http://marakana.com/tutorials/android/2d-graphics-example.html
我正在使用下面的示例,但当我在屏幕上快速移动手指时,线条会变成单个点。
我不确定是否可以加速绘制。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个似乎是一个不错的选择,除非您在移动手指时非常快,则会出现长时间的直线段和锐角曲线。
如果有其他解决方案,很高兴听到他们的意见。
谢谢提前帮助。
http://marakana.com/tutorials/android/2d-graphics-example.html
我正在使用下面的示例,但当我在屏幕上快速移动手指时,线条会变成单个点。
我不确定是否可以加速绘制。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个似乎是一个不错的选择,除非您在移动手指时非常快,则会出现长时间的直线段和锐角曲线。
如果有其他解决方案,很高兴听到他们的意见。
谢谢提前帮助。
如你所提及的,一种简单的解决方案是用一条直线连接这些点。以下是实现代码:
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);
}
确保将画笔从填充(fill)更改为描边(stroke):
paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(2);
paint.setColor(Color.WHITE);
另一种选项是使用quadTo方法通过插值来连接点:
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);
}
这仍然会导致一些锐利的边缘。
如果你非常有雄心壮志,可以按照以下方式开始计算立方样条:
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);
}
此外,我发现你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);
}
将dx和dy的值添加到Point类中:
class Point {
float x, y;
float dx, dy;
@Override
public String toString() {
return x + ", " + y;
}
}
这会产生平滑的线条,但有时必须使用循环连接点。此外,在长时间绘图会话中,计算变得计算密集。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;
}
}
我使用了android手指绘图的样例,并进行了一些修改,使其能够存储每一个路径,而不仅仅是最后一个!希望能对某些人有所帮助!
祝好。
mCanvas
有什么用?你在 touch_up()
中提到了“将路径提交到我们的离屏”,但似乎 mCanvas
在其他任何地方都没有被使用过。 - Jake Stoeffler我尝试了几种方法来呈现运动事件的积累点。最终,我通过计算两个点之间的中点,并将列表中的点视为二次贝塞尔曲线的锚点(除了第一个和最后一个点,它们通过简单的线连接到下一个中点),得到了最佳结果。
这样可以得到平滑的曲线而没有任何拐角。绘制的路径将不会碰到列表中实际的点,但会经过每一个中点。
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);
}
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;
}
}
在这个活动中:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new DrawByFingerCanvas(this));
}
结果:
要清除所有绘画,请旋转屏幕。
我遇到了非常类似的问题。当你调用onTouch方法时,你也应该使用onTouch(MotionEvent event)方法(在onTouch方法内部)。
event.getHistorySize();
以及类似的内容。
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
}
ACTION_MOVE
的运动事件可能会在单个对象中批量包含多个移动样本。最新的指针坐标可使用 getX(int) 和 getY(int) 获取。批处理中较早的坐标可使用 getHistoricalX(int, int)
和 getHistoricalY(int, int)
访问。在构建路径时使用它们使得路径更加平滑:
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);
这里有一篇来自Square的好教程:http://corner.squareup.com/2010/07/smooth-signatures.html
canvas.drawPath()
方法在for循环外部调用,所以不会被多次调用。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;
}
}
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;
}
}
它可以让你比较好地画线,唯一的问题是如果你把线条变粗,那么画出来的线条会看起来有点奇怪,所以我仍然建议使用第一个。
你可能在MotionEvent
中有更多的信息可用,而你并没有意识到这些信息可以提供一些数据。
你链接中的示例忽略了事件中包含的历史触摸点。请参阅MotionEvent
文档顶部的“批处理”部分:http://developer.android.com/reference/android/view/MotionEvent.html 此外,使用线连接这些点可能也不是一个坏主意。
我曾经遇到过这个问题,我画了一个点而不是一条线。你应该先创建一个路径来保存你的线条。只在第一次触摸事件上调用path.moveto。然后在你的画布上绘制路径,最后在完成后重置或倒回路径(path.reset)...
Path.quadTo
,Path.cubicTo
... https://dev59.com/IVDTa4cB1Zd3GeqPL8aU - HostileFork says dont trust SE