如何在 p5.js 框架中将对象居中 8x8 网格的任何单元格中

Question

这是我制作国际象棋游戏的代码。

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;
			}
		}
	}
}

<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放的对象时，它将在拖放的单元格中居中。我想代码会作为 else 语句进入"拖动函数 "，但除此之外我卡住了。谁能帮忙？

提前感谢！

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;  

I 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，并通过int()截断结果。 例如：

var cell_ix = int(mouseX / cell_w);
var cell_iy = int(mouseY / cell_h);

计算鼠标所在的单元格的中心点：

var cell_cx = (cell_ix+0.5) * cell_w;
var cell_cy = (cell_iy+0.5) * cell_h;

根据单元格的中心和对象的大小计算对象的新位置：

pawn1.x = cell_cx - pawn1.w/2;
pawn1.y = cell_cy - pawn1.h/2;

您可以在mouseReleased()回电中执行此操作。这导致对象可以平滑拖动，但在释放鼠标时立即"跳跃"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>