Related
I have to create a custom view where I have to draw a rectangle. I'm trying to use the canvas.drawRect method. I wanted to create rectangles somethig like this
the gray colored one is my custom view which is extending the View class.
Inside the onDraw method I'm trying to draw the rectangle.
But actually I'm confused with the parameters of the drawRect method.
As per the documentation
/**
* Draw the specified Rect using the specified paint. The rectangle will
* be filled or framed based on the Style in the paint.
*
* #param left The left side of the rectangle to be drawn
* #param top The top side of the rectangle to be drawn
* #param right The right side of the rectangle to be drawn
* #param bottom The bottom side of the rectangle to be drawn
* #param paint The paint used to draw the rect
*/
What I assume is that left and top forms the x,y coordinates of the starting point, and right is the width and bottom is the height. But it doesn't seem to work that way.
I tried something like this to draw one rectangle but it does not draw anything
paint.setColor(Color.BLUE);
canvas.drawRect(5, canvas.getHeight()/2, 30, 30, paint );
Can anyone please tell how exactly a rectangle is drawn using these values?
It would be very helpful if someone could show the code to draw at least the first rectangle.
My requirement is like, the number of inner rectangles are dynamic, so if I pass some 4 to this View, it should create 4 equal width rectangles horizontally. something like
Thanks in advance!!
But actually I'm confused with the parameters of the drawRect method.
The drawRect method requires only two coordinates to draw a rectangle.
The top left corner and the bottom right corner. So the 4 points form these 2 coordinates
in your canvas. Hope it is clear from the below images
P1 and P2 are points formed by (left,top) and (right,bottom), So the drawn rectangle would be like this.
To draw rectangles dynamically like you have shown in you image , try something like this
int[] colors = new int[]{Color.RED, Color.GREEN, Color.BLUE, Color.YELLOW}; // given some fixed colors
in you onDraw method
#Override
protected void onDraw(Canvas canvas) {
int padding = 5;
float rectangleWidth = (getMeasuredWidth() - padding * 2) / colors.length;
for (int i = 0; i < colors.length; i++) {
paint.setColor(colors[i]);
canvas.drawRect(padding + (rectangleWidth * i),
getMeasuredHeight() / 2,
padding + rectangleWidth * (i + 1),
getMeasuredHeight() - padding, paint
); // 5 px is the padding given to the canvas
}
}
drawRect(float left, float top, float right, float bottom, Paint paint)
It seems in your case the problem is that if right is less than left or bottom is less than top then the rectangle is not drawn. But it seems it happens only in some devices , as #David Medenjak commented
I also recommend you to use the View dimensions and not the Canvas dimensions, that is better to use getWidth() & getHeight() and not Canvas.getWidth() & Canvas.getHeight()
Use this method to draw rectangle at X & Y coordinate with width and height params
fun drawRectangle(left: Int, top: Int, right: Int, bottom: Int, canvas: Canvas, paint: Paint?) {
var right = right
var bottom = bottom
right = left + right // width is the distance from left to right
bottom = top + bottom // height is the distance from top to bottom
canvas.drawRect(left.toFloat(), top.toFloat(), right.toFloat(), bottom.toFloat(), paint!!)
}
Usage
//drawing rectangle
drawRectangle(posX, posY, 60, 40, canvas, paint)
I want to create a rounded graph that will display a range of values from my app. The values can be classified to 3 categories: low, mid, high - that are represented by 3 colors: blue, green and red (respectively).
Above this range, I want to show the actually measured values - in a form of a "thumb" over the relevant range part:
The location of the white thumb over the range arc may change, according to the measured values.
Currently, I'm able to draw the 3-colored range by drawing 3 arcs over the same center, inside the view's onDraw method:
width = (float) getWidth();
height = (float) getHeight();
float radius;
if (width > height) {
radius = height / 3;
} else {
radius = width / 3;
}
paint.setAntiAlias(true);
paint.setStrokeWidth(arcLineWidth);
paint.setStrokeCap(Paint.Cap.ROUND);
paint.setStyle(Paint.Style.STROKE);
center_x = width / 2;
center_y = height / 1.6f;
left = center_x - radius;
float top = center_y - radius;
right = center_x + radius;
float bottom = center_y + radius;
oval.set(left, top, right, bottom);
//blue arc
paint.setColor(colorLow);
canvas.drawArc(oval, 135, 55, false, paint);
//red arc
paint.setColor(colorHigh);
canvas.drawArc(oval, 350, 55, false, paint);
//green arc
paint.setColor(colorNormal);
canvas.drawArc(oval, 190, 160, false, paint);
And this is the result arc:
My question is, how do I:
Create a smooth gradient between those 3 colors (I tried using
SweepGradient but it didn't give me the correct result).
