如何使黑色背景和红色绘制？

Question

我一直在开发绘图应用程序。 我有以下主要活动代码：

@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    Display display = getWindow().getWindowManager().getDefaultDisplay();
    mMainView = new MyView(this, display.getWidth(), display.getHeight());
    setContentView(mMainView);

    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setDither(true);
    mPaint.setColor(0xFFFF0000);
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeWidth(12);

    mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 }, 0.4f, 6, 3.5f);
    mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
}

并为我的自定义视图编写代码：

public class MyView extends View {

    private static final float TOUCH_TOLERANCE = 4;
    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;

    private float mX, mY;

    public MyView(Context context, int width, int height) {
        super(context);

        this.setDrawingCacheEnabled(true);
        mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBitmap);
        mPath = new Path();
        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(0xFF000000);
        canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
        canvas.drawPath(mPath, mPaint);
    }

    public void clearView() {
        mBitmap.eraseColor(Color.TRANSPARENT);
    }

    public Bitmap getState() {
        return mBitmap;
    }

    private void touchStart(float x, float y) {
        mPath.reset();
        mPath.moveTo(x, y);
        mX = x;
        mY = y;
    }

    private void touchMove(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 touchUp() {
        mPath.lineTo(mX, mY);
        // commit the path to our offscreen
        mCanvas.drawPath(mPath, mPaint);
        // 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:
            touchStart(x, y);
            invalidate();
            break;
        case MotionEvent.ACTION_MOVE:
            touchMove(x, y);
            invalidate();
            break;
        case MotionEvent.ACTION_UP:
            touchUp();
            invalidate();
            break;
        }
        return true;
    }
}

因此，因为如果我尝试使用位图压缩将结果位图另存为jpeg文件，那么一切都很好，但是如果我尝试另存为png文件，则将获得具有透明背景（白色）和红色图片的文件。 我需要我可以将JPEG / PNG与黑色背景和红色图片一起保存。 保存代码不错，不用担心。 谢谢。

Answer 1

您可以在位图上绘制一个黑色矩形，如下所示：

Bitmap myBitmap = Bitmap.createBitmap(width, height, ...);
Canvas mCanvas = new Canvas(myBitmap);

// create a black rectangle
final int color = 0xffffffff;
final Paint p1 = new Paint();
final Rect rect = new Rect(0, 0, width, height);
final RectF rectF = new RectF(rect);

// draw it to the canvas
mCanvas.drawARGB(0, 0, 0, 0);
p1.setColor(color);
mCanvas.drawRect(rectF, p1);

这将强制使用黑色背景，并且您可以在画布上覆盖其他位图，最后使用myBitmap导出为png。 我认为您现在拥有的黑色背景是jpeg默认设置，因为它没有透明度。