Canvas translate,scale,rotate

下面使用三个小例子作为讲解：
1.translate:将canvas默认的原点（0，0），进行移动


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;public class TranslateDemo extends View {Paint mPaint;// 刻度尺高度private static final int RULE_HEIGHT = 200;private static final int SUM_IN_MM = 30;int mTotalWidth = 0;int mRuleLeftMargin = 20;// 厘米之间的像素数int mLineInterval = 5;public TranslateDemo(Context context) {super(context);initData(context);}private void initData(Context context) {mTotalWidth = mRuleLeftMargin * 2 + mLineInterval * SUM_IN_MM;mPaint = new Paint();mPaint.setARGB(255, 255, 0, 0);}public TranslateDemo(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);initData(context);}public TranslateDemo(Context context, AttributeSet attrs) {super(context, attrs);initData(context);}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);mPaint.setColor(Color.BLACK);canvas.translate(0, RULE_HEIGHT);canvas.drawLine(0, 0, mTotalWidth, 0, mPaint);drawLines(canvas);}private void drawLines(Canvas canvas) {// 刻度线的长度int ruleLength = 0;canvas.save();canvas.translate(mRuleLeftMargin, 0);for (int i = 0; i <= SUM_IN_MM; i++) {if (i % 10 == 0) {ruleLength = 100;} else if (i % 5 == 0) {ruleLength = 50;} else {ruleLength = 10;}canvas.drawLine(0, 0, 0, -ruleLength, mPaint);canvas.translate(mLineInterval, 0);}canvas.restore();}}

2.scale:将canvas进行缩放


import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.View;public class ScaleDemo extends View {Paint mPaint;final int TOTAL_SQUARE_COUNT = 30;int mHalfWidth = 0;int mHalfHeight = 0;public ScaleDemo(Context context) {super(context);initData(context);}private void initData(Context context) {mPaint = new Paint();mPaint.setARGB(255, 255, 0, 0);mPaint.setStyle(Style.STROKE);mPaint.setStrokeWidth(4);DisplayMetrics metric = new DisplayMetrics();((Activity) context).getWindowManager().getDefaultDisplay().getMetrics(metric);mHalfHeight = metric.heightPixels / 2;mHalfWidth = metric.widthPixels / 2;}public ScaleDemo(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);initData(context);}public ScaleDemo(Context context, AttributeSet attrs) {super(context, attrs);initData(context);}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);canvas.drawColor(Color.BLUE);drawSquare(canvas);}private void drawSquare(Canvas canvas) {canvas.translate(mHalfWidth, mHalfHeight);for (int i = 0; i < TOTAL_SQUARE_COUNT; i++) {// 保存画布canvas.save();float fraction = (float) i / TOTAL_SQUARE_COUNT;// 将画布以正方形中心进行缩放canvas.scale(fraction, fraction, 0, 0);canvas.drawCircle(0, 0, 360, mPaint);// 画布回滚canvas.restore();}}
}

3.rotate进行旋转


import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.View;public class RotateDemo extends View {Paint mPaint;final int TOTAL_SQUARE_COUNT = 30;int mHalfWidth = 0;int mHalfHeight = 0;public RotateDemo(Context context) {super(context);initData(context);}private void initData(Context context) {mPaint = new Paint();mPaint.setARGB(255, 255, 0, 0);mPaint.setStyle(Style.STROKE);mPaint.setStrokeWidth(4);DisplayMetrics metric = new DisplayMetrics();((Activity) context).getWindowManager().getDefaultDisplay().getMetrics(metric);mHalfHeight = metric.heightPixels / 2;mHalfWidth = metric.widthPixels / 2;}public RotateDemo(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);initData(context);}public RotateDemo(Context context, AttributeSet attrs) {super(context, attrs);initData(context);}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);canvas.drawColor(Color.BLUE);canvas.translate(mHalfWidth, mHalfHeight);canvas.drawCircle(0, 0, mHalfWidth, mPaint);drawLines(canvas);}public void drawLines(Canvas canvas) {canvas.save();int lineLength = 0;for (int i = 0; i < 60; i++) {if (i % 5 == 0) {lineLength = 100;} else {lineLength = 10;}canvas.drawLine(-mHalfWidth, 0,-mHalfWidth + lineLength, 0, mPaint);canvas.rotate(6);}canvas.restore();}}

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