1、绘制几何图像/位图
void drawBitmap(Bitmap bitmap, float left, float top, Paint paint):在指定位置绘制位图.
void drawLine(float startX, float startY, float stopX, float stopY,Paint paint)：根据给定的起始点和结束点之间绘制连线.
void drawPath(Path path, Paint paint):根据给定的path，绘制连线.
void drawPoint(float x, float y, Paint paint):根据给定的坐标，绘制点.
2、位置/形状变换
1、平移操作
//1、平移操作
mPaint.setColor(Color.RED);
canvas.drawRect(0,0, 400, 400, mPaint);
canvas.translate(50, 50);
mPaint.setColor(Color.GRAY);
canvas.drawRect(0,0, 400, 400, mPaint);
2、缩放操作
//缩放操纵
canvas.drawRect(200,200, 700,700, mPaint);
canvas.scale(0.5f, 0.5f);
mPaint.setColor(Color.GRAY);
canvas.drawRect(200,200, 700,700, mPaint);
//缩放操纵
canvas.drawRect(200,200, 700,700, mPaint);
//先translate(px, py),再scale(sx, sy),再反translate
canvas.scale(0.5f, 0.5f, 200,200);
mPaint.setColor(Color.GRAY);
canvas.drawRect(200,200, 700,700, mPaint);
3、旋转操作
//旋转操作
canvas.translate(50,50);
canvas.drawRect(0,0, 700,700, mPaint);
canvas.rotate(45);
mPaint.setColor(Color.GRAY);
canvas.drawRect(0,0, 700,700, mPaint);
//旋转操作
canvas.drawRect(400, 400, 900, 900, mPaint);
canvas.rotate(45, 650, 650); //px, py表示旋转中心的坐标
mPaint.setColor(Color.GRAY);
canvas.drawRect(400, 400, 900, 900, mPaint);
4、倾斜操作
//倾斜操作
canvas.skew(1, 0); //在X方向倾斜45度,Y轴逆时针旋转45
canvas.skew(0, 1); //在y方向倾斜45度， X轴顺时针旋转45
5、切割操作
//切割
canvas.drawRect(200, 200,700, 700, mPaint);
mPaint.setColor(Color.GRAY);
canvas.drawRect(200, 800,700, 1300, mPaint);
canvas.clipRect(200, 200,700, 700); //画布被裁剪
canvas.drawCircle(100,100, 100,mPaint); //坐标超出裁剪区域，无法绘制
canvas.drawCircle(300, 300, 100, mPaint); //坐标区域在裁剪范围内，绘制成功
//切割
canvas.drawRect(200, 200,700, 700, mPaint);
mPaint.setColor(Color.GRAY);
canvas.drawRect(200, 800,700, 1300, mPaint);
canvas.clipOutRect(200,200,700,700); //画布裁剪外的区域
canvas.drawCircle(100,100,100,mPaint); //坐标区域在裁剪范围内，绘制成功
canvas.drawCircle(300, 300, 100, mPaint);//坐标超出裁剪区域，无法绘制
6、通过matrix实现平移，缩放，旋转等操作
//矩阵
canvas.drawRect(0,0,700,700, mPaint);
Matrix matrix = new Matrix();
matrix.setTranslate(50,50);
matrix.setRotate(45);
matrix.setScale(0.5f, 0.5f);
canvas.setMatrix(matrix);
mPaint.setColor(Color.GRAY);
canvas.drawRect(0,0,700,700, mPaint);
3、状态保存和恢复
Canvas调用了translate、rotate、scale、skew、clipRect等变化后，后续的操作都是基于变换后的Canvas，都会受到影响，对于后续的操作很不方便，Canvas提供了save、saveLayer、saveLayerAlpha、restore、restoreToCount来保护和恢复状态。
1.canvas内部对于状态的保存存放在栈中
2.可以多次调用save保存canvas的状态，并且可以通过getSaveCount方法获取保存的状态个数
3.可以通过restore方法返回最近一次save前的状态，也可以通过restoreToCount返回指定save状态。指定save状态之后的状态全部被清除
4.saveLayer可以创建新的图层，之后的绘制都会在这个图层之上绘制，直到调用restore方法
注意：绘制的坐标系不能超过图层的范围， saveLayerAlpha对图层增加了透明度信息
int state = canvas.save();//第一次保存
canvas.translate(50,50);
mPaint.setColor(Color.GRAY);
canvas.drawRect(0,0,500,500, mPaint);
