I've written my own media player interface using javascript and html5. Currently my volume slider maps to the browser's volume attribute 1:1. I'd quite like to adjust this to account for perceived loudness.
The volume attribute section of the html5 specs say:
... 0.0 being silent, and 1.0 being the loudest setting, values in between increasing in loudness. The range need not be linear.
This seems to imply that there's no standard for what scale browsers should use. I'm worried that if I adjust for perceived loudness in one browser, another browser might already be doing this resulting in an overcorrection.
Does anyone know what volume scales browsers currently use and whether these are likely to change in future?
Assuming you cannot acquire directly the information on each browser, I would suggest developing a set of empirical tests. Off-hand, I can't imagine the browser vendors using anything other than logarithmic or linear volume control, so that leaves only two outcomes to consider in your tests. Once your test flow is created, you can reuse it whenever a new browser version is released.
As for the tests themselves, they could be by your own perception (test the loudness at 100% vs. 50%, and guage whether 50% actually sounds half as loud, or only 75%-ish as loud); or they could be through recording the "what you hear" channel on your soundcard, and analyzing the waveform in a custom app or tool, this time looking for a .5 drop in (peak) amplititude if simple linear, or a greater than .5 drop if logarithmic. If building your own analysis tool, PCM waveform data is not too difficult to work with, assuming you are comfortable with C/C++/C#/et.al.
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I've found lots of information about measuring load time for pages and quite a bit about profiling FPS performance of interactive applications, but this is something slightly different than that.
Say I have a chart rendered in SVG and every click I make causes the chart to render slightly differently. I want to get a sense of the complete time elapsed between the click and the point in time that the pixels on the screen actually change. Is there a way to do this?
Measuring the Javascript time is straight forward but that doesn't take into consideration any of the time the browser spends doing any layout, flow, paint, etc.
I know that Chrome timeline view shows a ton of good information about this, which is great for digging into issues but not so great for taking measurements because the tool itself affects performance and, more importantly, it's Chrome only. I was hoping there was a browser independent technique that might work. Something akin to how the Navigation Performance API works for page load times.
you may consider using capturing hdmi capturing hardware (just google for it) or a high speed camera to create a video, which could be analyzed offline.
http://www.webpagetest.org/ supports capturing using software only, but I guess it would be too slow for what you want to measure.
Is there any way to be able to query the GPU to tell me if my viewport in my webpage is currently on screen or not? For example, if I had a 3d scene rendering in a canvas in an iframe, is there a way to query the hardware (within my iframe and only the pixels or verts in the viewport) to say if I am on screen or scrolled off screen?
I'm curious as to whether this is something I can do at the vertex shader level. Does WebGL even perform the shader program on a viewport that is offscreen? Lets say if it is scrolled below the canvas, or the viewport is obstructed by another webpage browser window? Is there a way to query the compositing portion of webgl to see if it is even in view or Iterate through the "RenderObject" Tree to test if it is even onscreen and then return this value? I am trying to get much more performance out of a project I am working on and I am trying to only render what is visible on screen.
Any possible ideas? Is this even possible? Thanks!
RequestAnimationFrame is only reasonable way to handle unnecessary performance loss even semantically because window.requestAnimationFrame tells the browser that you wish to perform an animation... So browser will figure out how it should handle your wish in optimal way taking into account current page state.
But since iframes communicate using local storage you can push to them your base page state so each of them will decide should it RequestAnimationFrame or not. But im not shure that it is a good thing to have multiply render contexts on your page, they all eat resources and can't share them (data that stored in GPU is sandboxed) so eventually they will start to push each other from GPU memory and cause lags + GPU pipeline might be not so happy with all those tiny standalone entities. Fragmentation is main GPU performance enemy.
You don't ask this question at the canvas/WebGL level, because it might, for example, be scrolled back on screen before you draw another frame, and browsers don't want to not have content to show, so there's no provision to not draw.
I believe you will have to consult the DOM geometry properties (e.g. .scrollLeft) of your scrollable areas to determine whether the canvas is visible. There is enough information in said properties that you can do this generically without hardcoding knowledge of your page structure.
