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Sample code sharing of basic features of html5 Canvas

黄舟

Mar 28, 2017 pm 03:53 PM

html5 Canvas Introduction

canvas The basic attributes and methods: width, height, getContext(), etc.;

through width and heightTo get and set the width and height of the current canvas;

Get the drawing environment (context) of the current canvas through the getContext() method;

context=canvas.getContext("2d");

context contains all the methods and properties we need to draw on canvas;

In the Cartesian coordinate system of context, canvas's The upper left corner is the origin; from the origin to the right is the positive direction of the It is used in combination with

current

state

; Before we truly understand how Canvas works, current state is a concept that must be mastered; current state is actually a stack of drawing states, which applies to the entire canvas globally;

We can operate the following states:

Transformation matrix Matrix)

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title>s3</title>
        <script type="text/javascript" src="../script/modernizr-latest.js"></script>
        <script type="text/javascript">
            window.addEventListener("load", eventWindowLoaded, false);
            var Debugger = function() {
            };
            Debugger.log = function(message) {
                try {
                    console.log(message);
                } catch (exception) {
                    return;
                }
            }
            function eventWindowLoaded() {
                canvasApp();
            }

            function canvasSupport() {
                return Modernizr.canvas;
            }

            function eventWindowLoaded() {
                canvasApp();
            }

            function canvasApp() {

                if(!canvasSupport()) {
                    return;
                }
                var theCanvas = document.getElementById("canvasOne");
                var context = theCanvas.getContext("2d");

                function drawScreen() {
                    //以下代码来源于<http://www.cnblogs.com/nothingbrother/archive/2011/12/23/2299856.html>
for(var x = 0.5; x < 550; x += 10) {
                        context.moveTo(x, 0);
                        context.lineTo(x, 400);
                    }
                    for(var y = 0.5; y < 400; y += 10) {
                        context.moveTo(0, y);
                        context.lineTo(550, y);
                    }
                    context.strokeStyle = "#cecece";
                    context.stroke();
                    context.beginPath();
                    context.moveTo(50, 150);
                    context.lineTo(300, 150);
                    context.moveTo(250, 100);
                    context.lineTo(300, 150);
                    context.moveTo(300, 50);
                    context.lineTo(250, 100);
                    context.moveTo(450, 200);
                    context.lineTo(300, 50);
                    /*symmetry*/
                    context.moveTo(50, 250);
                    context.lineTo(300, 250);
                    context.moveTo(250, 300);
                    context.lineTo(300, 250);
                    context.moveTo(300, 350);
                    context.lineTo(250, 300);
                    context.moveTo(450, 200);
                    context.lineTo(300, 350);
                    /*end*/
                    context.moveTo(50, 150);
                    context.lineTo(50, 250);
                    /*write coordinate*/
                    context.font = "bold 12px sans-serif";
                    context.fillText("( 0 , 0 )", 8, 5);
                    context.fillText("(50, 150)", 58, 155);
                    context.fillText("(300, 150)", 308, 155);
                    context.fillText("(250, 100)", 258, 105);
                    context.fillText("(300, 150)", 308, 155);
                    context.fillText("(300, 50)", 308, 55);
                    context.fillText("(50, 250)", 58, 255);
                    context.fillText("(300, 250)", 308, 255);
                    context.fillText("(250, 350)", 258, 355);
                    context.fillText("(450, 200)", 458, 205);
                    context.strokeStyle = "#f00";
                    context.stroke();

                }
                drawScreen();
            }
        </script>
    </head>
    <body>
        <div style="position: absolute; top: 50px; left: 50px;">
            <canvas id="canvasOne" width="550" height="400">
                Your browser does not support HTML5 Canvas.
            </canvas>
        </div>
    </body>
</html>

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Clipping region

Method:clip()

Properties of the context (context attribute)

Methods:scale, rotate, transform, and translate

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Let’s take a brief look at it first. We will slowly analyze the use of these attributes and methods in future articles; Written by foreign [oreilly] A small program (guess letters):

Properties: strokeStyle, fillStyle, globalAlpha, lineWidth, lineCap, line Join, miterLimit, shadowOffsetX, shadowOffsetY,
shadowBlur, shadowColor, global CompositeOperation, font, textAlign, and textBaseline.

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