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HTML5 Programming Practice Part 2 - Using animation to switch picture code cases
- 黄舟Original
- 2017-03-30 13:30:211759browse
The knowledge mainly used in this article
This article mainly uses the knowledgeCanvasThe drawImage method in API is briefly introduced below.
Use the drawImage method to draw images in the Canvas API. This is an overloaded method. , defined as follows:
context.drawImage(image,x,y); context.drawImage(image,x,y,w,h); context.drawImage(image,sx,sy,sw,sh,dx,dy,dw,dh);
The first method has three parameters. The first parameter is the image to be drawn (it can also be a video element), and x and y are the starting coordinates of the image in the canvas.
The second method has five parameters. The first three have the same meaning as the first method. w and h refer to the width and height of the image when drawing, which can be used for image scaling.
The third method has nine parameters. The first parameter has the same meaning as the first two methods. The first four of the last eight parameters take a rectangle on the source image, and the last four parameters are used to define a rectangle on the canvas. , the function of the entire method is to copy part of the source image (the part defined by the second to fifth parameters) to the canvas (the part defined by the last four parameters). This article mainly uses the third one. The method completes drawing.
Source code
<!DOCTYPE html><html><head>
<meta charset="UTF-8">
<title>用动画的形式切换图片</title>
<script type="text/javascript">
var width, height;
var context, image, functionId;
var drawLeft, drawWidth;
var drawTop, drawHeight;
var spaceWidth, spaceHeight;
var speed=5000;
var images = ["http://i.6.cn/cvbnm/4e/7e/bb/75f251a8e2ae935d598f17b4f8275060.jpg",
"http://i.6.cn/cvbnm/4a/6e/fb/805175016e502c483b75276f29801df3.jpg",
"http://i.6.cn/cvbnm/6a/72/18/1787a3b2754ef48e374bbd14635f5c36.jpg",
"http://i.6.cn/cvbnm/94/55/6c/b1ba743ba617be2891fa06b67d795511.jpg",
"http://i.6.cn/cvbnm/02/1b/04/8018ee9e5756ac6b30f27d7ad6396b03.jpg",
"http://i.6.cn/cvbnm/85/ea/d1/65f15857b971afb3b6e38b5fcdadc9c0.jpg"];
function selectFrom(iFirstValue, iLastValue) {
var iChoices = iLastValue - iFirstValue + 1;
return Math.floor(Math.random() * iChoices + iFirstValue);
} function showPicture(effects) {
var count = 0;
for (var o in effects) {
count++;
}
var canvas = document.getElementById('canvas');
context = canvas.getContext('2d');
width = canvas.width;
height = canvas.height;
var currImage = 0;
image = new Image();
image.src = images[currImage];
context.drawImage(image, 0, 0, width, height);
currImage++;
if (count > 0) {
setInterval(function () {
var rand = selectFrom(0, count - 1);
image.src = images[currImage];
currImage++;
if (currImage == images.length) {
currImage = 0;
}
var index = 0;
for (var effect in effects) {
if (index++ == rand) {
effects[effect]();
break;
}
}
}, speed);
}
}
window.onload=function(){
showPicture({
leftToRight: function () {
context.fillStyle = "#EEEEFF";
context.fillRect(0, 0, width, height);
drawWidth = 0;
functionId = self.setInterval("drawleftToRight()", 10);
},
topToBottom: function () {
context.fillStyle = "#EEEEFF";
context.fillRect(0, 0, width, height);
drawHeight = 0;
functionId = self.setInterval("drawtopToBottom()", 10);
},
hcenter: function () {
context.fillStyle = "#EEEEFF";
context.fillRect(0, 0, width, height);
drawLeft = width / 2;
drawWidth = 0;
functionId = self.setInterval("drawhcenter()", 10);
},
vcenter: function () {
context.fillStyle = "#EEEEFF";
context.fillRect(0, 0, width, height);
drawTop = height / 2;
drawHeight = 0;
functionId = self.setInterval("drawvcenter()", 10);
},
hwindow: function () {
context.fillStyle = "#EEEEFF";
context.fillRect(0, 0, width, height);
spaceWidth = width / 10;
drawWidth = 0;
