Android Canvas Draw Rectangle

Android canvas draw rectangle

Try paint.setStyle(Paint.Style.STROKE)?

How canvas.drawRect draws a rectangle

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
}

}

how to draw rectangle canvas?

You need to make method and pass value from activity to draw class:-

Draw draw = new Draw(this,100, 300, 600, 800);
constraintLayout.addView(draw);

Draw class

public class Draw extends View {

Paint paint;
Path path;

float left; 
float top; 
float right; 
float bottom;

public Draw(Context context,float left, float top, float right, float bottom) {
    super(context);
    this.left = left;
    this.top = top;
    this.right = right;
    this.bottom = bottom;
    init();
}

public Draw(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
}

public Draw(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    init();
}

public void init(){
    paint = new Paint();
    paint.setColor(Color.BLACK);
    paint.setStrokeWidth(10);
    paint.setStyle(Paint.Style.STROKE);
}

@Override
protected void onDraw(Canvas canvas) {
    // TODO Auto-generated method stub
    super.onDraw(canvas);
    canvas.drawRect(left, top, right, bottom, paint);
 }
 }

Drawing rectangles on android canvas

Assuming that you only want this to be for this specific pattern and not expandable then the following should work. Though it is unlikely that it will look right because it is unlikely that a screen will be 1:2 aspect ratio, so you might need to make your canvas a set size that conforms to a 1:2 aspect ratio.

int width =canvas.getWidth();
int height = canvas.getHeight();
float a = (height*3)/5;
flaot b = (height*2)/5;
float c = (width*3)/5;
float d = (width*4)/5;

//5x5 square
canvas.drawRect(0,a,width,height);
//3x3 square 
canvas.drawRect(0,0,a,c);
//2x2 square 
canvas.drawRect(c,0,width,b);
//first 1x1 square 
canvas.drawRect(d,b,width,a);
//second 1x1 square 
canvas.drawRect(c,b,d,a);

The variables a,b,c,d are explained in the following image

The parameters in drawRect are the coordinates of the corresponding edge of the rectangle in the canvas coordinate system. The canvas coordinate system has (0,0) in the top left of the screen. So if you wanted a triangle to fill the whole screen you would have canvas.drawRect(0,0,canvas.get(width),canvas.getheight());

This would put the left edge of the rectangle along 0 in the x axis, the top along 0 in the y axis, the right edge along the x axis at the width of the canvas and the bottom along the y axis at the height of the canvas.

Hope this helps.

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

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

Understanding how actually drawRect or drawing coordinates work in Android

X runs horizontally, from left to right. Y runs vertically, from top to bottom. It's exactly the same as on your graphics. So (0/0) is at top left.

When you go "up" Y will of course get smaller, as it grows from top to bottom.

You have to pay attention to laying out elements like ListViews, these will give a partial (or new, you cannot tell) canvas to your views that are drawn. These views will have 0x0 at their own top/left position. If you need the absolute you have to subsequently call View.getLocationOnScreen() and calculate offsets yourself.

Drawing a filled rectangle with a border in android

You draw a rectangle with the color of the border and the size of the rectangle plus the border, you change the color of the paint and draw again the rectangle with the normal size.

How do i draw only corners of a rectangle in android canvas

Image

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

        Paint paint = new Paint(Paint.DITHER_FLAG);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(50);
        paint.setColor(0xFF2287BB);

        paint.setStrokeJoin(Paint.Join.MITER);
        canvas.drawPath(createCornersPath(getWidth()/2 - 500, getHeight()/2 - 500, getWidth()/2  +500, getHeight()/2 + 500, 150), paint);
    }

    private Path createCornersPath(int left, int top, int right, int bottom, int cornerWidth){
        Path path = new Path();

        path.moveTo(left, top + cornerWidth);
        path.lineTo(left, top);
        path.lineTo(left + cornerWidth, top);

        path.moveTo(right - cornerWidth, top);
        path.lineTo(right, top);
        path.lineTo(right , top + cornerWidth);

        path.moveTo(left, bottom - cornerWidth);
        path.lineTo(left, bottom);
        path.lineTo(left + cornerWidth, bottom);

        path.moveTo(right - cornerWidth, bottom);
        path.lineTo(right, bottom);
        path.lineTo(right, bottom - cornerWidth);

        return path;
    }

Draw canvas drawRect with dynamic co ordinates

You are copying the Bitmap into memory and never displaying, draw on the one that you set as ImageResource:

setImageBitmap(bitmap);
Canvas canvas = new Canvas(bitmap);

If you need to copy as ARGB_8888 then

Bitmap drawableBitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true);
Canvas canvas = new Canvas(drawableBitmap);
//Draw everything, then after (at end of method)
setImageBitmap(drawableBitmap);

As for your coordinates:

X     Y  Width Height
600, 100, 50,   50
440, 125, 50,   50
685, 270, 50,   50
420, 350, 50,   50
...

They are (X,Y,W,H) while Android Rectangles are (L,T,R,B)

To convert your coordinates use:

 Rectangle area = new Rectangle(x, y, x + w, y + h);

Then draw the area into the Canvas.

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