Monday, June 2, 2014

Draw rotated path by rotating canvas

This example show how to draw rotated path by roatating canvas.

  //Save and rotate canvas 
  canvas.save();
  canvas.rotate(rotate, x, y);
  
  canvas.drawPath(...);
  
  //restore canvas
  canvas.restore();


Modify MyView.java in last example "Rotate Path with Matrix", all other files, MainActivity.java, MyShape.java and /res/layout/activity_main.xml, keep no change.

package com.example.androiddrawpath;

import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.View;
import android.widget.TextView;

public class MyView extends View {
 
 MyShape myShape;
 float ratioRadius, ratioInnerRadius;
 int numberOfPoint = 3; //default
 
 float rotate;
 
 //corresponding to UI element
 TextView textLayerInfo;

 public MyView(Context context) {
  super(context);
  initMyView();
 }

 public MyView(Context context, AttributeSet attrs) {
  super(context, attrs);
  initMyView();
 }

 public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  initMyView();
 }
 
 public void initMyView(){
  myShape = new MyShape();
 }
 
 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  
  long starting = System.nanoTime();
  
  int w = getWidth();
  int h = getHeight();
  
  if((w==0) || (h==0)){
   return;
  }
  
  float x = (float)w/2.0f;
  float y = (float)h/2.0f;
  float radius, innerRadius;
  if(w > h){
   radius = h * ratioRadius;
   innerRadius = h * ratioInnerRadius;
  }else{
   radius = w * ratioRadius;
   innerRadius = w * ratioInnerRadius;
  }
  
  myShape.setStar(x, y, radius, innerRadius, numberOfPoint);
  
  //Save and rotate canvas 
  canvas.save();
  canvas.rotate(rotate, x, y);
  
  canvas.drawPath(myShape.getPath(), myShape.getPaint());
  
  //restore canvas
  canvas.restore();
  
  long end = System.nanoTime();
  
  String info = "myView.isHardwareAccelerated() = " + isHardwareAccelerated() + "\n"
    + "canvas.isHardwareAccelerated() = " + canvas.isHardwareAccelerated() + "\n"
    + "processing time (reference only) : " + String.valueOf(end - starting) + " (ns)";
  textLayerInfo.setText(info);
  
 }
 
 public void setShapeRadiusRatio(float ratio){
  ratioRadius = ratio;
 }
 
 public void setShapeInnerRadiusRatio(float ratio){
  ratioInnerRadius = ratio;
 }
 
 public void setNumberOfPoint(int pt){
  numberOfPoint = pt;
 }
 
 public void passElements(TextView textLayerInfo){
  this.textLayerInfo = textLayerInfo;
 }

 public void setShapeRotate(int rot){
  rotate = (float)rot;
 }

}

More example of Drawing Path on canvas of custom View.

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