Develop Reference

How to get text BaseLine from Paint

I am trying to draw a text at the centre of canvas, Since canvas starts drawing text at BaseLine, I am not able to Place it at centre. If i can get the baseLine, then i can calculate the centre.
I have tried with paint.getFontMetrics() this gives ascent and descent but not baseLine.

Did you try this code
private void drawCenter(Canvas canvas, Paint paint, String text) {
canvas.getClipBounds(r);
int cHeight = r.height();
int cWidth = r.width();
paint.setTextAlign(Paint.Align.LEFT);
paint.getTextBounds(text, 0, text.length(), r);
float x = cWidth / 2f - r.width() / 2f - r.left;
float y = cHeight / 2f + r.height() / 2f - r.bottom;
canvas.drawText(text, x, y, paint);
}

All the calculations of paint.getFontMetrics() will happen with respect to baseLine. So if i just subtract (getMeasuredHeight() / 2f) - (fontMetrics.ascent / 2f) it will draw from center

Android: canvas.drawText on a circle sides

I want to draw texts on the sides of a circle and another one below it. I edited the code in this answer but the problem is that the circle and arc are taking the whole space of the rect, which makes no space for the text to be drawn.
Here is my code
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// getHeight() is not reliable, use getMeasuredHeight() on first run:
// Note: mRect will also be null after a configuration change,
// so in this case the new measured height and width values will be used:
if (mRect == null) {
// take the minimum of width and height here to be on he safe side:
centerX = getMeasuredWidth() / 2;
centerY = getMeasuredHeight() / 2;
radius = Math.min(centerX, centerY);
// mRect will define the drawing space for drawArc()
// We have to take into account the STROKE_WIDTH with drawArc() as well as drawCircle():
// circles as well as arcs are drawn 50% outside of the bounds defined by the radius (radius for arcs is calculated from the rectangle mRect).
// So if mRect is too large, the lines will not fit into the View
int startTop = STROKE_WIDTH / 2;
int startLeft = startTop;
int endBottom = 2 * radius - startTop;
int endRight = endBottom;
mRect = new RectF(startTop, startLeft, endRight, endBottom);
}
// subtract half the stroke width from radius so the blue circle fits inside the View
canvas.drawCircle(centerX, centerY, radius - STROKE_WIDTH / 2, mBasePaint);
// Or draw arc from degree 192 to degree 90 like this ( 258 = (360 - 192) + 90:
// canvas.drawArc(mRect, 192, 258, false, mBasePaint);
// draw an arc from 90 degrees to 192 degrees (102 = 192 - 90)
// Note that these degrees are not like mathematical degrees:
// they are mirrored along the y-axis and so incremented clockwise (zero degrees is always on the right hand side of the x-axis)
canvas.drawArc(mRect, 270, mTemp * 6, false, mDegreesPaint); // Each degree in the temp scale = 6 degrees on circle
canvas.drawArc(mRect, 270 + mSeparator * 6, 3, false, mSeparatorPaint); // The separator size = 3 degrees
// subtract stroke width from radius so the white circle does not cover the blue circle/ arc
canvas.drawCircle(centerX, centerY, radius - STROKE_WIDTH, mCenterPaint);
drawCenter(canvas, mTextPaint, mTemp + "°");
canvas.drawText("Temp 1", mRect.centerX(), radius * 2, mTextPaint);
}
This code produces what I need as an arc and circles, but I'm not able to draw degrees on the circle sides and a text below it
Any help??

