将位图加载到画布并在其上绘制

时间：2013-06-07 17:24:07

标签： java android bitmap android-canvas draw

我喜欢制作一个应用程序，就像一个小小的颜料，我必须得到一个位图，在画布上绘制它，接下来，画上它（用闪光灯）...所以，我实际上有这个代码：< / p> 

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<Path> paths = new ArrayList<Path>();
    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，我可以在画布上绘制，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事情呢？我的意思是，得到Bitmap，然后画出来......

4 个答案:

答案 0 :(得分：0)

如果将canvas.drawBitmap（）移到if语句之外，则应该有效。保持解码，但将实际绘图移出它。

答案 1 :(得分：0)

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？

您不必做的就是在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);

答案 2 :(得分：0)

这会让你的观点变得非常慢，但是如果删除if(start)语句，那么你的位图就不会消失。

更好的方法是将canvas.drawBitmap()置于if(start)方法之外，但这仍然会很慢，因为每次触摸屏幕时都会绘制位图。

实际上这种情况正在发生，因为每次调用onDraw()时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。

答案 3 :(得分：0)

解决了，我使用这段代码来加载图片并在上面绘图...... 

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<Path> paths = new ArrayList<Path>();
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;
}
}
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