functionId = self.setInterval("drawhwindow()", 50);
},
vwindow: function () {
context.fillStyle = "#EEEEFF";
context.fillRect(0, 0, width, height);
spaceHeight = height / 10;
drawHeight = 0;
functionId = self.setInterval("drawvwindow()", 50);
},
hvwindow: function () {
context.fillStyle = "#EEEEFF";
context.fillRect(0, 0, width, height);
spaceHeight = height / 10;
spaceWidth = width / 10;
drawWidth = 0;
drawHeight = 0;
functionId = self.setInterval("drawhvwindow()", 50);
}
});
} function drawleftToRight() {
context.drawImage(image, 0, 0, drawWidth, image.height, 0, 0, drawWidth, image.height);
drawWidth = drawWidth + 2;
if (drawWidth > width) {
window.clearInterval(functionId);
}
} function drawtopToBottom() {
context.save();
context.drawImage(image, 0, 0, image.width, drawHeight, 0, 0, image.width, drawHeight);
drawHeight = drawHeight + 2;
if (drawHeight > height) {
window.clearInterval(functionId);
}
context.restore();
}
function drawhcenter() {
context.save();
context.drawImage(image, drawLeft, 0, drawWidth, image.height, drawLeft, 0, drawWidth, image.height);
drawLeft = drawLeft - 1;
drawWidth = drawWidth + 2;
if (drawLeft <= 0) {
window.clearInterval(functionId);
}
context.restore();
}
function drawvcenter() {
context.save();
context.drawImage(image, 0, drawTop, image.width, drawHeight, 0, drawTop, image.width, drawHeight);
drawTop = drawTop - 1;
drawHeight = drawHeight + 2;
if (drawTop <= 0) {
window.clearInterval(functionId);
}
context.restore();
} function drawhwindow() {
for (i = 0; i < 10; i++) {
context.drawImage(image, 0 + i * spaceWidth, 0, drawWidth,
image.height, 0 + i * spaceWidth, 0, drawWidth, image.height);
}
drawWidth += 1;
if (drawWidth - 1 > spaceWidth) {
window.clearInterval(functionId);
}
} function drawvwindow() {
context.save();
context.clearRect(0, 0, width, height);
for (i = 0; i < 10; i++) {
context.drawImage(image, 0, 0 + i * spaceHeight, image.width,
drawHeight, 0, 0 + i * spaceHeight, image.width, drawHeight);
}
drawHeight += 1;
if (drawHeight - 1 > spaceHeight) {
window.clearInterval(functionId);
}
context.restore();
} function drawhvwindow() {
context.save();
context.clearRect(0, 0, width, height);
for (i = 0; i < 10; i++) {
for (j = 0; j < 10; j++) {
context.drawImage(image, 0 + j * spaceWidth, 0 + i *
spaceHeight, drawWidth, drawHeight, 0 + j * spaceWidth, 0 + i *
spaceHeight, drawWidth, drawHeight);
}
}
drawHeight += height / width;
drawWidth += 1;
if (drawHeight > spaceHeight) {
context.drawImage(image, 0, 0, width, height);
window.clearInterval(functionId);
}
context.restore();
} </script></head><body>
<h1>用动画的形式切换图片</h1>
<canvas id="canvas" width="192px" height="255px"></canvas></body></html>Code analysis
DrawleftToRight(): The effect is to display from left to right, mainly combining the fourth parameter and the fourth parameter. The eight parameters gradually increase from 0 to the width of the picture
drawtopToBottom(): The effect is to display from top to bottom, mainly increasing the fifth and ninth parameters from 0 to the height of the picture
Drawhcenter(): The effect is to display horizontally from the middle to both sides, mainly reducing the second and sixth parameters from half the image width to 0, and increasing the fourth and eighth parameters from 0 to the image width
Drawvcenter(): The effect is to display from the middle to both sides, similar to the previous one
drawhwindow(): The effect is horizontal blinds, similar to the principle of drawhcenter method, except that it is done from multiple places here
drawvwindow(): The effect is vertical blinds, the principle is similar to the drawvcenter method, except that it is done from multiple places here
drawhvwindow(): The effect is blinds, it is drawhwindow() Combination with drawvwindow()
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