2d-graphics.jd revision c2ad241504fcaa12d4579d3b0b4038d1ca8d08c9
1page.title=2D Graphics 2parent.title=2D and 3D Graphics 3parent.link=index.html 4@jd:body 5 6 7<div id="qv-wrapper"> 8 <div id="qv"> 9 <h2>In this document</h2> 10 <ol> 11 <li><a href="#drawables">Drawables</a> 12 <ol> 13 <li><a href="#drawable-images">Creating from resource images</a></li> 14 <li><a href="#drawable-xml">Creating from resource XML</a></li> 15 </ol> 16 </li> 17 <li><a href="#shape-drawable">ShapeDrawable</a></li> 18 <!-- <li><a href="#state-list">StateListDrawable</a></li> --> 19 <li><a href="#nine-patch">NinePatchDrawable</a></li> 20 <li><a href="#tween-animation">Tween Animation</a></li> 21 <li><a href="#frame-animation">Frame Animation</a></li> 22 </ol> 23 </div> 24</div> 25 26<p>Android offers a custom 2D graphics library for drawing and animating shapes and images. 27The {@link android.graphics.drawable} and {@link android.view.animation} 28packages are where you'll find the common classes used for drawing and animating in two-dimensions. 29</p> 30 31<p>This document offers an introduction to drawing graphics in your Android application. 32We'll discuss the basics of using Drawable objects to draw 33graphics, how to use a couple subclasses of the Drawable class, and how to 34create animations that either tween (move, stretch, rotate) a single graphic 35or animate a series of graphics (like a roll of film).</p> 36 37 38<h2 id="drawables">Drawables</h2> 39 40<p>A {@link android.graphics.drawable.Drawable} is a general abstraction for "something that can be drawn." 41You'll discover that the Drawable class extends to define a variety of specific kinds of drawable graphics, 42including {@link android.graphics.drawable.BitmapDrawable}, {@link android.graphics.drawable.ShapeDrawable}, 43{@link android.graphics.drawable.PictureDrawable}, {@link android.graphics.drawable.LayerDrawable}, and several more. 44Of course, you can also extend these to define your own custom Drawable objects that behave in unique ways.</p> 45 46<p>There are three ways to define and instantiate a Drawable: using an image saved in your project resouces; 47using an XML file that defines the Drawable properties; or using the normal class constructors. Below, we'll discuss 48each the first two techniques (using constructors is nothing new for an experienced developer).</p> 49 50 51<h3 id="drawables-from-images">Creating from resource images</h3> 52 53<p>A simple way to add graphics to your application is by referencing an image file from your project resources. 54Supported file types are PNG (preferred), JPG (acceptable) and GIF (discouraged). This technique would 55obviously be preferred for application icons, logos, or other graphics such as those used in a game.</p> 56 57<p>To use an image resource, just add your file to the <code>res/drawable/</code> directory of your project. 58From there, you can reference it from your code or your XML layout. 59Either way, it is referred using a resource ID, which is the file name without the file type 60extension (E.g., <code>my_image.png</code> is referenced as <var>my_image</var>).</p> 61 62<h4>Example code</h4> 63<p>The following code snippet demonstrates how to build an {@link android.widget.ImageView} that uses an image 64from drawable resources and add it to the layout.</p> 65<pre> 66LinearLayout mLinearLayout; 67 68protected void onCreate(Bundle savedInstanceState) { 69 super.onCreate(savedInstanceState); 70 71 // Create a LinearLayout in which to add the ImageView 72 mLinearLayout = new LinearLayout(this); 73 74 // Instantiate an ImageView and define its properties 75 ImageView i = new ImageView(this); 76 i.setImageResource(R.drawable.my_image); 77 i.setAdjustViewBounds(true); // set the ImageView bounds to match the Drawable's dimensions 78 i.setLayoutParams(new Gallery.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT)); 79 80 // Add the ImageView to the layout and set the layout as the content view 81 mLinearLayout.addView(i); 82 setContentView(mLinearLayout); 83} 84</pre> 85<p>In other cases, you may want to handle your image resource as a 86{@link android.graphics.drawable.Drawable} object. 