什麼是雙緩沖技術?雙緩沖技術就是當用戶操作界面完成後,會有一個緩沖區保存用戶操作的結果。
為什麼要使用雙緩沖技術?拿Android 游戲開發來說,界面貞每次都是全部重畫的,也就說畫了新的,舊的就沒了,所以需要使用雙緩沖技術保存之前的內容。
如何實現雙緩沖?使用一個Bitmap對象保留之前的畫布即可。
- package com.example.phonegaptest;
-
- import android.content.Context;
- import android.graphics.Bitmap;
- import android.graphics.Bitmap.Config;
- import android.graphics.Canvas;
- import android.graphics.Color;
- import android.graphics.Paint;
- import android.graphics.Path;
- import android.util.AttributeSet;
- import android.view.MotionEvent;
- import android.view.View;
-
- public class DrawView extends View {
- float preX;
- float preY;
- private Path path;
- public Paint paint = null;
- final int VIEW_WIDTH = 320;
- final int VIEW_HEIGHT = 480;
- Bitmap cacheBitmap = null;
- Canvas cacheCanvas = null;
-
- public DrawView(Context context, AttributeSet set) {
- super(context, set);
- cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH, VIEW_HEIGHT,
- Config.ARGB_8888);
- cacheCanvas = new Canvas();
-
- path = new Path();
- cacheCanvas.setBitmap(cacheBitmap);
-
- paint = new Paint(Paint.DITHER_FLAG);
- paint.setColor(Color.RED);
- paint.setStyle(Paint.Style.STROKE);
- paint.setStrokeWidth(1);
- paint.setAntiAlias(true);
- paint.setDither(true);
- }
-
- @Override
- public boolean onTouchEvent(MotionEvent event) {
- float x = event.getX();
- float y = event.getY();
-
- switch (event.getAction()) {
- case MotionEvent.ACTION_DOWN:
- path.moveTo(x, y);
- preX = x;
- preY = y;
- break;
- case MotionEvent.ACTION_MOVE:
- path.quadTo(preX, preY, x, y);
- preX = x;
- preY = y;
- break;
- case MotionEvent.ACTION_UP:
- cacheCanvas.drawPath(path, paint);
- path.reset();
- break;
- }
- invalidate();
- return true;
- }
-
- @Override
- protected void onDraw(Canvas canvas) {
- super.onDraw(canvas);
- Paint bmpPaint = new Paint();
- canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);
- canvas.drawPath(path, paint);
- }
-
- }