Android - Drawable 源码学习

/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0 *
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package android.graphics.drawable;

import android.annotation.NonNull;
import android.content.res.ColorStateList;
import android.content.res.Resources;
import android.content.res.Resources.Theme;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.ColorFilter;
import android.graphics.Insets;
import android.graphics.NinePatch;
import android.graphics.Outline;
import android.graphics.PixelFormat;
import android.graphics.PorterDuff;
import android.graphics.PorterDuff.Mode;
import android.graphics.PorterDuffColorFilter;
import android.graphics.Rect;
import android.graphics.Region;
import android.graphics.Xfermode;
import android.os.Trace;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.StateSet;
import android.util.TypedValue;
import android.util.Xml;
import android.view.View;

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;

import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.WeakReference;
import java.util.Arrays;
import java.util.Collection;

/**
* A Drawable is a general abstraction for "something that can be drawn."  Most
* often you will deal with Drawable as the type of resource retrieved for
* drawing things to the screen; the Drawable class provides a generic API for
* dealing with an underlying visual resource that may take a variety of forms.
* Unlike a {@link android.view.View}, a Drawable does not have any facility to
* receive events or otherwise interact with the user.
* Drawable是一个常见的抽象类，意味着可以被绘制的东西。你处理Drawable的大多数情况是把它当
* 做绘制在屏幕上的一种资源。Drawable通过了一些API用于处理不同类型的视觉资源，而不像View。
* Drawable没有任何的接收事件或者和用户交互的特性。
* <p>In addition to simple drawing, Drawable provides a number of generic
* mechanisms for its client to interact with what is being drawn:
* 除了简单的绘制，Drawable通过了一系列机制为客户端和被绘制的对象进行交互。
* <ul>
*     <li> The {@link #setBounds} method <var>must</var> be called to tell the
*     Drawable where it is drawn and how large it should be.  All Drawables
*     should respect the requested size, often simply by scaling their
*     imagery.  A client can find the preferred size for some Drawables with
*     the {@link #getIntrinsicHeight} and {@link #getIntrinsicWidth} methods.
*
*     <li> The {@link #getPadding} method can return from some Drawables
*     information about how to frame content that is placed inside of them.
*     For example, a Drawable that is intended to be the frame for a button
*     widget would need to return padding that correctly places the label
*     inside of itself.
*
*     <li> The {@link #setState} method allows the client to tell the Drawable
*     in which state it is to be drawn, such as "focused", "selected", etc.
*     Some drawables may modify their imagery based on the selected state.
*
*     <li> The {@link #setLevel} method allows the client to supply a single
*     continuous controller that can modify the Drawable is displayed, such as
*     a battery level or progress level.  Some drawables may modify their
*     imagery based on the current level.
*
*     <li> A Drawable can perform animations by calling back to its client
*     through the {@link Callback} interface.  All clients should support this
*     interface (via {@link #setCallback}) so that animations will work.  A
*     simple way to do this is through the system facilities such as
*     {@link android.view.View#setBackground(Drawable)} and
*     {@link android.widget.ImageView}.
* </ul>
*
* Though usually not visible to the application, Drawables may take a variety
* of forms:
*
* <ul>
*     <li> <b>Bitmap</b>: the simplest Drawable, a PNG or JPEG image.
*     <li> <b>Nine Patch</b>: an extension to the PNG format allows it to
*     specify information about how to stretch it and place things inside of
*     it.
*     <li> <b>Shape</b>: contains simple drawing commands instead of a raw
*     bitmap, allowing it to resize better in some cases.
*     <li> <b>Layers</b>: a compound drawable, which draws multiple underlying
*     drawables on top of each other.
*     <li> <b>States</b>: a compound drawable that selects one of a set of
*     drawables based on its state.
*     <li> <b>Levels</b>: a compound drawable that selects one of a set of
*     drawables based on its level.
*     <li> <b>Scale</b>: a compound drawable with a single child drawable,
*     whose overall size is modified based on the current level.
* </ul>
*
* <div class="special reference">
* <h3>Developer Guides</h3>
* <p>For more information about how to use drawables, read the
* <a href="{@docRoot}guide/topics/graphics/2d-graphics.html">Canvas and Drawables</a> developer
* guide. For information and examples of creating drawable resources (XML or bitmap files that
* can be loaded in code), read the
* <a href="{@docRoot}guide/topics/resources/drawable-resource.html">Drawable Resources</a>
* document.</p></div>
*/
public abstract class Drawable {
private static final Rect ZERO_BOUNDS_RECT = new Rect();

static final PorterDuff.Mode DEFAULT_TINT_MODE = PorterDuff.Mode.SRC_IN;

private int[] mStateSet = StateSet.WILD_CARD;
private int mLevel = 0;
private int mChangingConfigurations = 0;
private Rect mBounds = ZERO_BOUNDS_RECT;  // lazily becomes a new Rect()
private WeakReference<Callback> mCallback = null;
private boolean mVisible = true;

private int mLayoutDirection;

/**
* Draw in its bounds (set via setBounds) respecting optional effects such
* as alpha (set via setAlpha) and color filter (set via setColorFilter).
* 在它的边界内绘制一些相关可选的效果，例如透明度，颜色过滤
* @param canvas The canvas to draw into
*/
public abstract void draw(Canvas canvas);

/**
* Specify a bounding rectangle for the Drawable. This is where the drawable
* will draw when its draw() method is called.
* 为Drawable设置一个边界矩形。当draw()方法被调用，这个矩形是drawable会被绘制到的地方。
*/
public void setBounds(int left, int top, int right, int bottom) {
Rect oldBounds = mBounds;

if (oldBounds == ZERO_BOUNDS_RECT) {
oldBounds = mBounds = new Rect();
}

if (oldBounds.left != left || oldBounds.top != top ||
oldBounds.right != right || oldBounds.bottom != bottom) {
if (!oldBounds.isEmpty()) {
// first invalidate the previous bounds
invalidateSelf();
}
mBounds.set(left, top, right, bottom);
onBoundsChange(mBounds);
}
}

