2d-graphics.jd revision b2a3dd88a53cc8c6d19f6dc8ec4f3d6c4abd9b54
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>Drawable myImage = Resources.getDrawable(R.drawable.my_image);</pre> 89 90<p class="caution"><strong>Caution:</strong> Each unique resource in your project can maintain only one 91state, no matter how many different objects you may instantiate for it. For example, if you instantiate two 92Drawable objects from the same image resource, then change a property (such as the alpha) for one of the 93Drawables, then it will also affect the other. So when dealing with multiple instances of an image resource, 94instead of directly transforming the Drawable, you should perform a <a href="#tween-animation">tween animation</a>.</p> 95 96 97<h4>Example XML</h4> 98<p>The XML snippet below shows how to add a resource Drawable to an 99{@link android.widget.ImageView} in the XML layout (with some red tint just for fun). 100<pre> 101<ImageView 102 android:layout_width="wrap_content" 103 android:layout_height="wrap_content" 104 android:tint="#55ff0000" 105 android:src="@drawable/my_image"/> 106</pre> 107<p>For more information on using project resources, read about 108 <a href="{@docRoot}guide/topics/resources/index.html">Resources and Assets</a>.</p> 109 110 111<h3 id="drawables-from-xml">Creating from resource XML</h3> 112 113<p>By now, you should be familiar with Android's principles of developing a 114<a href="{@docRoot}guide/topics/ui/index.html">User Interface</a>. Hence, you understand the power 115and flexibility inherent in defining objects in XML. This philosophy caries over from Views to Drawables. 116If there is a Drawable object that you'd like to create, which is not initially dependent on variables defined by 117your applicaton code or user interaction, then defining the Drawable in XML is a good option. 118Even if you expect your Drawable to change its properties during the user's experience with your application, 119you should consider defining the object in XML, as you can always modify properties once it is instantiated.</p> 120 121<p>Once you've defined your Drawable in XML, save the file in the <code>res/drawable/</code> directory of 122your project. Then, retrieve and instantiate the object by calling 123{@link android.content.res.Resources#getDrawable(int) Resources.getDrawable()}, passing it the resource ID 124of your XML file. (See the <a href="#drawable-xml-example">example below</a>.)</p> 125 126<p>Any Drawable subclass that supports the <code>inflate()</code> method can be defined in 127XML and instantiated by your application. 128Each Drawable that supports XML inflation utilizes specific XML attributes that help define the object 129properties (see the class reference to see what these are). See the class documentation for each 130Drawable subclass for information on how to define it in XML. 131 132<h4 id="drawable-xml-example">Example</h4> 133<p>Here's some XML that defines a TransitionDrawable:</p> 134<pre> 135<transition xmlns:android="http://schemas.android.com/apk/res/android"> 136 <item android:drawable="@drawable/image_expand"> 137 <item android:drawable="@drawable/image_collapse"> 138</transition> 139</pre> 140 141<p>With this XML saved in the file <code>res/drawable/expand_collapse.xml</code>, 142the following code will instantiate the TransitionDrawable and set it as the content of an ImageView:</p> 143<pre> 144Resources res = mContext.getResources(); 145TransitionDrawable transition = (TransitionDrawable) res.getDrawable(R.drawable.expand_collapse); 146ImageView image = (ImageView) findViewById(R.id.toggle_image); 147image.setImageDrawable(transition); 148</pre> 149<p>Then this transition can be run forward (for 1 second) with:</p> 150<pre>transition.startTransition(1000);</pre> 151 152<p>Refer to the Drawable classes listed above for more information on the XML attributes supported by each.</p> 153 154 155 156<h2 id="shape-drawable">ShapeDrawable</h2> 157 158<p>When you want to dynamically draw some two-dimensional graphics, a {@link android.graphics.drawable.ShapeDrawable} 159object will probably suit your needs. With a ShapeDrawable, you can programmatically draw 160primitive shapes and style them in any way imaginable.</p> 161 162<p>A ShapeDrawable is an extension of {@link android.graphics.drawable.Drawable}, so you can use one where ever 163a Drawable is expected — perhaps for the background of a View, set with 164{@link android.view.View#setBackgroundDrawable(android.graphics.drawable.Drawable) setBackgroundDrawable()}. 165Of course, you can also draw your shape as its own custom {@link android.view.View}, 166to be added to your layout however you please. 167Because the ShapeDrawable has its own <code>draw()</code> method, you can create a subclass of View that 168draws the ShapeDrawable during the <code>View.onDraw()</code> method. 