Saving and restoring state
Before we look at the transformation methods, let's look at two other methods which are indispensable once you start generating ever more complex drawings.

save()
 Saves the entire state of the canvas.

restore()
 Restores the most recently saved canvas state.
Canvas states are stored on a stack. Every time the save()
method is called, the current drawing state is pushed onto the stack. A drawing state consists of
 The transformations that have been applied (i.e. translate, rotate and scale  see below).
 The values of
strokeStyle
,fillStyle
,globalAlpha
,lineWidth
,lineCap
,lineJoin
,miterLimit
,shadowOffsetX
,shadowOffsetY
,shadowBlur
,shadowColor
,globalCompositeOperation
properties.  The current clipping path, which we'll see in the next section.
You can call the save()
method as many times as you like. Each time the restore()
method is called, the last saved state is popped off the stack and all saved settings are restored.
A save and restore canvas state example
This example tries to illustrate how the stack of drawing states functions by drawing a set of consecutive rectangles.
function draw() { var ctx = document.getElementById('canvas').getContext('2d'); ctx.fillRect(0,0,150,150); // Draw a rectangle with default settings ctx.save(); // Save the default state ctx.fillStyle = '#09F' // Make changes to the settings ctx.fillRect(15,15,120,120); // Draw a rectangle with new settings ctx.save(); // Save the current state ctx.fillStyle = '#FFF' // Make changes to the settings ctx.globalAlpha = 0.5; ctx.fillRect(30,30,90,90); // Draw a rectangle with new settings ctx.restore(); // Restore previous state ctx.fillRect(45,45,60,60); // Draw a rectangle with restored settings ctx.restore(); // Restore original state ctx.fillRect(60,60,30,30); // Draw a rectangle with restored settings }
<canvas id="canvas" width="150" height="150"></canvas>
draw();
The first step is to draw a large rectangle with the default settings. Next we save this state and make changes to the fill color. We then draw the second and smaller blue rectangle and save the state. Again we change some drawing settings and draw the third semitransparent white rectangle.
So far this is pretty similar to what we've done in previous sections. However once we call the first restore()
statement, the top drawing state is removed from the stack, and settings are restored. If we hadn't saved the state using save()
, we would need to change the fill color and transparency manually in order to return to the previous state. This would be easy for two properties, but if we have more than that, our code would become very long, very fast.
When the second restore()
statement is called, the original state (the one we set up before the first call to save
) is restored and the last rectangle is once again drawn in black.
Screenshot  Live sample 

Translating
The first of the transformation methods we'll look at is translate()
. This method is used to move the canvas and its origin to a different point in the grid.

translate(x, y)

Moves the canvas and its origin on the grid.
x
indicates the horizontal distance to move, andy
indicates how far to move the grid vertically.
It's a good idea to save the canvas state before doing any transformations. In most cases, it is just easier to call the restore
method than having to do a reverse translation to return to the original state. Also if you're translating inside a loop and don't save and restore the canvas state, you might end up missing part of your drawing, because it was drawn outside the canvas edge.
A translate
example
This example demonstrates some of the benefits of translating the canvas origin. We'll create a drawSpirograph()
function that draws spirograph patterns. These are drawn around the origin. Without the translate()
function, we would only see a quarter of the pattern on the canvas. The translate()
method also gives us the freedom to place it anywhere on the canvas without having to manually adjust coordinates in the spirograph function. This makes it a little easier to understand and use.
In the draw()
function, we call the drawSpirograph()
nine times using two for
loops. In each loop, the canvas is translated, the spirograph is drawn, and the canvas is returned back to its original state.
function draw() { var ctx = document.getElementById('canvas').getContext('2d'); ctx.fillRect(0,0,300,300); for (var i=0;i<3;i++) { for (var j=0;j<3;j++) { ctx.save(); ctx.strokeStyle = "#9CFF00"; ctx.translate(50+j*100,50+i*100); drawSpirograph(ctx,20*(j+2)/(j+1),8*(i+3)/(i+1),10); ctx.restore(); } } } function drawSpirograph(ctx,R,r,O){ var x1 = RO; var y1 = 0; var i = 1; ctx.beginPath(); ctx.moveTo(x1,y1); do { if (i>20000) break; var x2 = (R+r)*Math.cos(i*Math.PI/72)  (r+O)*Math.cos(((R+r)/r)*(i*Math.PI/72)); var y2 = (R+r)*Math.sin(i*Math.PI/72)  (r+O)*Math.sin(((R+r)/r)*(i*Math.PI/72)); ctx.lineTo(x2,y2); x1 = x2; y1 = y2; i++; } while (x2 != RO && y2 != 0 ); ctx.stroke(); }
<canvas id="canvas" width="300" height="300"></canvas>
draw();
Screenshot  Live sample 