Also, make sure you are exclusively using requestAnimationFrame for your drawing/simulation scheduling; it will pause animations if the page is hidden/minimized/in another tab/otherwise explicitly invisible.
I am trying to choose the right technology to use for updating a project that basically renders thousands of points in a zoomable, pannable graph. The current implementation, using Protovis, is underperformant. Check it out here:
http://www.planethunters.org/classify
There are about 2000 points when fully zoomed out. Try using the handles on the bottom to zoom in a bit, and drag it to pan around. You will see that it is quite choppy and your CPU usage probably goes up to 100% on one core unless you have a really fast computer. Each change to the focus area calls a redraw to protovis which is pretty darn slow and is worse with more points drawn.
I would like to make some updates to the interface as well as change the underlying visualization technology to be more responsive with animation and interaction. From the following article, it seems like the choice is between another SVG-based library, or a canvas-based one:
http://www.sitepoint.com/how-to-choose-between-canvas-and-svg/
d3.js, which grew out of Protovis, is SVG-based and is supposed to be better at rendering animations. However, I'm dubious as to how much better and what its performance ceiling is. For that reason, I'm also considering a more complete overhaul using a canvas-based library like KineticJS. However, before I get too far into using one approach or another, I'd like to hear from someone who has done a similar web application with this much data and get their opinion.
The most important thing is performance, with a secondary focus on ease of adding other interaction features and programming the animation. There will probably be no more than 2000 points at once, with those small error bars on each one. Zooming in, out, and panning around need to be smooth. If the most recent SVG libraries are decent at this, then perhaps the ease of using d3 will outweigh the increased setup for KineticJS, etc. But if there is a huge performance advantage to using a canvas, especially for people with slower computers, then I would definitely prefer to go that way.
Example of app made by the NYTimes that uses SVG, but still animates acceptably smoothly:
http://www.nytimes.com/interactive/2012/05/17/business/dealbook/how-the-facebook-offering-compares.html . If I can get that performance and not have to write my own canvas drawing code, I would probably go for SVG.
I noticed that some users have used a hybrid of d3.js manipulation combined with canvas rendering. However, I can't find much documentation about this online or get in contact with the OP of that post. If anyone has any experience doing this kind of DOM-to-Canvas (demo, code) implementation, I would like to hear from you as well. It seems to be a good hybrid of being able to manipulate data and having custom control over how to render it (and therefore performance), but I'm wondering if having to load everything into the DOM is still going to slow things down.
I know that there are some existing questions that are similar to this one, but none of them exactly ask the same thing. Thanks for your help.
Follow-up: the implementation I ended up using is at https://github.com/zooniverse/LightCurves
Fortunately, drawing 2000 circles is a pretty easy example to test. So here are four possible implementations, two each of Canvas and SVG:
Canvas geometric zooming
Canvas semantic zooming
SVG geometric zooming
SVG semantic zooming
These examples use D3's zoom behavior to implement zooming and panning. Aside from whether the circles are rendered in Canvas or SVG, the other major distinction is whether you use geometric or semantic zooming.
Geometric zooming means you apply a single transform to the entire viewport: when you zoom in, circles become bigger. Semantic zooming in contrast means you apply transforms to each circle individually: when you zoom in, the circles remain the same size but they spread out. Planethunters.org currently uses semantic zooming, but it might be useful to consider other cases.
Geometric zooming simplifies the implementation: you apply a translate and scale once, and then all the circles are re-rendered. The SVG implementation is particularly simple, updating a single "transform" attribute. The performance of both geometric zooming examples feels more than adequate. For semantic zooming, you'll notice that D3 is significantly faster than Protovis. This is because it's doing a lot less work for each zoom event. (The Protovis version has to recalculate all attributes on all elements.) The Canvas-based semantic zooming is a bit more zippy than SVG, but SVG semantic zooming still feels responsive.
Yet there is no magic bullet for performance, and these four possible approaches don't begin to cover the full space of possibilities. For example, you could combine geometric and semantic zooming, using the geometric approach for panning (updating the "transform" attribute) and only redrawing individual circles while zooming. You could probably even combine one or more of these techniques with CSS3 transforms to add some hardware acceleration (as in the hierarchical edge bundling example), although that can be tricky to implement and may introduce visual artifacts.
