android中apidemos中的fingerpaint学习
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本人刚刚接触android，然后想和大家一起讨论一下学习经验，不对的地方请大家指教！
这个截图什么的就不添加了，我自己主要在这个代码中加了一点注释，希望能帮助大家理解！
不过在这个效果中我也有一些不会的地方，在这里提出来，希望大家帮我解答一下！
问题如下：
在使用橡皮擦擦除原有笔记的时候，橡皮的轨迹是黑色的，虽然却是能起到橡皮擦除的效果，但是觉得不好，不知道有没有哪位兄弟能够不吝解答！
这个是主要activity
import android.app.Activity;import android.content.Context;import android.graphics.*;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.view.MotionEvent;import android.view.View;public class FingerPaintActivity extends Activity implements ColorPickerDialog.OnColorChangedListener { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(new MyView(this)); mPaint = new Paint();//创建画笔渲染对象 mPaint.setAntiAlias(true);//设置抗锯齿，让绘画比较平滑 mPaint.setDither(true);//设置递色 mPaint.setColor(0xFF0000FF);//设置画笔的颜色 mPaint.setStyle(Paint.Style.STROKE);//画笔的类型有三种（1.FILL 2.FILL_AND_STROKE 3.STROKE ） mPaint.setStrokeJoin(Paint.Join.ROUND);//默认类型是MITER（1.BEVEL 2.MITER 3.ROUND ） mPaint.setStrokeCap(Paint.Cap.ROUND);//默认类型是BUTT（1.BUTT 2.ROUND 3.SQUARE ） mPaint.setStrokeWidth(12);//设置描边的宽度，如果设置的值为0那么边是一条极细的线 mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },//设置浮雕格式 0.4f, 6, 3.5f); mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);//设置模糊格式 } private Paint mPaint;//用来话图形的画笔 private MaskFilter mEmboss;//浮雕格式 private MaskFilter mBlur;//模糊格式 public void colorChanged(int color) {//实现ColorPickerDialog.OnColorChangedListener以改变画笔 mPaint.setColor(color); } public class MyView extends View { // private static final float MINP = 0.25f;// private static final float MAXP = 0.75f; private Bitmap mBitmap; private Canvas mCanvas; private Path mPath; private Paint mBitmapPaint; public MyView(Context c) { super(c); mBitmap = Bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);//绘制固定大小的bitmap对象，每个像素4个字节 mCanvas = new Canvas(mBitmap);//将固定的bitmap对象嵌入到canvas对象中 mPath = new Path();//创建画笔路径 mBitmapPaint = new Paint(Paint.DITHER_FLAG); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); } @Override protected void onDraw(Canvas canvas) { canvas.drawColor(0xFFAAAAAA);//Fill the entire canvas' bitmap canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);//use mBitmapPaint to draw mBitmap canvas.drawPath(mPath, mPaint);//use mPaint to draw mPath } private float mX, mY; private static final float TOUCH_TOLERANCE = 4;//绘图时当屏幕上手指触点移动距离超过4才有效 private void touch_start(float x, float y) {//开始绘画 mPath.reset(); mPath.moveTo(x, y);//设置新的路径“轮廓”的开始 mX = x; mY = y; } private void touch_move(float x, float y) { float dx = Math.abs(x - mX); float dy = Math.abs(y - mY); if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) { mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);//添加曲线，这一步我不太懂，为什么后一个点的坐标是移动的中点 mX = x; mY = y; } } private void touch_up() { mPath.lineTo(mX, mY);//从最后一个指定的xy点绘制一条线，如果没有用moveTo方法，那么起始点表示（0，0）点。 // commit the path to our offscreen mCanvas.drawPath(mPath, mPaint);//手指离开屏幕后，绘制创建的“所有”路径。 // kill this so we don't double draw mPath.reset(); } @Override public boolean onTouchEvent(MotionEvent event) { float x = event.getX(); float y = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN://手指开始按压屏幕，这个动作包含了初始化位置 touch_start(x, y); invalidate();//刷新画布，重新运行onDraw（）方法 break; case MotionEvent.ACTION_MOVE://手指按压屏幕时，位置的改变触发，这个方法在ACTION_DOWN和ACTION_UP之间。 