Blurring the Strains. Android RenderEffects #1: the blur… | by Chet Haase | Android Builders | Nov, 2022 | Loop Tech

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Android RenderEffects #1: the blur impact

This text (and the following one) is basically a written model of my half from a video that sumir kataria and recorded for this yr’s Android Developer Summit:

Right here is the video model of this text (and extra!)

Once I began studying how one can use the blur impact, it wasn’t apparent to me how one can incorporate it right into a normal utility, so I believed it’d assist make clear what it is for, the place it matches into Android’s normal rendering toolbox, and how one can create and use blur results.

On the most elementary stage, visible components in Android—resembling buttons, textual content, and different UI or customized components—are sometimes rendered by calls to the Canvas APIs, resembling drawLine(), drawText(), drawBitmap(), and so. These strategies will not be referred to as straight by your code except you might be drawing objects in a customized view, however they’re referred to as in your behalf when UI parts are drawn in your utility.

Most of those drawing instructions present three items of knowledge to the rendering system. You may consider these because the what, the placeY What info for the drawing, the place what is the operation itself (the “primitive” of drawing), the place is the situation (location and dimension) of the thing, and What is the set of drawing attributes. It’s these attributes that concern us as we speak, as a result of that’s the place the blur is available in.

Every drawing primitive tells the renderer what, the place, and the way to attract the thing.

Drawing attributes are supplied by aPaint object, which has default attributes that may be modified by the caller (your utility or the UI system in your behalf). most of Paint APIs are comparatively easy and apparent, like setColor() by the colour that the primitives must be drawn, setStyle() to know if the thing must be crammed or “stroked” (for an object’s define), plus a veritable plethora of textual content attributes that I will not go into right here.

There are additionally extra highly effective and complicated attributes that you could assign to a Paint object. These embrace ColorFilter subclasses (like my private favourite, ColorMatrixColorFilterwhich deserves an award for the LongestAndMostRepetitiveClassRepetitiveNameEver) for altering the colours of the primitives, and shaders. Shaders embrace varied gradient objects along with bitmaps, and supply supply colours from which a draw operation is sampled to offer the ensuing colours of the geometry being drawn. Utilizing shaders permits you, for instance, to fill a rectangle with a linear or round gradient, or use the values ​​of a bitmap to fill or stroke that rectangle as an alternative. (Trailer: There is a new ‘shader’ API in Android 13 that allows you to go a lot additional than these results – keep tuned for the following article on this collection for extra on that.)

All the above APIs can help you set attributes for people draw*() calls, while you need to have an effect on particular person drawing operations (resembling drawing a line inside a customized view). However what if you wish to use attributes for all drawing operations in a View? For instance, what in case you needed to use a colour tint to a button (which internally consists of a number of separate draw operations) or apply a shadow to a button? View?

that is the place RenderEffect is available in. RenderEffect teams a number of shaders and applies them to a set View— or to a RenderNode (the underlying rendering mechanism for Views)—to maintain issues easy by having the renderer apply these results to a whole View. you need to use just one RenderEffect or chain a number of collectively to use a number of results.

When RenderEffect was launched, in API stage 31, it supplied methods to gather current attribute results like ColorFilter , BitmapY Shader in results, along with chaining them, with manufacturing facility strategies like these:

static RenderEffect createBitmapEffect(Bitmap bitmap)
static RenderEffect createColorFilterEffect(ColorFilter colorFilter)
static RenderEffect createShaderEffect(Shader shader)
static RenderEffect createChainEffect(RenderEffect outer,
RenderEffect interior)

However RenderEffect additionally launched a brand new drawing impact alongside the best way: Blur.

Along with objects that encapsulate current ones Paint attributes, RenderEffect additionally launched a brand new impact that permits simple blurring View both RenderNode contents:

static RenderEffect createBlurEffect(float radiusX, float radiusY,
Shader.TileMode edgeTreatment)
static RenderEffect createBlurEffect(float radiusX, float radiusY,
RenderEffect inputEffect,
Shader.TileMode edgeTreatment)

With these strategies, now you can simply create a blur impact on a View (or, utilizing the second overload above, one other RenderEffect) to blur all content material because it renders. Consider it as sending the unique content material of the view via a filter that blurs it alongside the best way. That is primarily what’s taking place, although the precise approach it achieves that is by rendering the content material off-screen, making use of the blur, after which copying the blurred outcome again to the unique vacation spot.

the radius The parameters decide how huge the blur is (what number of pixels exterior of every pixel within the enter supply are blended in every course), and the TileMode determines what occurs on the edges of the blur. This final parameter is required as a result of a blur operates on pixels exterior of the pixel being computed, so it must know what to do when these different pixels are exterior of the enter content material.

After getting created the blur, you’ll be able to set it to a View calling:

View.setRenderEffect(renderEffect RenderEffect)

Equally, you may set it to a RenderNode:

RenderNode.setRenderEffect(renderEffect RenderEffect)

… And that’s! After getting configured the RenderEffect, any drawing that occurs on that object will use the impact you set on it. If you wish to change the attributes of the impact (such because the blur radius), recreate it and set it up once more, as above.

I wrote a easy app to see how blurs may very well be utilized in a UI. Particularly, I needed to exhibit how a blur can be utilized to assist “pop” foreground content material from the background, simply as digital camera focus helps isolate the topic of the picture from the background.

First, I acquired blurs engaged on the background. On this case, that background is a photograph gallery; a structure containing a set of picture thumbnails.

A structure containing picture thumbnails. Clicking on a picture shows an enlarged view of the picture.

Clicking on one of many photographs enlarges it and shows a caption for that photograph. Would not it’s good if we might blur the background so the remainder of the photographs would not create an excessive amount of visible noise once we tried to deal with the foreground picture and its caption?

I added a SeekBar to the app to permit altering the blur dynamically. This isn’t one thing you would wish in a completed app (simply choose a blur that works and keep it up – the consumer will not need to tweak that form of factor, so preserve the UI easy). However I needed to make use of it initially to mess around with completely different blurs and present how one can recreate them with completely different parameters. seekBar passes in a worth from 0 to 50 (the min/max values ​​within the SeekBar consumer interface part).

seekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener
override enjoyable onProgressChanged(seekBar: SeekBar, progress: Int,
fromUser: Boolean)
updateEffect(progress.toFloat())

// begin/cease overrides stubbed out...
)

updateEffect() use the progress worth for a blur radius (I take advantage of the identical worth for x and y). Vital be aware: a worth of 0 is used to point that the blur must be eliminated, which is completed by setting RenderEffect a null. It seems that asking for a blur of radius 0 (mathematically equal to no blur) will crash. 0 apparently not a worth the system expects when requesting a blur impact. That is poorly documented (we’re fixing it…), so I believed you may need to know in case you do that at residence. I do know you have been questioning what was happening when my preliminary code didn’t deal with that worth.

enjoyable updateEffect(progress: Float) 
if (progress > 0)
val blur = RenderEffect.createBlurEffect(
progress, progress, Shader.TileMode.CLAMP)
pictureGrid.setRenderEffect(blur)
else
pictureGrid.setRenderEffect(null)

updateEffect() creates the RenderEffect (or overrides it to take away it), with the progress worth for the radius, then units it within the picture structure, and voilànow we have blur:

Picture gallery with blur RenderEffect utilized to the container

Now that now we have the blur job, it is time to work on the enlarged picture on prime. That impact is dealt with via the brand new AGSL. RuntimeShader on Android 13 and is described in Half 2 of this collection: AGSL: Made within the Shade(r).


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