Draw text below Circle

I want to draw text below circle in canvas. Following is my code but text is drawn above circle.
canvas.drawCircle(getWidth() / 2, getHeight() / 2, radius, paint);
canvas.drawText(text, 0, (radius*2), textPaint);

Looking at it properly you need to set the y value based on height of the canvas, same way you did the circle, then adjust it to be Below based on radius.
canvas.drawCircle(getWidth() / 2, getHeight() / 2, radius, paint);
canvas.drawText(text, 0, (getHeight() / 2) + radius, textPaint);
One thing that may be confusing you is that the origion is the top left. And that increase in Y is downwards
You may need to add a few extra pixels based on text height. so (getHeight() / 2) + radius + 20

Android Rotating Rectangle and understanding the Canvas

I'm looking at making something that looks like the following:
Which is basically a rectangle shape on the top left thats been rotated, and then two underneath it, tiled like it is.
I've had a go at doing it but just can't get it done, basically I use:
int x = getWidth();
int y = getHeight();
canvas.save();
canvas.rotate(-45);
canvas.drawRect(x/2, y/2, x/2+100, y/2+40, paint);
canvas.restore();
And I've noticed that what should be a rectangle rotated near the centre of the screen is instead one that is to the top right of the screen. When I try doing something similar to (0,0, 100,100) I don't get any rectangle at all.
I guess I'm confused whether the coordinate system changes when the rotation of the canvas is done, and what would be the easiest way in looking into getting the image above on android (besides just creating it in photoshop and adding the png).

The single argument rotate(angle) will use 0,0 as the pivot point.
If you want to rotate about your object, you should calculate some point on it to rotate about and use the 3 argument rotate(angle, pivotX, pivotY), ie:
int x = getWidth();
int y = getHeight();
canvas.save();
canvas.rotate(-45, x / 2, y / 2);
canvas.drawRect(x / 2, y / 2, x / 2 + 100, y / 2 + 40, paint);
canvas.restore();
I made your design just for fun:
int x = getWidth();
canvas.rotate(-45);
canvas.drawRect(-x, 0, x, h, green);
canvas.drawRect(-x, h, 0, 2 * h, purple);
canvas.drawRect(0, h, x, 2 * h, blue);
Where h is the height of the rectangle.

How to use android canvas to draw a Rectangle with only topleft and topright corners round?

I found a function for rectangles with all 4 corners being round, but I want to have just the top 2 corners round. What can I do?
canvas.drawRoundRect(new RectF(0, 100, 100, 300), 6, 6, paint);

For API 21 and above the Path class added a new method addRoundRect() which you can use it like this.
corners = new float[]{
80, 80, // Top left radius in px
80, 80, // Top right radius in px
0, 0, // Bottom right radius in px
0, 0 // Bottom left radius in px
};
final Path path = new Path();
path.addRoundRect(rect, corners, Path.Direction.CW);
canvas.drawPath(path, mPaint);
in Kotlin
val corners = floatArrayOf(
80f, 80f, // Top left radius in px
80f, 80f, // Top right radius in px
0f, 0f, // Bottom right radius in px
0f, 0f // Bottom left radius in px
)
val path = Path()
path.addRoundRect(rect, corners, Path.Direction.CW)
canvas.drawPath(path, mPaint)