Create the overlay white thumb as shown in the picture, so that I'll be able to control where to display it.
Animate this white thumb over my range arc.
Note: the 3-colored range is static - so another solution can be to just take the drawable and paint the white thumb over it (and animate it), so I'm open to hear such a solution as well :)
I would use masks for your first two problems.
1. Create a smooth gradient
The very first step would be drawing two rectangles with a linear gradient. The first
rectangle contains the colors blue and green while the second rectangle contains green
and red as seen in the following picture. I marked the line where both rectangles touch each other
black to clarify that they are infact two different rectangles.
This can be achieved using the following code (excerpt):
// Both color gradients
private Shader shader1 = new LinearGradient(0, 400, 0, 500, Color.rgb(59, 242, 174), Color.rgb(101, 172, 242), Shader.TileMode.CLAMP);
private Shader shader2 = new LinearGradient(0, 400, 0, 500, Color.rgb(59, 242, 174), Color.rgb(255, 31, 101), Shader.TileMode.CLAMP);
private Paint paint = new Paint();
// ...
#Override
protected void onDraw(Canvas canvas) {
float width = 800;
float height = 800;
float radius = width / 3;
// Arc Image
Bitmap.Config conf = Bitmap.Config.ARGB_8888; // See other config types
Bitmap mImage = Bitmap.createBitmap(800, 800, conf); // This creates a mutable bitmap
Canvas imageCanvas = new Canvas(mImage);
// Draw both rectangles
paint.setShader(shader1);
imageCanvas.drawRect(0, 0, 400, 800, paint);
paint.setShader(shader2);
imageCanvas.drawRect(400, 0, 800, 800, paint);
// /Arc Image
// Draw the rectangle image
canvas.save();
canvas.drawBitmap(mImage, 0, 0, null);
canvas.restore();
}
As your goal is having a colored arc with rounded caps, we next need to define the area of
both rectangles that should be visible to the user. This means that most of both rectangles
will be masked away and thus not visible. Instead the only thing to remain is the arc area.
The result should look like this:
In order to achieve the needed behavior we define a mask that only reveals the arc area within
the rectangles. For this we make heavy use of the setXfermode method of Paint. As argument
we use different instances of a PorterDuffXfermode.
private Paint maskPaint;
private Paint imagePaint;
// ...
// To be called within all constructors
private void init() {
// I encourage you to research what this does in detail for a better understanding
maskPaint = new Paint();
maskPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
imagePaint = new Paint();
imagePaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OVER));
}
#Override
protected void onDraw(Canvas canvas) {
// #step1
// Mask
Bitmap mMask = Bitmap.createBitmap(800, 800, conf);
Canvas maskCanvas = new Canvas(mMask);
paint.setColor(Color.WHITE);
paint.setShader(null);
paint.setStrokeWidth(70);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeCap(Paint.Cap.ROUND);
paint.setAntiAlias(true);
final RectF oval = new RectF();
center_x = 400;
center_y = 400;
oval.set(center_x - radius,
center_y - radius,
center_x + radius,
center_y + radius);
maskCanvas.drawArc(oval, 135, 270, false, paint);
// /Mask
canvas.save();
// This is new compared to step 1
canvas.drawBitmap(mMask, 0, 0, maskPaint);
canvas.drawBitmap(mImage, 0, 0, imagePaint); // Notice the imagePaint instead of null
canvas.restore();
}
2. Create the overlay white thumb
This solves your first problem. The second one can be achieved using masks again, though this
time we want to achieve something different. Before, we wanted to show only a specific area (the arc)
of the background image (being the two rectangles). This time we want to do the opposite:
We define a background image (the thumb) and mask away its inner content, so that only
the stroke seems to remain. Applied to the arc image the thumb overlays the colored arc with
a transparent content area.
So the first step would be drawing the thumb. We use an arc for this with the same radius as
the background arc but different angles, resulting in a much smaller arc. But becaus the
thumb should "surround" the background arc, its stroke width has to be bigger than the
background arc.
#Override
protected void onDraw(Canvas canvas) {
// #step1
// #step2
// Thumb Image
mImage = Bitmap.createBitmap(800, 800, conf);
imageCanvas = new Canvas(mImage);
paint.setColor(Color.WHITE);
paint.setStrokeWidth(120);
final RectF oval2 = new RectF();
center_x = 400;
center_y = 400;
oval2.set(center_x - radius,
center_y - radius,
center_x + radius,
center_y + radius);
imageCanvas.drawArc(oval2, 270, 45, false, paint);
// /Thumb Image
canvas.save();
canvas.drawBitmap(RotateBitmap(mImage, 90f), 0, 0, null);
canvas.restore();
}
public static Bitmap RotateBitmap(Bitmap source, float angle)
{
Matrix matrix = new Matrix();
matrix.postRotate(angle);
return Bitmap.createBitmap(source, 0, 0, source.getWidth(), source.getHeight(), matrix, true);
}
The result of the code is shown below.
