将位图加载到canvas并在其上绘制

我喜欢制作一个应用程序，比如一个小小的颜料，我必须得到一个位图，在canvas上绘制它，然后绘制它（用figer）…所以，我实际上有这个代码：

import java.io.File; import java.io.FileOutputStream; import java.util.ArrayList; import android.content.Context; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.Path; import android.os.Environment; import android.util.Log; import android.graphics.Bitmap; import android.view.MotionEvent; import android.view.View; import android.view.View.OnTouchListener; public class DrawView extends View implements OnTouchListener { private Canvas mCanvas; private Path mPath; public Paint mPaint; private ArrayList paths = new ArrayList(); private boolean start = true; public DrawView(Context context) { super(context); setFocusable(true); setFocusableInTouchMode(true); this.setOnTouchListener((OnTouchListener) this); mPaint = new Paint(); mPaint.setAntiAlias(true); mPaint.setDither(true); mPaint.setColor(Color.BLACK); mPaint.setStyle(Paint.Style.STROKE); mPaint.setStrokeJoin(Paint.Join.ROUND); mPaint.setStrokeCap(Paint.Cap.ROUND); mPaint.setStrokeWidth(4); mPaint.setDither(true); mPaint.setFilterBitmap(true); mCanvas = new Canvas(); mPath = new Path(); paths.add(mPath); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); } @Override protected void onDraw(Canvas canvas) { for (Path p : paths) { canvas.drawPath(p, mPaint); } if (start) { Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.v01); canvas.drawBitmap(bmp, 0, 0, mPaint); start = false; } } private float mX, mY; private static final float TOUCH_TOLERANCE = 4; private void touch_start(float x, float y) { mPath.reset(); mPath.moveTo(x, y); 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); mX = x; mY = y; } } private void touch_up() { mPath.lineTo(mX, mY); // commit the path to our offscreen mCanvas.drawPath(mPath, mPaint); // kill this so we don't double draw mPath = new Path(); paths.add(mPath); } public boolean onTouch(View arg0, MotionEvent event) { float x = event.getX(); float y = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: touch_start(x, y); invalidate(); break; case MotionEvent.ACTION_MOVE: touch_move(x, y); invalidate(); break; case MotionEvent.ACTION_UP: touch_up(); invalidate(); break; } return true; } } 

使用此代码，我可以在canvas上绘制，并通过第一种方式获取位图…但是，如果我触摸，位图消失，这是每个onTouch事件的原因我再次根据路径绘制…我怎么能做我喜欢的？，我的意思是，获取位图，并绘制它…

Answer 1

如果你在if语句之外移动canvas.drawBitmap（）应该工作。 保持解码，但移动实际绘图。

Answer 2

我不确定你的问题在这里。 每次运行onDraw时都必须重绘位图，否则就不会有任何内容。 你有没有注意到那里的性能损失？

您不必做的是在每个invalidate上解码资源。

将bmp声明为全局变量

 Bitmap bmp; 

将位图存储在构造函数中：

 DrawView(Context context){ ... bmp = BitmapFactory.decodeResource(getResources(), R.drawable.v01); } 

并删除绘制方法中的if。 你不希望它在那里。 每次调用invalidate时都必须重绘位图。 但这不应该导致任何性能问题。

 canvas.drawBitmap(bmp, 0, 0, mPaint); 

Answer 3

这将使您的视图非常慢，但如果您删除if(start)语句，那么您的位图将不会消失。

稍微好一点的方法是在if(start)方法之外使用canvas.drawBitmap() ，但这仍然很慢，因为每次触摸屏幕时都会绘制位图。

---

实际上这是发生的，因为每次调用onDraw()都会传递一个空白位图。 这意味着每次调用onDraw时都必须重绘所有内容，但是因为你只是第一次设置位图，所以当再次调用draw时，位图不会再次添加，因此就会消失。

Answer 4

解决了，我使用这段代码可以加载图像并绘制它…

 DrawView.java package com.example.com.dibuja; import java.util.ArrayList; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.Path; import android.view.MotionEvent; import android.view.View; import android.view.View.OnTouchListener; public class DrawView extends View implements OnTouchListener { private Canvas mCanvas; private Path mPath; public Paint mPaint; private ArrayList paths = new ArrayList(); Bitmap bmp; public DrawView(Context context) { super(context); setFocusable(true); setFocusableInTouchMode(true); this.setOnTouchListener(this); bmp = BitmapFactory.decodeResource(getResources(), R.drawable.v01); mPaint = new Paint(); mPaint.setAntiAlias(true); mPaint.setDither(true); mPaint.setColor(Color.BLUE); mPaint.setStyle(Paint.Style.STROKE); mPaint.setStrokeJoin(Paint.Join.ROUND); mPaint.setStrokeCap(Paint.Cap.ROUND); mPaint.setStrokeWidth(6); mCanvas = new Canvas(); mPath = new Path(); paths.add(mPath); } @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.drawBitmap(bmp, 0, 0, mPaint); for (Path p : paths) { canvas.drawPath(p, mPaint); } } private float mX, mY; private static final float TOUCH_TOLERANCE = 0; Draw dw = new Draw(); private void touch_start(float x, float y) { mPath.reset(); mPath.moveTo(x, y); 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); mX = x; mY = y; } } private void touch_up() { mPath.lineTo(mX, mY); // commit the path to our offscreen mCanvas.drawPath(mPath, mPaint); // kill this so we don't double draw mPath = new Path(); paths.add(mPath); } @Override public boolean onTouch(View arg0, MotionEvent event) { float x = event.getX(); float y = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: touch_start(x, y); invalidate(); break; case MotionEvent.ACTION_MOVE: touch_move(x, y); invalidate(); break; case MotionEvent.ACTION_UP: touch_up(); invalidate(); break; } return true; } }