/**
* Specify a bounding rectangle for the Drawable. This is where the drawable
* will draw when its draw() method is called.
* 为Drawable设置一个边界矩形。当draw()方法被调用，这个矩形是drawable会被绘制到的地方。
*/
public void setBounds(Rect bounds) {
setBounds(bounds.left, bounds.top, bounds.right, bounds.bottom);
}

/**
* Return a copy of the drawable's bounds in the specified Rect (allocated
* by the caller). The bounds specify where this will draw when its draw()
* method is called.
* 返回Drawable的bounds的复制
* @param bounds Rect to receive the drawable's bounds (allocated by the
*               caller).
*/
public final void copyBounds(Rect bounds) {
bounds.set(mBounds);
}

/**
* Return a copy of the drawable's bounds in a new Rect. This returns the
* same values as getBounds(), but the returned object is guaranteed to not
* be changed later by the drawable (i.e. it retains no reference to this
* rect). If the caller already has a Rect allocated, call copyBounds(rect).
* 返回Drawable的bounds的复制。这个和getBounds()返回一样的值，不过返回的是拷贝，保证
* 这个对象不会被drawabel修改.
* @return A copy of the drawable's bounds
*/
public final Rect copyBounds() {
return new Rect(mBounds);
}

/**
* Return the drawable's bounds Rect. Note: for efficiency, the returned
* object may be the same object stored in the drawable (though this is not
* guaranteed), so if a persistent copy of the bounds is needed, call
* copyBounds(rect) instead.
* You should also not change the object returned by this method as it may
* be the same object stored in the drawable.
* 返回drawable的边界矩形。你不应该修改返回的对象，因为它可能和drawable里面的是同一个
* 引用。
* @return The bounds of the drawable (which may change later, so caller
*         beware). DO NOT ALTER the returned object as it may change the
*         stored bounds of this drawable.
*
* @see #copyBounds()
* @see #copyBounds(android.graphics.Rect)
*/
public final Rect getBounds() {
if (mBounds == ZERO_BOUNDS_RECT) {
mBounds = new Rect();
}

return mBounds;
}

/**
* Return the drawable's dirty bounds Rect. Note: for efficiency, the
* returned object may be the same object stored in the drawable (though
* this is not guaranteed).
* 获取脏的边界矩形。
* <p>
* By default, this returns the full drawable bounds. Custom drawables may
* override this method to perform more precise invalidation.
* 默认返回整个矩形。常见的drawable可能会重载这个方法来实现更精确的失效。
* @return The dirty bounds of this drawable
*/
public Rect getDirtyBounds() {
return getBounds();
}

/**
* Set a mask of the configuration parameters for which this drawable
* may change, requiring that it be re-created.
*
* @param configs A mask of the changing configuration parameters, as
* defined by {@link android.content.pm.ActivityInfo}.
*
* @see android.content.pm.ActivityInfo
*/
public void setChangingConfigurations(int configs) {
mChangingConfigurations = configs;
}

/**
* Return a mask of the configuration parameters for which this drawable
* may change, requiring that it be re-created.  The default implementation
* returns whatever was provided through
* {@link #setChangingConfigurations(int)} or 0 by default.  Subclasses
* may extend this to or in the changing configurations of any other
* drawables they hold.
*
* @return Returns a mask of the changing configuration parameters, as
* defined by {@link android.content.pm.ActivityInfo}.
*
* @see android.content.pm.ActivityInfo
*/
public int getChangingConfigurations() {
return mChangingConfigurations;
}

/**
* Set to true to have the drawable dither its colors when drawn to a device
* with fewer than 8-bits per color component. This can improve the look on
* those devices, but can also slow down the drawing a little.
* 设置为true,当华仔设备生的每个颜色组件小于8位时，保证drawable颜色效果。这个可以提高
* 外观，但是会稍微减慢绘制。
*/
public void setDither(boolean dither) {}

/**
* Set to true to have the drawable filter its bitmap when scaled or rotated
* (for drawables that use bitmaps). If the drawable does not use bitmaps,
* this call is ignored. This can improve the look when scaled or rotated,
* but also slows down the drawing.
* 设置为true,drawable在被缩放或旋转的时候，会过滤它的bitmap(为那些使用bitmap的drawable准备)。
* 如果drawable没有使用bitmap，这个设置会被忽略。在缩放和旋转时这个可以提高外观，但是会稍微减慢绘制。
*/
public void setFilterBitmap(boolean filter) {}

/**
* Implement this interface if you want to create an animated drawable that
* extends {@link android.graphics.drawable.Drawable Drawable}.
* Upon retrieving a drawable, use
* {@link Drawable#setCallback(android.graphics.drawable.Drawable.Callback)}
* to supply your implementation of the interface to the drawable; it uses
* this interface to schedule and execute animation changes.
* 继承这个接口如果你想创建一个继承自drawable动画drawable。对于drawable,使用它的setCallback()
* 方法去提供这个接口的实现。它使用这个接口去定时和执行动画转变。
*/
public static interface Callback {
/**
* Called when the drawable needs to be redrawn.  A view at this point
* should invalidate itself (or at least the part of itself where the
* drawable appears).
* 当drawable需要重绘时，调用这个方法。View在这里应该使自己不可用(或者至少使drawable
* 出现的部分不可用)。
* @param who The drawable that is requesting the update.
*/
public void invalidateDrawable(Drawable who);

/**
* A Drawable can call this to schedule the next frame of its
* animation.  An implementation can generally simply call
* {@link android.os.Handler#postAtTime(Runnable, Object, long)} with
* the parameters <var>(what, who, when)</var> to perform the
* scheduling.
* Drawable通过这个方法去安排动画的下一帧。实现者可以简单地调用android.os.Handler#postAtTime(Runnable, Object, long)
* @param who The drawable being scheduled.
* @param what The action to execute.
* @param when The time (in milliseconds) to run.  The timebase is
*             {@link android.os.SystemClock#uptimeMillis}
*/
public void scheduleDrawable(Drawable who, Runnable what, long when);

