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Canvas.drawLines() produces gaps between lines

Paint.setStrokeJoin doesn't work with canvas.drawLinesWhat is the difference between “px”, “dip”, “dp” and “sp”?How do I pass data between Activities in Android application?What is the difference between gravity and layout_gravity in Android?Drawing a line with a certain pixel widthWhat is the difference between match_parent and fill_parent?Android: onDraw method using DrawPoint() causing jitter and distortion on canvasDrawing a line on imageViewAndroid android.graphics.Path width limited to 2036?drawLines method produces strange effect on scaled CanvasUndo/Redo not working in android Canvas

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I use drawLines() on my dataset of points. It's drawn perfectly when it starts from (0,0), but when the dataset starts from another point it produces some gaps.

Here the chart starting with (0, 0) (added small line at left bottom):

enter image description here

Here it starts from from (83, 56) and produces gap:

enter image description here

What I've tried:

Setting on/off anti-alias.

Different datasets (they all produce gap at the top y point if there is nothing drawn at (0, 0).

I've read about trying drawPath(), but since I need to draw lots of lines it was said to be not as effecient as drawLines().

Here are some snippets from my project:

My dataset:
x = 0,12,83,84,84,121,121,128,128,151,151,173,173,203,203,217,217,224,224,229,229,253,253,294,294,305,305,331,331,355,355,364,364,409,409,411,411,416,416,431,431,448,448,497,497,504,504,508,508,536,536,582,582,586,586,630,630,646,646,660,660,689,689,728,728,761,761,768,768,798,798,822,822,860,860,894,894,908,908,952,952,996,996,1039,1039,1085,1085,1085,1085,1099,1099,1119,1119,1133,1133,1169

y = 0,12,56,115,115,220,220,232,232,170,170,350,350,117,117,157,157,205,205,290,290,184,184,127,127,181,181,231,231,210,210,278,278,142,142,120,120,299,299,29,29,290,290,50,50,258,258,127,127,203,203,168,168,27,27,27,27,83,83,116,116,228,228,295,295,62,62,299,299,121,121,216,216,266,266,164,164,234,234,116,116,182,182,130,130,208,208,218,218,202,202,85,85,59,59,114

How I set my Paint:

private void init() 
 chartPaint = new Paint();
 chartPaint.setStyle(Paint.Style.STROKE);
 chartPaint.setStrokeWidth(4);
 chartPaint.setColor(color);

My onDraw():

@Override
protected void onDraw(Canvas canvas) 
 super.onDraw(canvas);

 canvas.save();

 // let chart start from the most left without gaps
 canvas.translate(0, viewHeight);

 // TODO: find place to move calcs outside onDraw()
 final float xScale = (float) viewWidth / (Util.getMax(x) - Util.getMin(x));
 final float yScale = (float) -viewHeight / (Util.getMax(y) - Util.getMin(y));

 valuesScaled = new float[values.length];

 for (int i = 0; i < values.length; i++) 
 valuesScaled[i] = (i%2==0) ? values[i] * xScale : values[i] * yScale;
 

 canvas.drawLines(valuesScaled, chartPaint);
 canvas.restore();

values array is where x and y arrays are stored alternatively, i.e. first 4 elements of values are x[0], y[0], x[1], y[1], ...

viewWidth and viewHeight are taken from onSizeChange().

edited Mar 24 at 21:49

asked Mar 24 at 21:43

pushandpop

227718

1

The answer is here. You cannot use Canvas.drawLines() you have to use drawPath() to get what you want. You could use drawLines() as a kind of preview and in the background run drawPath() and then use that when it has finished drawing.

– Jon Goodwin
Mar 25 at 1:47

@JonGoodwin Thanks for the comment. I've tried drawPath() and set stroke join. It produces the same gap. Do you know the possible reason for this?

– pushandpop
Mar 25 at 6:14

1

Yes. When the angle is really sharp (as in your second, highlighted peak), the miter end-point can recede to infinity. What you do is set a limit with .e.g. chartPaint.setStrokeMiter(6) see these image examples stroke-miterlimit. You could use a round end-point, or use a cap. With thin lines, maybe you just need a cap and so use the faster Canvas.drawLines(). Have a play and see...

– Jon Goodwin
Mar 25 at 7:21

@JonGoodwin thank you. you can post an answer - I'll accept it. Btw, you know any good resources (articles/talks/book) on android canvas/custom views?

– pushandpop
Mar 25 at 8:00

look at my back catalog of answers on graphics (my specialty) I will give you an answer, but time-poor and I only give what I consider a good answer...stay tuned... ;O)

– Jon Goodwin
Mar 27 at 23:29

add a comment |

I use drawLines() on my dataset of points. It's drawn perfectly when it starts from (0,0), but when the dataset starts from another point it produces some gaps.

Here the chart starting with (0, 0) (added small line at left bottom):

enter image description here

Here it starts from from (83, 56) and produces gap:

enter image description here

What I've tried:

Setting on/off anti-alias.

Different datasets (they all produce gap at the top y point if there is nothing drawn at (0, 0).