169Here's a basic extension of the View class that does just this, to draw a ShapeDrawable as a View:</p> 170<pre> 171public class CustomDrawableView extends View { 172 private ShapeDrawable mDrawable; 173 174 public CustomDrawableView(Context context) { 175 super(context); 176 177 int x = 10; 178 int y = 10; 179 int width = 300; 180 int height = 50; 181 182 mDrawable = new ShapeDrawable(new OvalShape()); 183 mDrawable.getPaint().setColor(0xff74AC23); 184 mDrawable.setBounds(x, y, x + width, y + height); 185 } 186 187 protected void onDraw(Canvas canvas) { 188 mDrawable.draw(canvas); 189 } 190} 191</pre> 192 193<p>In the constructor, a ShapeDrawable is defines as an {@link android.graphics.drawable.shapes.OvalShape}. 194It's then given a color and the bounds of the shape are set. If you do not set the bounds, then the 195shape will not be drawn, whereas if you don't set the color, it will default to black.</p> 196<p>With the custom View defined, it can be drawn any way you like. With the sample above, we can 197draw the shape progammatically in an Activity:</p> 198<pre> 199CustomDrawableView mCustomDrawableView; 200 201protected void onCreate(Bundle savedInstanceState) { 202 super.onCreate(savedInstanceState); 203 mCustomDrawableView = new CustomDrawableView(this); 204 205 setContentView(mCustomDrawableView); 206} 207</pre> 208 209<p>If you'd like to draw this custom drawable from the XML layout instead of from the Activity, 210then 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 211instantiating a View via inflation from XML. Then add a CustomDrawable element to the XML, 212like so:</p> 213<pre> 214<com.example.shapedrawable.CustomDrawableView 215 android:layout_width="fill_parent" 216 android:layout_height="wrap_content" 217 /> 218</pre> 219 220<p>The ShapeDrawable class (like many other Drawable types in the {@link android.graphics.drawable} package) 221allows you to define various properties of the drawable with public methods. 222Some properties you might want to adjust include 223alpha transparency, color filter, dither, opacity and color.</p> 224 225<!-- TODO 226<h2 id="state-list">StateListDrawable</h2> 227 228<p>A StateListDrawable is an extension of the DrawableContainer class, making it little different. 229The primary distinction is that the 230StateListDrawable manages a collection of images for the Drawable, instead of just one. 231This means that it can switch the image when you want, without switching objects. However, the 232intention of the StateListDrawable is to automatically change the image used based on the state 233of the object it's attached to. 234--> 235 236<h2 id="nine-patch">NinePatchDrawable</h2> 237 238<p>A {@link android.graphics.drawable.NinePatchDrawable} graphic is a stretchable bitmap image, which Android 239will automatically resize to accomodate the contents of the View in which you have placed it as the background. 240An example use of a NinePatch is the backgrounds used by standard Android buttons — 241buttons must stretch to accommodate strings of various lengths. A NinePatch drawable is a standard PNG 242image that includes an extra 1-pixel-wide border. It must be saved with the extension <code>.9.png</code>, 243and saved into the <code>res/drawable/</code> directory of your project. 244</p> 245<p> 246 The border is used to define the stretchable and static areas of 247 the image. You indicate a stretchable section by drawing one (or more) 1-pixel-wide 248 black line(s) in the left and top part of the border. (You can have as 249 many stretchable sections as you want.) The relative size of the stretchable 250 sections stays the same, so the largest sections always remain the largest. 251</p> 252<p> 253 You can also define an optional drawable section of the image (effectively, 254 the padding lines) by drawing a line on the right and bottom lines. 255 If a View object sets the NinePatch as its background and then specifies the 256 View's text, it will stretch itself so that all the text fits inside only 257 the area designated by the right and bottom lines (if included). If the 258 padding lines are not included, Android uses the left and top lines to 259 define this drawable area. 260</p> 261<p>To clarify the difference between the different lines, the left and top lines define 262which pixels of the image are allowed to be replicated in order to strech the image. 263The bottom and right lines define the relative area within the image that the contents 264of the View are allowed to lie within.</p> 265<p> 266 Here is a sample NinePatch file used to define a button: 267</p> 268 <img src="{@docRoot}images/ninepatch_raw.png" alt="" /> 269 270<p>This NinePatch defines one stretchable area with the left and top lines 271and the drawable area with the bottom and right lines. In the top image, the dotted grey 272lines identify the regions of the image that will be replicated in order to strech the image. The pink 273rectangle in the bottom image identifies the region in which the contents of the View are allowed. 274If the contents don't fit in this region, then the image will be stretched so that they do. 275</p> 276 277<p>The <a href="{@docRoot}guide/developing/tools/draw9patch.html">Draw 9-patch</a> tool offers 278 an extremely handy way to create your NinePatch images, using a WYSIWYG graphics editor. It 279even raises warnings if the region you've defined for the stretchable area is at risk of 280producing drawing artifacts as a result of the pixel replication. 