gecko-dev/mobile/android/base/CanvasDelegate.java

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.gecko;

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuffXfermode;
import android.graphics.PorterDuff.Mode;
import android.os.Build;

public class CanvasDelegate { 
    Paint mPaint;
    PorterDuffXfermode mMode;
    DrawManager mDrawManager;

    // DrawManager would do a default draw of the background.
    public static interface DrawManager {
        public void defaultDraw(Canvas cavas);
    }

    public CanvasDelegate(DrawManager drawManager, Mode mode) {
        mDrawManager = drawManager;

        // DST_IN masks, DST_OUT clips.
        mMode = new PorterDuffXfermode(mode);

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setColor(0xFFFF0000);
    }

    public void draw(Canvas canvas, Path path, int width, int height) {
        // Save the canvas. All PorterDuff operations should be done in a offscreen bitmap.
        int count = canvas.saveLayer(0, 0, width, height, null,
                                     Canvas.MATRIX_SAVE_FLAG |
                                     Canvas.CLIP_SAVE_FLAG |
                                     Canvas.HAS_ALPHA_LAYER_SAVE_FLAG |
                                     Canvas.FULL_COLOR_LAYER_SAVE_FLAG |
                                     Canvas.CLIP_TO_LAYER_SAVE_FLAG);

        // Do a default draw.
        mDrawManager.defaultDraw(canvas);

        if (path != null && !path.isEmpty()) {
            // ICS added double-buffering, which made it easier for drawing the Path directly over the DST.
            // In pre-ICS, drawPath() doesn't seem to use ARGB_8888 mode for performance, hence transparency is not preserved.
            if (Build.VERSION.SDK_INT >= 14) {
                mPaint.setXfermode(mMode);
                canvas.drawPath(path, mPaint);
            } else {
                // Allocate a bitmap and draw the masking/clipping path.
                Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
                (new Canvas(bitmap)).drawPath(path, mPaint);

                mPaint.setXfermode(mMode);
                canvas.drawBitmap(bitmap, 0, 0, mPaint);

                mPaint.setXfermode(null);
            }
        }

        // Restore the canvas.
        canvas.restoreToCount(count);
    }
}