canvas | 易学教程

Drawing a nice looking Laser (Star Wars) on the canvas

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问题 Im currently in the process of animation some laser effects on the canvas for the purpose of making my game a bit more enjoyable. For the purpose of that, i require the drawing and animation of "laser" weapons fire, something along the lines of Star Wars. So far, im basicly only drawing a short line in red or blue and then drawing a thinner, white, line on top of it, so it gives the impression of a gradient. I also use linecap = "round"; my current code: function drawProjectile(weapon, ox, oy

Waving text on canvas

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问题 How could I make waving text on a canvas element similar to what is found on this page? 回答1: EDIT : @Ben, forget about the downvotes for no reason on your question, and... BE MY GUEST! :) I never coded with <canvas> before, it was very fun. At this point, there is no bilinear interpolation. I might rework it and add more bells and whistles. If you want to achieve such an effect in javascript, you'll effectively have to use the <canvas> tag. The principle consists in precalculating a

How to optimize draw area in pixel art editor

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问题 I have pixel art creator program, and I have rectangles on canvas that are one field (pixel?). And this is good solution on not huge amount of it (for example 128x128). if i want to create 1024x1024 rectangles on canvas this process is very long, ram usage is about 1-2 gb and after that program runs very slowly. How to optimize this, or create better solution? 回答1: Using a Rectangle to represent each pixel is the wrong way to do this. As a FrameworkElement , every rectangle participates in

How to optimize draw area in pixel art editor

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Canvas tainted by CORS data and S3

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问题 My application is displaying images stored in AWS S3 (in a private bucket for security reasons). To allow users to see the images from their browser I generate signed URLs like https://s3.eu-central-1.amazonaws.com/my.bucket/stuff/images/image.png?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=...&X-Amz-Date=20170701T195504Z&X-Amz-Expires=900&X-Amz-Signature=bbe277...3358e8&X-Amz-SignedHeaders=host . This is working perfectly with <img src="S3URL" /> : the images are correctly displayed. I

QWT基础教程之refreshtest

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2020-2-1 今天我们介绍的这个例子要比之前的几个复杂一些，如下是其效果图。本次案例的文件不止一个，如下是其文件目录树 . | | -----Headers | | ---cicularbuffer.h | | ---mainwindow.h | | ---panel.h | | ---plot.h | | ---setting.h | | -----Sources | | ---cicularbuffer.cpp | | ---main.cpp | | ---mainwindow.cpp | | ---panel.cpp | | ---plot.cpp | 上面的目录树只包含了.c和.h文件。一个头文件对应一个类。下面我会逐个介绍每一个类的具体实现。 CircularBuffer类，其类图如下这个类继承自QwtSeriesData，属性都是私有的，行为都是公有的，下面我们到circularbuffer.cpp文件中看这些属性与方法的实现。构造函数CircularBuffer CircularBuffer :: CircularBuffer ( double interval , size_t numPoints ) : d_y ( NULL ) , d_referenceTime ( 0.0 ) , d_startIndex ( 0 ) , d_offset ( 0.0

运用样式与颜色 --Canvas的基本操作

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1.fillStyle 和 strokeStyle属性如果想要给图形上色，有两个重要的属性可以做到： fillStyle 和 strokeStyle 。这两个属性的定义方法如下所示。 fillStyle = color strokeStyle = color strokeStyle 是用于设置图形轮廓的颜色，而 fillStyle 用于设置填充颜色。 color 可以是表示 CSS 颜色值的字符串、渐变对象或者图案对象。默认情况下，线条和填充颜色都是黑色(CSS 颜色值 #000000)。这里需要注意的是如果自定义颜色则应该保证输入符合 CSS颜色值标准的有效字符串。下面的代码都是符合标准的颜色表示方式，都表示同一种颜色（橙色）。 context.fillStyle = "orange"; context.fillStyle = "#FFA500"; context.fillStyle = "rgb(255,165,0)"; context.fillStyle = "rgba(255,165,0,1)"; 2.透明度 globalAlpha 通过设置 globalAlpha属性或者使用一个半透明颜色作为轮廓或填充的样式来绘制透明或半透明的图形。globalAlpha属性定义代码如下所示： globalAlpha = transparency value 这个属性影响到

Using drawImage() to output fixed size images on a canvas?

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问题 How do I use drawImage() to output full size images on a 300px X 380px canvas regardless of the source image size? Example: 1). If there is a image of 75px X 95px I want to be able to draw it to fit a 300px X 380px canvas. 2). If there is a image of 1500px X 1900px I want to be able to draw it to fit a 300px X 380px canvas. var c=document.getElementById("myCanvas"); var ctx=c.getContext("2d"); var img=document.getElementById("myPic"); ctx.drawImage(img,10,10); What options are available to

Poor results with source-over alpha blending (HTML5 canvas)

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问题 Edit: I don't necessarily need a solution to this problem--rather I'd like to understand why it's occurring. I don't see why I should be getting the odd results below... Although this question is directed towards an issue I'm having with an HTML5 canvas application, I think the problem is less specific. I have an HTML5 canvas app that allows you to stamp images on the screen. These images are 32bit PNG's, so I'm working with transparency. If I stamp a highly transparent image in the same

In Fabric.js how do I modify the object class so all sub-classes will have a new custom attribute?

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问题 I am looking for a way to extend the base fabric.Object class with a custom attribute I can save to JSON and load from JSON that would propagate all the way into the various sub classes. Specifically i want to store a depth attribute so when i load the objects from the JSON i will be able to add the appropriate parallax to the object. I imagine the solution would include modifying the fabric.Object.prototype. But i am still learning how to work with prototypes. Here is some examples of what i