Develop Reference

Changing the color of part of a path while it is being drawn

I managed to create my own custom path drawing application and it is as follows
public class CanvasView extends View {
Context context;
HashMap<Integer,PathWrapper> locToPath=new HashMap<>();
ArrayList<PathWrapper> activePaths=new ArrayList<>();
CoMingleAndroidRuntime<Screenshare> screenRuntime;
boolean inited=false;
Integer myLocation;
public CanvasView(Context context,AttributeSet attr) {
super(context, attr);
setWillNotDraw(false);
this.context = context;
}
public void init(CoMingleAndroidRuntime<Screenshare> screenRuntime){
inited=true;
this.screenRuntime=screenRuntime;
this.myLocation=screenRuntime.getLocation();
addPath(myLocation);
invalidate();
}
public void addPath(int Location){
Paint mPaint=new Paint();
mPaint.setColor(Color.BLACK);
mPaint.setAlpha(195);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeWidth(50f);
locToPath.put(Location, new PathWrapper(new Path(), mPaint, Location));
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
for(PathWrapper path:activePaths){
canvas.drawPath(path.path, path.paint);
}
invalidate();
}
public void respondActionColorChanged(int R,int G,int B){
locToPath.get(myLocation).paint.setColor(Color.rgb(R, G, B));
}
public void respondActionColorChanged(int loc,int R,int G,int B){
locToPath.get(loc).paint.setColor(Color.rgb(R, G, B));
}
public void respondActionDown(final Integer loc, int xTouch,int yTouch){
activePaths.add(locToPath.get(loc));
locToPath.get(loc).path.moveTo(xTouch, yTouch);
locToPath.get(loc).lastPoint = new Point(xTouch, yTouch);
if(loc==myLocation){
screenRuntime.getRewriteMachine().addActionDown(xTouch, yTouch);
}
}
public void respondActionMove(final Integer loc,int xTouch,int yTouch){
float dx = Math.abs(xTouch - locToPath.get(loc).lastPoint.x);
float dy = Math.abs(yTouch - locToPath.get(loc).lastPoint.y);
if (dx >= 5 || dy >= 5) {
locToPath.get(loc).path.quadTo(locToPath.get(loc).lastPoint.x, locToPath.get(loc).lastPoint.y, (xTouch + locToPath.get(loc).lastPoint.x) / 2, (yTouch + locToPath.get(loc).lastPoint.y) / 2);
locToPath.get(loc).lastPoint = new Point(xTouch, yTouch);
if(loc==myLocation){
screenRuntime.getRewriteMachine().addActionMove(xTouch, yTouch);
}
}
}
public void respondActionUp(final Integer loc,int x,int y){
locToPath.get(loc).path.lineTo(locToPath.get(loc).lastPoint.x, locToPath.get(loc).lastPoint.y);
if(loc==myLocation){
screenRuntime.getRewriteMachine().addActionUp(x, y);
}
activePaths.remove(locToPath.get(loc));
locToPath.get(loc).path.reset();
}
#Override
public boolean onTouchEvent(MotionEvent event) {
if(inited) {
int xTouch;
int yTouch;
xTouch = (int) event.getX(0);
yTouch = (int) event.getY(0);
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
respondActionDown(myLocation,xTouch,yTouch);
break;
case MotionEvent.ACTION_MOVE:
respondActionMove(myLocation, xTouch,yTouch);
break;
case MotionEvent.ACTION_UP:
respondActionUp(myLocation, xTouch,yTouch);
break;
}
return true;
}
return false;
}
This code works perfectly for my app (Ignore the location stuff and the runtime and rewriteMachine stuff).
My question is, I would like to have parts of the path be colored differently, the ultimate goal is that I would like only the last few pixels of the path to be visible and the remainder should have an Alpha of 0, such that when the user draws, he only sees the last few pixels of the path which then slowly turns invisible. Is this possible? and if so how would I do it?
Thanks.

Instead of adding points to a path, create a list of paths, and every time add a new path to the list that has only a small chunk that starts at the end point of the previous path, and has only one other point (end-point). Then you can draw each path with a different color:
Paint mPaint=new Paint();
mPaint.setColor(Color.BLACK);
//rest of mPaint...
canvas.drawPath(path1, mPaint);
mPaint=new Paint();
mPaint.setColor(Color.BLUE);
//rest of mPaint...
canvas.drawPath(path2, mPaint);
Note that path1 is different from path2, and more importantly you create a new mPaint for each color. I'm not sure if it would work if you just would call mPaint.setColor(Color.BLUE) on the previously created and used paint.

