http://marakana.com/tutorials/android/2d-graphics-example.html
我在下面使用这个例子。但是,当我在屏幕上移动手指的速度过快时,线条会变成单个点。
我不确定是否可以加快绘图速度。或者我应该用一条直线连接最后两个点。这两种解决方案中的第二种似乎是一个不错的选择,除了快速移动手指时,您会得到一条较长的直线段,然后是锐利的曲线。
如果还有其他解决方案,那将是非常高兴的。
感谢您的任何提前帮助。
http://marakana.com/tutorials/android/2d-graphics-example.html
我在下面使用这个例子。但是,当我在屏幕上移动手指的速度过快时,线条会变成单个点。
我不确定是否可以加快绘图速度。或者我应该用一条直线连接最后两个点。这两种解决方案中的第二种似乎是一个不错的选择,除了快速移动手指时,您会得到一条较长的直线段,然后是锐利的曲线。
如果还有其他解决方案,那将是非常高兴的。
感谢您的任何提前帮助。
Answers:
正如您提到的,一个简单的解决方案是简单地将点与直线连接起来。这是这样做的代码:
public void onDraw(Canvas canvas) {
Path path = new Path();
boolean first = true;
for(Point point : points){
if(first){
first = false;
path.moveTo(point.x, point.y);
}
else{
path.lineTo(point.x, point.y);
}
}
canvas.drawPath(path, paint);
}
确保将涂料从填充更改为描边:
paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(2);
paint.setColor(Color.WHITE);
另一个选择是使用quadTo方法将点与迭代连接:
public void onDraw(Canvas canvas) {
Path path = new Path();
boolean first = true;
for(int i = 0; i < points.size(); i += 2){
Point point = points.get(i);
if(first){
first = false;
path.moveTo(point.x, point.y);
}
else if(i < points.size() - 1){
Point next = points.get(i + 1);
path.quadTo(point.x, point.y, next.x, next.y);
}
else{
path.lineTo(point.x, point.y);
}
}
canvas.drawPath(path, paint);
}
这仍然会导致一些尖锐的边缘。
如果您确实有野心,则可以开始如下计算三次样条:
public void onDraw(Canvas canvas) {
Path path = new Path();
if(points.size() > 1){
for(int i = points.size() - 2; i < points.size(); i++){
if(i >= 0){
Point point = points.get(i);
if(i == 0){
Point next = points.get(i + 1);
point.dx = ((next.x - point.x) / 3);
point.dy = ((next.y - point.y) / 3);
}
else if(i == points.size() - 1){
Point prev = points.get(i - 1);
point.dx = ((point.x - prev.x) / 3);
point.dy = ((point.y - prev.y) / 3);
}
else{
Point next = points.get(i + 1);
Point prev = points.get(i - 1);
point.dx = ((next.x - prev.x) / 3);
point.dy = ((next.y - prev.y) / 3);
}
}
}
}
boolean first = true;
for(int i = 0; i < points.size(); i++){
Point point = points.get(i);
if(first){
first = false;
path.moveTo(point.x, point.y);
}
else{
Point prev = points.get(i - 1);
path.cubicTo(prev.x + prev.dx, prev.y + prev.dy, point.x - point.dx, point.y - point.dy, point.x, point.y);
}
}
canvas.drawPath(path, paint);
}
另外,我发现您需要更改以下内容以避免重复的运动事件:
public boolean onTouch(View view, MotionEvent event) {
if(event.getAction() != MotionEvent.ACTION_UP){
Point point = new Point();
point.x = event.getX();
point.y = event.getY();
points.add(point);
invalidate();
Log.d(TAG, "point: " + point);
return true;
}
return super.onTouchEvent(event);
}
并将dx和dy值添加到Point类:
class Point {
float x, y;
float dx, dy;
@Override
public String toString() {
return x + ", " + y;
}
}
这样可以产生平滑的线条,但有时必须使用循环将点连接起来。同样,对于较长的绘制会话,这将变得计算量大。
希望对您有所帮助。
编辑
我汇总了一个快速项目,演示了这些不同的技术,包括Square的建议签名实现。享受:https://github.com/johncarl81/androiddraw
这对您而言可能不再重要,但我为解决该问题付出了很多努力,我想与他人分享,可能对其他人很有用。
提供了@johncarl解决方案的教程非常适合绘制,但是出于我的目的,它们提供了一个限制。如果将手指从屏幕上移开然后放回去,此解决方案将在最后一次点击和新点击之间画一条线,使整个图形始终保持连接状态。所以我试图为此找到解决方案,最后我明白了!(对不起,我是图形初学者)
public class MainActivity extends Activity {
DrawView drawView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Set full screen view
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
requestWindowFeature(Window.FEATURE_NO_TITLE);
drawView = new DrawView(this);
setContentView(drawView);
drawView.requestFocus();
}
}
