I'm working on a 2d isometric map with HTML5 and canvas.
So, i can have a map with an infinity of tiles, but, I only displayed the tiles around the player and it's my problem.
When i retrieve the image with toDataURL(), I just retrieves the small part of the map that I displayed around the player...
I need to retrieve all the canvas, even that is not displayed, is it possible ?
No, it's not possible. toDataURL do give you the whole canvas but the whole canvas is simply what you see on the screen. Canvas does not know about anything outside this (anything drawn outside the canvas is clipped and forgotten).
If you need to get the complete map you will need to create a big enough canvas and draw the complete map then extract the image. There is no way around (using canvas).
Related
There I am creating a stamp maker in HTML,Jquery and javascript. In the editor of my application image is adding to HTML canvas (simple) and also the text, I just create new line element and then append it to the canvas.But the problem is that I want my image to be in back of text. I googled it alot and also search stackoverflow I got the solution of creating multiple canvases but in last I have to download the canvas to file for user. There is the problem. And I want to export whole canvas along with text one and second image together.If I create seperate canvas for the text and another for image and give image one low zindex it would be fine but there will be one canvas to be exported as image.
Link to multiple layers in canvas html5 - canvas element - Multiple layers
I am hopping that we would come up with an idea of how to download both canvases as an image or find a method to take image to back of the canvas.
Any answer would be appreciated.
If you store the text, second image and first image in variables, you could just draw them on the canvas in the order you prefer. This means that, whenever there's some change in the image or text, you should clean the canvas and redraw everything.
Also, you may be interested in Compositing, since it allows you to decide where a new object is drawn in relation to the existing drawing (on top, behind, etc.)
I have an Image holding the map of a country. Now I need to copy a small part of it (a city) to another Image, so as to calculate how many pixels that city occupies (using a Flood Fill algorithm). I know the Canvas element has the drawImage method, I need something similar to copy from one Image to the other, no canvas involved. Is this possible? Or I'll have to create a canvas to do that?
I try to do some video manipulation in javascript. I read some article about it and looks like everybody uses 2 canvas to do the trick. First of all, they draw the video on the first canvas, they read the image data from it, do some pixel manipulation and after that they draw it on the second canvas. I was wondering that I really have to use 2 canvas to do this? Isn't there any method to grab the image data directly from the video? Or we have some performance issue and this is the solution?
Because you can't get the pixel data from video.
The Canvas API has a method getImageData() which gives back a floating point array with values for every colour (and alpha) for every pixel. Unfortunately, the video element can't do that :(
You can use one canvas which draws the video frame and manipulates it too. I guess people prefer doing it on two canvases so that they can keep the original pixel data in case you there's a change manipulation before a new frame is loaded or something...
I'm currently working on a top-down MMORPG, in JavaScript. As you can imagine, this requires a lot of sprite sheets, and herein lies the problem.
I can simply place the clipped version of a sprite sheet onto the canvas using the canvas.drawImage method. However, this must require more performance than simply loading the clipped version of the image into a new image object which I'd then place onto the canvas using the canvas.drawImage method, as I'd only have to clip it once.
Is this at all possible, and if so, how?
It's a sprite. Any "clipping" is a convenient illusion. Loading a clipped version adds more HTTP traffic which will certainly take more time than drawing canvas image, regardless of the image source, especially when you have the image on the client already.
I'm new to HTML5 and JavaScript, and I'm trying to use the canvas element to create a high(ish) quality output image.
The current purpose is to allow users to all their own images (jpeg, png, svg). this works like a charm. however when I render the image it's always a 32-bit png. how can I create a higher quality picture using JavaScript(preferably) ?
when I output the file, it always seems to keep the same resolution as the canvas, how can I change this using JavaScript(preferably)
Thanks in Advance guys, I looked around for a while but I couldn't find the answer to this :(
If you want to create a larger image with getImageData or toDataURL then you have to:
Create an in-memory canvas that is larger than your normal canvas
Redraw your entire scene onto your in-memory canvas. You will probably want to call ctx.scale(theScale, theScale) on your in-memory context in order to scale your images, but this heavily depends on how they were created in the first place (images? Canvas paths?)
Call getImageData or toDataURL on the in-memory canvas and not your
normal canvas
By in-memory canvas I mean:
var inMem = document.createElement('canvas');
// The larger size
inMem.width = blah;
inMem.height = blah;
Well firstly, when you draw the image to the canvas it's not a png quite yet, it's a simple raw bitmap where the canvas API works on as you call it's methods, then it's converted to a png in order for the browser to display it, and that's what you get when you use toDataURL. When using toDataURL you're able to choose which image format you want the output to be, I think jpeg and bmp are supported along with png. (Don't think of it as a png converted to another format, cause it's not)
And I don't know what exactly do you mean by higher quality by adding more bits to a pixel, you see 32 bits are enough for all RGBA channels to have a true color 8 bits depth giving you way more colors than the human eye can see at once. I know depending on the lighting and angle in which the user is exposed to your picture his perception of the colors may vary but not the quality of it which I'd say only depends on the resolution it has. Anyway the canvas was not designed to work with those deeper colors and honestly that much color information isn't even necessary on any kind of scene you could render on the canvas, that's only relevant for high definition movies and games made by big studios, also, even if you could use deep colors on the canvas it would really depend on the support of the user's videocard and screen which I think the majority of people doesn't have.
If you wish to add information not directly concerned to the color of each pixel but maybe on potencial transformations they could have you better create your own type capable of carrying the imageData acceptable by the canvas API, keeping it's 32-bit format, and the additional information on a corresponding array.
And yes, the output image has the same resolution as the canvas do but there are a couple of ways provided for you to resize your final composition. Just do as Simon Sarris said, create an offscreen canvas which resolution is the final resolution you want your image to be, then, you can either:
Resize the raster image by calling drawImage while providing the toDataURL generated image making use of the resizing parameters
Redraw your scene there, as Simon said, which will reduce quality loss if your composition contains shapes created through the canvas API and not only image files put together
In case you know the final resolution you want it to be beforehand then just set the width and height of the canvas to it, but the CSS width and height can be set differently in order for your canvas to fit in your webpage as you wish.