/**
* A Drawable can call this to unschedule an action previously
* scheduled with {@link #scheduleDrawable}.  An implementation can
* generally simply call
* {@link android.os.Handler#removeCallbacks(Runnable, Object)} with
* the parameters <var>(what, who)</var> to unschedule the drawable.
* Drawable通过这个方法去取消scheduleDrawable()方法安排的行为。
* @param who The drawable being unscheduled.
* @param what The action being unscheduled.
*/
public void unscheduleDrawable(Drawable who, Runnable what);
}

/**
* Bind a {@link Callback} object to this Drawable.  Required for clients
* that want to support animated drawables.
* 给Drawable绑定一个Callback对象。那些使用动态drawables的客户端会需要。
* @param cb The client's Callback implementation.
*
* @see #getCallback()
*/
public final void setCallback(Callback cb) {
mCallback = new WeakReference<Callback>(cb);
}

/**
* Return the current {@link Callback} implementation attached to this
* Drawable.
* 返回绑定在当前drawable的Callback实现
* @return A {@link Callback} instance or null if no callback was set.
*
* @see #setCallback(android.graphics.drawable.Drawable.Callback)
*/
public Callback getCallback() {
if (mCallback != null) {
return mCallback.get();
}
return null;
}

/**
* Use the current {@link Callback} implementation to have this Drawable
* redrawn.  Does nothing if there is no Callback attached to the
* Drawable.
* 使用当前Callback的实现去使这个Drawable重绘。如果没有为Drawable设置Callable，
* 则什么都不做
* @see Callback#invalidateDrawable
* @see #getCallback()
* @see #setCallback(android.graphics.drawable.Drawable.Callback)
*/
public void invalidateSelf() {
final Callback callback = getCallback();
if (callback != null) {
callback.invalidateDrawable(this);
}
}

/**
* Use the current {@link Callback} implementation to have this Drawable
* scheduled.  Does nothing if there is no Callback attached to the
* Drawable.
* 使用当前Callback的实现去使这个Drawable定时。如果没有为Drawable设置Callable，
* @param what The action being scheduled.
* @param when The time (in milliseconds) to run.
*
* @see Callback#scheduleDrawable
*/
public void scheduleSelf(Runnable what, long when) {
final Callback callback = getCallback();
if (callback != null) {
callback.scheduleDrawable(this, what, when);
}
}

/**
* Use the current {@link Callback} implementation to have this Drawable
* unscheduled.  Does nothing if there is no Callback attached to the
* Drawable.
* 使用当前Callback的实现去使这个Drawable取消定时。如果没有为Drawable设置Callable，
* @param what The runnable that you no longer want called.
*
* @see Callback#unscheduleDrawable
*/
public void unscheduleSelf(Runnable what) {
final Callback callback = getCallback();
if (callback != null) {
callback.unscheduleDrawable(this, what);
}
}

/**
* Returns the resolved layout direction for this Drawable.
* 返回Drawable的布局方向
* @return One of {@link android.view.View#LAYOUT_DIRECTION_LTR},
*   {@link android.view.View#LAYOUT_DIRECTION_RTL}
*
* @hide
*/
public int getLayoutDirection() {
return mLayoutDirection;
}

/**
* Set the layout direction for this drawable. Should be a resolved direction as the
* Drawable as no capacity to do the resolution on his own.
* 为Drawable设置布局方向。当Drawable没有能力解决方向问题的时候使用。
* @param layoutDirection One of {@link android.view.View#LAYOUT_DIRECTION_LTR},
*   {@link android.view.View#LAYOUT_DIRECTION_RTL}
*
* @hide
*/
public void setLayoutDirection(@View.ResolvedLayoutDir int layoutDirection) {
if (getLayoutDirection() != layoutDirection) {
mLayoutDirection = layoutDirection;
}
}

/**
* Specify an alpha value for the drawable. 0 means fully transparent, and
* 255 means fully opaque.
* 设置透明度。0表示完全透明，255表示完全不透明。
*/
public abstract void setAlpha(int alpha);

/**
* Gets the current alpha value for the drawable. 0 means fully transparent,
* 255 means fully opaque. This method is implemented by
* Drawable subclasses and the value returned is specific to how that class treats alpha.
* The default return value is 255 if the class does not override this method to return a value
* specific to its use of alpha.
* 获得当前透明度。这个方法被Drawable的子类使用并且返回值和子类怎么处理透明度有关。
* 默认返回255如果子类没有重载这个方法。
*/
public int getAlpha() {
return 0xFF;
}

/**
* @hide Consider for future API inclusion
* 未来的API
*/
public void setXfermode(Xfermode mode) {
// Base implementation drops it on the floor for compatibility. Whee!
// TODO: For this to be included in the API proper, all framework drawables need impls.
// For right now only BitmapDrawable has it.
}

/**
* Specify an optional color filter for the drawable. Pass {@code null} to
* remove any existing color filter.
* 指定一个颜色过滤器。传入null可以移除当前所有的过滤器。
* @param cf the color filter to apply, or {@code null} to remove the
*            existing color filter
*/
public abstract void setColorFilter(ColorFilter cf);

/**
* Specify a color and Porter-Duff mode to be the color filter for this
* drawable.
* 为过滤器设置颜色和波特达夫模式
*/
public void setColorFilter(int color, PorterDuff.Mode mode) {
setColorFilter(new PorterDuffColorFilter(color, mode));
}

/**
* Specifies a tint for this drawable.
* <p>
* Setting a color filter via {@link #setColorFilter(ColorFilter)} overrides
* tint.
* 设置明调。
* @param tint Color to use for tinting this drawable
* @see #setTintMode(PorterDuff.Mode)
*/
public void setTint(int tint) {
setTintList(ColorStateList.valueOf(tint));
}

/**
* Specifies a tint for this drawable as a color state list.
* <p>
* Setting a color filter via {@link #setColorFilter(ColorFilter)} overrides
* tint.
* 通过一个color state list设置明调
* @param tint Color state list to use for tinting this drawable, or null to
*            clear the tint
* @see #setTintMode(PorterDuff.Mode)
*/
public void setTintList(ColorStateList tint) {}