Use a path. It has the advantage of working for APIs less than 21 (Arc is also limited thusly, which is why I quad). Which is a problem because not everybody has Lollipop yet. You can however specify a RectF and set the values with that and use arc back to API 1, but then you wouldn't get to use a static (without declaring a new object to build the object).
Drawing a rounded rect:
path.moveTo(right, top + ry);
path.rQuadTo(0, -ry, -rx, -ry);
path.rLineTo(-(width - (2 * rx)), 0);
path.rQuadTo(-rx, 0, -rx, ry);
path.rLineTo(0, (height - (2 * ry)));
path.rQuadTo(0, ry, rx, ry);
path.rLineTo((width - (2 * rx)), 0);
path.rQuadTo(rx, 0, rx, -ry);
path.rLineTo(0, -(height - (2 * ry)));
path.close();
As a full function:
static public Path RoundedRect(float left, float top, float right, float bottom, float rx, float ry, boolean conformToOriginalPost) {
Path path = new Path();
if (rx < 0) rx = 0;
if (ry < 0) ry = 0;
float width = right - left;
float height = bottom - top;
if (rx > width/2) rx = width/2;
if (ry > height/2) ry = height/2;
float widthMinusCorners = (width - (2 * rx));
float heightMinusCorners = (height - (2 * ry));
path.moveTo(right, top + ry);
path.rQuadTo(0, -ry, -rx, -ry);//top-right corner
path.rLineTo(-widthMinusCorners, 0);
path.rQuadTo(-rx, 0, -rx, ry); //top-left corner
path.rLineTo(0, heightMinusCorners);
if (conformToOriginalPost) {
path.rLineTo(0, ry);
path.rLineTo(width, 0);
path.rLineTo(0, -ry);
}
else {
path.rQuadTo(0, ry, rx, ry);//bottom-left corner
path.rLineTo(widthMinusCorners, 0);
path.rQuadTo(rx, 0, rx, -ry); //bottom-right corner
}
path.rLineTo(0, -heightMinusCorners);
path.close();//Given close, last lineto can be removed.
return path;
}
You'd want to line all the way to those corner bits, rather than quad across them. This is what setting true to conformToOriginalPost does. Just line to the control point there.
If you want to do that all but don't care about pre-Lollipop stuff, and urgently insist that if your rx and ry are high enough, it should draw a circle.
#TargetApi(Build.VERSION_CODES.LOLLIPOP)
static public Path RoundedRect(float left, float top, float right, float bottom, float rx, float ry, boolean conformToOriginalPost) {
Path path = new Path();
if (rx < 0) rx = 0;
if (ry < 0) ry = 0;
float width = right - left;
float height = bottom - top;
if (rx > width/2) rx = width/2;
if (ry > height/2) ry = height/2;
float widthMinusCorners = (width - (2 * rx));
float heightMinusCorners = (height - (2 * ry));
path.moveTo(right, top + ry);
path.arcTo(right - 2*rx, top, right, top + 2*ry, 0, -90, false); //top-right-corner
path.rLineTo(-widthMinusCorners, 0);
path.arcTo(left, top, left + 2*rx, top + 2*ry, 270, -90, false);//top-left corner.
path.rLineTo(0, heightMinusCorners);
if (conformToOriginalPost) {
path.rLineTo(0, ry);
path.rLineTo(width, 0);
path.rLineTo(0, -ry);
}
else {
path.arcTo(left, bottom - 2 * ry, left + 2 * rx, bottom, 180, -90, false); //bottom-left corner
path.rLineTo(widthMinusCorners, 0);
path.arcTo(right - 2 * rx, bottom - 2 * ry, right, bottom, 90, -90, false); //bottom-right corner
}
path.rLineTo(0, -heightMinusCorners);
path.close();//Given close, last lineto can be removed.
return path;
}
So,
conformToOriginalPost actually draws a rounded rect without the bottom two bits rounded.

I would draw two rectangles:
canvas.drawRect(new RectF(0, 110, 100, 290), paint);
canvas.drawRoundRect(new RectF(0, 100, 100, 200), 6, 6, paint);
Or something like that, you just overlap them so that the upper corners will be round. Preferably you should write a method for this

