canvas not clearing while radius of circle decreasing..?

» javascript » canvas not clearing while radius of circle decreasing..?

By : user3045151

Date : December 01 2020, 04:52 PM

This might help you You should call beginPath() every time you want to start a new path - that is a new circle.
When your circle is so big, the smaller inner circles are also drawn from top down the larger ones - so, they are not visible.

code :

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

// First path
ctx.beginPath();
ctx.strokeStyle = 'blue';
ctx.moveTo(20, 20);
ctx.lineTo(200, 20);
ctx.stroke();

// Second path
ctx.beginPath();
ctx.strokeStyle = 'green';
ctx.moveTo(20, 20);
ctx.lineTo(120, 120);
ctx.stroke();

Share :

Can circle be converted into oval using radius in Canvas

By : Daniyal Ahmad

Date : March 29 2020, 07:55 AM

fixed the issue. Will look into that further Not clear what you are trying to do but one mistake is that you need to change the set call:

code :

ovalBounds.set(x, y, x + 2 * radius, y + 2 * radius);

Drawing arc to fit angle in html canvas by Circle tangles point with known radius 2D

By : user3636939

Date : March 29 2020, 07:55 AM

hop of those help? Yes, you can use arcTo():
Set your first line start point with moveTo() then the intersection point between the two lines as first pair then the end point of the second line (what you call "startpoint line 2") the last pair. Provide a radius To actually draw the last line (it's only used for calculation with arcTo()) add a lineTo() for the last point pair in the arc, stroke/fill.

code :

var ctx = document.querySelector("canvas").getContext("2d");

ctx.moveTo(0, 0);                 // start point
ctx.arcTo(50, 150, 100, 0, 20);   // intersection, outpoint, radius
ctx.lineTo(100, 0);               // line from arc-end to outpoint

ctx.translate(130, 0);
ctx.moveTo(0, 0);                 // start point
ctx.arcTo(50, 150, 80, 50, 8);   // intersection, outpoint, radius
ctx.lineTo(80, 50);               // line from arc-end to outpoint

ctx.stroke();

<canvas></canvas>

function extendLine(line, scale) {
  var sx = line.startPoint.x,
      sy = line.startPoint.y,
      ex = line.endPoint.x,
      ey = line.endPoint.y;

   return {
     startPoint: {x: sx, y: sy},
     endPoint: {
       x: sx + (ex - sx) * scale,
       y: sy + (ey - sy) * scale
     }
   }
}

var line1 = ...,
    line2 = ...,
    line1tmp = extendLine(line1, 10000),
    line2tmp = extendLine(line2, 10000),
    ipoint = getIntersection(line1, line2); // see link above

// define the line + arcTo
ctx.moveTo(line1.startPoint.x, line1.startPoint.y);
ctx.arcTo(ipoint.x, ipoint.y, 
          line2.endPoint.x, line2.endPoint.y,
          Math.abs(line2.startPoint.x - line1.endPoint.x) / 2);
ctx.lineTo(line2.endPoint.x, line2.endPoint.y);
ctx.stroke();

How to get number of pixels equals to a radius of Geozone circle according to zoom level? OR Radius of zone circle to sc

By : Hovhannes Gyurjyan

Date : March 29 2020, 07:55 AM

This might help you Credits to and thanks a ton to Android Maps API v2 draw circle post.
I could calculate the width of circle in pixels given latitude, longitude and radius (from given lat, long) in meters.

code :

private int convertZoneRadiusToPixels(double lat, double lng, double radiusInMeters) {
    double EARTH_RADIUS = 6378100.0;
    double lat1 = radiusInMeters / EARTH_RADIUS;
    double lng1 = radiusInMeters / (EARTH_RADIUS * Math.cos((Math.PI * lat / 180)));

    double lat2 = lat + lat1 * 180 / Math.PI;
    double lng2 = lng + lng1 * 180 / Math.PI;

    Point p1 = mMap.getProjection().toScreenLocation(new LatLng(lat, lng));
    Point p2 = mMap.getProjection().toScreenLocation(new LatLng(lat2, lng2));
    return Math.abs(p1.x - p2.x);
}

Change a circle radius programmatically - Canvas

By : user1478117

Date : March 29 2020, 07:55 AM

wish of those help Your Drawable can implement the AnimatorUpdateListener interface:

code :

public void onAnimationUpdate(ValueAnimator animator) {

    float radius = (float)animator.getAnimatedValue();

    // Clear canvas and draw next frame

    invalidateSelf();
}

public void init() {

    ...

    ValueAnimator valueAnimator = ValueAnimator.ofFloat(START_RADIUS, END_RADIUS);
    valueAnimator.setDuration(DURATION_MILLIS)
    valueAnimator.addUpdateListener(this);
    valueAnimator.setRepeatCount(ValueAnimator.INFINITE);
    valueAnimator.start();

}

How to remove the radius lines in html canvas when drawing a circle with arc in javascript?

By : Pranay Chinta

Date : March 29 2020, 07:55 AM

it should still fix some issue Your moveTo() calls are going to the center point of each of the arcs. The arcs are actually drawn starting from the perimeter, so your path goes from the center to the perimeter before starting the arc.
To fix this just change the moveTo() calls to the right most point on the arc (this is where the drawing starts). Here is my fix: