Android example source code file (PolyToPoly.java)

This example Android source code file (PolyToPoly.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, app, content, graphicsactivity, matrix, os, override, paint, polytopoly, sampleview, ui, view

The PolyToPoly.java Android example source code

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.graphics;

// Need the following import to get access to the app resources, since this
// class is in a sub-package.
//import com.example.android.apis.R;

import android.app.Activity;
import android.content.Context;
import android.graphics.*;
import android.os.Bundle;
import android.view.View;

public class PolyToPoly extends GraphicsActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new SampleView(this));
    }
    
    private static class SampleView extends View {
        private Paint   mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        private Matrix  mMatrix = new Matrix();
        private Paint.FontMetrics mFontMetrics;

        private void doDraw(Canvas canvas, float src[], float dst[]) {
            canvas.save();
            mMatrix.setPolyToPoly(src, 0, dst, 0, src.length >> 1);
            canvas.concat(mMatrix);
            
            mPaint.setColor(Color.GRAY);
            mPaint.setStyle(Paint.Style.STROKE);
            canvas.drawRect(0, 0, 64, 64, mPaint);
            canvas.drawLine(0, 0, 64, 64, mPaint);
            canvas.drawLine(0, 64, 64, 0, mPaint);
            
            mPaint.setColor(Color.RED);
            mPaint.setStyle(Paint.Style.FILL);
            // how to draw the text center on our square
            // centering in X is easy... use alignment (and X at midpoint)
            float x = 64/2;
            // centering in Y, we need to measure ascent/descent first
            float y = 64/2 - (mFontMetrics.ascent + mFontMetrics.descent)/2;
            canvas.drawText(src.length/2 + "", x, y, mPaint);
            
            canvas.restore();
        }

        public SampleView(Context context) {
            super(context);

            // for when the style is STROKE
            mPaint.setStrokeWidth(4);
            // for when we draw text
            mPaint.setTextSize(40);
            mPaint.setTextAlign(Paint.Align.CENTER);
            mFontMetrics = mPaint.getFontMetrics();
        }
        
        @Override protected void onDraw(Canvas canvas) {
            Paint paint = mPaint;

            canvas.drawColor(Color.WHITE);

            canvas.save();
            canvas.translate(10, 10);
            // translate (1 point)
            doDraw(canvas, new float[] { 0, 0 }, new float[] { 5, 5 });
            canvas.restore();
            
            canvas.save();
            canvas.translate(160, 10);
            // rotate/uniform-scale (2 points)
            doDraw(canvas, new float[] { 32, 32, 64, 32 },
                           new float[] { 32, 32, 64, 48 });
            canvas.restore();

            canvas.save();
            canvas.translate(10, 110);
            // rotate/skew (3 points)
            doDraw(canvas, new float[] { 0, 0, 64, 0, 0, 64 },
                           new float[] { 0, 0, 96, 0, 24, 64 });
            canvas.restore();

            canvas.save();
            canvas.translate(160, 110);
            // perspective (4 points)
            doDraw(canvas, new float[] { 0, 0, 64, 0, 64, 64, 0, 64 },
                           new float[] { 0, 0, 96, 0, 64, 96, 0, 64 });
            canvas.restore();
        }
    }
}