I changed this answer so you can set which corner you want to be round and which one you want to be sharp. also works on pre-lolipop
Usage Example:
only top-right and botton-right corners are rounded
Path path = RoundedRect(0, 0, fwidth , fheight , 5,5,
false, true, true, false);
canvas.drawPath(path,myPaint);
RoundRect:
public static Path RoundedRect(
float left, float top, float right, float bottom, float rx, float ry,
boolean tl, boolean tr, boolean br, boolean bl
){
Path path = new Path();
if (rx < 0) rx = 0;
if (ry < 0) ry = 0;
float width = right - left;
float height = bottom - top;
if (rx > width / 2) rx = width / 2;
if (ry > height / 2) ry = height / 2;
float widthMinusCorners = (width - (2 * rx));
float heightMinusCorners = (height - (2 * ry));
path.moveTo(right, top + ry);
if (tr)
path.rQuadTo(0, -ry, -rx, -ry);//top-right corner
else{
path.rLineTo(0, -ry);
path.rLineTo(-rx,0);
}
path.rLineTo(-widthMinusCorners, 0);
if (tl)
path.rQuadTo(-rx, 0, -rx, ry); //top-left corner
else{
path.rLineTo(-rx, 0);
path.rLineTo(0,ry);
}
path.rLineTo(0, heightMinusCorners);
if (bl)
path.rQuadTo(0, ry, rx, ry);//bottom-left corner
else{
path.rLineTo(0, ry);
path.rLineTo(rx,0);
}
path.rLineTo(widthMinusCorners, 0);
if (br)
path.rQuadTo(rx, 0, rx, -ry); //bottom-right corner
else{
path.rLineTo(rx,0);
path.rLineTo(0, -ry);
}
path.rLineTo(0, -heightMinusCorners);
path.close();//Given close, last lineto can be removed.
return path;
}

you can easily achieve this by using Path:
val radiusArr = floatArrayOf(
15f, 15f,
15f, 15f,
0f, 0f,
0f, 0f
)
val myPath = Path()
myPath.addRoundRect(
RectF(0f, 0f, 400f, 400f),
radiusArr,
Path.Direction.CW
)
canvas.drawPath(myPath, paint)

Simple helper function written in Kotlin.
private fun Canvas.drawTopRoundRect(rect: RectF, paint: Paint, radius: Float) {
// Step 1. Draw rect with rounded corners.
drawRoundRect(rect, radius, radius, paint)
// Step 2. Draw simple rect with reduced height,
// so it wont cover top rounded corners.
drawRect(
rect.left,
rect.top + radius,
rect.right,
rect.bottom,
paint
)
}
Usage:
canvas.drawTopRoundRect(rect, paint, radius)

public static Path composeRoundedRectPath(RectF rect, float topLeftDiameter, float topRightDiameter,float bottomRightDiameter, float bottomLeftDiameter){
Path path = new Path();
topLeftDiameter = topLeftDiameter < 0 ? 0 : topLeftDiameter;
topRightDiameter = topRightDiameter < 0 ? 0 : topRightDiameter;
bottomLeftDiameter = bottomLeftDiameter < 0 ? 0 : bottomLeftDiameter;
bottomRightDiameter = bottomRightDiameter < 0 ? 0 : bottomRightDiameter;
path.moveTo(rect.left + topLeftDiameter/2 ,rect.top);
path.lineTo(rect.right - topRightDiameter/2,rect.top);
path.quadTo(rect.right, rect.top, rect.right, rect.top + topRightDiameter/2);
path.lineTo(rect.right ,rect.bottom - bottomRightDiameter/2);
path.quadTo(rect.right ,rect.bottom, rect.right - bottomRightDiameter/2, rect.bottom);
path.lineTo(rect.left + bottomLeftDiameter/2,rect.bottom);
path.quadTo(rect.left,rect.bottom,rect.left, rect.bottom - bottomLeftDiameter/2);
path.lineTo(rect.left,rect.top + topLeftDiameter/2);
path.quadTo(rect.left,rect.top, rect.left + topLeftDiameter/2, rect.top);
path.close();
return path;
}

I achieved this by following the below steps.
These are the pre-requisites for the rounded rectangle to look neat
The radius of the edges have to be equal to the (height of the rectangle / 2). This is because if its any different value then the place where the curve meets straight line of the rectangle will not be
Next is the steps to draw the rounded rectangle.
First we draw 2 circles on the left and right side, with the radius = height of rectange / 2
Then we draw a rectangle between these circles to get the desired rounded rectangle.
I am posting the code below
private void drawRoundedRect(Canvas canvas, float left, float top, float right, float bottom) {
float radius = getHeight() / 2;
canvas.drawCircle(radius, radius, radius, mainPaint);
canvas.drawCircle(right - radius, radius, radius, mainPaint);
canvas.drawRect(left + radius, top, right - radius, bottom, mainPaint);
}
Now this results in a really nice rounded rectangle like the one shown below