public class DrawingPanel extends View implements OnTouchListener {
private static final String TAG = "DrawView";
private static final float MINP = 0.25f;
private static final float MAXP = 0.75f;
private Canvas mCanvas;
private Path mPath;
private Paint mPaint;
private LinkedList<Path> paths = new LinkedList<Path>();
public DrawingPanel(Context context) {
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(Color.BLACK);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(6);
mCanvas = new Canvas();
mPath = new Path();
paths.add(mPath);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
@Override
protected void onDraw(Canvas canvas) {
for (Path p : paths){
canvas.drawPath(p, mPaint);
}
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
mX = x;
mY = y;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
// commit the path to our offscreen
mCanvas.drawPath(mPath, mPaint);
// kill this so we don't double draw
mPath = new Path();
paths.add(mPath);
}
@Override
public boolean onTouch(View arg0, MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
touch_start(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}
我拿了一个用手指绘制的android示例,并对其做了一些修改以存储每个路径,而不仅仅是最后一个!希望它能对某人有所帮助!
干杯。
mCanvas
用途是什么?您曾在其中提到“提交到屏幕外的路径”,touch_up()
但看起来mCanvas
从未在其他任何地方使用过。
我已经尝试了几种方法来渲染运动事件的累积点。最后,通过计算两个点之间的中点并将列表中的点作为二次贝塞尔曲线的锚点(除了第一个和最后一个点,它们之间通过简单的线连接到下一个中点),我获得了最佳结果)。
这样就可以形成没有任何拐角的平滑曲线。绘制的路径不会碰到列表中的实际点,而是经过每个中点。
Path path = new Path();
if (points.size() > 1) {
Point prevPoint = null;
for (int i = 0; i < points.size(); i++) {
Point point = points.get(i);
if (i == 0) {
path.moveTo(point.x, point.y);
} else {
float midX = (prevPoint.x + point.x) / 2;
float midY = (prevPoint.y + point.y) / 2;
if (i == 1) {
path.lineTo(midX, midY);
} else {
path.quadTo(prevPoint.x, prevPoint.y, midX, midY);
}
}
prevPoint = point;
}
path.lineTo(prevPoint.x, prevPoint.y);
}
如果您想简单:
public class DrawByFingerCanvas extends View {
private Paint brush = new Paint(Paint.ANTI_ALIAS_FLAG);
private Path path = new Path();
public DrawByFingerCanvas(Context context) {
super(context);
brush.setStyle(Paint.Style.STROKE);
brush.setStrokeWidth(5);
}
@Override
protected void onDraw(Canvas c) {
c.drawPath(path, brush);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
path.moveTo(x,y);
break;
case MotionEvent.ACTION_MOVE:
path.lineTo(x, y);
break;
default:
return false;
}
invalidate();
return true;
}
}
在活动中:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new DrawByFingerCanvas(this));
}
结果:
要删除所有图形,只需旋转屏幕。
我有非常相似的问题。调用onTouch方法时,还应该使用方法(在onTouch(MotionEvent事件)内部)
event.getHistorySize();
像这样
int histPointsAmount = event.getHistorySize();
for(int i = 0; i < histPointsAmount; i++){
// get points from event.getHistoricalX(i);
// event.getHistoricalY(i); and use them for your purpouse
}
我最近不得不对此做一些修改,现在我开发了我认为是最好的解决方案,因为它可以完成三件事:
canvas.drawPath()
方法在for循环之外,因此不会被多次调用。public class DrawView extends View implements OnTouchListener {
private static final String TAG = "DrawView";
List<Point> points = new ArrayList<Point>();
Paint paint = new Paint();
List<Integer> newLine = new ArrayList<Integer>();
public DrawView(Context context, AttributeSet attrs){
super(context, attrs);
setFocusable(true);
setFocusableInTouchMode(true);
setClickable(true);
this.setOnTouchListener(this);
paint.setColor(Color.WHITE);
paint.setAntiAlias(true);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(20);