touch_move(x, y); invalidate(); break; case MotionEvent.ACTION_UP://手指离开屏幕，不再按压屏幕 touch_up(); invalidate(); break; } return true; } } private static final int COLOR_MENU_ID = Menu.FIRST;//菜单上ID private static final int EMBOSS_MENU_ID = Menu.FIRST + 1; private static final int BLUR_MENU_ID = Menu.FIRST + 2; private static final int ERASE_MENU_ID = Menu.FIRST + 3; private static final int SRCATOP_MENU_ID = Menu.FIRST + 4; @Override public boolean onCreateOptionsMenu(Menu menu) { super.onCreateOptionsMenu(menu); menu.add(0, COLOR_MENU_ID, 0, "Color").setShortcut('3', 'c');//设置菜单并设定快捷键 menu.add(0, EMBOSS_MENU_ID, 0, "Emboss").setShortcut('4', 's'); menu.add(0, BLUR_MENU_ID, 0, "Blur").setShortcut('5', 'z'); menu.add(0, ERASE_MENU_ID, 0, "Erase").setShortcut('5', 'z'); menu.add(0, SRCATOP_MENU_ID, 0, "SrcATop").setShortcut('5', 'z'); /**** Is this the mechanism to extend with filter effects? Intent intent = new Intent(null, getIntent().getData()); intent.addCategory(Intent.CATEGORY_ALTERNATIVE); menu.addIntentOptions( Menu.ALTERNATIVE, 0, new ComponentName(this, NotesList.class), null, intent, 0, null); *****/ return true; } @Override public boolean onPrepareOptionsMenu(Menu menu) {//每次menu出现前会被调用 super.onPrepareOptionsMenu(menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) {//对菜单情况进行判断 mPaint.setXfermode(null); mPaint.setAlpha(0xFF); switch (item.getItemId()) { case COLOR_MENU_ID: new ColorPickerDialog(this, this, mPaint.getColor()).show(); return true; case EMBOSS_MENU_ID: if (mPaint.getMaskFilter() != mEmboss) { mPaint.setMaskFilter(mEmboss); } else { mPaint.setMaskFilter(null); } return true; case BLUR_MENU_ID: if (mPaint.getMaskFilter() != mBlur) { mPaint.setMaskFilter(mBlur); } else { mPaint.setMaskFilter(null); } return true; case ERASE_MENU_ID: mPaint.setXfermode(new PorterDuffXfermode(//此处是起到橡皮擦效果，不明白为什么橡皮擦的轨迹市很色的，希望大家告诉我一下 PorterDuff.Mode.CLEAR)); return true; case SRCATOP_MENU_ID: mPaint.setXfermode(new PorterDuffXfermode( PorterDuff.Mode.SRC_ATOP)); mPaint.setAlpha(0x80); return true; } return super.onOptionsItemSelected(item); }}这个是调色板的代码import android.os.Bundle;import android.app.Dialog;import android.content.Context;import android.graphics.*;import android.view.MotionEvent;import android.view.View;public class ColorPickerDialog extends Dialog { public interface OnColorChangedListener { void colorChanged(int color); } private OnColorChangedListener mListener; private int mInitialColor; private static class ColorPickerView extends View { private Paint mPaint; private Paint mCenterPaint; private final int[] mColors; private OnColorChangedListener mListener;//用该接口来改变画笔颜色，详见FingerPaintActivity中对该接口的实现 ColorPickerView(Context c, OnColorChangedListener l, int color) { super(c); mListener = l; /*定义了一个颜色数组，用来完成外面一圈取色圈*/ mColors = new int[] { 0xFFFF0000, 0xFFFF00FF, 0xFF0000FF, 0xFF00FFFF, 0xFF00FF00, 0xFFFFFF00, 0xFFFF0000 };//注意：这样设置带来的问题是无法获取黑色 Shader s = new SweepGradient(0, 0, mColors, null);//利用上面的数组产生外面一层渐变的取色圈 mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);//一些画取色圈的画笔的设定 mPaint.setShader(s); mPaint.setStyle(Paint.Style.STROKE); mPaint.setStrokeWidth(32); mCenterPaint = new Paint(Paint.ANTI_ALIAS_FLAG);//画中心颜色点画笔的设定 mCenterPaint.setColor(color); mCenterPaint.setStrokeWidth(5); } private boolean mTrackingCenter;//按下屏幕时的位置是否在中心颜色区域 