87To do so, create a Drawable from the resource like so: 88<pre> 89Resources res = mContext.getResources(); 90Drawable myImage = res.getDrawable(R.drawable.my_image); 91</pre> 92 93<p class="caution"><strong>Caution:</strong> Each unique resource in your project can maintain only one 94state, no matter how many different objects you may instantiate for it. For example, if you instantiate two 95Drawable objects from the same image resource, then change a property (such as the alpha) for one of the 96Drawables, then it will also affect the other. So when dealing with multiple instances of an image resource, 97instead of directly transforming the Drawable, you should perform a <a href="#tween-animation">tween animation</a>.</p> 98 99 100<h4>Example XML</h4> 101<p>The XML snippet below shows how to add a resource Drawable to an 102{@link android.widget.ImageView} in the XML layout (with some red tint just for fun). 103<pre> 104<ImageView 105 android:layout_width="wrap_content" 106 android:layout_height="wrap_content" 107 android:tint="#55ff0000" 108 android:src="@drawable/my_image"/> 109</pre> 110<p>For more information on using project resources, read about 111 <a href="{@docRoot}guide/topics/resources/index.html">Resources and Assets</a>.</p> 112 113 114<h3 id="drawables-from-xml">Creating from resource XML</h3> 115 116<p>By now, you should be familiar with Android's principles of developing a 117<a href="{@docRoot}guide/topics/ui/index.html">User Interface</a>. Hence, you understand the power 118and flexibility inherent in defining objects in XML. This philosophy caries over from Views to Drawables. 119If there is a Drawable object that you'd like to create, which is not initially dependent on variables defined by 120your applicaton code or user interaction, then defining the Drawable in XML is a good option. 121Even if you expect your Drawable to change its properties during the user's experience with your application, 122you should consider defining the object in XML, as you can always modify properties once it is instantiated.</p> 123 124<p>Once you've defined your Drawable in XML, save the file in the <code>res/drawable/</code> directory of 125your project. Then, retrieve and instantiate the object by calling 126{@link android.content.res.Resources#getDrawable(int) Resources.getDrawable()}, passing it the resource ID 127of your XML file. (See the <a href="#drawable-xml-example">example below</a>.)</p> 128 129<p>Any Drawable subclass that supports the <code>inflate()</code> method can be defined in 130XML and instantiated by your application. 131Each Drawable that supports XML inflation utilizes specific XML attributes that help define the object 132properties (see the class reference to see what these are). See the class documentation for each 133Drawable subclass for information on how to define it in XML. 134 135<h4 id="drawable-xml-example">Example</h4> 136<p>Here's some XML that defines a TransitionDrawable:</p> 137<pre> 138<transition xmlns:android="http://schemas.android.com/apk/res/android"> 139 <item android:drawable="@drawable/image_expand"> 140 <item android:drawable="@drawable/image_collapse"> 141</transition> 142</pre> 143 144<p>With this XML saved in the file <code>res/drawable/expand_collapse.xml</code>, 145the following code will instantiate the TransitionDrawable and set it as the content of an ImageView:</p> 146<pre> 147Resources res = mContext.getResources(); 148TransitionDrawable transition = (TransitionDrawable) res.getDrawable(R.drawable.expand_collapse); 149ImageView image = (ImageView) findViewById(R.id.toggle_image); 150image.setImageDrawable(transition); 151</pre> 152<p>Then this transition can be run forward (for 1 second) with:</p> 153<pre>transition.startTransition(1000);</pre> 154 155<p>Refer to the Drawable classes listed above for more information on the XML attributes supported by each.</p> 156 157 158 159<h2 id="shape-drawable">ShapeDrawable</h2> 160 161<p>When you want to dynamically draw some two-dimensional graphics, a {@link android.graphics.drawable.ShapeDrawable} 162object will probably suit your needs. With a ShapeDrawable, you can programmatically draw 163primitive shapes and style them in any way imaginable.