I've read about trying drawPath(), but since I need to draw lots of lines it was said to be not as effecient as drawLines().

Here are some snippets from my project:

How I set my Paint:

private void init() 
 chartPaint = new Paint();
 chartPaint.setStyle(Paint.Style.STROKE);
 chartPaint.setStrokeWidth(4);
 chartPaint.setColor(color);

My onDraw():

@Override
protected void onDraw(Canvas canvas) 
 super.onDraw(canvas);

 canvas.save();

 // let chart start from the most left without gaps
 canvas.translate(0, viewHeight);

 // TODO: find place to move calcs outside onDraw()
 final float xScale = (float) viewWidth / (Util.getMax(x) - Util.getMin(x));
 final float yScale = (float) -viewHeight / (Util.getMax(y) - Util.getMin(y));

 valuesScaled = new float[values.length];

 for (int i = 0; i < values.length; i++) 
 valuesScaled[i] = (i%2==0) ? values[i] * xScale : values[i] * yScale;
 

 canvas.drawLines(valuesScaled, chartPaint);
 canvas.restore();

values array is where x and y arrays are stored alternatively, i.e. first 4 elements of values are x[0], y[0], x[1], y[1], ...

viewWidth and viewHeight are taken from onSizeChange().

edited Mar 24 at 21:49

asked Mar 24 at 21:43

pushandpop

227718

1

The answer is here. You cannot use Canvas.drawLines() you have to use drawPath() to get what you want. You could use drawLines() as a kind of preview and in the background run drawPath() and then use that when it has finished drawing.

– Jon Goodwin
Mar 25 at 1:47

@JonGoodwin Thanks for the comment. I've tried drawPath() and set stroke join. It produces the same gap. Do you know the possible reason for this?

– pushandpop
Mar 25 at 6:14

1

Yes. When the angle is really sharp (as in your second, highlighted peak), the miter end-point can recede to infinity. What you do is set a limit with .e.g. chartPaint.setStrokeMiter(6) see these image examples stroke-miterlimit. You could use a round end-point, or use a cap. With thin lines, maybe you just need a cap and so use the faster Canvas.drawLines(). Have a play and see...

– Jon Goodwin
Mar 25 at 7:21

@JonGoodwin thank you. you can post an answer - I'll accept it. Btw, you know any good resources (articles/talks/book) on android canvas/custom views?

– pushandpop
Mar 25 at 8:00

look at my back catalog of answers on graphics (my specialty) I will give you an answer, but time-poor and I only give what I consider a good answer...stay tuned... ;O)

– Jon Goodwin
Mar 27 at 23:29

add a comment |

I use drawLines() on my dataset of points. It's drawn perfectly when it starts from (0,0), but when the dataset starts from another point it produces some gaps.

Here the chart starting with (0, 0) (added small line at left bottom):

enter image description here

Here it starts from from (83, 56) and produces gap:

enter image description here

What I've tried:

Setting on/off anti-alias.

Different datasets (they all produce gap at the top y point if there is nothing drawn at (0, 0).

I've read about trying drawPath(), but since I need to draw lots of lines it was said to be not as effecient as drawLines().

Here are some snippets from my project:

How I set my Paint:

private void init() 
 chartPaint = new Paint();
 chartPaint.setStyle(Paint.Style.STROKE);
 chartPaint.setStrokeWidth(4);
 chartPaint.setColor(color);

My onDraw():

@Override
protected void onDraw(Canvas canvas) 
 super.onDraw(canvas);

 canvas.save();

 // let chart start from the most left without gaps
 canvas.translate(0, viewHeight);

 // TODO: find place to move calcs outside onDraw()
 final float xScale = (float) viewWidth / (Util.getMax(x) - Util.getMin(x));
 final float yScale = (float) -viewHeight / (Util.getMax(y) - Util.getMin(y));

 valuesScaled = new float[values.length];

 for (int i = 0; i < values.length; i++) 
 valuesScaled[i] = (i%2==0) ? values[i] * xScale : values[i] * yScale;
 

 canvas.drawLines(valuesScaled, chartPaint);
 canvas.restore();

values array is where x and y arrays are stored alternatively, i.e. first 4 elements of values are x[0], y[0], x[1], y[1], ...

viewWidth and viewHeight are taken from onSizeChange().

edited Mar 24 at 21:49

asked Mar 24 at 21:43

pushandpop

227718

I use drawLines() on my dataset of points. It's drawn perfectly when it starts from (0,0), but when the dataset starts from another point it produces some gaps.

Here the chart starting with (0, 0) (added small line at left bottom):

enter image description here

Here it starts from from (83, 56) and produces gap:

enter image description here

What I've tried:

Setting on/off anti-alias.

Different datasets (they all produce gap at the top y point if there is nothing drawn at (0, 0).

I've read about trying drawPath(), but since I need to draw lots of lines it was said to be not as effecient as drawLines().

