We're using google maps and want to keep our traffic to that site to a minimum. At present we have an <li> element that contains an href to a generated maps.google.com URL. That link can change based on the orientation of the device-- the same map address, but we use a resized map to fit the screen appropriately.
We're storing the portrait and landscape google maps' <href> values to keep from regenerating them every time the device is reoriented. Then, on every orientation change we flip the <li>'s html property using jQuery like this:
//on an orientation change...
if (window.orientation == "portrait") {
$(#mapLi).html(portraitMapHref);
}
else {
$(#mapLi).html(landscapeMapHref);
}
The google API generates the hrefs and the embedded <img> tags for us on the page load, and the first time an orientation change occurs. This of course leads to a connection to maps.google.com.
When we swap back and forth using the .html function with the cached hrefs there doesn't appear to be a simultaneous call to maps.google.com, which is what we're after, but I wondered if this is due to browser caching or the nature of the .html function in jqm? I thought that swapping the html value in that element would trigger a call to the maps.google.com address. Should it not, or are we getting lucky with browser caching?
It's not clear what exactly you store in portraitMapHref and landscapeMapHref, but I guess you store nodes.
In this case when you use $.html(), the new content will replace the current content, but the old content(node) will not be deleted, it's still a node, no matter if it's attached to the DOM or not.
There is nothing to load when you re-use the replaced node.
Related
For images in my webpage, instead of just specifying some image url, I need to load the image data from my own API as a binary data, and then set the src as data/jpeg;base64,..... i.e, I probably need a customized function to load the image content.
However I also want to do the loading lazily. So the ways I can think of are:
set src as empty initially, and listen to various mouse events myself or use Intersection Observer API to trigger my customized function to actually load and set src
find some way to override image's loading function? so that I could still use the native lazy loading provided by chrome?
Is option 2 possible? If so, how to override?
Thanks!
How to extract the image from this https://www.google.com/maps/#45.8118462,15.9725486,3a,75y/data=!3m7!1e2!3m5!1sAF1QipOH6lgU7bug2ndyW-9-Uq0kgKqcKDtnGei2N5Qo!2e10!6shttps:%2F%2Flh5.googleusercontent.com%2Fp%2FAF1QipOH6lgU7bug2ndyW-9-Uq0kgKqcKDtnGei2N5Qo%3Dw150-h150-k-no-p!7i3024!8i4032
(If the link disappears let me describe how to reproduce the question. Find any shop on Google Maps that has the "shop title image" appearing in the shop details on the left side when you click on that shop. Click on that image to expand it across the whole viewport.)
I found the <canvas> element that I guess contains the image. I tried to do .getContext('2d') on that canvas element, but I keep getting null.
If you are getting null when doing getContext("2d") it's because an other type of context was created already, in this case, a "webgl" one.
To convert that canvas to a new image, you'd normally call canvas.toBlob() (whatever the context type).
And if you need to crop that canvas content, you'd draw it on an other canvas.
But since they did not prevent the WebGL context to throw away its drawing buffer (by passing preserveDrawingBuffer in the getContext call), you'll only get a transparent image back from it.
Anyway none of these methods will retrieve the original image, but they will create a new image entirely (probably of lesser quality, and bigger in size). To retrieve the original image, check the network tab of your dev tools, or if you need to do it programmatically, inject a script that will spoof all fetch, XHR and HTMLImageElement objects in order to log their resource URL. But that becomes dirty.
Please bear in mind that I have never used Web Workers before and I'm having some trouble wrapping my head around them.
Here's an explanation of a simplified version of what I'm doing.
My page has links to various files - some are text, some are images, etc. Each file has an image showing a generic file icon.
I want the script to replace each generic icon with a preview of the file's contents.
The script will request the file from the server (thereby adding it to the cache, like a preloader), then create a canvas and draw the preview onto it (a thumbnail for images, an excerpt of text for text files, a more specific icon for media files...) and finally replace the generic icon's source with the canvas using a data URL.
I can do this quite easily. However, I would prefer to have it in the background so that it doesn't interfere with the UI while it's working.
Before I dive right in to this, I need to know: can Workers work with a canvas, and if so how would I create one? I don't think document.createElement('canvas') would work because Workers can't access the DOM, or am I misunderstanding when all the references I've found say they "can't access the DOM"?
You cannot access the DOM from web workers. You cannot load images. You cannot create canvas elements and draw to them from web workers. For now, web workers are pretty much limited to doing ajax calls and doing compute intensive things. See this related question/answer on web workers and canvas objects: Web Workers and Canvas and this article about using webworkers to speed up image manipulation: http://blogs.msdn.com/b/eternalcoding/archive/2012/09/20/using-web-workers-to-improve-performance-of-image-manipulation.aspx
Your simplest bet is to chunk your work into small chunks (without web workers) and do a chunk at a time, do a setTimeout(), then process the next chunk of work. This will allow the UI to be responsive while still getting your work done. If there is any CPU consuming computation to be done (like doing image analysis), this can be farmed out to a web worker and the result can be sent via message back to the main thread to be put into the DOM, but if not, then just do your work in smaller chunks to keep the UI alive.
Parts of the tasks like loading images, fetching data from servers, etc... can also be done asynchronously so it won't interfere with the responsiveness of the UI anyway if done properly.