This is an old question, however I wanted to add my solution because it uses the native SDK without lots of custom code or hacky drawing. This solution is supported back to API 1.
The way to do this properly is to create a path (as mentioned in other answers) however the previous answers seem to overlook the addRoundedRect function call that takes radii for each corner.
Variables
private val path = Path()
private val paint = Paint()
Setup Paint
paint.color = Color.RED
paint.style = Paint.Style.FILL
Update Path with Size Changes
Call this somewhere that isn't onDraw, such as onMeasure for a view or onBoundChange for a drawable. If it doesn't change (like this example) you could put this code where you set up your paint.
val radii = floatArrayOf(
25f, 25f, //Top left corner
25f, 25f, //Top right corner
0f, 0f, //Bottom right corner
0f, 0f, //Bottom left corner
)
path.reset() //Clears the previously set path
path.addRoundedRect(0f, 0f, 100f, 100f, radii, Path.Direction.CW)
This code creates a 100x100 rounded rect with the top corners rounded with a 25 radius.
Draw Path
Call this in onDraw for a view or draw for a drawable.
canvas.drawPath(path, paint)

A Path#arcTo() version to draw the rounded side if the radius is half of the height.
fun getPathOfRoundedRectF(
rect: RectF,
topLeftRadius: Float = 0f,
topRightRadius: Float = 0f,
bottomRightRadius: Float = 0f,
bottomLeftRadius: Float = 0f
): Path {
val tlRadius = topLeftRadius.coerceAtLeast(0f)
val trRadius = topRightRadius.coerceAtLeast(0f)
val brRadius = bottomRightRadius.coerceAtLeast(0f)
val blRadius = bottomLeftRadius.coerceAtLeast(0f)
with(Path()) {
moveTo(rect.left + tlRadius, rect.top)
//setup top border
lineTo(rect.right - trRadius, rect.top)
//setup top-right corner
arcTo(
RectF(
rect.right - trRadius * 2f,
rect.top,
rect.right,
rect.top + trRadius * 2f
), -90f, 90f
)
//setup right border
lineTo(rect.right, rect.bottom - trRadius)
//setup bottom-right corner
arcTo(
RectF(
rect.right - brRadius * 2f,
rect.bottom - brRadius * 2f,
rect.right,
rect.bottom
), 0f, 90f
)
//setup bottom border
lineTo(rect.left + blRadius, rect.bottom)
//setup bottom-left corner
arcTo(
RectF(
rect.left,
rect.bottom - blRadius * 2f,
rect.left + blRadius * 2f,
rect.bottom
), 90f, 90f
)
//setup left border
lineTo(rect.left, rect.top + tlRadius)
//setup top-left corner
arcTo(
RectF(
rect.left,
rect.top,
rect.left + tlRadius * 2f,
rect.top + tlRadius * 2f
),
180f,
90f
)
close()
return this
}
}

One simple and efficient way to draw a solid side is to use clipping - rect clipping is essentially free, and a lot less code to write than a custom Path.
If I want a 300x300 rect, with the top left and right rounded by 50 pixels, you can do:
canvas.save();
canvas.clipRect(0, 0, 300, 300);
canvas.drawRoundRect(new RectF(0, 0, 300, 350), 50, 50, paint);
canvas.restore();
This approach will only work for rounding on 2 or 3 adjacent corners, so it's a little less configurable than a Path based approach, but using round rects is more efficient, since drawRoundRect() is fully hardware accelerated (that is, tessellated into triangles) while drawPath() always falls back to software rendering (software-draw a path bitmap, and upload that to be cached on the GPU).
Not a huge performance issue for small infrequent drawing, but if you're animating paths, the cost of software draw can make your frame times longer, and increase your chance to drop frames. The path mask also costs memory.
If you do want to go with a Path-based approach, I'd recommend using GradientDrawable to simplify the lines of code (assuming you don't need to set a custom shader, e.g. to draw a Bitmap).
mGradient.setBounds(0, 0, 300, 300);
mGradient.setCornerRadii(new int[] {50,50, 50,50, 0,0, 0,0});
With GradientDrawable#setCornerRadii(), you can set any corner to be any roundedness, and reasonably animate between states.

