I am trying to develop a "Web App" (for lack of better terminology) that displays a sort of interactive map using the HTML5 Canvas element for mobile devices. The map has about 30 buildings (made from semi-transparent PNG images on it) of different shapes and sizes. I want the user to be able to tap on any of the buildings to get information about them. The buildings are often within the same theoretical bounding box of others, so it isn't as simple as just detecting when the user taps in a bounding box (imagine a U shaped building with another building inside the U). Therefore, it should use some sort of raster pixel detection. To make matters more complicated, I need to allow the user to zoom in/out and pan around on the map (because 30 buildings and a map are way too much to show a user on a tiny cellphone screen). So scaling and moving smoothly is a necessity.
I am looking for a JavaScript library that can support these functions:
Image pixel detection
Mobile touch events
Canvas (or stage?) scaling
Usable on mobile devices
So far, I have found KineticJS which supports all of these features. But when I try to move the map with more than 4 buildings on the stage, it is way too jumpy. I tried checking into Fabric.js but it doesn't seem to have pixel detection (as it selects the image when you click within the bounding box, not the actual image itself).
Is there any other JavaScript library out there that can do these things?
Thanks for any help!
The KineticJS is pretty good ( the best lib i found so far )
I never tried to use png images with it, but zooming and panning with a few hundreds primitive objects is pretty smooth (without pixel detection - I imagine the pixel detection is quite cpu expensive operation ).
Maybe you could try overlay standard polygons ( a few for one building ) and attach to the same click/tap event.
Also you don't necessary need to move objects on the canvas you can just put bigger canvas in smaller div ( with overflow:hidden) and drag the whole canvas element.
Related
I have created a website to allow users to design playing cards online using fabricjs and have made the canvas responsive so it will work equally well on mobile devices as desktop. Almost everything works perfect... On smaller screens the objects are scaled correctly with the canvas and positioned correctly based on the canvas size but selecting/manipulating the objects doesn't work properly. When the canvas is scaled down from it's original (desktop based) size I cannot click on the object. I have noticed that the point on the canvas you need to click to select the object is shifted down and right from the object itself. The smaller the canvas gets, the further from the object the selection point gets. Is there a way to fix this?
Thanks!
Steve Sherrin
vI know to some extent this is a known issue that has been asked here but never answered, but I'm hoping for some additional insight.
I have a simple SVG image in a div on a web page. I want to be able to zoom the image using pinch gestures and have the SVG render sharply. It doesn't need to be sharp during the zoom, but should be sharp after the gesture is complete.
I'm doing my testing on a Windows 8.1 computer with a touch monitor, on an iPad, and on an old Android Galaxy Tab. On the main computer, I'm using IE11 and Chrome. For handling touch gestures, I'm using Hammer.js. I'm doing the zooming by modifying the transform CSS using the jQuery css() function (I'm setting scale3d and translate3d).
IE11 on my computer works exactly like I would like it to. It keeps the SVG image sharp throughout the pinch zoom and the image is always sharp regardless of when I set the CSS.
Chrome on my computer always renders the SVG blocky when I am zoomed in using pinch zoom. It is blocky during the zoom and does not get sharp afterwards. If I add a call to zoom the image after the page (x13) is loaded, the image is sharp. If I use a setTimeout() call to reset the zoom and then rezoom the image after the pinch zoom ends, the image is sharp.
On the iPad and Android tablet, the SVG never renders sharply, regardless of when I zoom it in code.
Does anyone have any ideas of how to reliably end up with a sharp rendering of SVG after a pinch-zoom is completed? Does anyone have a better solution? Using the SVG viewBox to zoom and pan during the gesture does not provide good enough performance for our more complex SVG images. I'm thinking of attempting to use the hardware accelerated scale3d/translate3d during the gesture and then attempt to convert this to new SVG viewBox settings afterwards, but this is a challenge and I'm not sure panning will work correctly after this is done. Any pointers or ideas are greatly appreciated.
Having just tried to answer your other SVG Question I will have a try at this one.
Michael Mullany is spot on that GPU translations will never give you a sharp image. This is because the GPU just maps one array of pixels to a new one. Because it has no concept of lines or rectangles the resolution is set by the time the GPU gets the image. The CPU will always struggle to re-render in time for a smooth drag.
What happens to allow some browsers to produce a sharp image is they do clever manipulations like rendering more pixels than they need so some zooming can happen without loss of resolution. These however are completely inconsistent and just not possible to rely on.
The as I see it 'correct' solution is to translate and zoom with hardware accelerated transformations during a pinch or zoom and then to refresh the viewbox with no css transformation when the translation has finished.
Challenges to overcome are
The css transformation will use screen coordinates but the viewBox manipulation will use the SVG coordinate system.
There are browser inconsistencies in both screenCTM and device pixel ratio
limits so that people don't drag or zoom too far need to be calculated in both systems
Pinch centerpoints also need to be calculated in both
To improve performance further the css transforms will be wrapped into updating on the requestAnimationFrame loop.
My working solution is hammerhead2. I am concentrating on desktops and android mobiles first and it seams to be working for them. To simplify the problem zoom is always centered to the screen center. I do however thing this is currently one of the only solutions. Here is an example of it working.
I'm using some javascript to make my images draggable
I want to be able to move my images over each other and create a similar effect to the multiply blending mode in photoshop.
I've seen how this is possible with static images, but I want these to change as they are moved around the screen, rather than just loading up with the effect already applied.
Is this possible within the canvas? Is there a better way?
Yes, it is possibile with Canvas and processing.js, but you will not be able to use your actual draggable plugin (it doesn't seem HTML5).
Read this http://processingjs.org/reference/blend_/ but remember Blending on Canvas could be very slow (it depends by images' resolution and by Browser' engine).
Since I dont have either of these devices handy to test, which method would be faster on an iphone/ipad?
One large canvas (overlayed over a bg of the same size), that is cleared, and has new pixel data drawn to it each frame, at a certain position
or
A small canvas that updates each frame, contained in a div that is animated across a background
As it turns out iphone/ipad aren't even capable of running this small animation either way. I will have to look at alternative solutions for mobile/tablet devices.
Yes, I've found the iPhone too slow in all my canvas experiment.
Even moving a simple div around (CSS3 styled, no canvas) is barely accettable ( my test with the new motion API: http://www.omiod.com/i.htm )
I have a web page which displays a large image, for example a page from a magazine. I have no control over the image size or orientation. It's possible that the image may need to be rotated by the user to orient it correctly.
Are there any Javascript or Flash solutions that will allow someone to rotate and zoom a given image? Ideally I'd specify a single image and the dimensions to use when displaying it. If the image is larger than those dimensions, the user could zoom in and view a portion of the image in greater detail.
I've seen a couple of solutions for rotating images with straight Javascript and CSS. Raphael would do the trick. There is apparently even an example featuring rotating an image. (it uses SVG but is support on all major browsers)
This one is not cross browser, but is an interesting exercise nevertheless.
As for flash rotation etc...
For rotating images, I used jquery-rotate and it works very well.
It is not totally cross-browser, it doesn't work with IE6 (and probably other old browsers).
For zooming, I guess you could make your own implementation using javascript, you can just resize the image (easy with jQuery).