Rotating
The second transformation method is rotate()
. We use it to rotate the canvas around the current origin.

rotate(angle)

Rotates the canvas clockwise around the current origin by the
angle
number of radians.
The rotation center point is always the canvas origin. To change the center point, we will need to move the canvas by using the translate()
method.
A rotate
example
In this example, we'll use the rotate()
method to draw shapes in a circular pattern. You could also calculate the individual x and y coordinates (x = r*Math.cos(a); y = r*Math.sin(a)
). In this case it doesn't really matter which method we choose, because we're drawing circles. Calculating the coordinates results in only rotating the center positions of the circles and not the circles themselves, while using rotate()
results in both, but of course circles look the same no matter how far they are rotated about their centers.
Again we have two loops. The first determines the number of rings, and the second determines the number of dots drawn in each ring. Before drawing each ring, we save the canvas state, so we can easily retrieve it. For each dot that is drawn, we rotate the canvas coordinate space by an angle that is determined by the number of dots in the ring. The innermost circle has six dots, so in each step, I rotate over an angle of 360/6 or 60 degrees. With each additional ring, the number of dots is doubled, and the angle in turn is halved.
function draw() { var ctx = document.getElementById('canvas').getContext('2d'); ctx.translate(75,75); for (var i=1;i<6;i++){ // Loop through rings (from inside to out) ctx.save(); ctx.fillStyle = 'rgb('+(51*i)+','+(25551*i)+',255)'; for (var j=0;j<i*6;j++){ // draw individual dots ctx.rotate(Math.PI*2/(i*6)); ctx.beginPath(); ctx.arc(0,i*12.5,5,0,Math.PI*2,true); ctx.fill(); } ctx.restore(); } }
<canvas id="canvas" width="150" height="150"></canvas>
draw();
Screenshot  Live sample 

