroke();
}
//note
var mypent = new Token(100, 100, 20, "rgb(0,0,250)", 5);
Everything.push(mypent);
function init()
{
canvas = document.getElementById("canvas");
ctx = canvas.getContext('2d');
//note
canvas.addEventListener('mousedown', start_wall, false);
canvas.addEventListener('mousemove', stretch_wall, false);
canvas.addEventListener('mouseup', finish_wall, false);
window.addEventListener('keydown', getkey_and_move, false);
draw_all();
}
function start_wall(ev)
{
var mx;
var my;
if (ev.layerX || ev.layerx == 0)
{
mx = ev.layerX;
my = ev.layerY;
}
else if (ev.offsetX || ev.offsetX == 0)
{
mx = ev.offsetX;
my = ev.offsetY;
}
cur_wall = new Wall(mx, my, mx + 1, my + 1, wall_width, wall_style);
in_motion = true;
Everything.push(cur_wall);
draw_all();
}
function stretch_wall(ev)
{
if (in_motion)
{
var mx;
var my;
if (ev.layerX || ev.layerX == 0)
{
mx = ev.layerX;
my = ev.layerY;
}
else if (ev.offsetX || ev.offsetX == 0)
{
mx = ev.offsetX;
my = ev.offsetY;
}
cur_wall.fx = mx;
cur_wall.fy = my;
draw_all();
}
}
function finish_wall(ev)
{
in_motion = false;
walls.push(cur_wall);
}
function draw_all()
{
ctx.clearRect(0, 0, canvas_width, canvas_height);
var i;
for (i = 0; i < everything.length; i++)
{
Everything[i].draw();
}
}
function getkey_and_move(event)
{
var keyCode;
if (event == null)
{
keyCode = window.event.keyCode;
window.event.preventDefault();
}
else
{
keyCode = event.keyCode;
event.preventDefault();
}
switch (keyCode)
{
case 37://left arrow
mypent.move(-unit, 0);
break;
case 38://up arrow
mypent.move(0, -unit);
break;
case 39://right arrow
mypent.move(unit, 0);
break;
case 40:
mypent.move(0, unit);
break;
default:
//window.removeEventListener('keydown', getkey_and_move, false);
}
draw_all();
}
function intersect(sx, sy, fx, fy, cx, cy, rad)
{
var dx;
var dy;
var t;
var rt;
dx = fx - sx;
dy = fy - sy;
t = 0.0 - (((sx - cx) * dx + (sy - cy) * dy) / (dx * dx + dy * dy));
if (t < 0.0)
{
t = 0.0;
}
else if (t > 1.0)
t = 1.0;
var dx1 = (sx + t * dx) - cx;
var dy1 = (sy + t * dy) - cy;
var rt = dx1 * dx1 + dy1 * dy1;
if (rt < rad * rad)
return true;
else
return false;
}
</script>
<body>
<canvas></canvas>
</body>
</html>
difficulty
Methods for detecting collisions between polygons and line segments
The function intersect() is responsible for detecting whether the polygon and line segment intersect.
Note a point p(x,y) on the line segment
The two endpoints of the line segment are (sx,sy) and (fx,fy)
remember
dx=fx-sx
dy=fy-sy
x and y can be represented as follows
x=sx+t*dx
y=sy+t*dy
To determine whether the line segment and the polygon intersect, it is transformed into determining whether the line segment and the polygon intersect.
To do this, you need to find the point p nearest to the center of the circle o on the line segment
If |op|< the radius of the circle, you can judge the intersection of the line segment and the circle.
Otherwise, they will not intersect.
How to find the point closest to the center of the circle on the line segment?
The distance from point p to point o can be expressed as
distance=sqrt((x-cx)*(x-cx)+(y-cy)*(y-cy));
Substitute
x=sx+t*dx and y=sy+t*dy
You can get distance is a function about t
Derivative of this function
Find the corresponding t value when the function value is 0 and you can get the point closest to the center of the circle