281</p> 282 283<h3>Example XML</h3> 284 285<p>Here's some sample layout XML that demonstrates how to add a NinePatch image to a 286couple of buttons. (The NinePatch image is saved as <code>res/drawable/my_button_background.9.png</code> 287<pre> 288<Button id="@+id/tiny" 289 android:layout_width="wrap_content" 290 android:layout_height="wrap_content" 291 android:layout_alignParentTop="true" 292 android:layout_centerInParent="true" 293 android:text="Tiny" 294 android:textSize="8sp" 295 android:background="@drawable/my_button_background"/> 296 297<Button id="@+id/big" 298 android:layout_width="wrap_content" 299 android:layout_height="wrap_content" 300 android:layout_alignParentBottom="true" 301 android:layout_centerInParent="true" 302 android:text="Biiiiiiig text!" 303 android:textSize="30sp" 304 android:background="@drawable/my_button_background"/> 305</pre> 306<p>Note that the width and height are set to "wrap_content" to make the button fit neatly around the text. 307</p> 308 309<p>Below are the two buttons rendered from the XML and NinePatch image shown above. 310Notice how the width and height of the button varies with the text, and the background image 311stretches to accommodate it. 312</p> 313 314<img src="{@docRoot}images/ninepatch_examples.png" alt=""/> 315 316 317<h2 id="tween-animation">Tween Animation</h2> 318 319<p>A tween animation can perform a series of simple transformations (position, size, rotation, and transparency) on 320the contents of a View object. So, if you have a TextView object, you can move, rotate, grow, or shrink the text. 321If it has a background image, the background image will be transformed along with the text. 322The {@link android.view.animation animation package} provides all the classes used in a tween animation.</p> 323 324<p>A sequence of animation instructions defines the twen animation, defined by either XML or Android code. 325Like defining a layout, an XML file is recommended because it's more readable, reusable, and swappable 326than hard-coding the animation. In the example below, we use XML. (To learn more about defining an animation 327in your application code, instead of XML, refer to the 328{@link android.view.animation.AnimationSet} class and other {@link android.view.animation.Animation} subclasses.)</p> 329 330<p>The animation instructions define the transformations that you want to occur, when they will occur, 331and how long they should take to apply. Transformations can be sequential or simultaneous — 332for example, you can have the contents of a TextView move from left to right, and then 333rotate 180 degrees, or you can have the text move and rotate simultaneously. Each transformation 334takes a set of parameters specific for that transformation (starting size and ending size 335for size change, starting angle and ending angle for rotation, and so on), and 336also a set of common parameters (for instance, start time and duration). To make 337several transformations happen simultaneously, give them the same start time; 338to make them sequential, calculate the start time plus the duration of the preceding transformation. 339</p> 340 341<p>The animation XML file belongs in the <code>res/anim/</code> directory of your Android project. 342The file must have a single root element: this will be either a single <code><alpha></code>, 343<code><scale></code>, <code><translate></code>, <code><rotate></code>, interpolator element, 344or <code><set></code> element that holds groups of these elements (which may include another 345<code><set></code>). By default, all animation instructions are applied simultaneously. 346To make them occur sequentially, you must specify the <code>startOffset</code> attribute, as shown in the example below. 347</p> 348 349<p>The following XML from one of the ApiDemos is used to stretch, 350then simultaneously spin and rotate a View object. 351</p> 352<pre> 353<set android:shareInterpolator="false"> 354 <scale 355 android:interpolator="@android:anim/accelerate_decelerate_interpolator" 356 android:fromXScale="1.0" 357 android:toXScale="1.4" 358 android:fromYScale="1.0" 359 android:toYScale="0.6" 360 android:pivotX="50%" 361 android:pivotY="50%" 362 android:fillAfter="false" 363 android:duration="700" /> 364 <set android:interpolator="@android:anim/decelerate_interpolator"> 365 <scale 366 android:fromXScale="1.4" 367 android:toXScale="0.0" 368 android:fromYScale="0.6" 369 android:toYScale="0.0" 370 android:pivotX="50%" 371 android:pivotY="50%" 372 android:startOffset="700" 373 android:duration="400" 374 android:fillBefore="false" /> 375 <rotate 376 android:fromDegrees="0" 377 android:toDegrees="-45" 378 android:toYScale="0.0" 379 android:pivotX="50%" 380 android:pivotY="50%" 381 android:startOffset="700" 382 android:duration="400" /> 383 </set> 384</set> 385</pre> 386<p>Screen coordinates (not used in this example) are (0,0) at the upper left hand corner, 387and increase as you go down and to the right.</p> 388 389<p>Some values, such as pivotX, can be specified relative to the object itself or relative to the parent. 390Be sure to use the proper format for what you want ("50" for 50% relative to the parent, or "50%" for 50% 391relative to itself).