Here are some snippets from my project:

How I set my Paint:

private void init() 
 chartPaint = new Paint();
 chartPaint.setStyle(Paint.Style.STROKE);
 chartPaint.setStrokeWidth(4);
 chartPaint.setColor(color);

My onDraw():

@Override
protected void onDraw(Canvas canvas) 
 super.onDraw(canvas);

 canvas.save();

 // let chart start from the most left without gaps
 canvas.translate(0, viewHeight);

 // TODO: find place to move calcs outside onDraw()
 final float xScale = (float) viewWidth / (Util.getMax(x) - Util.getMin(x));
 final float yScale = (float) -viewHeight / (Util.getMax(y) - Util.getMin(y));

 valuesScaled = new float[values.length];

 for (int i = 0; i < values.length; i++) 
 valuesScaled[i] = (i%2==0) ? values[i] * xScale : values[i] * yScale;
 

 canvas.drawLines(valuesScaled, chartPaint);
 canvas.restore();

values array is where x and y arrays are stored alternatively, i.e. first 4 elements of values are x[0], y[0], x[1], y[1], ...

viewWidth and viewHeight are taken from onSizeChange().

android canvas

edited Mar 24 at 21:49

asked Mar 24 at 21:43

pushandpop

227718

edited Mar 24 at 21:49

asked Mar 24 at 21:43

pushandpop

227718

edited Mar 24 at 21:49

asked Mar 24 at 21:43

pushandpop

227718

asked Mar 24 at 21:43

pushandpop

227718

asked Mar 24 at 21:43

pushandpop

227718

1

The answer is here. You cannot use Canvas.drawLines() you have to use drawPath() to get what you want. You could use drawLines() as a kind of preview and in the background run drawPath() and then use that when it has finished drawing.

– Jon Goodwin
Mar 25 at 1:47

@JonGoodwin Thanks for the comment. I've tried drawPath() and set stroke join. It produces the same gap. Do you know the possible reason for this?

– pushandpop
Mar 25 at 6:14

1

Yes. When the angle is really sharp (as in your second, highlighted peak), the miter end-point can recede to infinity. What you do is set a limit with .e.g. chartPaint.setStrokeMiter(6) see these image examples stroke-miterlimit. You could use a round end-point, or use a cap. With thin lines, maybe you just need a cap and so use the faster Canvas.drawLines(). Have a play and see...

– Jon Goodwin
Mar 25 at 7:21

@JonGoodwin thank you. you can post an answer - I'll accept it. Btw, you know any good resources (articles/talks/book) on android canvas/custom views?

– pushandpop
Mar 25 at 8:00

look at my back catalog of answers on graphics (my specialty) I will give you an answer, but time-poor and I only give what I consider a good answer...stay tuned... ;O)

– Jon Goodwin
Mar 27 at 23:29

add a comment |

1

The answer is here. You cannot use Canvas.drawLines() you have to use drawPath() to get what you want. You could use drawLines() as a kind of preview and in the background run drawPath() and then use that when it has finished drawing.

– Jon Goodwin
Mar 25 at 1:47

@JonGoodwin Thanks for the comment. I've tried drawPath() and set stroke join. It produces the same gap. Do you know the possible reason for this?

– pushandpop
Mar 25 at 6:14

1

Yes. When the angle is really sharp (as in your second, highlighted peak), the miter end-point can recede to infinity. What you do is set a limit with .e.g. chartPaint.setStrokeMiter(6) see these image examples stroke-miterlimit. You could use a round end-point, or use a cap. With thin lines, maybe you just need a cap and so use the faster Canvas.drawLines(). Have a play and see...

– Jon Goodwin
Mar 25 at 7:21

@JonGoodwin thank you. you can post an answer - I'll accept it. Btw, you know any good resources (articles/talks/book) on android canvas/custom views?

– pushandpop
Mar 25 at 8:00

look at my back catalog of answers on graphics (my specialty) I will give you an answer, but time-poor and I only give what I consider a good answer...stay tuned... ;O)

– Jon Goodwin
Mar 27 at 23:29

The answer is here. You cannot use Canvas.drawLines() you have to use drawPath() to get what you want. You could use drawLines() as a kind of preview and in the background run drawPath() and then use that when it has finished drawing.

– Jon Goodwin
Mar 25 at 1:47

@JonGoodwin Thanks for the comment. I've tried drawPath() and set stroke join. It produces the same gap. Do you know the possible reason for this?

– pushandpop
Mar 25 at 6:14

Yes. When the angle is really sharp (as in your second, highlighted peak), the miter end-point can recede to infinity. What you do is set a limit with .e.g. chartPaint.setStrokeMiter(6) see these image examples stroke-miterlimit. You could use a round end-point, or use a cap. With thin lines, maybe you just need a cap and so use the faster Canvas.drawLines(). Have a play and see...

– Jon Goodwin
Mar 25 at 7:21

@JonGoodwin thank you. you can post an answer - I'll accept it. Btw, you know any good resources (articles/talks/book) on android canvas/custom views?

– pushandpop
Mar 25 at 8:00

look at my back catalog of answers on graphics (my specialty) I will give you an answer, but time-poor and I only give what I consider a good answer...stay tuned... ;O)

– Jon Goodwin
Mar 27 at 23:29

add a comment |

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