Here's the general idea of chunking:
function doMyWork() {
// state variables
// initialize state
var x, y, z;
function doChunk() {
// do a chunk of work
// updating state variables to represent how much you've done or what remains
if (more work to do) {
// schedule the next chunk
setTimeout(doChunk, 1);
}
}
// start the whole process
doChunk();
}
Another (frustrating) limitation of Web Workers is that it can't access geolocation on Chrome.
Just my two cents.
So as others have stated, you cannot access the DOM, or do any manipulations on the DOM from a web worker. However, you can outsource some of the more complete calculations on the web worker. Then once you get your return message from the web worker inside of your main JS thread, you can extract the values you need and use them on the DOM there.
This may be unrelated to your question, but you mentioned canvas so i'll share this with you.
if you need to improve the performance of drawling to canvas, I highly recommend having two canvas objects. One that's rendered to the UI, the other hidden. That way you can build everything on the hidden canvas, then draw the hidden canvas on the displayed one. It may not sound like it will do much if anything, but it will increase performance significantly.
See this link for more details about improving canvas performance.
I am developing an Windows Forms application using VB.NET that offers the user to lookup addresses on Google Maps through a Web Browser. I can also successfully show the directions between two points to the user, as well as allow the user to drag the route as he/she pleases. My question now is - is it possible for me to get the lattitude/longitude information of the route, i.e. the overview_polyline array of encoded lattitude/longitude points and save it to e.g. a text file on my computer? Or is it possible to get a list of all the addresses located both sides of the route over the entire length of the route, and then save the data to a file on my computer? I'm using HTML files to access and display the Google Maps data in the Web Browser item.
Thank you
This is actually pretty simple if your just looking for the screen coordinates.
// this probably should be in your form initialization
this.MouseClick += new MouseEventHandler(MouseClickEvent);
void MouseClickEvent(object sender, MouseEventArgs e)
{
// do whatever you need with e.Location
}
if your strictly looking for the point in the browser, you need to consider the functions
browser.PointToClient();
browser.PointToScreen();
So, this method is usable if you know exactly where your form is (easy to get its coords) and where you webbrowser control is (easy to get coords of this as well since it's just a control in your form) and then, as long as you know how many pixels from the left or right, and from the top or bottom the image will be displayed, once you get the global mouse click coords (which is easy) you can predict where it was clicked on the image.
Alternatively, there are some scarier or uglier ways to do it here...
You can use the ObjectForScripting property to embed code to do this in the webbrowser. It's ugly to say the least. MSDN has some documentation on the process here: http://msdn.microsoft.com/en-us/library/system.windows.forms.webbrowser.objectforscripting.aspx
Because its really ugly, maybe a better solution is to use AxWebBrowser - it's ugly too but not so scary.
In addition, I found this post of someone wanting to do it on a pdf document, and a MSFT person saying its not possible, but really what he is trying to say is that it isn't built in, even with a pdf document its still possible to predict with high to certain accuracy where it was clicked if you use the first method i described. Here is the post anyway: http://social.msdn.microsoft.com/Forums/en/csharpgeneral/thread/2c41b74a-d140-4533-9009-9fcb382dcb60
However, it is possible, and there are a few ways to do it, so don't get scared from that last link I gave ya.
Also, this post may help if you want to do it in javascript:
http://www.devx.com/tips/Tip/29285
Basically, you can add an attribute on the image through methods available in the webbrowser control, you can add something like onclick="GetCoords();" so when it is clicked, the JavaScript function will get the coords, and then you can use javascript to place the values in a hidden input field (input type="hidden") which you can add through the webbrowser control, or if there is one already on the page, you can use that. So, once you place the coords using javacript into that input field, you can easily grab the value in that using the webbrowser control, eg:
webbrowser1.document.getElementById("myHiddenInputField").value
That will get the value in that field, which you've set through JavaScript. Also, the "GetCoords()" function i mentioned is called SetValues() in the javascript method link i provided above (in the devx.com site) but I named it GetCoords because it makes more sense and didn't want to confuse you with the actual name they used, you can change this to any name you want of course. Here is the javascript they were using, this only gets the coords into a variable, doesn't put it into a hidden input field, we will need to do that in addition (at the end of the javascript SetValues/GetCoords function).
function SetValues()
{
var s = 'X=' + window.event.clientX + ' Y=' + window.event.clientY ;
document.getElementById('divCoord').innerText = s;
}
These guys are just saving it inside a div element, which is visible to users, but you can make the div invisible if you want to use a div field, there is no advantage or disadvantage in doing that, you would just need to set the visible property to false using javascript or css, but still, it is easier to use a hidden input field so you don't need to mess with any of that.
Let me know how you get along.
I've got a plain-vanilla google maps widget sitting in a page and I'd like it if the driving directions opened up in a new window instead of taking over the current window. Is there a setting for this?
The driving directions go into whatever HTML element you specify as the second argument when you construct the GDirections object. So I guess that means you'd have to create the window before you create the GDirections object, which is likely not what you want.
The other thing that jumps out, looking at the documentation, is that you can call the load() method with the option getSteps = true. It's not clear what the "steps" data looks like, but I assume it essentially comes back as an HTML string. (Actually, it's not even clear how you get the data in the first place, but I assume it's GDirections.getSteps() or something similar.) So then when the "load" event happens, you can create the new window then put the "steps" data in it.