HTML5 Canvas - Save and Restore States

HTML5 canvas provides two important methods to save and restore the canvas states. The canvas drawing state is basically a snapshot of all the styles and transformations that have been applied and consists of the followings −

  • The transformations such as translate, rotate and scale etc.

  • The current clipping region.

  • The current values of the following attributes − strokeStyle, fillStyle, globalAlpha, lineWidth, lineCap, lineJoin, miterLimit, shadowOffsetX, shadowOffsetY, shadowBlur, shadowColor, globalCompositeOperation, font, textAlign, textBaseline.

Canvas states are stored on a stack every time the save method is called, and the last saved state is returned from the stack every time the restore method is called.

Sr.No. Method and Description
1

save()

This method pushes the current state onto the stack..
2

restore()

This method pops the top state on the stack, restoring the context to that state.

Example

Following is a simple example which makes use of above mentioned methods to show how the restore is called, to restore the original state and the last rectangle is once again drawn in black.

Live Demo 
<!DOCTYPE HTML>

<html>
   <head>
      
      <style>
         #test {
            width: 100px;
            height:100px;
            margin: 0px auto;
         }
      </style>
      
      <script type = "text/javascript">
         function drawShape() {
            
            // get the canvas element using the DOM
            var canvas = document.getElementById('mycanvas');
            
            // Make sure we don't execute when canvas isn't supported
            if (canvas.getContext) {
            
               // use getContext to use the canvas for drawing
               var ctx = canvas.getContext('2d');
               
               //  draw a rectangle with default settings
               ctx.fillRect(0,0,150,150);
               
               //  Save the default state
               ctx.save();
               
               // Make changes to the settings
               ctx.fillStyle = '#66FFFF'
               ctx.fillRect( 15,15,120,120); 
               
               // Save the current state
               ctx.save();
               
               // Make the new changes to the settings
               ctx.fillStyle = '#993333'
               ctx.globalAlpha = 0.5;
               ctx.fillRect(30,30,90,90);
               
               // Restore previous state
               ctx.restore();
               
               // Draw a rectangle with restored settings
               ctx.fillRect(45,45,60,60);   
               
               // Restore original state
               ctx.restore();
               
               // Draw a rectangle with restored settings
               ctx.fillRect(40,40,90,90);  
            } else {
               alert('You need Safari or Firefox 1.5+ to see this demo.');
            }
         }
      </script>
   </head>
   
   <body id = "test" onload = "drawShape();">
      <canvas id = "mycanvas"></canvas>
   </body>
   
</html>

The above example would produce the following result −

html5_canvas.htm
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