html5-canvas | 易学教程

What makes a CanvasRenderingContext2D a CanvasRenderingContext2D?

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问题 Consider the following web page. <html> <body> <canvas id="canvas" width="300" height="300" style="border:1px solid #000000;"> </canvas> </body> </html> I open this page in Firefox, open the JS console and type the following. > document.getElementById("canvas").getContext("2d") The output is as follows: CanvasRenderingContext2D { canvas: canvas#canvas, mozCurrentTransform: (6) […], mozCurrentTransformInverse: (6) […], mozTextStyle: "10px sans-serif", mozImageSmoothingEnabled: true,

What makes a CanvasRenderingContext2D a CanvasRenderingContext2D?

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Raycaster displays phantom perpendicular wall faces

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问题 The output looks like this: You should just see a flat, continuous red wall on one side, blue wall on another, green on another, yellow on another (see the definition of the map, testMapTiles , it's just a map with four walls). Yet there are these phantom wall faces of varying height, which are perpendicular to the real walls. Why? Note that the white "gaps" aren't actually gaps: it's trying to draw a wall of height Infinity (distance 0). If you specifically account for it (this version of

How to add multiple images to html5 canvas

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问题 I am trying to add multiple images to Html5 canvas but every time I try to remove the last image and show the most recent one it fails. Here's my code: var imgArray = ['abc.png','455.jpg']; for(i = 0; i < 2; i++){ var canvas = document.getElementById('canvas'); var context = canvas.getContext("2d"); var imageObj = new Image(); imageObj.src = imgArray[i]; imageObj.onload = function() { context.drawImage(this,0,0); }; } If I run this code, it shows the 2nd image on the canvas and removes the

How to draw responsive lines between divs

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问题 Here's a photo of what I'm trying to translate into code. I have a few more "Concept" areas I'm going to need to lay out and am having difficulty figuring out a method to embark upon in order to achieve this in a manner that works responsively. My original idea was to just lay everything out except the lines so I can adjust their positions accordingly to each screen size then come back and do a set of lines for each shift of elements using media queries to toggle them. For small tablet and

How can I get the intersection of three shapes colliding and delete the parts that are not colliding using HMTL5 Javascript Canvas?

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问题 I've recently posted a similar question specifically for KonvaJs here, however, I have not gotten any answer and wanted to go directly to the root of what KonvaJs uses. I would like to know if there's a standard way of solving the following problem using HMTL5 Javascript Canvas. If I am given 3 circles and they are positioned as the primary color circles (3 circles intersecting each other), is there a function that might help me to delete the parts that are not colliding with anything and

Convert a B-Spline into Bezier curves

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问题 I have a B-Spline curve. I have all the knots, and the x,y coordinates of the Control Points. I need to convert the B-Spline curve into Bezier curves. My end goal is to be able to draw the shape on an html5 canvas element. The B-Spline is coming from a dxf file which doesn't support Beziers, while a canvas only supports Beziers. I've found several articles which attempt to explain the process, however they are quite a bit over my head and really seem to be very theory intensive. I really need

Convert a B-Spline into Bezier curves

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Overlay HTML5 canvas over image

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问题 I want to have an image which is uploaded from my database and on top of it the exact same size in the same position is a HTML5 canvas. Most of the solutions I have found I have been using JQuery/JavaScript, however I want a similar solution if possible just using CSS3 as the images are being outputted from a database and there can be more than one image on the page and each image will have a canvas. How can I achieve this? 回答1: Yes. You can do this entirely in CSS, but you will have to add

Will rendering images outside an HTML5 canvas hurt performance?

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问题 I'm building a 2D platformer game and I'll have a bunch of the level off the screen. Will it hurt performance to render these, or should I develop some form of 2D occlusion culling to avoid rendering this? Furthermore, how much of a performance hit would this cause? 回答1: The rendering engine should throw out render calls to areas outside the canvas, but I would still recommend not trying to draw to those areas to begin with just to reduce the overall overhead of performing unnecessary logic.