/**
* Specifies a tint blending mode for this drawable.
* <p>
* Setting a color filter via {@link #setColorFilter(ColorFilter)} overrides
* tint.
* 设置色彩混合模式
* @param tintMode Color state list to use for tinting this drawable, or null to
*            clear the tint
* @param tintMode A Porter-Duff blending mode
*/
public void setTintMode(PorterDuff.Mode tintMode) {}

/**
* Returns the current color filter, or {@code null} if none set.
* 获得当前颜色过滤器
* @return the current color filter, or {@code null} if none set
*/
public ColorFilter getColorFilter() {
return null;
}

/**
* Removes the color filter for this drawable.
* 清楚颜色过滤器
*/
public void clearColorFilter() {
setColorFilter(null);
}

/**
* Specifies the hotspot's location within the drawable.
* 在drawable中指定热区
* @param x The X coordinate of the center of the hotspot
* @param y The Y coordinate of the center of the hotspot
*/
public void setHotspot(float x, float y) {}

/**
* Sets the bounds to which the hotspot is constrained, if they should be
* different from the drawable bounds.
* 如果热区的边界要和drawable的边界不同，那么设置边界
* @param left
* @param top
* @param right
* @param bottom
*/
public void setHotspotBounds(int left, int top, int right, int bottom) {}

/** @hide For internal use only. Individual results may vary. */
public void getHotspotBounds(Rect outRect) {
outRect.set(getBounds());
}

/**
* Whether this drawable requests projection.
* 是否需要投影
* @hide magic!
*/
public boolean isProjected() {
return false;
}

/**
* Indicates whether this drawable will change its appearance based on
* state. Clients can use this to determine whether it is necessary to
* calculate their state and call setState.
* Drawable是否会根据状态改变外观。使用者可以以此决定是否需要去计算它们的状态和
* 设置状态
* @return True if this drawable changes its appearance based on state,
*         false otherwise.
* @see #setState(int[])
*/
public boolean isStateful() {
return false;
}

/**
* Specify a set of states for the drawable. These are use-case specific,
* so see the relevant documentation. As an example, the background for
* widgets like Button understand the following states:
* [{@link android.R.attr#state_focused},
*  {@link android.R.attr#state_pressed}].
* 为drawable设置一系列状态。有一些特殊的使用例子可以看相关文档。例如，Button之类的
* 控件背景，有以下状态focused，pressed
*
* <p>If the new state you are supplying causes the appearance of the
* Drawable to change, then it is responsible for calling
* {@link #invalidateSelf} in order to have itself redrawn, <em>and</em>
* true will be returned from this function.
* 如果你使用的新状态会导致外观变化，那么主动调用nvalidateSelf引起重绘并且该方法将返回true
* <p>Note: The Drawable holds a reference on to <var>stateSet</var>
* until a new state array is given to it, so you must not modify this
* array during that time.</p>
* Drawable持有stateSet的引用直到赋给它一个新的状态数组，所以你必须在这段时间修改数组
* @param stateSet The new set of states to be displayed.
*
* @return Returns true if this change in state has caused the appearance
* of the Drawable to change (hence requiring an invalidate), otherwise
* returns false.
*/
public boolean setState(final int[] stateSet) {
if (!Arrays.equals(mStateSet, stateSet)) {
mStateSet = stateSet;
return onStateChange(stateSet);
}
return false;
}

/**
* Describes the current state, as a union of primitve states, such as
* 返回当前状态数组
* {@link android.R.attr#state_focused},
* {@link android.R.attr#state_selected}, etc.
* Some drawables may modify their imagery based on the selected state.
* @return An array of resource Ids describing the current state.
*/
public int[] getState() {
return mStateSet;
}

/**
* If this Drawable does transition animations between states, ask that
* it immediately jump to the current state and skip any active animations.
* 如果drwaable在状态之间有属性动画，调用这个方法立刻跳到当前状态，跳过所有动画
*/
public void jumpToCurrentState() {
}

/**
* @return The current drawable that will be used by this drawable. For simple drawables, this
*         is just the drawable itself. For drawables that change state like
*         {@link StateListDrawable} and {@link LevelListDrawable} this will be the child drawable
*         currently in use.
* 返回当前被使用的drawale.对于简单的drawable，会返回本身。对于改变状态的drawable，会返回当前使用的子drawable
*/
public Drawable getCurrent() {
return this;
}

/**
* Specify the level for the drawable.  This allows a drawable to vary its
* imagery based on a continuous controller, for example to show progress
* or volume level.
* 指定当前层。这允许drawable根据连续的控制者改变自己的图像，例如进度和音量水平。
* <p>If the new level you are supplying causes the appearance of the
* Drawable to change, then it is responsible for calling
* {@link #invalidateSelf} in order to have itself redrawn, <em>and</em>
* true will be returned from this function.
* 如果你使用的新层会导致外观变化，那么主动调用nvalidateSelf引起重绘并且该方法将返回true
* @param level The new level, from 0 (minimum) to 10000 (maximum).
*
* @return Returns true if this change in level has caused the appearance
* of the Drawable to change (hence requiring an invalidate), otherwise
* returns false.
*/
public final boolean setLevel(int level) {
if (mLevel != level) {
mLevel = level;
return onLevelChange(level);
}
return false;
}

/**
* Retrieve the current level.
* 获取当前层
* @return int Current level, from 0 (minimum) to 10000 (maximum).
*/
public final int getLevel() {
return mLevel;
}

/**
* Set whether this Drawable is visible.  This generally does not impact
* the Drawable's behavior, but is a hint that can be used by some
* Drawables, for example, to decide whether run animations.
* 设置是否可见。一般不会影响drawable的行为。但是可以被一些drawable作为依据，例如决定
* 是否运行动画
* @param visible Set to true if visible, false if not.
* @param restart You can supply true here to force the drawable to behave
*                as if it has just become visible, even if it had last
*                been set visible.  Used for example to force animations
*                to restart.
*                你可以设置为true强制drawable表现得就像刚可见一样，即使它持续了一段
*                时间才被设置为可见，例如强制动画重新启动。
*
* @return boolean Returns true if the new visibility is different than
*         its previous state.
*/
public boolean setVisible(boolean visible, boolean restart) {
boolean changed = mVisible != visible;
if (changed) {
mVisible = visible;
invalidateSelf();
}
return changed;
}

public final boolean isVisible() {
return mVisible;
}

/**
* Set whether this Drawable is automatically mirrored when its layout direction is RTL
* (right-to left). See {@link android.util.LayoutDirection}.
* 设置Drawable是否自动映像当它的布局方向被设置为从右到左
* @param mirrored Set to true if the Drawable should be mirrored, false if not.
*/
public void setAutoMirrored(boolean mirrored) {
}