How to draw with precision (e.g. a line) in Android?

I've been trying to make a drawing canvas in my app, but I'm unable to draw the points precisely. I'm using an OnTouchListener and I add every point in the historical pointer to the canvas and paint it with black.
Unfortunately, it's not working because it's not drawing all the points touched by the user (for example, when tracing a line). I'll show you an example:
The code I'm using is the following:
public class DrawView extends View implements OnTouchListener {
List<Point> points = new ArrayList<Point>();
Paint paint = new Paint();
public DrawView(Context context) {
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
paint.setColor(Color.BLACK);
paint.setAntiAlias(true);
}
public DrawView(Context context,AttributeSet attrs) {
super(context,attrs);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
paint.setColor(Color.BLACK);
paint.setAntiAlias(true);
}
public DrawView(Context context,AttributeSet attrs,int defStyle) {
super(context,attrs,defStyle);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
paint.setColor(Color.BLUE);
paint.setAntiAlias(true);
}
#Override
public void onDraw(Canvas canvas) {
for (Point point : points) {
canvas.drawCircle(point.x, point.y, 12, paint);
}
}
public boolean onTouch(View view, MotionEvent event) {
Point point = new Point();
final int historySize = event.getHistorySize();
final int pointerCount = event.getPointerCount();
for (int h = 0; h < historySize; h++) {
for (int p = 0; p < pointerCount; p++) {
point.x=event.getHistoricalX(p, h);
point.y=event.getHistoricalY(p, h);
points.add(point);
invalidate();
Log.d("debug","pointer: "+
event.getPointerId(p)+" "+ event.getHistoricalX(p, h)+" "+ event.getHistoricalY(p, h));
}
}
/*point.x = (int)event.getX();
point.y = (int)event.getY();*/
Log.d("debug", "really saved: "+
event.getX()+" "+ event.getY());
//points.add(point);
//invalidate();
return true;
}
}
class Point {
float x, y;
#Override
public String toString() {
return x + ", " + y;
}
}
Any ideas?
Thank you in advance

The problem is that you are only drawing points you get touch events for. If the user moves quickly you only get some of the points. The solution is to draw lines between consecutive points rather than just the points themselves.

You are missing many points here, you should capture all points here rather than capturing historical points only.
Check this -
http://www.codeproject.com/Articles/458042/Touch-handling-in-Android

How to Move a ShapeDrawable in Canvas on Touch Events

I am trying to implement a Drawing Application in Android. Where the user should be able to select and move the drawn shapes.
Currently i have statically drawn some rects and text on my Drawing Canvas:
View mDrawingCanvas = new View(mContext)
{
ShapeDrawable rectangle;
#Override
public boolean isFocused() {
// TODO Auto-generated method stub
Log.d(TAG, "View's On focused is called !");
return super.isFocused();
}
#Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
return super.onTouchEvent(event);
}
#Override
protected void onDraw(final Canvas canvas) {
super.onDraw(canvas);
// Work out current total scale factor
// from source to view
final float scale = mSourceScale*(float)getWidth()/(float)mSize.x;
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.WHITE);
//Custom View
rectangle = new ShapeDrawable(new RectShape());
rectangle.getPaint().setColor(Color.GRAY);
rectangle.getPaint().setStyle(Paint.Style.FILL_AND_STROKE);
rectangle.getPaint().setStrokeWidth(3);
rectangle.setBounds((int)(50*scale), (int)(30*scale), (int)(200*scale), (int)(150*scale));
rectangle.draw(canvas);
rectangle.getPaint().setColor(Color.BLUE);
rectangle.getPaint().setStyle(Paint.Style.FILL_AND_STROKE);
rectangle.getPaint().setStrokeWidth(3);
rectangle.setBounds((int)(200*scale), (int)(200*scale), (int)(400*scale), (int)(350*scale));
rectangle.draw(canvas);
}
};
I want to select (draw borders on the selected shape) and move the drawn Shapes in onTouch events of the drawing canvas.
Can some one please guide me about this, any help is Highly Appreciated.