Still, my personal preference is to keep as much in SVG as possible, and use Canvas only for the "inner loop" when rendering is the bottleneck. SVG has so many conveniences for development—such as CSS, data-joins and the element inspector—that it is often premature optimization to start with Canvas. Combining Canvas with SVG, as in the Facebook IPO visualization you linked, is a flexible way to retain most of these conveniences while still eking out the best performance. I also used this technique in Cubism.js, where the special case of time-series visualization lends itself well to bitmap caching.
As these examples show, you can use D3 with Canvas, even though parts of D3 are SVG-specific. See also this force-directed graph and this collision detection example.
I think that in your case the decision between canvas and svg is not like a decision between »riding a Horse« or driving a »Porsche«. For me it is more like the decision about the cars color.
Let me explain:
Assuming that, based on the framework the operations
draw a star,
add a star and
remove a star
take linear time. So, if your decision of the framework was good it is a bit faster, otherwise a bit slower.
If you go on assuming that the framework is just fast, than it becomes totally obvious that the lack of performance is caused be the high amount of stars and handling them is something none of the frameworks can do for you, at least I do not know about this.
What I want to say is that the base of the problem leads to a basic problem of computational geometry, namely: range searching and another one of computer graphics: level of detail.
To solve your performance problem you need to implement a good preprocessor which is able to find very fast which stars to display and is perhaps able to cluster stars which are close together, depending on the zoom. The only thing that keeps your view vivid and fast is keeping the number of stars to draw as low possible.
As you stated, that the most important thing is performance, than I would tend to use canvas, because it works without DOM operations. It also offers the opportunity to use webGL, what increases graphic performance a lot.
BTW: did you check paper.js? It uses canvas, but emulates vector graphics.
PS: In this Book you can find a very detailed discussion about graphics on the web, the technologies, pros and cons of canvas, SVG and DHTML.
I recently worked on a near-realtime dashboard (refresh every 5 seconds) and chose to use charts that render using canvas.
We tried Highcharts(SVG based JavaScript Charting library) and CanvasJS(Canvas based JavaScript Charting library). Although Highcharts is a fantastic charting API and offers way more features we decided to use CanvasJS.
We needed to display at least 15 minutes of data per chart (with option to pick range of max two hours).
So for 15 minutes: 900 points(data point per second) x2(line and bar combination chart) x4 charts = 7200 points total.
Using chrome profiler, with CanvasJS the memory never went above 30MB while with Highcharts memory usage exceeded 600MB.
Also with refresh time of 5 seconds CanvasJS rendering was allot more responsive then Highcharts.
We used one timer (setInterval 5 seconds) to make 4 REST API calls to pull the data from back end server which connected to Elasticsearch. Each chart updated as data is received by JQuery.post().
That said for offline reports I would go with Highcharts since its more flexible API.
There's also Zing charts which claims to use either SVG or Canvas but haven't looked at them.
Canvas should be considered when performance is really critical. SVG for flexibility. Not that canvas frameworks aren't flexible, but it takes allot more work for canvas framework to get the same functionality as an svg framework.
Might also look into Meteor Charts, which is built on top of the uber fast KineticJS framework: http://meteorcharts.com/
I also found when we print to PDF a page with SVG graphics, the resulting PDF still contains a vector-based image, while if you print a page with Canvas graphics, the image in the resulting PDF file is rasterized.
I hope this isn't too open ended.
I'm wondering if there is a better (more battery-friendly) way of doing this --
I have a small HTML 5 game, drawn in a canvas (let's say 500x500). I have some objects whose positions I update every 50ms or so. My current implementation re-draws the entire canvas every 50ms. I can't imagine that being very good for battery life on mobile platforms.
Is there a better way to do this? This must be a common pattern with games.
EDIT:
as requested, here are some more updates:
Right now, the objects are geometric primitives drawn via arcs and lines. I'm not opposed to making these small png/jpg/gif files instead of that'd help out. These are small graphics -- just 15x15 or so.
As the game progresses, more and more of the screen changes at a time. However, at the start, the screen changes relatively slowly (the objects randomly moved a few pixels every 50ms).