</p> 164 165<p>A ShapeDrawable is an extension of {@link android.graphics.drawable.Drawable}, so you can use one where ever 166a Drawable is expected — perhaps for the background of a View, set with 167{@link android.view.View#setBackgroundDrawable(android.graphics.drawable.Drawable) setBackgroundDrawable()}. 168Of course, you can also draw your shape as its own custom {@link android.view.View}, 169to be added to your layout however you please. 170Because the ShapeDrawable has its own <code>draw()</code> method, you can create a subclass of View that 171draws the ShapeDrawable during the <code>View.onDraw()</code> method. 172Here's a basic extension of the View class that does just this, to draw a ShapeDrawable as a View:</p> 173<pre> 174public class CustomDrawableView extends View { 175 private ShapeDrawable mDrawable; 176 177 public CustomDrawableView(Context context) { 178 super(context); 179 180 int x = 10; 181 int y = 10; 182 int width = 300; 183 int height = 50; 184 185 mDrawable = new ShapeDrawable(new OvalShape()); 186 mDrawable.getPaint().setColor(0xff74AC23); 187 mDrawable.setBounds(x, y, x + width, y + height); 188 } 189 190 protected void onDraw(Canvas canvas) { 191 mDrawable.draw(canvas); 192 } 193} 194</pre> 195 196<p>In the constructor, a ShapeDrawable is defines as an {@link android.graphics.drawable.shapes.OvalShape}. 197It's then given a color and the bounds of the shape are set. If you do not set the bounds, then the 198shape will not be drawn, whereas if you don't set the color, it will default to black.</p> 199<p>With the custom View defined, it can be drawn any way you like. With the sample above, we can 200draw the shape progammatically in an Activity:</p> 201<pre> 202CustomDrawableView mCustomDrawableView; 203 204protected void onCreate(Bundle savedInstanceState) { 205 super.onCreate(savedInstanceState); 206 mCustomDrawableView = new CustomDrawableView(this); 207 208 setContentView(mCustomDrawableView); 209} 210</pre> 211 212<p>If you'd like to draw this custom drawable from the XML layout instead of from the Activity, 213then the CustomDrawable class must override the {@link android.view.View#View(android.content.Context, android.util.AttributeSet) View(Context, AttributeSet)} constructor, which is called when 214instantiating a View via inflation from XML. Then add a CustomDrawable element to the XML, 215like so:</p> 216<pre> 217<com.example.shapedrawable.CustomDrawableView 218 android:layout_width="fill_parent" 219 android:layout_height="wrap_content" 220 /> 221</pre> 222 223<p>The ShapeDrawable class (like many other Drawable types in the {@link android.graphics.drawable} package) 224allows you to define various properties of the drawable with public methods. 225Some properties you might want to adjust include 226alpha transparency, color filter, dither, opacity and color.</p> 227 228<!-- TODO 229<h2 id="state-list">StateListDrawable</h2> 230 231<p>A StateListDrawable is an extension of the DrawableContainer class, making it little different. 232The primary distinction is that the 233StateListDrawable manages a collection of images for the Drawable, instead of just one. 234This means that it can switch the image when you want, without switching objects. However, the 235intention of the StateListDrawable is to automatically change the image used based on the state 236of the object it's attached to. 237--> 238 239<h2 id="nine-patch">NinePatchDrawable</h2> 240 241<p>A {@link android.graphics.drawable.NinePatchDrawable} graphic is a stretchable bitmap image, which Android 242will automatically resize to accomodate the contents of the View in which you have placed it as the background. 243An example use of a NinePatch is the backgrounds used by standard Android buttons — 244buttons must stretch to accommodate strings of various lengths. A NinePatch drawable is a standard PNG 245image that includes an extra 1-pixel-wide border. It must be saved with the extension <code>.9.png</code>, 246and saved into the <code>res/drawable/</code> directory of your project. 