/**
* Tells if this Drawable will be automatically mirrored  when its layout direction is RTL
* right-to-left. See {@link android.util.LayoutDirection}.
* 返回Drawable是否自动映像当它的布局方向被设置为从右到左
* @return boolean Returns true if this Drawable will be automatically mirrored.
*/
public boolean isAutoMirrored() {
return false;
}

/**
* Applies the specified theme to this Drawable and its children.
* 为Drawable和它的孩子设置主题
*/
public void applyTheme(@SuppressWarnings("unused") Theme t) {
}

public boolean canApplyTheme() {
return false;
}

/**
* Return the opacity/transparency of this Drawable.  The returned value is
* one of the abstract format constants in
* {@link android.graphics.PixelFormat}:
* {@link android.graphics.PixelFormat#UNKNOWN},
* {@link android.graphics.PixelFormat#TRANSLUCENT},
* {@link android.graphics.PixelFormat#TRANSPARENT}, or
* {@link android.graphics.PixelFormat#OPAQUE}.
* 返回透明度或者不透明度。返回值是以下格式的常量
* <p>Generally a Drawable should be as conservative as possible with the
* value it returns.  For example, if it contains multiple child drawables
* and only shows one of them at a time, if only one of the children is
* TRANSLUCENT and the others are OPAQUE then TRANSLUCENT should be
* returned.  You can use the method {@link #resolveOpacity} to perform a
* standard reduction of two opacities to the appropriate single output.
* 保守地返回值。例如如果有多个子drawable，并且一次只显示一个，如果其中一个是TRANSLUCENT，
* 而其他是OPAQUE，你应该返回TRANSLUCENT。你可以用resolveOpacity()老判断两个不透明度
* 哪个是合理的.
* <p>Note that the returned value does <em>not</em> take into account a
* custom alpha or color filter that has been applied by the client through
* the {@link #setAlpha} or {@link #setColorFilter} methods.
* 注意，返回值没有考虑alpha或者color filter
* @return int The opacity class of the Drawable.
*
* @see android.graphics.PixelFormat
*/
public abstract int getOpacity();

/**
* Return the appropriate opacity value for two source opacities.  If
* either is UNKNOWN, that is returned; else, if either is TRANSLUCENT,
* that is returned; else, if either is TRANSPARENT, that is returned;
* else, OPAQUE is returned.
* 从两个不透明度中返回一个合理的。
* <p>This is to help in implementing {@link #getOpacity}.
*
* @param op1 One opacity value.
* @param op2 Another opacity value.
*
* @return int The combined opacity value.
*
* @see #getOpacity
*/
public static int resolveOpacity(int op1, int op2) {
if (op1 == op2) {
return op1;
}
if (op1 == PixelFormat.UNKNOWN || op2 == PixelFormat.UNKNOWN) {
return PixelFormat.UNKNOWN;
}
if (op1 == PixelFormat.TRANSLUCENT || op2 == PixelFormat.TRANSLUCENT) {
return PixelFormat.TRANSLUCENT;
}
if (op1 == PixelFormat.TRANSPARENT || op2 == PixelFormat.TRANSPARENT) {
return PixelFormat.TRANSPARENT;
}
return PixelFormat.OPAQUE;
}

/**
* Returns a Region representing the part of the Drawable that is completely
* transparent.  This can be used to perform drawing operations, identifying
* which parts of the target will not change when rendering the Drawable.
* The default implementation returns null, indicating no transparent
* region; subclasses can optionally override this to return an actual
* Region if they want to supply this optimization information, but it is
* not required that they do so.
* 返回Drawable中完全透明的部分。这个可在绘制操作时使用，分辨哪些部分是不会改变的。默认实现
* 返回null,表明没有透明区域。子类可以有选择地复写从而返回确切区域，如果它希望提供这些优化信息的话。
* 但是不是要求它们都这样做。
* @return Returns null if the Drawables has no transparent region to
* report, else a Region holding the parts of the Drawable's bounds that
* are transparent.
*/
public Region getTransparentRegion() {
return null;
}

/**
* Override this in your subclass to change appearance if you recognize the
* specified state.
* 在子类中复写用于改变外观，如果你认识指定的状态的话。
* @return Returns true if the state change has caused the appearance of
* the Drawable to change (that is, it needs to be drawn), else false
* if it looks the same and there is no need to redraw it since its
* last state.
*/
protected boolean onStateChange(int[] state) { return false; }
/** Override this in your subclass to change appearance if you vary based
*  on level.
*  如果你希望根据层变化，在子类中复写去改变外观。
* @return Returns true if the level change has caused the appearance of
* the Drawable to change (that is, it needs to be drawn), else false
* if it looks the same and there is no need to redraw it since its
* last level.
*/
protected boolean onLevelChange(int level) { return false; }
/**
* Override this in your subclass to change appearance if you vary based on
* the bounds.
*  在子类中复写用于改变外观，如果你希望根据边界改变。
*/
protected void onBoundsChange(Rect bounds) {}

/**
* Return the intrinsic width of the underlying drawable object.  Returns
* -1 if it has no intrinsic width, such as with a solid color.
* 返回底层drawable对象的固有宽度。如果没有固有宽度返回-1，例如只有纯色。
*/
public int getIntrinsicWidth() {
return -1;
}

/**
* Return the intrinsic height of the underlying drawable object. Returns
* -1 if it has no intrinsic height, such as with a solid color.
* 返回底层drawable对象的固有高度。如果没有固有宽度返回-1，例如只有纯色。
*/
public int getIntrinsicHeight() {
return -1;
}

