If I have a png image that is 127 alpha, and I have the same image with normal alpha (255) and a CSS style of opacity:0.5, which will render faster?
The reason I'm asking is I want a few partially transparent clouds in a webgame, and I'm interested to know which is a better technique to put less strain on the computer.
PNG will do better.
To render element with opacity < 1.0 the browser will 1) create bitmap buffer, 2) render your image there and then 3) render that buffer to the target.
With PNG it will do just #3.
Particular details may vary but these steps will be there in one form or another.
Related
Here's the issue at hand. I need to be able to pick a background (an image showing an object, let's say, a starship model). I want to be able to apply various previously prepared textures to various areas on it, as some kind of a "colour your own object" app, but without the need to prepare dozens of individual segments.
Ok, so this is one, newbie way to do it. We have those images:
Two kind of different versions, an original photo and a quickly Photoshopped one. Let's say we only want the Borg-ish green deflector and warp nacelle from the second picture, without the odd pink hull. You have to have a mask, basicly an image of an equal resolution (or at least the same aspect ratio, which you can reliably scale to image's resolution), with the area filled with color (or whatever else), and transparent area everywhere else. As the mask, I've used a few strokes of brush on an empty layer, set to overlay mode, and then saved as PNG, with transparency. And this is how the code went:
First, import images.
QPixmap background("orig.png"); //import base image
//import alt version/texture/whatever you want, anything will work with a good mask
QPixmap element("alt.png");
QPixmap mask("deflector.png"); //mask. Just nacelles and deflector.
Then, isolate the area that interests us from alt version
QPainter painter(&element);
painter.setCompositionMode(QPainter::CompositionMode_DestinationIn);
painter.drawPixmap(0, 0, mask.width(), mask.height(), mask);
And finally draw it onto the target object.
QPainter inter(&background);
inter.drawPixmap(0, 0, element);
ui->label->setPixmap(background);
The result:
This method respects any and all transparency you could've done in Photoshop or another image editing software.
Simple, but an effective solution, for when your app has to work with graphics prepared by someone else, elsewhere.
I'm having several buttons that I want to get darker when user hovers over. Which method is better (faster, more efficient, more safe in terms of browser compatibility):
Create 2 separate .png images, one normal one _hover
Use transition:opacity css property.
Images are small, each approx. 600 bytes big (20x20 pxl), but having approximately 30 of them makes me wonder which method is better in terms of speed efficiency and older browsers support (but not to the point trying to please IE6 either)
if opacity is doing your job of darkening the image- Use it.
You said darkening image? so i assume u start with lower opacity value and chage to something higher.opacity is more like transparency of the pic-dosent darken it.
If opacity is not giving the desired results you can use hover change of image-use image sprites this way you dont have to request for 60 svg's(30 svgs considering you use a combination of 2 pics instead of one)
LINK for sprites.
I suggest using SVG filter gives you better image effects-Browser support
Supposing that I have a polygon image PNG file like this (No border, the shape is filled with one color, no gradient, and background of the image is transparent) http://www.enchantedlearning.com/crafts/books/shapes/gifs/4.GIF
I'm thinking of using that polygon image as a background image and it will be changed (to another image with different color) when the user hovers on it.
But I also want the color of the background image to be customizable. So, I'm thinking if there is any possibility to draw the polygon instead of using image files so that the color will be customizable (I don't think it's a good idea to create one file for one color and so on so forth).
What is the best solution for this case? Using png or drawing it by css?
Is there a tool/website to convert my png to css code?
Make the white areas transparent (colour to alpha in GIMP)
Convert the image to a data URI (it's optional but it will make your site load faster)
Use the url in (2) as the background-image and use any background-color you want.
Use this to convert an image: http://codepen.io/blazeeboy/pen/bCaLE
I think it's much better to use converted images because browsers load them faster.
I think CSS is the wrong thing to use for this. Yes, it is possible to create a lot of shapes using CSS, but there are limitations, and in any case, drawing shapes with CSS is a bit of a hack, even when it's just a simple triangle.
Rather than CSS, I would suggest SVG is the appropriate tools for this job.