Scaling
The next transformation method is scaling. We use it to increase or decrease the units in our canvas grid. This can be used to draw scaled down or enlarged shapes and bitmaps.
 scale(x, y)
 Scales the canvas units by x horizontally and by y vertically. Both parameters are real numbers. Negative values reduce the unit size and positive values increase the unit size. Values of 1.0 leave the units the same size.
Using negative numbers you can do axis mirroring (for example using translate(0,canvas.height); scale(1,1);
you will have the wellknown Cartesian coordinate system, with the origin in the bottom left corner).
By default, one unit on the canvas is exactly one pixel. If we apply, for instance, a scaling factor of 0.5, the resulting unit would become 0.5 pixels and so shapes would be drawn at half size. In a similar way setting the scaling factor to 2.0 would increase the unit size and one unit now becomes two pixels. This results in shapes being drawn twice as large.
A scale
example
In this last example, we'll use the spirograph function from the previous example to draw nine shapes with different scaling factors.
function draw() { var ctx = document.getElementById('canvas').getContext('2d'); ctx.strokeStyle = "#fc0"; ctx.lineWidth = 1.5; ctx.fillRect(0,0,300,300); // Uniform scaling ctx.save() ctx.translate(50,50); drawSpirograph(ctx,22,6,5); ctx.translate(100,0); ctx.scale(0.75,0.75); drawSpirograph(ctx,22,6,5); ctx.translate(133.333,0); ctx.scale(0.75,0.75); drawSpirograph(ctx,22,6,5); ctx.restore(); // Non uniform scaling (y direction) ctx.strokeStyle = "#0cf"; ctx.save() ctx.translate(50,150); ctx.scale(1,0.75); drawSpirograph(ctx,22,6,5); ctx.translate(100,0); ctx.scale(1,0.75); drawSpirograph(ctx,22,6,5); ctx.translate(100,0); ctx.scale(1,0.75); drawSpirograph(ctx,22,6,5); ctx.restore(); // Non uniform scaling (x direction) ctx.strokeStyle = "#cf0"; ctx.save() ctx.translate(50,250); ctx.scale(0.75,1); drawSpirograph(ctx,22,6,5); ctx.translate(133.333,0); ctx.scale(0.75,1); drawSpirograph(ctx,22,6,5); ctx.translate(177.777,0); ctx.scale(0.75,1); drawSpirograph(ctx,22,6,5); ctx.restore(); } function drawSpirograph(ctx,R,r,O){ var x1 = RO; var y1 = 0; var i = 1; ctx.beginPath(); ctx.moveTo(x1,y1); do { if (i>20000) break; var x2 = (R+r)*Math.cos(i*Math.PI/72)  (r+O)*Math.cos(((R+r)/r)*(i*Math.PI/72)) var y2 = (R+r)*Math.sin(i*Math.PI/72)  (r+O)*Math.sin(((R+r)/r)*(i*Math.PI/72)) ctx.lineTo(x2,y2); x1 = x2; y1 = y2; i++; } while (x2 != RO && y2 != 0 ); ctx.stroke(); }
<canvas id="canvas" width="300" height="300"></canvas>
draw();
The top left shape has been drawn with no scaling applied. The yellow shapes to the right both have a uniform scaling factor (the same value for x and y parameters). If you look at the code below you'll see that we've used the scale()
method twice with equal parameter values for the second and third spirograph. Because we didn't restore the canvas state, the third shape is drawn with a scaling factor of 0.75 × 0.75 = 0.5625.
The second row of blue shapes have a nonuniform scaling applied in a vertical direction. Each of the shapes has the x scaling factor set to 1.0 which means no scaling. The y scaling factor is set to 0.75. This results in the three shapes being squashed down. The original circular shape has now become an ellipse. If you look closely you'll see that the line width has also been reduced in the vertical direction.
The third row of green shapes is similar to the one above but now we've applied a scaling in the horizontal direction.
Screenshot  Live sample 

Transforms
The final transformation methods allow modifications directly to the transformation matrix.

transform(m11, m12, m21, m22, dx, dy)
 This method must multiply the current transformation matrix with the matrix described by:

m11 m21 dx m12 m22 dy 0 0 1

If any of the arguments are
Infinity
the transformation matrix must be marked as infinite instead of the method throwing an exception. 
setTransform(m11, m12, m21, m22, dx, dy)

Resets the current transform to the identity matrix, and then invokes the
transform()
method with the same arguments. This basically undoes the current transformation, then sets the specified transform, all in one step.
transform
/ setTransform
examples
function draw() { var ctx = document.getElementById('canvas').getContext('2d'); var sin = Math.sin(Math.PI/6); var cos = Math.cos(Math.PI/6); ctx.translate(100, 100); var c = 0; for (var i=0; i <= 12; i++) { c = Math.floor(255 / 12 * i); ctx.fillStyle = "rgb(" + c + "," + c + "," + c + ")"; ctx.fillRect(0, 0, 100, 10); ctx.transform(cos, sin, sin, cos, 0, 0); } ctx.setTransform(1, 0, 0, 1, 100, 100); ctx.fillStyle = "rgba(255, 128, 255, 0.5)"; ctx.fillRect(0, 50, 100, 100); }
<canvas id="canvas" width="200" height="250"></canvas>
draw();
Screenshot  Live sample 