/**
* Returns the minimum width suggested by this Drawable. If a View uses this
* Drawable as a background, it is suggested that the View use at least this
* value for its width. (There will be some scenarios where this will not be
* possible.) This value should INCLUDE any padding.
* 返回该Drawable建议的最小宽度。如果一个view使用这个drawable作为背景，它建议View至少
* 使用这个宽度(有些情景下这是不可能的)。这个值不包含任何的内边距。
* @return The minimum width suggested by this Drawable. If this Drawable
*         doesn't have a suggested minimum width, 0 is returned.
*/
public int getMinimumWidth() {
final int intrinsicWidth = getIntrinsicWidth();
return intrinsicWidth > 0 ? intrinsicWidth : 0;
}

/**
* Returns the minimum height suggested by this Drawable. If a View uses this
* Drawable as a background, it is suggested that the View use at least this
* value for its height. (There will be some scenarios where this will not be
* possible.) This value should INCLUDE any padding.
* 返回该Drawable建议的最小高度。如果一个view使用这个drawable作为背景，它建议View至少
* 使用这个高度(有些情景下这是不可能的)。这个值不包含任何的内边距。
* @return The minimum height suggested by this Drawable. If this Drawable
*         doesn't have a suggested minimum height, 0 is returned.
*/
public int getMinimumHeight() {
final int intrinsicHeight = getIntrinsicHeight();
return intrinsicHeight > 0 ? intrinsicHeight : 0;
}

/**
* Return in padding the insets suggested by this Drawable for placing
* content inside the drawable's bounds. Positive values move toward the
* center of the Drawable (set Rect.inset).
* 返回为那些被放置在drawable边界里面的插入物设置的内边距。走向Drawable中心的正值。
* @return true if this drawable actually has a padding, else false. When false is returned,
* the padding is always set to 0.
*/
public boolean getPadding(@NonNull Rect padding) {
padding.set(0, 0, 0, 0);
return false;
}

/**
* Return in insets the layout insets suggested by this Drawable for use with alignment
* operations during layout.
* 返回Drawable在布局时的对准操作使用的插入物
* @hide
*/
public Insets getOpticalInsets() {
return Insets.NONE;
}

/**
* Called to get the drawable to populate the Outline that defines its drawing area.
* <p>
* This method is called by the default {@link android.view.ViewOutlineProvider} to define
* the outline of the View.
* <p>
* The default behavior defines the outline to be the bounding rectangle of 0 alpha.
* Subclasses that wish to convey a different shape or alpha value must override this method.
* 调用这个方法去填充决定绘制区域的框架。
* 这个方法默认被ViewOutlineProvider调用，用于决定View的框架。
* 默认设置框架为0透明度的边界矩形。希望传递不同形状或者透明度的子类，必须复写这个方法。
* @see android.view.View#setOutlineProvider(android.view.ViewOutlineProvider)
*/
public void getOutline(@NonNull Outline outline) {
outline.setRect(getBounds());
outline.setAlpha(0);
}

/**
* Make this drawable mutable. This operation cannot be reversed. A mutable
* drawable is guaranteed to not share its state with any other drawable.
* This is especially useful when you need to modify properties of drawables
* loaded from resources. By default, all drawables instances loaded from
* the same resource share a common state; if you modify the state of one
* instance, all the other instances will receive the same modification.
* Calling this method on a mutable Drawable will have no effect.
* 使drawable易变。这个操作没有逆操作。一个易变的drawable保证不和其他drawable共享它的
* 状态。当你需要修改那些从资源加载的drawable的属性时，显得特别有用。所以从相同的资源加载
* 的drawable默认共享一个相同的状态。如果你修改其中一个，所有的其他对象会受到相同的而修改。
* 调用这个方法使其他不会受到影响。
*
* @return This drawable.
* @see ConstantState
* @see #getConstantState()
*/
public Drawable mutate() {
return this;
}

/**
* Clears the mutated state, allowing this drawable to be cached and
* mutated again.
* <p>
* This is hidden because only framework drawables can be cached, so
* custom drawables don't need to support constant state, mutate(), or
* clearMutated().
* 清除异变状态，允许drawable被缓存并且再次易变。这是个隐藏方法，因为只有frameword
* drawable可以被缓存，所有一般的drawable不需要支持这个状态。
* @hide
*/
public void clearMutated() {
// Default implementation is no-op.
}

/**
* Create a drawable from an inputstream
* 从输入流中创建drawable
*/
public static Drawable createFromStream(InputStream is, String srcName) {
Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, srcName != null ? srcName : "Unknown drawable");
try {
return createFromResourceStream(null, null, is, srcName);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
}
}

/**
* Create a drawable from an inputstream, using the given resources and
* value to determine density information.
* 从输入流中创建drawable，使用给定的资源是值去决定密度信息。
*/
public static Drawable createFromResourceStream(Resources res, TypedValue value,
InputStream is, String srcName) {
Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, srcName != null ? srcName : "Unknown drawable");
try {
return createFromResourceStream(res, value, is, srcName, null);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
}
}

/**
* Create a drawable from an inputstream, using the given resources and
* value to determine density information.
* 从输入流中创建drawable，使用给定的资源是值去决定密度信息。
*/
public static Drawable createFromResourceStream(Resources res, TypedValue value,
InputStream is, String srcName, BitmapFactory.Options opts) {
if (is == null) {
return null;
}

/*  ugh. The decodeStream contract is that we have already allocated
the pad rect, but if the bitmap does not had a ninepatch chunk,
then the pad will be ignored. If we could change this to lazily
alloc/assign the rect, we could avoid the GC churn of making new
Rects only to drop them on the floor.
解析流协议是我们已经在pad rect中配置的，但是如果bitmap没有ninepatch块，
pad会被忽略。如果我们可以改变这个去设置rect,我们可以避免。。。(不会翻)
*/
Rect pad = new Rect();