private boolean mHighlightCenter;//是否高亮外围一圈，当按下位置在中心颜色区域时，会在中心颜色区域周围画出一个小圆圈，若此时手指不离开屏幕，但移动到中心颜色区域外面，则会使小圆圈变暗 @Override protected void onDraw(Canvas canvas) { float r = CENTER_X - mPaint.getStrokeWidth()*0.5f;//取色圈半径 canvas.translate(CENTER_X, CENTER_X); canvas.drawOval(new RectF(-r, -r, r, r), mPaint);//外围取色圈 canvas.drawCircle(0, 0, CENTER_RADIUS, mCenterPaint);//中心颜色区域 if (mTrackingCenter) {//该段代码详见该变量定义 int c = mCenterPaint.getColor(); mCenterPaint.setStyle(Paint.Style.STROKE); if (mHighlightCenter) { mCenterPaint.setAlpha(0xFF); } else { mCenterPaint.setAlpha(0x80); } canvas.drawCircle(0, 0, CENTER_RADIUS + mCenterPaint.getStrokeWidth(), mCenterPaint); mCenterPaint.setStyle(Paint.Style.FILL); mCenterPaint.setColor(c); } } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {//设置view大小 这个不是很懂 谁看懂了告诉我一声 setMeasuredDimension(CENTER_X*2, CENTER_Y*2); } private static final int CENTER_X = 100;//中心在屏幕上的坐标，并且和外围取色圈半径有关（取色圈那个很明显是对的，那个屏幕中心什么的可能不对，谁看懂了告诉我一声） private static final int CENTER_Y = 100; private static final int CENTER_RADIUS = 32;//中心颜色区域半径 private int ave(int s, int d, float p) {//加权平均数 return s + java.lang.Math.round(p * (d - s)); } private int interpColor(int colors[], float unit) {//计算周围的颜色圈 if (unit <= 0) { return colors[0]; } if (unit >= 1) { return colors[colors.length - 1]; } float p = unit * (colors.length - 1); int i = (int)p; p -= i; // now p is just the fractional part [0...1) and i is the index int c0 = colors[i]; int c1 = colors[i+1]; int a = ave(Color.alpha(c0), Color.alpha(c1), p);//加权平均值 int r = ave(Color.red(c0), Color.red(c1), p); int g = ave(Color.green(c0), Color.green(c1), p); int b = ave(Color.blue(c0), Color.blue(c1), p); return Color.argb(a, r, g, b); } private static final float PI = 3.1415926f; @Override public boolean onTouchEvent(MotionEvent event) {//处理触屏时间 float x = event.getX() - CENTER_X; float y = event.getY() - CENTER_Y; boolean inCenter = java.lang.Math.sqrt(x*x + y*y) <= CENTER_RADIUS;//判断是否在中心区域 switch (event.getAction()) { case MotionEvent.ACTION_DOWN: mTrackingCenter = inCenter; if (inCenter) { mHighlightCenter = true; invalidate(); break; } case MotionEvent.ACTION_MOVE: if (mTrackingCenter) { if (mHighlightCenter != inCenter) { mHighlightCenter = inCenter; invalidate(); } } else { float angle = (float)java.lang.Math.atan2(y, x);//选中外围颜色，这个颜色不是精确的 // need to turn angle [-PI ... PI] into unit [0....1] float unit = angle/(2*PI); if (unit < 0) { unit += 1; } mCenterPaint.setColor(interpColor(mColors, unit)); invalidate(); } break; case MotionEvent.ACTION_UP: if (mTrackingCenter) { if (inCenter) { mListener.colorChanged(mCenterPaint.getColor());//就是这一步改变了FingerPaintActivity中的mPaint } mTrackingCenter = false; invalidate(); } break; } return true; } } public ColorPickerDialog(Context context,//构造函数 OnColorChangedListener listener, int initialColor) { super(context); mListener = listener; mInitialColor = initialColor; } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); OnColorChangedListener l = new OnColorChangedListener() { public void colorChanged(int color) { mListener.colorChanged(color); dismiss(); } }; setContentView(new ColorPickerView(getContext(), l, mInitialColor)); setTitle("Pick a Color"); }}- android中apidemos中的fingerpaint学习
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