canvas.save();
canvas.translate(50,50);
mPaint.setColor(Color.BLUE);
canvas.drawRect(0,0,500,500, mPaint);
canvas.restoreToCount(state);
canvas.drawRect(200,200, 700,700, mPaint);
int layerId = canvas.saveLayer(0,0, 700, 700, mPaint);
mPaint.setColor(Color.GRAY);
Matrix matrix = new Matrix();
matrix.setTranslate(100,100);
canvas.setMatrix(matrix);
canvas.drawRect(0,0,700,700, mPaint); //由于平移操作，导致绘制的矩形超出了图层的大小，所以绘制不完全
canvas.restoreToCount(layerId);
mPaint.setColor(Color.RED);
canvas.drawRect(0,0,100,100, mPaint);
3、粒子爆炸效果
这个动画效果是通过属性动画的更新不断的去更新粒子x，y, vX,vY的值，重新绘制，通过不断的绘制达到爆炸的效果。
/**
* 粒子封装对象
*/
public class Ball {
public int color; //图片像素点颜色值
public float x; //粒子圆心坐标x
public float y; //粒子圆心坐标y
public float r; //粒子半径
public float vX;//粒子运动水平方向速度
public float vY;//粒子运动垂直方向速度
public float aX;//粒子运动水平方向加速度
public float aY;//粒子运动垂直方向加速度
}
public class SplitView extends View {
private Paint mPaint;
private Bitmap mBitmap;
private float d = 3;//粒子直径
private ValueAnimator mAnimator;
private List<Ball> mBalls = new ArrayList<>();
public SplitView(Context context) {
this(context, null);
}
public SplitView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public SplitView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
mPaint = new Paint();
mBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.pic);
for (int i = 0; i < mBitmap.getWidth(); i++) {
for (int j = 0; j < mBitmap.getHeight(); j++) {
Ball ball = new Ball();
ball.color = mBitmap.getPixel(i, j);
ball.x = i * d + d / 2;
ball.y = j * d + d / 2;
ball.r = d / 2;
//速度(-20,20)
ball.vX = (float) (Math.pow(-1, Math.ceil(Math.random() * 1000)) * 20 * Math.random());
ball.vY = rangInt(-15, 35);
//加速度
ball.aX = 0;
ball.aY = 0.98f;
mBalls.add(ball);
}
}
mAnimator = ValueAnimator.ofFloat(0, 1);
mAnimator.setRepeatCount(1);
mAnimator.setDuration(2000);
mAnimator.setInterpolator(new LinearInterpolator());
mAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
updateBall();
invalidate();
}
});
}
private int rangInt(int i, int j) {
int max = Math.max(i, j);
int min = Math.min(i, j) - 1;
//在0到(max - min)范围内变化，取大于x的最小整数 再随机
return (int) (min + Math.ceil(Math.random() * (max - min)));
}
private void updateBall() {
//更新粒子的位置
for (Ball ball : mBalls) {
ball.x += ball.vX;
ball.y += ball.vY;
ball.vX += ball.aX;
ball.vY += ball.aY;
}
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.translate(500, 500);
for (Ball ball : mBalls) {
mPaint.setColor(ball.color);
canvas.drawCircle(ball.x, ball.y, ball.r, mPaint);
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN) {
//执行动画
mAnimator.start();
}
return super.onTouchEvent(event);
}
}
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