247</p> 248<p> 249 The border is used to define the stretchable and static areas of 250 the image. You indicate a stretchable section by drawing one (or more) 1-pixel-wide 251 black line(s) in the left and top part of the border. (You can have as 252 many stretchable sections as you want.) The relative size of the stretchable 253 sections stays the same, so the largest sections always remain the largest. 254</p> 255<p> 256 You can also define an optional drawable section of the image (effectively, 257 the padding lines) by drawing a line on the right and bottom lines. 258 If a View object sets the NinePatch as its background and then specifies the 259 View's text, it will stretch itself so that all the text fits inside only 260 the area designated by the right and bottom lines (if included). If the 261 padding lines are not included, Android uses the left and top lines to 262 define this drawable area. 263</p> 264<p>To clarify the difference between the different lines, the left and top lines define 265which pixels of the image are allowed to be replicated in order to strech the image. 266The bottom and right lines define the relative area within the image that the contents 267of the View are allowed to lie within.</p> 268<p> 269 Here is a sample NinePatch file used to define a button: 270</p> 271 <img src="{@docRoot}images/ninepatch_raw.png" alt="" /> 272 273<p>This NinePatch defines one stretchable area with the left and top lines 274and the drawable area with the bottom and right lines. In the top image, the dotted grey 275lines identify the regions of the image that will be replicated in order to strech the image. The pink 276rectangle in the bottom image identifies the region in which the contents of the View are allowed. 277If the contents don't fit in this region, then the image will be stretched so that they do. 278</p> 279 280<p>The <a href="{@docRoot}guide/developing/tools/draw9patch.html">Draw 9-patch</a> tool offers 281 an extremely handy way to create your NinePatch images, using a WYSIWYG graphics editor. It 282even raises warnings if the region you've defined for the stretchable area is at risk of 283producing drawing artifacts as a result of the pixel replication. 284</p> 285 286<h3>Example XML</h3> 287 288<p>Here's some sample layout XML that demonstrates how to add a NinePatch image to a 289couple of buttons. (The NinePatch image is saved as <code>res/drawable/my_button_background.9.png</code> 290<pre> 291<Button id="@+id/tiny" 292 android:layout_width="wrap_content" 293 android:layout_height="wrap_content" 294 android:layout_alignParentTop="true" 295 android:layout_centerInParent="true" 296 android:text="Tiny" 297 android:textSize="8sp" 298 android:background="@drawable/my_button_background"/> 299 300<Button id="@+id/big" 301 android:layout_width="wrap_content" 302 android:layout_height="wrap_content" 303 android:layout_alignParentBottom="true" 304 android:layout_centerInParent="true" 305 android:text="Biiiiiiig text!" 306 android:textSize="30sp" 307 android:background="@drawable/my_button_background"/> 308</pre> 309<p>Note that the width and height are set to "wrap_content" to make the button fit neatly around the text. 310</p> 311 312<p>Below are the two buttons rendered from the XML and NinePatch image shown above. 313Notice how the width and height of the button varies with the text, and the background image 314stretches to accommodate it. 315</p> 316 317<img src="{@docRoot}images/ninepatch_examples.png" alt=""/> 318 319 320<h2 id="tween-animation">Tween Animation</h2> 321 322<p>A tween animation can perform a series of simple transformations (position, size, rotation, and transparency) on 323the contents of a View object. So, if you have a TextView object, you can move, rotate, grow, or shrink the text. 324If it has a background image, the background image will be transformed along with the text. 325The {@link android.view.animation animation package} provides all the classes used in a tween animation.</p> 326 327<p>A sequence of animation instructions defines the twen animation, defined by either XML or Android code. 328Like defining a layout, an XML file is recommended because it's more readable, reusable, and swappable 329than hard-coding the animation. In the example below, we use XML. (To learn more about defining an animation 330in your application code, instead of XML, refer to the 331{@link android.view.animation.AnimationSet} class and other {@link android.view.animation.Animation} subclasses.)