</p> 392 393<p>You can determine how a transformation is applied over time by assigning an 394{@link android.view.animation.Interpolator}. Android includes 395several Interpolator subclasses that specify various speed curves: for instance, 396{@link android.view.animation.AccelerateInterpolator} tells 397a transformation to start slow and speed up. Each one has an attribute value that can be applied in the XML.</p> 398 399<p>With this XML saved as <code>hyperspace_jump.xml</code> in the <code>res/anim/</code> directory of the 400project, the following Java code will reference it and apply it to an {@link android.widget.ImageView} object 401from the layout. 402</p> 403<pre> 404ImageView spaceshipImage = (ImageView) findViewById(R.id.spaceshipImage); 405Animation hyperspaceJumpAnimation = AnimationUtils.loadAnimation(this, R.anim.hyperspace_jump); 406spaceshipImage.startAnimation(hyperspaceJumpAnimation); 407</pre> 408 409<p>As an alternative to <code>startAnimation()</code>, you can define a starting time for the animation with 410<code>{@link android.view.animation.Animation#setStartTime(long) Animation.setStartTime()}</code>, 411then assign the animation to the View with 412<code>{@link android.view.View#setAnimation(android.view.animation.Animation) View.setAnimation()}</code>. 413</p> 414 415<p>For more information on the XML syntax, available tags and attributes, see the discussion on animation 416in the <a href="{@docRoot}guide/topics/resources/available-resources.html#animation">Available Resources</a>.</p> 417 418<p class="note"><strong>Note:</strong> Regardless of how your animation may move or resize, the bounds of the 419View that holds your animation will not automatically adjust to accomodate it. Even so, the animation will still 420be drawn beyond the bounds of its View and will not be clipped. However, clipping <em>will occur</em> 421if the animation exceeds the bounds of the parent View.</p> 422 423 424<h2 id="frame-animation">Frame Animation</h2> 425 426<p>This is a traditional animation in the sense that it is created with a sequence of different 427images, played in order, like a roll of film. The {@link android.graphics.drawable.AnimationDrawable} 428class is the basis for frame animations.</p> 429 430<p>While you can define the frames of an animation in your code, using the 431{@link android.graphics.drawable.AnimationDrawable} class API, it's more simply accomplished with a single XML 432file that lists the frames that compose the animation. Like the tween animation above, the XML file for this kind 433of animation belongs in the <code>res/anim/</code> directory of your Android project. In this case, 434the instructions are the order and duration for each frame of the animation.</p> 435 436<p>The XML file consists of an <code><animation-list></code> element as the root node and a series 437of child <code><item></code> nodes that each define a frame: a drawable resource for the frame and the frame duration. 438Here's an example XML file for a frame-by-frame animation:</p> 439<pre> 440<animation-list xmlns:android="http://schemas.android.com/apk/res/android" 441 android:oneshot="true"> 442 <item android:drawable="@drawable/rocket_thrust1" android:duration="200" /> 443 <item android:drawable="@drawable/rocket_thrust2" android:duration="200" /> 444 <item android:drawable="@drawable/rocket_thrust3" android:duration="200" /> 445</animation-list> 446</pre> 447 448<p>This animation runs for just three frames. By setting the <code>android:oneshot</code> attribute of the 449list 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 450the animation will loop. With this XML saved as <code>rocket_thrust.xml</code> in the <code>res/anim/</code> directory 451of the project, it can be added as the background image to a View and then called to play. Here's an example Activity, 452in which the animation is added to an {@link android.widget.ImageView} and then animated when the screen is touched:</p> 453<pre> 454AnimationDrawable rocketAnimation; 455 456public void onCreate(Bundle savedInstanceState) { 457 super.onCreate(savedInstanceState); 458 setContentView(R.layout.main); 459 460 ImageView rocketImage = (ImageView) findViewById(R.id.rocket_image); 461 rocketImage.setBackgroundResource(R.anim.rocket_thrust); 462 rocketAnimation = (AnimationDrawable) rocketImage.getBackground(); 463} 464 465public boolean onTouchEvent(MotionEvent event) { 466 if (event.getAction() == MotionEvent.ACTION_DOWN) { 467 rocketAnimation.start(); 468 return true; 469 } 470 return super.onTouchEvent(event); 471} 472</pre> 473<p>It's important to note that the <code>start()</code> method called on the AnimationDrawable cannot be 474called during the <code>onCreate()</code> method of your Activity, because the AnimationDrawable is not yet fully attached 475to the window. If you want to play the animation immediately, without 476requiring interaction, then you might want to call it from the 477<code>{@link android.app.Activity#onWindowFocusChanged(boolean) onWindowFocusChanged()}</code> method in 478your Activity, which will get called when Android brings your window into focus.</p> 479 480 481