Related
I'm drawing arc with canvas.drawArc(...) and use below code to add gradient to paint object but the gradient just applied on the body of arc and not the stroke. how to draw a gradient stroke?
paint = new Paint();
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth((float) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 50, getResources().getDisplayMetrics()));
paint.setShader(new RadialGradient(getWidth()/2,getHeight()/2,mRadius/2,Color.BLUE,Color.YELLOW, Shader.TileMode.CLAMP));
canvas.drawArc(new RectF(getWidth()/2-mRadius, getHeight()/2-mRadius, getWidth()/2+mRadius, getHeight()/2+mRadius),270f,mProgressDegree,true,paint);
I am trying to create an arc (variable number of degrees) that gradually goes from one color to another. From example from blue to red:
This is my code:
SweepGradient shader = new SweepGradient(center.x, center.y, resources.getColor(R.color.startColor),resources.getColor(R.color.endColor));
Paint paint = new Paint()
paint.setStrokeWidth(1);
paint.setStrokeCap(Paint.Cap.FILL);
paint.setStyle(Paint.Style.FILL);
paint.setShader(shader);
canvas.drawArc(rectF, startAngle, sweepAngle, true, paint);
But the result is the entire arc is painted with the same color.
Edit:
After more experimenting, I found out that the color spread is determined by the angle of the arc. If I draw an arc with a small angle, only the first color is displayed. The larger the angle, more colors are drawn. If the angle is small it seems that there is no gradient. Here is an example. I am drawing 4 arcs - 90, 180, 270 and 360:
RectF rect1 = new RectF(50, 50, 150, 150);
Paint paint1 = new Paint();
paint1.setStrokeWidth(1);
paint1.setStrokeCap(Paint.Cap.SQUARE);
paint1.setStyle(Paint.Style.FILL);
SweepGradient gradient1 = new SweepGradient(100, 100,
Color.RED, Color.BLUE);
paint1.setShader(gradient1);
canvas.drawArc(rect1, 0, 90, true, paint1);
RectF rect2 = new RectF(200, 50, 300, 150);
Paint paint2 = new Paint();
paint2.setStrokeWidth(1);
paint2.setStrokeCap(Paint.Cap.SQUARE);
paint2.setStyle(Paint.Style.FILL);
SweepGradient gradient2 = new SweepGradient(250, 100,
Color.RED, Color.BLUE);
paint2.setShader(gradient2);
canvas.drawArc(rect2, 0, 180, true, paint2);
RectF rect3 = new RectF(50, 200, 150, 300);
Paint paint3 = new Paint();
paint3.setStrokeWidth(1);
paint3.setStrokeCap(Paint.Cap.SQUARE);
paint3.setStyle(Paint.Style.FILL);
SweepGradient gradient3 = new SweepGradient(100, 250,
Color.RED, Color.BLUE);
paint3.setShader(gradient3);
canvas.drawArc(rect3, 0, 270, true, paint3);
RectF rect4 = new RectF(200, 200, 300, 300);
Paint paint4 = new Paint();
paint4.setStrokeWidth(1);
paint4.setStrokeCap(Paint.Cap.SQUARE);
paint4.setStyle(Paint.Style.FILL);
SweepGradient gradient4 = new SweepGradient(250, 250,
Color.RED, Color.BLUE);
paint4.setShader(gradient4);
canvas.drawArc(rect4, 0, 360, true, paint4);
And here is the result:
This is surprising because I'd expect the RED to be at the start of the arc, the BLUE at the end and enything between to be spread evenly regardless of angle.
I tried to space the colors manually using the positions parameter but the results were the same:
int[] colors = {Color.RED, Color.BLUE};
float[] positions = {0,1};
SweepGradient gradient = new SweepGradient(100, 100, colors , positions);
Any idea how to solve this?
The solution for this is to set the position of BLUE. This is done like so:
int[] colors = {Color.RED, Color.BLUE};
float[] positions = {0,1};
SweepGradient gradient = new SweepGradient(100, 100, colors , positions);
The problem here is that when setting the position of BLUE to '1' this does not mean that it will be positioned at the end of the drawn arc, but instead at the end of the circle of which the arc is part of.
To solve this, BLUE position should take into account the number of degrees in the arc. So if I'm drawing an arc with X degrees, position will be set like so:
float[] positions = {0,Xf/360f};
So if X is 90, the gradient will place BLUE at 0.25 of the circle:
To add to Yoav's solution.
On my Galaxy Nexus 4.2 stock Android, the solution given doesn't work.
If the array doesn't contain a 0.0f and 1.0f, it appears to be ignored.