So now that we have a thumb that is overlaying the background arc, we need to define the mask
that removes the inner part of the thumb, so that the background arc becomes visible again.
To achieve this we basically use the same parameters as before to create another arc, but
this time the stroke width has to be identical to the width used for the background arc as
this marks the area we want to remove inside the thumb.
Using the following code, the resulting image is shown in picture 4.
#Override
protected void onDraw(Canvas canvas) {
// #step1
// #step2
// Thumb Image
// ...
// /Thumb Image
// Thumb Mask
mMask = Bitmap.createBitmap(800, 800, conf);
maskCanvas = new Canvas(mMask);
paint.setColor(Color.WHITE);
paint.setStrokeWidth(70);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
final RectF oval3 = new RectF();
center_x = 400;
center_y = 400;
oval3.set(center_x - radius,
center_y - radius,
center_x + radius,
center_y + radius);
maskCanvas.drawBitmap(mImage, 0, 0, null);
maskCanvas.drawArc(oval3, 270, 45, false, paint);
// /Thumb Mask
canvas.save();
canvas.drawBitmap(RotateBitmap(mMask, 90f), 0, 0, null); // Notice mImage changed to mMask
canvas.restore();
}
3. Animate the white thumb
The last part of your question would be animating the movement of the arc. I have no solid
solution for this, but maybe can guide you in a useful direction. I would try the following:
First define the thumb as a ImageView that is part of your whole arc graph. When changing
the selected values of your graph, you rotate the thumb image around the center of the background
arc. Because we want to animate the movement, just setting the rotation of the thumb image would
not be adequate. Instead we use a RotateAnimation kind of like so:
final RotateAnimation animRotate = new RotateAnimation(0.0f, -90.0f, // You have to replace these values with your calculated angles
RotateAnimation.RELATIVE_TO_SELF, // This may be a tricky part. You probably have to change this to RELATIVE_TO_PARENT
0.5f, // x pivot
RotateAnimation.RELATIVE_TO_SELF,
0.5f); // y pivot
animRotate.setDuration(1500);
animRotate.setFillAfter(true);
animSet.addAnimation(animRotate);
thumbView.startAnimation(animSet);
This is far from final I guess, but it very well may aid you in your search for the needed
solution. It is very important that your pivot values have to refer to the center of your
background arc as this is the point your thumb image should rotate around.
I have tested my (full) code with API Level 16 and 22, 23, so I hope that this answer at least
gives you new ideas on how to solve your problems.
Please note that allocation operations within the onDraw method are a bad idea and should
be avoided. For simplicity I failed to follow this advise. Also the code is to be used as
a guide in the right direction and not to be simply copy & pasted, because it makes heavy
use of magic numbers and generally does not follow good coding standards.
I would change a bit of the way you draw your view, by looking on the original design, instead of drawing 3 caps I would draw just 1 line, that way the SweepGradient will work.
This migth be a bit tricky, you have 2 options:
create a Path with 4 arcs
draw 2 arcs- one is the big white (filled with white so you still want to use Paint.Style.STROKE) and another on top of that make it fill transparent, you can achieve it with PorterDuff xfermode, it probably take you couple of tries until you get that without clearing the green circle too.
I imagine you want to animate thumb position, so just use simple Animation that invalidate the view and draw the thumb view position accordingly.
Hopes this helps
Create a gradient than follow a path is not so simple.
So I can suggest you to use some libraries than already did it.
Include the library:
dependencies {
...