</p> 332 333<p>The animation instructions define the transformations that you want to occur, when they will occur, 334and how long they should take to apply. Transformations can be sequential or simultaneous — 335for example, you can have the contents of a TextView move from left to right, and then 336rotate 180 degrees, or you can have the text move and rotate simultaneously. Each transformation 337takes a set of parameters specific for that transformation (starting size and ending size 338for size change, starting angle and ending angle for rotation, and so on), and 339also a set of common parameters (for instance, start time and duration). To make 340several transformations happen simultaneously, give them the same start time; 341to make them sequential, calculate the start time plus the duration of the preceding transformation. 342</p> 343 344<p>The animation XML file belongs in the <code>res/anim/</code> directory of your Android project. 345The file must have a single root element: this will be either a single <code><alpha></code>, 346<code><scale></code>, <code><translate></code>, <code><rotate></code>, interpolator element, 347or <code><set></code> element that holds groups of these elements (which may include another 348<code><set></code>). By default, all animation instructions are applied simultaneously. 349To make them occur sequentially, you must specify the <code>startOffset</code> attribute, as shown in the example below. 350</p> 351 352<p>The following XML from one of the ApiDemos is used to stretch, 353then simultaneously spin and rotate a View object. 354</p> 355<pre> 356<set android:shareInterpolator="false"> 357 <scale 358 android:interpolator="@android:anim/accelerate_decelerate_interpolator" 359 android:fromXScale="1.0" 360 android:toXScale="1.4" 361 android:fromYScale="1.0" 362 android:toYScale="0.6" 363 android:pivotX="50%" 364 android:pivotY="50%" 365 android:fillAfter="false" 366 android:duration="700" /> 367 <set android:interpolator="@android:anim/decelerate_interpolator"> 368 <scale 369 android:fromXScale="1.4" 370 android:toXScale="0.0" 371 android:fromYScale="0.6" 372 android:toYScale="0.0" 373 android:pivotX="50%" 374 android:pivotY="50%" 375 android:startOffset="700" 376 android:duration="400" 377 android:fillBefore="false" /> 378 <rotate 379 android:fromDegrees="0" 380 android:toDegrees="-45" 381 android:toYScale="0.0" 382 android:pivotX="50%" 383 android:pivotY="50%" 384 android:startOffset="700" 385 android:duration="400" /> 386 </set> 387</set> 388</pre> 389<p>Screen coordinates (not used in this example) are (0,0) at the upper left hand corner, 390and increase as you go down and to the right.</p> 391 392<p>Some values, such as pivotX, can be specified relative to the object itself or relative to the parent. 393Be sure to use the proper format for what you want ("50" for 50% relative to the parent, or "50%" for 50% 394relative to itself).</p> 395 396<p>You can determine how a transformation is applied over time by assigning an 397{@link android.view.animation.Interpolator}. Android includes 398several Interpolator subclasses that specify various speed curves: for instance, 399{@link android.view.animation.AccelerateInterpolator} tells 400a transformation to start slow and speed up. Each one has an attribute value that can be applied in the XML.</p> 401 402<p>With this XML saved as <code>hyperspace_jump.xml</code> in the <code>res/anim/</code> directory of the 403project, the following Java code will reference it and apply it to an {@link android.widget.ImageView} object 404from the layout. 405</p> 406<pre> 407ImageView spaceshipImage = (ImageView) findViewById(R.id.spaceshipImage); 408Animation hyperspaceJumpAnimation = AnimationUtils.loadAnimation(this, R.anim.hyperspace_jump); 409spaceshipImage.startAnimation(hyperspaceJumpAnimation); 410</pre> 411 412<p>As an alternative to <code>startAnimation()</code>, you can define a starting time for the animation with 413<code>{@link android.view.animation.Animation#setStartTime(long) Animation.setStartTime()}</code>, 414then assign the animation to the View with 415<code>{@link android.view.View#setAnimation(android.view.animation.Animation) View.setAnimation()}</code>. 