SVG is a graphics format for vector graphics that can be embedded in a site, and can be created or altered via Javascript directly within the site. Changing the colour and shape of a simple polygon is about as easy as it gets with SVG.
The other advantage of using SVG is that because it's a vector graphic, it's scalable, so you could display it at any size.
The only down-side of SVG is that it isn't supported by old versions of IE (IE8 and earlier). However, these browsers do support an alternative language called VML, and several good Javascript libraries exist which will work with either, thus allowing you complete cross-browser compatibility. The one I'd recommend is Raphael.js.
So a tiny (and very easy) bit of Javascript code instead of a very messy bit of CSS. Seems like a winner to me.
Maybe u could use this: https://javier.xyz/img2css/, the principle is to use box-shadow,it's fine if the picture is small, so u should consider performance
i have a 100x100px image and i need to show that in 3 different dimensions in html,
50x50 60x60 70x70
so my dubt is if better to save img in 3 dimensions then do not use css or html width and height or if to use same img with css rules about dimensions... which solution is faster rendered ?
It depends.
If you are using the same image, Only 1 time image cache is required by the browser. So If you are displaying more than 1 type of image in the same page then dont go for multiple images. Otherwise go for multiple images.
But honestly, 100x100 if you have, It should not be a problem to load. Only in slow connections it will be problem (<128kbps). Otherwise i dont see a considerable difference.
I wouldn't worry too much about rendering speed, the main difference you'll see is in terms of image quality. Some browsers (Chrome) perform very high quality image interpolation, while others (IE, Firefox) opt for a faster algorithm that does not give as nice of a result. So you'll get the best, most consistent image quality by having the three separate image files, one for each size.
That said, since you're only scaling from 100x100 to a minimum size of 50x50 you probably don't need to worry too much about interpolation artifacts either. So I'd recommend just doing whatever is most convenient for you to implement.
And in terms of pure rendering speed, having the separate images will be faster, because no interpolation step is required in that case. In terms of initial page-load speed, however, having a single image will be faster, because there is only 1 file to download instead of 3 (or 4). As for using CSS or HTML tag attributes to set the width and height, there will be practically no difference in speed. The expensive operation is the interpolation of the image itself, and it doesn't make much difference if you specify the interpolation through CSS or through tag attributes.
Is the only benefit of using css image sprites that there is less http requests?
Or is there other benefits?
Also is there an easy way of detiming which area of a sprite to show?
Like you said, one of the main advantage is to reduce the number of requests to the server, improving the response time (especially if you're loading a large amount of small images). But this is not the only reasons people use sprites.
If you don't use sprites for a "mouse over" display, the user will see the image disappear for a second... and it looks really bad. This is because if you change the image instead of just moving the sprite around it will load a new image and the loading time can be visible to the end user.
.bad{
background:url(abc.jpg);
}
.bad:hover{
background:url(abcHover.jpg);
}
.good{
background:url(abc.jpg) 0px 0px;
}
.good:hover{
background-position:15px 0px;
}
Another advantage of sprites is that you can keep all your images in one location and in some cases it makes more sense (for menus and so on).
To determine which area of a sprite to show, just use photoshop or any other image editing software.
The primary benefit is your pages load faster, mainly because of reduced HTTP requests.
You could generate your sprite using a tool.
Disclaimer - I wrote this tool.
It is much easier to get image placement (especially next to text) the same cross-browser. You can adjust images up/down/left/right with out using vertical-align and padding.
I find it easier to keep track of all the images if they are in a single file. Especially since I usually have a transparent png images and and then use gif images for ie6. I save my png sprite map as a gif and add one line with background-image in my ie6 css and my images are switched.
I use photoshop or gimp to get approximate locations in the sprite map and then use firefox to fine-tune the placement.
Yes, there is another benefit. Every image file has his own headers, describing image type, colors etc. So when you combine images to a single sprite, you win some kb.
But as you said before, mostly you win by reducing HTTP requests count.
In terms of determining the area to show, I will typically place my elements on pixels that are multiples of 100. So if there's a sprite with a bunch of 64x64 pixel icons, I'll typically have them at (0, 100), (0, 200), (0, 300), etc.
This way, I don't have to type in an exact measurement (or any other developer for that matter) and save keystrokes when setting all my background-position properties.