This answer has demonstrated the Shape Moving Methodology that i was looking for.
And my problem is solved now. The Link is :
Drag and move a circle drawn on canvas

You should save the X and Y positions in the touch event and use them when drawing your shapes.
Below is a very basic example of how to do this, but you need to improve it (check if the touch is inside the object and only change values for that object)
Example:
public class DrawTest extends View {
private static final String TAG = "Desenho";
private ShapeDrawable rectangle;
private Paint paint;
private float currX, currY;
private Rect blue, gray;
public DrawTest(Context context) {
super(context);
currX = 1;
currY = 1;
gray = new Rect(50,30,200,150);
blue = new Rect(200,200,400,350);
paint = new Paint();
rectangle = new ShapeDrawable(new RectShape());
}
#Override
public boolean isFocused() {
Log.d(TAG, "View's On focused is called !");
return super.isFocused();
}
#Override
public boolean onTouchEvent(MotionEvent event) {
currX = event.getX();
currY = event.getY();
invalidate();
Log.d(TAG, "View's On touch is called! X= "+currX + ", Y= "+currY);
return super.onTouchEvent(event);
}
#Override
protected void onDraw(final Canvas canvas) {
super.onDraw(canvas);
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.WHITE);
//Custom View
rectangle.getPaint().setColor(Color.GRAY);
rectangle.getPaint().setStyle(Paint.Style.FILL_AND_STROKE);
rectangle.getPaint().setStrokeWidth(3);
gray.set((int)(50+currX), (int)(30+currY), (int)(200+currX), (int)(150+currY));
rectangle.setBounds(gray);
gray = rectangle.getBounds();
rectangle.draw(canvas);
rectangle.getPaint().setColor(Color.BLUE);
rectangle.getPaint().setStyle(Paint.Style.FILL_AND_STROKE);
rectangle.getPaint().setStrokeWidth(3);
blue.set((int)(200+currX), (int)(200+currY), (int)(400+currX), (int)(350+currY));
rectangle.setBounds(blue);
blue = rectangle.getBounds();
rectangle.draw(canvas);
}
}

android line draw

I want to draw lines on the screen but my application is drawing only dotted. So what should I add in my code?
List<Point> points = new ArrayList<Point>();
Paint paint = new Paint();
public DrawView(Context context) {
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
paint.setColor(Color.BLUE);
paint.setAntiAlias(true);
}
#Override
public void onDraw(Canvas canvas) {
for (Point point : points) {
canvas.drawCircle(point.x, point.y, 5, paint);
// Log.d(TAG, "Painting: "+point);
}
}
public boolean onTouch(View view, MotionEvent event) {
// if(event.getAction() != MotionEvent.ACTION_DOWN)
// return super.onTouchEvent(event);
Point point = new Point();
point.x = event.getX();
point.y = event.getY();
points.add(point);
invalidate();
Log.d(TAG, "point: " + point);
return true;
}
}
class Point
{
float x, y;
#Override
public String toString() {
return x + ", " + y;
}
}

Edit
Use drawLine or drawPath instead of drawCircle.
I would suggest you to take a look on the Fingerpaint example of the API Demos

Use drawLine bewteen 2 sets of points
For smoother lines, get all the historic events in onTouch and process them first
for faster/smoother, invalidate only the rect where points have changes
Read more here

How to get current canvas?

I have DrawView. If I touch this view it draws small circles. I wont to draw circles but not to touch view - with help function "setPoints". What I do:
package com.samples;
import ...
public class DrawView extends View {
ArrayList<Point> points = new ArrayList<Point>();
Paint paint = new Paint();
private int pSize = 5;
private int pColor = Color.BLACK;
public DrawView(Context context, AttributeSet attrs) {
super(context, attrs);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
v.setOnTouchListener(this);
Point point = new Point();
point.x = event.getX();
point.y = event.getY();
points.add(point);
invalidate();
}
return true;
}
});
requestFocus();
}
#Override
public void onDraw(Canvas canvas) {
for (Point point : points) {
canvas.drawCircle(point.x, point.y, pSize, paint);
}
}
public void setPoints(Float xP, Float yP)
{
Point point = new Point();
point.x = xP;
point.y = yP;
points.add(point);
postInvalidate();
}
}
class Point {
float x, y;
#Override
public String toString() {
return x + ", " + y;
}
}
Please tell me, how get canvas out setPoints function?
Update:
Wow, it's really interesting problem. My DrawView contains in HorizontalScrollView. Because if I set in this DrawView right coordinates, no one knows where are drawable circles.

You can't. The canvas is managed by the system and is passed to your onDraw(). I don't understand why you'd need it outside of there. Just redeclare setPoints like this
public void setPoints(Canvas canvas, Float xP, Float Yp)
You can keep a cache of the previous drawings (or store the previous points)

Try declaring canvas2 as a public variable in the DrawView class.

You draw your circles in onDraw(). That's the way View is supposed to work (technically it's actually in the draw() method but we'll overlook that). In setPoints(), set the points of the circle in variables within the class scope, call invalidate(), then draw the circle like that in onDraw(). If you follow this method, you're following the class flow that the view was designed for.