416</p> 417 418<p>For more information on the XML syntax, available tags and attributes, see the discussion on animation 419in the <a href="{@docRoot}guide/topics/resources/available-resources.html#animation">Available Resources</a>.</p> 420 421<p class="note"><strong>Note:</strong> Regardless of how your animation may move or resize, the bounds of the 422View that holds your animation will not automatically adjust to accomodate it. Even so, the animation will still 423be drawn beyond the bounds of its View and will not be clipped. However, clipping <em>will occur</em> 424if the animation exceeds the bounds of the parent View.</p> 425 426 427<h2 id="frame-animation">Frame Animation</h2> 428 429<p>This is a traditional animation in the sense that it is created with a sequence of different 430images, played in order, like a roll of film. The {@link android.graphics.drawable.AnimationDrawable} 431class is the basis for frame animations.</p> 432 433<p>While you can define the frames of an animation in your code, using the 434{@link android.graphics.drawable.AnimationDrawable} class API, it's more simply accomplished with a single XML 435file that lists the frames that compose the animation. Like the tween animation above, the XML file for this kind 436of animation belongs in the <code>res/anim/</code> directory of your Android project. In this case, 437the instructions are the order and duration for each frame of the animation.</p> 438 439<p>The XML file consists of an <code><animation-list></code> element as the root node and a series 440of child <code><item></code> nodes that each define a frame: a drawable resource for the frame and the frame duration. 441Here's an example XML file for a frame-by-frame animation:</p> 442<pre> 443<animation-list xmlns:android="http://schemas.android.com/apk/res/android" 444 android:oneshot="true"> 445 <item android:drawable="@drawable/rocket_thrust1" android:duration="200" /> 446 <item android:drawable="@drawable/rocket_thrust2" android:duration="200" /> 447 <item android:drawable="@drawable/rocket_thrust3" android:duration="200" /> 448</animation-list> 449</pre> 450 451<p>This animation runs for just three frames. By setting the <code>android:oneshot</code> attribute of the 452list to <var>true</var>, it will cycle just once then stop and hold on the last frame. If it is set <var>false</var> then 453the animation will loop. With this XML saved as <code>rocket_thrust.xml</code> in the <code>res/anim/</code> directory 454of the project, it can be added as the background image to a View and then called to play. Here's an example Activity, 455in which the animation is added to an {@link android.widget.ImageView} and then animated when the screen is touched:</p> 456<pre> 457AnimationDrawable rocketAnimation; 458 459public void onCreate(Bundle savedInstanceState) { 460 super.onCreate(savedInstanceState); 461 setContentView(R.layout.main); 462 463 ImageView rocketImage = (ImageView) findViewById(R.id.rocket_image); 464 rocketImage.setBackgroundResource(R.anim.rocket_thrust); 465 rocketAnimation = (AnimationDrawable) rocketImage.getBackground(); 466} 467 468public boolean onTouchEvent(MotionEvent event) { 469 if (event.getAction() == MotionEvent.ACTION_DOWN) { 470 rocketAnimation.start(); 471 return true; 472 } 473 return super.onTouchEvent(event); 474} 475</pre> 476<p>It's important to note that the <code>start()</code> method called on the AnimationDrawable cannot be 477called during the <code>onCreate()</code> method of your Activity, because the AnimationDrawable is not yet fully attached 478to the window. If you want to play the animation immediately, without 479requiring interaction, then you might want to call it from the 480<code>{@link android.app.Activity#onWindowFocusChanged(boolean) onWindowFocusChanged()}</code> method in 481your Activity, which will get called when Android brings your window into focus.</p> 482 483 484