// Special stuff for compatibility mode: if the target density is not
// the same as the display density, but the resource -is- the same as
// the display density, then don't scale it down to the target density.
// This allows us to load the system's density-correct resources into
// an application in compatibility mode, without scaling those down
// to the compatibility density only to have them scaled back up when
// drawn to the screen.
/**
* 兼容方式：如果目标密度和设备密度不同，但是资源密度和设备密度相同，就不会缩放它
* 使之适用目标密度。这允许我们在兼容模式下，去加载系统的正确密度资源进app，不需
* 要去缩放它们到兼容密度，只是当它们被绘制到屏幕上时，缩放。
*/
if (opts == null) opts = new BitmapFactory.Options();
opts.inScreenDensity = res != null
? res.getDisplayMetrics().noncompatDensityDpi : DisplayMetrics.DENSITY_DEVICE;
Bitmap  bm = BitmapFactory.decodeResourceStream(res, value, is, pad, opts);
if (bm != null) {
byte[] np = bm.getNinePatchChunk();
if (np == null || !NinePatch.isNinePatchChunk(np)) {
np = null;
pad = null;
}

final Rect opticalInsets = new Rect();
bm.getOpticalInsets(opticalInsets);
return drawableFromBitmap(res, bm, np, pad, opticalInsets, srcName);
}
return null;
}

/**
* Create a drawable from an XML document. For more information on how to
* create resources in XML, see
* <a href="{@docRoot}guide/topics/resources/drawable-resource.html">Drawable Resources</a>.
* 从xml文件中返回drawable.
*/
public static Drawable createFromXml(Resources r, XmlPullParser parser)
throws XmlPullParserException, IOException {
return createFromXml(r, parser, null);
}

/**
* Create a drawable from an XML document using an optional {@link Theme}.
* For more information on how to create resources in XML, see
* <a href="{@docRoot}guide/topics/resources/drawable-resource.html">Drawable Resources</a>.
* 适用特定的主题从xml文件返回drawable
*/
public static Drawable createFromXml(Resources r, XmlPullParser parser, Theme theme)
throws XmlPullParserException, IOException {
AttributeSet attrs = Xml.asAttributeSet(parser);

int type;
while ((type=parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
// Empty loop
}

if (type != XmlPullParser.START_TAG) {
throw new XmlPullParserException("No start tag found");
}

Drawable drawable = createFromXmlInner(r, parser, attrs, theme);

if (drawable == null) {
throw new RuntimeException("Unknown initial tag: " + parser.getName());
}

return drawable;
}

/**
* Create from inside an XML document.  Called on a parser positioned at
* a tag in an XML document, tries to create a Drawable from that tag.
* Returns null if the tag is not a valid drawable.
* 从xml文件中返回drawable.调用在xml中的parser，尝试从这些标志中创建drawable.
* 返回null如果tag不是一个有效的drawable.
*/
public static Drawable createFromXmlInner(Resources r, XmlPullParser parser, AttributeSet attrs)
throws XmlPullParserException, IOException {
return createFromXmlInner(r, parser, attrs, null);
}

/**
* Create a drawable from inside an XML document using an optional
* {@link Theme}. Called on a parser positioned at a tag in an XML
* document, tries to create a Drawable from that tag. Returns {@code null}
* if the tag is not a valid drawable.
* 适用特定的主题从xml文件返回drawable.调用在xml中的parser，尝试从这些标志中创建drawable.
* 返回null如果tag不是一个有效的drawable.
*/
public static Drawable createFromXmlInner(Resources r, XmlPullParser parser, AttributeSet attrs,
Theme theme) throws XmlPullParserException, IOException {
final Drawable drawable;

final String name = parser.getName();
switch (name) {
case "selector":
drawable = new StateListDrawable();
break;
case "animated-selector":
drawable = new AnimatedStateListDrawable();
break;
case "level-list":
drawable = new LevelListDrawable();
break;
case "layer-list":
drawable = new LayerDrawable();
break;
case "transition":
drawable = new TransitionDrawable();
break;
case "ripple":
drawable = new RippleDrawable();
break;
case "color":
drawable = new ColorDrawable();
break;
case "shape":
drawable = new GradientDrawable();
break;
case "vector":
drawable = new VectorDrawable();
break;
case "animated-vector":
drawable = new AnimatedVectorDrawable();
break;
case "scale":
drawable = new ScaleDrawable();
break;
case "clip":
drawable = new ClipDrawable();
break;
case "rotate":
drawable = new RotateDrawable();
break;
case "animated-rotate":
drawable = new AnimatedRotateDrawable();
break;
case "animation-list":
drawable = new AnimationDrawable();
break;
case "inset":
drawable = new InsetDrawable();
break;
case "bitmap":
drawable = new BitmapDrawable(r);
if (r != null) {
((BitmapDrawable) drawable).setTargetDensity(r.getDisplayMetrics());
}
break;
case "nine-patch":
drawable = new NinePatchDrawable();
if (r != null) {
((NinePatchDrawable) drawable).setTargetDensity(r.getDisplayMetrics());
}
break;
default:
throw new XmlPullParserException(parser.getPositionDescription() +
": invalid drawable tag " + name);

}
drawable.inflate(r, parser, attrs, theme);
return drawable;
}

/**
* Create a drawable from file path name.
* 从文件路径中创建drawable
*/
public static Drawable createFromPath(String pathName) {
if (pathName == null) {
return null;
}

Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, pathName);
try {
Bitmap bm = BitmapFactory.decodeFile(pathName);
if (bm != null) {
return drawableFromBitmap(null, bm, null, null, null, pathName);
}
} finally {
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
}

return null;
}

/**
* Inflate this Drawable from an XML resource. Does not apply a theme.
* 从xml资源找到drwale,没有使用主题
* @see #inflate(Resources, XmlPullParser, AttributeSet, Theme)
*/
public void inflate(Resources r, XmlPullParser parser, AttributeSet attrs)
throws XmlPullParserException, IOException {
inflate(r, parser, attrs, null);
}

