百度T7 課程 canvas 學習 5--- 面向物件畫折現圖 (老師版)
阿新 • • 發佈：2018-12-10
實際上你 會發現，老師寫的程式碼和我寫程式碼差距很大，因為我寫的很Low
這就是差距，這是為啥，因為你寫的少， 沒有調！！
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> <style> canvas { border: 1px solid #ccc; } </style> </head> <body> <canvas width="600" height="400"></canvas> <script> /*1.建構函式*/ var LineChart = function (ctx) { /*獲取繪圖工具*/ this.ctx = ctx || document.querySelector('canvas').getContext('2d'); /*畫布的大小*/ this.canvasWidth = this.ctx.canvas.width; this.canvasHeight = this.ctx.canvas.height; /*網格的大小*/ this.gridSize = 10; /*座標系的間距*/ this.space = 20; /*座標原點*/ this.x0 = this.space; this.y0 = this.canvasHeight - this.space; /*箭頭的大小*/ this.arrowSize = 10; /*繪製點*/ this.dottedSize = 6; /*點的座標 和資料有關係 資料視覺化*/ } /*2.行為方法*/ LineChart.prototype.init = function (data) { this.drawGrid(); this.drawAxis(); this.drawDotted(data); }; /*繪製網格*/ LineChart.prototype.drawGrid = function () { /*x方向的線*/ var xLineTotal = Math.floor(this.canvasHeight / this.gridSize); this.ctx.strokeStyle = '#eee'; for (var i = 0; i <= xLineTotal; i++) { this.ctx.beginPath(); this.ctx.moveTo(0, i * this.gridSize - 0.5); this.ctx.lineTo(this.canvasWidth, i * this.gridSize - 0.5); this.ctx.stroke(); } /*y方向的線*/ var yLineTotal = Math.floor(this.canvasWidth / this.gridSize); for (var i = 0; i <= yLineTotal; i++) { this.ctx.beginPath(); this.ctx.moveTo(i * this.gridSize - 0.5, 0); this.ctx.lineTo(i * this.gridSize - 0.5, this.canvasHeight); this.ctx.stroke(); } }; /*繪製座標系*/ LineChart.prototype.drawAxis = function () { /*X軸*/ this.ctx.beginPath(); this.ctx.strokeStyle = '#000'; this.ctx.moveTo(this.x0, this.y0); this.ctx.lineTo(this.canvasWidth - this.space, this.y0); this.ctx.lineTo(this.canvasWidth - this.space - this.arrowSize, this.y0 + this.arrowSize / 2); this.ctx.lineTo(this.canvasWidth - this.space - this.arrowSize, this.y0 - this.arrowSize / 2); this.ctx.lineTo(this.canvasWidth - this.space, this.y0); this.ctx.stroke(); this.ctx.fill(); /*Y軸*/ this.ctx.beginPath(); this.ctx.strokeStyle = '#000'; this.ctx.moveTo(this.x0, this.y0); this.ctx.lineTo(this.space, this.space); this.ctx.lineTo(this.space + this.arrowSize / 2, this.space + this.arrowSize); this.ctx.lineTo(this.space - this.arrowSize / 2, this.space + this.arrowSize); this.ctx.lineTo(this.space, this.space); this.ctx.stroke(); this.ctx.fill(); }; /*繪製所有點*/ LineChart.prototype.drawDotted = function (data) { /*1.資料的座標 需要轉換 canvas座標*/ /*2.再進行點的繪製*/ /*3.把線連起來*/ var that = this; /*記錄當前座標*/ var prevCanvasX = 0; var prevCanvasY = 0; data.forEach(function (item, i) { /* x = 原點的座標 + 資料的座標 */ /* y = 原點的座標 - 資料的座標 */ var canvasX = that.x0 + item.x; var canvasY = that.y0 - item.y; /*繪製點*/ that.ctx.beginPath(); that.ctx.moveTo(canvasX - that.dottedSize / 2, canvasY - that.dottedSize / 2); that.ctx.lineTo(canvasX + that.dottedSize / 2, canvasY - that.dottedSize / 2); that.ctx.lineTo(canvasX + that.dottedSize / 2, canvasY + that.dottedSize / 2); that.ctx.lineTo(canvasX - that.dottedSize / 2, canvasY + that.dottedSize / 2); that.ctx.closePath(); that.ctx.fill(); /*點的連線*/ /*當時第一個點的時候 起點是 x0 y0*/ /*當時不是第一個點的時候 起點是 上一個點*/ if(i == 0){ that.ctx.beginPath(); that.ctx.moveTo(that.x0,that.y0); that.ctx.lineTo(canvasX,canvasY); that.ctx.stroke(); }else{ /*上一個點*/ that.ctx.beginPath(); that.ctx.moveTo(prevCanvasX,prevCanvasY); that.ctx.lineTo(canvasX,canvasY); that.ctx.stroke(); } /*記錄當前的座標，下一次要用*/ prevCanvasX = canvasX; prevCanvasY = canvasY; }); }; /*3.初始化*/ var data = [ { x: 100, y: 120 }, { x: 200, y: 160 }, { x: 300, y: 240 }, { x: 400, y: 120 }, { x: 500, y: 80 } ]; var lineChart = new LineChart(); lineChart.init(data); </script> </body> </html>