compile 'com.github.paroca72:sc-gauges:3.0.7'
}
Create the gauge in XML:
<com.sccomponents.gauges.library.ScArcGauge
android:id="#+id/gauge"
android:layout_width="300dp"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal" />
Your code:
ScArcGauge gauge = this.findViewById(R.id.gauge);
gauge.setAngleSweep(270);
gauge.setAngleStart(135);
gauge.setHighValue(90);
int lineWidth = 50;
ScCopier baseLine = gauge.getBase();
baseLine.setWidths(lineWidth);
baseLine.setColors(Color.parseColor("#dddddd"));
baseLine.getPainter().setStrokeCap(Paint.Cap.ROUND);
ScCopier progressLine = gauge.getProgress();
progressLine.setWidths(lineWidth);
progressLine.setColors(
Color.parseColor("#65AAF2"),
Color.parseColor("#3EF2AD"),
Color.parseColor("#FF2465")
);
progressLine.getPainter().setStrokeCap(Paint.Cap.ROUND);
Your result:
You can find something more complex on this site:
ScComponents
int currentX = maze.getCurrentX(),currentY = maze.getCurrentY();
//draw the ball
canvas.drawCircle((currentX * totalCellWidth)+(cellWidth/2), //x of center
(currentY * totalCellHeight)+(cellWidth/2), //y of center
(cellWidth*0.45f), //radius
ball);
//draw the finishing point indicator
canvas.drawText("F",
(mazeFinishX * totalCellWidth)+(cellWidth*0.25f),
(mazeFinishY * totalCellHeight)+(cellHeight*0.75f),
ball);
}
You have to add the png to your drawable folder. then you can create a Bitmap using BitmapFactory.decodeResource(resourceId);. The bitmap can be drawn on the canvas using canvas.drawBitmap(Bitmap bmp, Rect source, Rect dest, Paint p). bmp is the bitmap to be drawn, obviously, source is the part of the bitmap that schould be drawn (in your case the whole bitmap), dest is the location on the canvas where the bitmap is drawn, p is the paint, which you don't need, so just use null.
I have a drawable resource that I need to draw on a canvas. I need to have the drawable centered at point (x,y). Right now if I do canvas.drawBitmap(mBitmap, x, y, mPaint), (x,y) represent (left,top). Does anyone know how I may get the center of my drawable so I can place it on the canvas correctly?
Get the width and height of the canvas.
Now, you need to draw it on width/2 and height/2.
To be more centered, you can subtract from width/2 half of the bitmap width, and from height/2 half of the bitmap height.
canvas.drawBitmap(mBitmap, width/2-mBitmap.getWidth()/2, height/2-mBitmap.getHeight()/2, mPaint);
A Simple math...
int centerX = drawable.getIntrinsicWidth() / 2;
int centerY = drawable.getIntrinsicHeight() / 2;
I want to rotate a bitmap image based on user click by 10 deg. Following numerous stackoverflow and google answers, I tried various combinations of Matrix rotation.
However the image doesn't really rotate as expected and gives a jittery view of rotation + oscillation about canvas center. To test I am increasing rotation angle by 10 deg (instead of clicks) each time object's draw method is called. The image is a symmetrical circle [64x64 enclosing rectangle] and I expect it to rotate at center of screen about it's own center like a wheel, but it rotates and moves diagonally towards right-down and moves back upto center of screen in an oscillatory fashion.
public void draw(Canvas canvas) {
Matrix matrix = new Matrix();
rotation += 10;
float px = this.viewWidth/2;
float py = this.viewHeight/2;
matrix.setRotate(rotation, bitmap.getWidth()/2, bitmap.getHeight()/2);
Bitmap newbmp = Bitmap.createBitmap(bitmap, 0, 0, getImgWidth(), getImgHeight(), matrix, true);
canvas.drawBitmap(newbmp, px - (getImgWidth()/2), py - (getImgHeight()/2), null);
}
Here is an example.
I broke it to 3 steps.
The first translate moves the bitmap so that it's center is at 0,0
Then a rotation,
and finally move the bitmap center to where you want it on the canvas.
You don't need the second bitmap.
Matrix matrix = new Matrix();
rotation += 10;
float px = this.viewWidth/2;
float py = this.viewHeight/2;
matrix.postTranslate(-bitmap.getWidth()/2, -bitmap.getHeight()/2);
matrix.postRotate(rotation);
matrix.postTranslate(px, py);
canvas.drawBitmap(bitmap, matrix, null);
As an optimization, create the Matrix once outside this method and replace the creation with a call to matrix.reset()
You need to translate the bitmap to the 0,0 point (or draw it at 0,0) and rotate it there, then translate it back, as such:
canvas.save();
canvas.translate(this.viewWidth, this.viewHeight);
canvas.rotate(rotation);
canvas.drawBitmap(newbmp, -(getImgWidth()/2), -(getImgHeight()/2), null);
canvas.restore();
Here I draw it with the center at 0,0 (I think), because when you rotate, it's about 0,0 and not the center of the screen as one would think. If you draw the center at 0,0 then it will rotate about the center of the bitmap.
If my code does not accomplish drawing the bitmap center at 0,0 then you can change my code to draw it at the center and it will work as you want.
Hope this helps!
// x : x coordinate of image position
// y : y coordinate of image position
// w : width of canvas
// h : height of canvas
canvas.save();
canvas.rotate(angle, x + (w/2), y + (h/2));
canvas.drawBitmap(image, x, y, null);
canvas.restore();
The steps are
Save the existing canvas
Rotate the canvas about the center of the bitmap, that you would draw on canvas with an angle of rotation
Draw the image
Restore the image