/**
* Inflate this Drawable from an XML resource optionally styled by a theme.
*  从xml资源找到drwale,使用主题指定的样式
* @param r Resources used to resolve attribute values
* @param parser XML parser from which to inflate this Drawable
* @param attrs Base set of attribute values
* @param theme Theme to apply, may be null
* @throws XmlPullParserException
* @throws IOException
*/
public void inflate(Resources r, XmlPullParser parser, AttributeSet attrs, Theme theme)
throws XmlPullParserException, IOException {
final TypedArray a;
if (theme != null) {
a = theme.obtainStyledAttributes(
attrs, com.android.internal.R.styleable.Drawable, 0, 0);
} else {
a = r.obtainAttributes(attrs, com.android.internal.R.styleable.Drawable);
}

inflateWithAttributes(r, parser, a, com.android.internal.R.styleable.Drawable_visible);
a.recycle();
}

/**
* Inflate a Drawable from an XML resource.
* 从xml资源找到drwale
* @throws XmlPullParserException
* @throws IOException
*/
void inflateWithAttributes(Resources r, XmlPullParser parser, TypedArray attrs, int visibleAttr)
throws XmlPullParserException, IOException {
mVisible = attrs.getBoolean(visibleAttr, mVisible);
}

/**
* This abstract class is used by {@link Drawable}s to store shared constant state and data
* between Drawables. {@link BitmapDrawable}s created from the same resource will for instance
* share a unique bitmap stored in their ConstantState.
* 这个抽象类被drawable用于在drawable之间存储共享的常量状态和数据。从同一资源创建的BitmapDrawable将会
* 共享一个唯一的存储在ConstantState中的bitmap
* <p>
* {@link #newDrawable(Resources)} can be used as a factory to create new Drawable instances
* from this ConstantState.
* newDrawable()方法可以当成工厂去从ConstantState创建一个新的Drawable
* </p>
*
* Use {@link Drawable#getConstantState()} to retrieve the ConstantState of a Drawable. Calling
* {@link Drawable#mutate()} on a Drawable should typically create a new ConstantState for that
* Drawable.
* 使用getConstantState()获取drawable的ConstantState。在Drawable调用#mutate()会为这个drawable创建一个
* 新的ConstantState
*/
public static abstract class ConstantState {
/**
* Create a new drawable without supplying resources the caller
* is running in.  Note that using this means the density-dependent
* drawables (like bitmaps) will not be able to update their target
* density correctly. One should use {@link #newDrawable(Resources)}
* instead to provide a resource.
* 创建drawable,不需要调用者提供资源。注意，使用它意味着依赖密度的drawables例如(bitmaps)
* 将不能正确更新它们的目标密度。应该使用newDrawable(Resources res)而不是提供一个资源。
*/
public abstract Drawable newDrawable();

/**
* Create a new Drawable instance from its constant state.  This
* must be implemented for drawables that change based on the target
* density of their caller (that is depending on whether it is
* in compatibility mode).
* 从常状态中创建一个新的drawable对象。这个必须被那些变化依赖于目标状态密度的调用者
* 实现。
*/
public Drawable newDrawable(Resources res) {
return newDrawable();
}

/**
* Create a new Drawable instance from its constant state. This must be
* implemented for drawables that can have a theme applied.
* 从常状态中创建一个新的drawable对象。这个必须被那些有主题的调用者实现。
*/
public Drawable newDrawable(Resources res, Theme theme) {
return newDrawable(null);
}

/**
* Return a bit mask of configuration changes that will impact
* this drawable (and thus require completely reloading it).
* 返回会影响drawable的一个bit掩码变化设置。
*/
public abstract int getChangingConfigurations();

/**
* @return Total pixel count 所有的像素
* @hide
*/
public int addAtlasableBitmaps(Collection<Bitmap> atlasList) {
return 0;
}

/** @hide */
protected final boolean isAtlasable(Bitmap bitmap) {
return bitmap != null && bitmap.getConfig() == Bitmap.Config.ARGB_8888;
}

/**
* Return whether this constant state can have a theme applied.
* 返回这个常状态是否可以有主题
*/
public boolean canApplyTheme() {
return false;
}
}

/**
* Return a {@link ConstantState} instance that holds the shared state of this Drawable.
* 返回Drawable共享的ConstantState实例
* @return The ConstantState associated to that Drawable.
* @see ConstantState
* @see Drawable#mutate()
*/
public ConstantState getConstantState() {
return null;
}

private static Drawable drawableFromBitmap(Resources res, Bitmap bm, byte[] np,
Rect pad, Rect layoutBounds, String srcName) {

if (np != null) {
return new NinePatchDrawable(res, bm, np, pad, layoutBounds, srcName);
}

return new BitmapDrawable(res, bm);
}

/**
* Ensures the tint filter is consistent with the current tint color and
* mode.
* 保证色彩过滤器和当前色彩和色彩模式一致。
*/
PorterDuffColorFilter updateTintFilter(PorterDuffColorFilter tintFilter, ColorStateList tint,
PorterDuff.Mode tintMode) {
if (tint == null || tintMode == null) {
return null;
}

final int color = tint.getColorForState(getState(), Color.TRANSPARENT);
if (tintFilter == null) {
return new PorterDuffColorFilter(color, tintMode);
}

tintFilter.setColor(color);
tintFilter.setMode(tintMode);
return tintFilter;
}

/**
* Obtains styled attributes from the theme, if available, or unstyled
* resources if the theme is null.
* 如果有效，从主题中取得样式属性。如果主题为空，则返回没有样式的资源。
*/
static TypedArray obtainAttributes(
Resources res, Theme theme, AttributeSet set, int[] attrs) {
if (theme == null) {
return res.obtainAttributes(set, attrs);
}
return theme.obtainStyledAttributes(set, attrs, 0, 0);
}

/**
* Parses a {@link android.graphics.PorterDuff.Mode} from a tintMode
* attribute's enum value.
* 从tintMode解析出PorterDuff.Mode
* @hide
*/
public static PorterDuff.Mode parseTintMode(int value, Mode defaultMode) {
switch (value) {
case 3: return Mode.SRC_OVER;
case 5: return Mode.SRC_IN;
case 9: return Mode.SRC_ATOP;
case 14: return Mode.MULTIPLY;
case 15: return Mode.SCREEN;
case 16: return Mode.ADD;
default: return defaultMode;
}
}
}