My final solution was:
int[] colors = {Color.RED, Color.BLUE, Color.RED};
float[] positions = {0, Xf/360f, 1};
five years later, but the right way is make 0.749f with 0.750f of the separate line, simple code is like:
val colors = intArrayOf(0xffff0000.toInt(), 0xff0000ff.toInt(), 0xffff0000.toInt(), 0xffff0000.toInt())
val positions = floatArrayOf(0.0f, 0.749f, 0.750f, 1.0f)
Using SweepGradient, you can pass null for positions (in case you want default gradient) and you can also rotate the gradient by setLocalMatrix
override fun onDraw(canvas: Canvas?) {
super.onDraw(canvas)
val centerX = width.toFloat() / 2
val centerY = height.toFloat() / 2
val paint = Paint()
paint.isAntiAlias = true
val colors = intArrayOf(Color.RED, Color.BLUE)
val gradient = SweepGradient(centerX, centerY, colors, null) // null position
val matrix = Matrix()
matrix.postRotate(270f, centerX, centerY) // rotate
gradient.setLocalMatrix(matrix)
paint.shader = gradient
val radius = 400f
val oval = RectF(centerX - radius,centerY - radius,centerX + radius,centerY + radius)
canvas?.drawArc(oval, 0f, 360f, false, paint)
}
I have several lines in my application. If somebody touches a line I have to highlight the line touched. I think if I could draw a transparent rectangle with light color, other than the clicked line color, then it will be highlighted properly.. So can anybody tell me how can I draw a transparent rectangle on Android canvas?
My line color is black. Please see the pic.
This will draw green 50% transparent rectangle on canvas:
Paint myPaint = new Paint();
myPaint.setStyle(Paint.Style.FILL);
myPaint.setColor(Color.rgba(0, 256, 0, 128)); // green color with 50% transparency
// c is your canvas
c.drawRect(100, 100, 200, 200, myPaint);
try this way
private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setColor(Color.RED);
mPaint.setStrokeWidth(3);
mPaint.setPathEffect(null);
canvas.drawRect(x, y, x + width, y + height, mPaint);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setColor(Color.WHITE);
mPaint.setStrokeWidth(3);
mPaint.setPathEffect(new DashPathEffect(new float[] { 5, 5 }, 5));
canvas.drawRect(x, y, x + width, y + height, mPaint);
you can use this:
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.MAGENTA);
DashPathEffect dashPath =new DashPathEffect(new float[ ]{70,2}, 30);
paint.setPathEffect(dashPath);
paint.setStrokeWidth(80);
canvas.drawRect(30, 300 , 320, 300, paint);
How can i do that? Is there an example for that? Can you show me ?
For ex. I have an circle like that
RadialGradient gradient = new RadialGradient(0, 0, 40, new int[]{Color.RED, Color.YELLOW}, new float[] {1,0}, android.graphics.Shader.TileMode.CLAMP);
paint2.setShader(gradient);
canvas.drawCircle(this.getWidth()/2, this.getHeight()/2, 40, paint2);
How this circle can draw a circle?
This must be an easy one but I'm really at a loss... The following code draws a rectangle with a linear gradient going from left to right, from white to black,
int x1 = 0, y1 = 0, x2 = 100, y2 = 40;
Shader shader = new LinearGradient(x1, y1, x2, y2, Color.WHITE, Color.BLACK, TileMode.CLAMP);
Paint paint = new Paint();
paint.setShader(shader);
canvas.drawRect(new RectF(x1, y1, x2, y2), paint);
Ok, fine. Now what I'd like to do is to change this gradient into a horizontal one, so that the color goes from white to black, from top to bottom. What I tried to do is to add:
Matrix trans = new Matrix();
trans.setRotate(90);
shader.setLocalMatrix(trans);
but instead the gradient goes at a funny angel, or there is just a single color... I also tried to play with the coordinates of the gradient in all sorts of way (thinking that maybe they should be transformed) to no avail. What am I missing?
I haven't done much android coding, but one approach worth trying is:
int x1 = 0, y1 = 0, x2 = 0, y2 = 40;
The x never changes in the gradient only the y does.
So what this might look like is:
Shader shader = new LinearGradient(0, 0, 0, 40, Color.WHITE, Color.BLACK, TileMode.CLAMP);
Paint paint = new Paint();
paint.setShader(shader);
canvas.drawRect(new RectF(0, 0, 100, 40), paint);
you can adjust the gradient orienation
Top to Bottom
LinearGradient(0, 0, 0, height, gradientStartColor, gradientEndColor, Shader.TileMode.CLAMP)
Bottom to Top
LinearGradient(0, height, 0, 0, gradientStartColor, gradientEndColor, Shader.TileMode.CLAMP)
Left to Right
LinearGradient(0, 0, width, 0, gradientStartColor, gradientEndColor, Shader.TileMode.CLAMP)
Right to Left
LinearGradient(width, 0, 0, 0, gradientStartColor, gradientEndColor, Shader.TileMode.CLAMP)