Nearly every game with continuous animation like this redraws everything every frame; clever updating algorithms are only applicable when a small part of the screen is changing and there is a nice rule to figure out what is overlapping that part.
Here is some general optimization advice:
Make sure that as much as possible of your graphics are handled by the GPU and not the CPU. (This may be impossible if the user's browser does not use the GPU for 2D canvas rendering, but you can expect upgrades may change that as HTML5 gaming gains popularity.)
This means that you should avoid elaborate clever algorithms in favor of doing as little work as possible in JS code — except that avoiding performing a lot of drawing when it is easy to determine that it will be invisible (e.g. outside the bounds of the screen) is generally worthwhile.
If your target platforms support it (generally not the case for current mobile devices), try using WebGL instead of 2D Canvas. You will have to do more detail work, but WebGL allows you to use operations which are much more likely to be provided efficiently by the GPU hardware.
If your game becomes idle — that is, nothing is actually animating at the moment — stop redrawing. Stop your update loop until the user interacts with the game or a timeout occurs.
It may be helpful for you to add to your question details of what types of graphics you are drawing (e.g. are you using sprites, or geometric primitives? Are you drawing images rotated/scaled? Does most of the screen change or just a few small objects? Are you blending many layers?) and perhaps even a screenshot or two; then we can suggest what sort of optimizations are suitable for your particular game.
Don't draw a background, make it an image and set the CSS background-image of the canvas.
Using requestAnimationFrame should help with battery life.
http://paulirish.com/2011/requestanimationframe-for-smart-animating/
Only do a redraw if something has actually changed. If you haven't already, introduce the concept of invalidations. (ie, the canvas is valid so nothing redraws until something moves. Anything moving within the window of the canvas causes the canvas to become invalid, thus needing a redraw)
If you want to be battery friendly you can use Crafty. This game engine is using modern CSS3 technology so it doesn't need to update a canvas all the time. Look at this example game here.
The way you don't want to redraw entire canvas every frame, it only can be the "Dirty-Check" or "Dirty Matrix" algorithms.
Dirty-check seems more efficient than entire redraw. but I think it depends on your render implementation.
it is not necessary to use it if you are using canvas2D to render. Nearly every game has complex sprites and animation. if you use dirty-check, when a part of sprite or background map need to update, you have to figure out what is overlapping this part. and then clearRect this small area of canvas, and then redraw every sprite or map. etc, what is overlapping.
It means your had to run canvas render api more times than normal render implementation because of the overlapping part. And Canvas2d render performance usually does't sounds efficient.
But if you use WebGL, that maybe quite difference. even though I am not family with WebGL, I do knew that maybe more efficient. Dirty-Check should be a good Choice to match your propose.
I am writing an HTML5 canvas app in javascript. I am using multiple canvas elements as layers to support animation without having to re-draw the whole image every frame.
Is there a maximum number of canvas elements that I can layer on top of each other in this way -- (and see an appropriate result on all of the HTML5 platforms, of course).
Thank you.
I imagine you will probably hit a practical performance ceiling long before you hit the hard specified limit of somewhere between several thousand and 2,147,483,647 ... depending on the browser and what you're measuring (number of physical elements allowed on the DOM or the maximum allowable z-index).
This is correlated to another of my favorite answers to pretty much any question that involves the phrase "maximum number" - if you have to ask, you're probably Doing It Wrong™. Taking an approach that is aligned with the intended design is almost always just as possible, and avoids these unpleasant murky questions like "will my user's iPhone melt if I try to render 32,768 canvas elements stacked on top of each other?"
This is a question of the limits of the DOM, which are large. I expect you will hit a performance bottleneck before you hit a hard limit.
The key in your situation, I would say, is to prepare some simple benchmarks/tests that dynamically generate Canvases (of arbitrary number), fill them with content, and add them to the DOM. You should be able to construct your tests in such a way where A) if there is a hard limit you will spot it (using identifiable canvas content or exception handling), or B) if there is a performance limit you will spot it (using profiling or timers). Then perform these tests on a variety of browsers to establish your practical "limit".
There are also great resources available here https://developers.facebook.com/html5/build/games/ from the Facebook HTML5 games initiative. Therein are links to articles and open source benchmarking tools that address and test different strategies similar to yours.