Here is my answer to the above question. Here, I have created Kotlin extension function which uses Path along with the quadTo function which can be used in lower-level APIs also.
fun Canvas.drawRoundRectPath(
rectF: RectF,
radius: Float,
roundTopLeft: Boolean,
roundTopRight: Boolean,
roundBottomLeft: Boolean,
roundBottomRight: Boolean,
paint: Paint) {
val path = Path()
//Move path cursor to start point
if (roundBottomLeft) {
path.moveTo(rectF.left, rectF.bottom - radius)
} else {
path.moveTo(rectF.left, rectF.bottom)
}
// drawing line and rounding top left curve
if (roundTopLeft) {
path.lineTo(rectF.left, rectF.top + radius)
path.quadTo(rectF.left, rectF.top, rectF.left + radius, rectF.top)
} else {
path.lineTo(rectF.left, rectF.top)
}
// drawing line an rounding top right curve
if (roundTopRight) {
path.lineTo(rectF.right - radius, rectF.top)
path.quadTo(rectF.right, rectF.top, rectF.right, rectF.top + radius)
} else {
path.lineTo(rectF.right, rectF.top)
}
// drawing line an rounding bottom right curve
if (roundBottomRight) {
path.lineTo(rectF.right, rectF.bottom - radius)
path.quadTo(rectF.right, rectF.bottom, rectF.right - radius, rectF.bottom)
} else {
path.lineTo(rectF.right, rectF.bottom)
}
// drawing line an rounding bottom left curve
if (roundBottomLeft) {
path.lineTo(rectF.left + radius, rectF.bottom)
path.quadTo(rectF.left, rectF.bottom, rectF.left, rectF.bottom - radius)
} else {
path.lineTo(rectF.left, rectF.bottom)
}
path.close()
drawPath(path, paint)
}
We can call the function with canvas object and pass the RectF with the dimension on which we want to apply the curve.
Also, we can pass the boolean for the corners which we want to round.
This answer can further be customized to accept radius for individual corners.

You can draw that piece by piece using drawLine() and drawArc() functions from the Canvas.

Maybe the following code can help you
Paint p = new Paint();
p.setColor(color);
float[] corners = new float[]{
15, 15, // Top, left in px
15, 15, // Top, right in px
15, 15, // Bottom, right in px
15, 15 // Bottom,left in px
};
final Path path = new Path();
path.addRoundRect(rect, corners, Path.Direction.CW);
// Draw
canvas.drawPath(path, p);

Use PaintDrawable could be better:
val topLeftRadius = 10
val topRightRadius = 10
val bottomLeftRadius = 0
val bottomRightRadius = 0
val rect = Rect(0, 0, 100, 100)
val paintDrawable = PaintDrawable(Color.RED)
val outter = floatArrayOf(topLeftRadius, topLeftRadius, topRightRadius, topRightRadius,
bottomLeftRadius, bottomLeftRadius, bottomRightRadius, bottomRightRadius)
paintDrawable.setCornerRadii(outter)
paintDrawable.bounds = rect
paintDrawable.draw(canvas)

draw round rect with left rounded corners
private void drawRoundRect(float left, float top, float right, float bottom, Paint paint, Canvas canvas) {
Path path = new Path();
path.moveTo(left, top);
path.lineTo(right, top);
path.lineTo(right, bottom);
path.lineTo(left + radius, bottom);
path.quadTo(left, bottom, left, bottom - radius);
path.lineTo(left, top + radius);
path.quadTo(left, top, left + radius, top);
canvas.drawPath(path, onlinePaint);
}