如何在 p5.js 框架中的 8x8 网格的任何单元格中居中对象

Question

这是我制作国际象棋游戏的代码。let pawn1; //variable for objectvar offset = 10;function setup(){  createCanvas(600,600); // canvas  pawn1 = new Pawn(); // pawn1 is a new Pawn object}function draw(){  background(0); //black background  checkboard();  //to make an 8x8 grid    pawn1.show();  //shows pawn1 object on canvas  drag();        //allows the pawn object to be dragged}function Pawn(){  this.x = 25; // x position of object  this.y = 25; // y position of object  this.w = 20; // width of object  this.h = 20; // height of object  this.show = function(){    fill(255); // object is white    rect(this.x, this.y, this.w, this.h); //object is a rectangle with x,y,w,h variables  }}// grid maker functionfunction checkboard(){  for (var x = 0; x < width; x += width / 8) {    for (var y = 0; y < height; y += height / 8) {      stroke(255); //grid lines is white      strokeWeight(1); // lines drawn are 1 units thick      line(x, 0, x, height); // vertical lines      line(0, y, width, y); // horizontal lines    }  }}function drag(){    // if mouse is clicked down and inside of the dimensions of the object then:  if(mouseIsPressed){    if(mouseX > pawn1.x && mouseY > pawn1.y){      if(mouseX<(pawn1.x+pawn1.w) && mouseY<(pawn1.y+pawn1.h)){                //square will move with the mouse pointer         pawn1.x = mouseX - offset;        pawn1.y = mouseY - offset;      }    }  }}<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.9.0/p5.js"></script>我不知道如何确保拖动的对象何时被放下，它会在它被放入的单元格中居中。我想代码会作为一个 else 语句进入“拖动函数”，但其他比我被卡住了。任何人都可以帮忙吗？

Answer 1

计算单元格的宽度和高度。例如：

var cell_w = width / 8;

var cell_h = height / 8;  

如果单元格的宽度和高度是固定的，那么您也可以使用常量值。例如：

var cell_w = 75;

var cell_h = 75;  

计算当前单元格的索引，将当前鼠标位置除以单元格的大小并将结果截断int()。例如：

var cell_ix = int(mouseX / cell_w);

var cell_iy = int(mouseY / cell_h);

计算鼠标所在单元格的中心点：

var cell_cx = (cell_ix+0.5) * cell_w;

var cell_cy = (cell_iy+0.5) * cell_h;

计算对象的新位置，取决于单元格的中心和对象的大小：

pawn1.x = cell_cx - pawn1.w/2;

pawn1.y = cell_cy - pawn1.h/2;

你可以在mouseReleased()回电中做到这一点。这会导致对象可以平滑拖动，但在释放鼠标时立即“跳”到单元格的中心：

function mouseReleased() {

    if (mouseX > pawn1.x && mouseY > pawn1.y &&

        mouseX<(pawn1.x+pawn1.w) && mouseY<(pawn1.y+pawn1.h)) {

        var cell_w = width / 8;

        var cell_h = height / 8;

        var cell_ix = int(mouseX / cell_w);

        var cell_iy = int(mouseY / cell_h);

        var cell_cx = (cell_ix+0.5) * cell_w;

        var cell_cy = (cell_iy+0.5) * cell_h;

        pawn1.x = cell_cx - pawn1.w/2;

        pawn1.y = cell_cy - pawn1.h/2;

    }

}

请参阅示例，其中我已将函数添加到您的原始代码中：

let pawn1; //variable for object

var offset = 10;

function setup(){

    createCanvas(600,600); // canvas

    pawn1 = new Pawn(); // pawn1 is a new Pawn object

}

function draw(){

    background(0); //black background

    checkboard();  //to make an 8x8 grid    

    pawn1.show();  //shows pawn1 object on canvas

    drag();        //allows the pawn object to be dragged

}

function Pawn(){

    this.x = 25; // x position of object

    this.y = 25; // y position of object

    this.w = 20; // width of object

    this.h = 20; // height of object

    this.show = function(){

        fill(255); // object is white

        rect(this.x, this.y, this.w, this.h); //object is a rectangle with x,y,w,h variables

    }

}

// grid maker function

function checkboard(){

    for (var x = 0; x < width; x += width / 8) {

        for (var y = 0; y < height; y += height / 8) {

            stroke(255); //grid lines is white

            strokeWeight(1); // lines drawn are 1 units thick

            line(x, 0, x, height); // vertical lines

            line(0, y, width, y); // horizontal lines

        }

    }

}

function drag(){

    // if mouse is clicked down and inside of the dimensions of the object then:

    if(mouseIsPressed){

        if(mouseX > pawn1.x && mouseY > pawn1.y){

            if(mouseX<(pawn1.x+pawn1.w) && mouseY<(pawn1.y+pawn1.h)){

                //square will move with the mouse pointer 

                pawn1.x = mouseX - offset;

                pawn1.y = mouseY - offset;

            }

        }

    }

}

function mouseReleased() {

    if (mouseX > pawn1.x && mouseY > pawn1.y &&

        mouseX<(pawn1.x+pawn1.w) && mouseY<(pawn1.y+pawn1.h)) {

        var cell_w = width / 8;

        var cell_h = height / 8;

        

        var cell_ix = int(mouseX / cell_w);

        var cell_iy = int(mouseY / cell_h);

        var cell_cx = (cell_ix+0.5) * cell_w;

        var cell_cy = (cell_iy+0.5) * cell_h;

        pawn1.x = cell_cx - pawn1.w/2;

        pawn1.y = cell_cy - pawn1.h/2;

    }

}

<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.9.0/p5.js"></script>