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

/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
 * 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.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.ComposeShader;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.PorterDuff;
import android.graphics.Rect;
import android.graphics.Shader;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;

/**
 * A special drawable used with lightweight themes. This draws a texture,
 * a color (usually with an alpha value) and a bitmap (with a linear gradient
 * to specify the alpha) in order. The bitmap is drawn either over a texture 
 * or over a color and rarely over both.
 */
public class LightweightThemeDrawable extends Drawable {
    private Paint mPaint;
    private Paint mColorPaint;
    private Paint mTexturePaint;

    private Bitmap mBitmap;
    private Resources mResources;

    private int mStartColor;
    private int mEndColor;

    public LightweightThemeDrawable(Resources resources, Bitmap bitmap) {
        mBitmap = bitmap;
        mResources = resources;

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setStrokeWidth(0.0f);
    }

    @Override
    protected void onBoundsChange(Rect bounds) {
        super.onBoundsChange(bounds);
        initializeBitmapShader();
    }

    @Override
    public void draw(Canvas canvas) {
	// Draw the texture, if available.
        if (mTexturePaint != null)
            canvas.drawPaint(mTexturePaint);

        // Draw the color, if available.
        if (mColorPaint != null)
            canvas.drawPaint(mColorPaint);

        // Draw the bitmap.
        canvas.drawPaint(mPaint);
    }

    @Override
    public int getOpacity() {
        return PixelFormat.TRANSLUCENT;
    }

    @Override
    public void setAlpha(int alpha) {
        // A StateListDrawable will reset the alpha value with 255.
        // We cannot use to be the bitmap alpha.
        mPaint.setAlpha(alpha);
    }

    @Override
    public void setColorFilter(ColorFilter filter) {
        mPaint.setColorFilter(filter);
    }		

    /**
     * Creates a shader based on a texture. The texture could be a resource in 
     * drawable-nodpi/ folder. In which case, the tile modes are set to repeat.
     * The texture could be a BitmapDrawable which could specify the tile mode 
     * in each direction. In that case, the intrinsic tile mode values are used.
     *
     * @param textureId The resource if of the texture.
     */
    public void setTexture(int textureId) {
        Shader.TileMode modeX = Shader.TileMode.REPEAT;
        Shader.TileMode modeY = Shader.TileMode.REPEAT;

        // The texture to be repeated.
        Bitmap texture = BitmapFactory.decodeResource(mResources, textureId);

        if (texture == null) {
            // Texture may be used inside a BitmapDrawable.
            Drawable drawable = mResources.getDrawable(textureId);
            if (drawable != null && drawable instanceof BitmapDrawable) {
                BitmapDrawable bitmapDrawable = (BitmapDrawable) drawable;
                texture = bitmapDrawable.getBitmap();
                modeX = bitmapDrawable.getTileModeX();
                modeY = bitmapDrawable.getTileModeY();
            }
        }

        // Set the shader for the texture paint.
        if (texture != null) {
            mTexturePaint = new Paint(mPaint);
            mTexturePaint.setShader(new BitmapShader(texture, modeX, modeY));
        }
    }

    /**
     * Creates a paint that paint a particular color.
     *
     * @param color The color to be painted.
     */
    public void setColor(int color) {
        mColorPaint = new Paint(mPaint);
        mColorPaint.setColor(color);
    }

    /**
     * Set the alpha for the linear gradient used with the bitmap's shader.
     *
     * @param startAlpha The starting alpha (0..255) value to be applied to the LinearGradient.
     * @param startAlpha The ending alpha (0..255) value to be applied to the LinearGradient.
     */
    public void setAlpha(int startAlpha, int endAlpha) {
        mStartColor = startAlpha << 24;
        mEndColor = endAlpha << 24;
        initializeBitmapShader();
    }

    private void initializeBitmapShader() {
	// A bitmap-shader to draw the bitmap.
        // Clamp mode will repeat the last row of pixels.
        // Hence its better to have an endAlpha of 0 for the linear-gradient.
	BitmapShader bitmapShader = new BitmapShader(mBitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);

	// A linear-gradient to specify the opacity of the bitmap.
	LinearGradient gradient = new LinearGradient(0, 0, 0, mBitmap.getHeight(), mStartColor, mEndColor, Shader.TileMode.CLAMP);

	// Make a combined shader -- a performance win.
        // The linear-gradient is the 'SRC' and the bitmap-shader is the 'DST'.
	// Drawing the DST in the SRC will provide the opacity.
	mPaint.setShader(new ComposeShader(bitmapShader, gradient, PorterDuff.Mode.DST_IN));
    }
}