}
public void setColor(int color){
paint.setColor(color);
}
public void setBrushSize(int size){
paint.setStrokeWidth((float)size);
}
public DrawView(Context context) {
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
paint.setColor(Color.BLUE);
paint.setAntiAlias(true);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(20);
}
@Override
public void onDraw(Canvas canvas) {
Path path = new Path();
path.setFillType(Path.FillType.EVEN_ODD);
for (int i = 0; i<points.size(); i++) {
Point newPoint = new Point();
if (newLine.contains(i)||i==0){
newPoint = points.get(i)
path.moveTo(newPoint.x, newPoint.y);
} else {
newPoint = points.get(i);
path.lineTo(newPoint.x, newPoint.y);
}
}
canvas.drawPath(path, paint);
}
public boolean onTouch(View view, MotionEvent event) {
Point point = new Point();
point.x = event.getX();
point.y = event.getY();
points.add(point);
invalidate();
Log.d(TAG, "point: " + point);
if(event.getAction() == MotionEvent.ACTION_UP){
// return super.onTouchEvent(event);
newLine.add(points.size());
}
return true;
}
}
class Point {
float x, y;
@Override
public String toString() {
return x + ", " + y;
}
}
这也可行,只是不太好
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.util.*;
public class DrawView extends View implements OnTouchListener {
private static final String TAG = "DrawView";
List<Point> points = new ArrayList<Point>();
Paint paint = new Paint();
List<Integer> newLine = new ArrayList<Integer>();
public DrawView(Context context, AttributeSet attrs){
super(context, attrs);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
paint.setColor(Color.WHITE);
paint.setAntiAlias(true);
}
public DrawView(Context context) {
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
paint.setColor(Color.WHITE);
paint.setAntiAlias(true);
}
@Override
public void onDraw(Canvas canvas) {
for (int i = 0; i<points.size(); i++) {
Point newPoint = new Point();
Point oldPoint = new Point();
if (newLine.contains(i)||i==0){
newPoint = points.get(i);
oldPoint = newPoint;
} else {
newPoint = points.get(i);
oldPoint = points.get(i-1);
}
canvas.drawLine(oldPoint.x, oldPoint.y, newPoint.x, newPoint.y, paint);
}
}
public boolean onTouch(View view, MotionEvent event) {
Point point = new Point();
point.x = event.getX();
point.y = event.getY();
points.add(point);
invalidate();
Log.d(TAG, "point: " + point);
if(event.getAction() == MotionEvent.ACTION_UP){
// return super.onTouchEvent(event);
newLine.add(points.size());
}
return true;
}
}
class Point {
float x, y;
@Override
public String toString() {
return x + ", " + y;
}
}
它可以让您合理地绘制线条,唯一的问题是如果将线条加粗,这会使绘制的线条看起来有些奇怪,实际上,我还是建议您使用第一个线条。
运动事件ACTION_MOVE
可能将单个对象内的多个运动样本汇总在一起。使用getX(int)和getY(int)可获得最新的指针坐标。使用getHistoricalX(int, int)
和访问批次中的较早坐标getHistoricalY(int, int)
。使用它们来构建路径会使其更加顺畅:
int historySize = event.getHistorySize();
for (int i = 0; i < historySize; i++) {
float historicalX = event.getHistoricalX(i);
float historicalY = event.getHistoricalY(i);
path.lineTo(historicalX, historicalY);
}
// After replaying history, connect the line to the touch point.
path.lineTo(eventX, eventY);
这是来自Square的一个很好的教程:http : //corner.squareup.com/2010/07/smooth-signatures.html
您可能MotionEvent
比自己意识到可以在两者之间提供一些数据的信息多得多。
链接中的示例忽略了事件中包含的历史接触点。请参见MotionEvent
文档顶部附近的“批处理”部分:http : //developer.android.com/reference/android/view/MotionEvent.html除此之外,用线连接点可能不是一个坏主意。