HTML5 CANVAS

HTML <canvas> Tag

Pembahasan kali ini bukan tentang "next tutorial MontageJS", tapi akan lebih mengenal attribute dari HTML5, salah satunya HTML <canvas> Tag .

Tag <canvas> merupakan fitur atau atribut terbaru yang ditawarkan HTML5 yang digunakan untuk menggambar grafik, dan dapat kita dukung dengan script biasanya Javascript, agar canvas yang kita buat benar-benar bisa menarik/menggambar grafis. Itu disebabkan karena Tag <canvas> hanya merupakan sebuah wadah untuk grafis.

Nah, contoh function script-nya yaitu getContext () method yaitu untul mengembalikan sebuah objek yang menyediakan metode dan properti untuk menggambar di kanvas.

Method ini mencakup sifat-sifat dan mengambil objek 2 dimensi, yang dapat digunakan untuk menggambar teks, garis, kotak, lingkaran, dan banyak lagi - di kanvas. 

Berikut properti yang dapat digunakan bersamaan dengan tag <canvas> :

Colors, Styles, and Shadows

Property	Description
fillStyle	Sets or returns the color, gradient, or pattern used to fill the drawing
strokeStyle	Sets or returns the color, gradient, or pattern used for strokes
shadowColor	Sets or returns the color to use for shadows
shadowBlur	Sets or returns the blur level for shadows
shadowOffsetX	Sets or returns the horizontal distance of the shadow from the shape
shadowOffsetY	Sets or returns the vertical distance of the shadow from the shape

Method	Description
createLinearGradient()	Creates a linear gradient (to use on canvas content)
createPattern()	Repeats a specified element in the specified direction
createRadialGradient()	Creates a radial/circular gradient (to use on canvas content)
addColorStop()	Specifies the colors and stop positions in a gradient object

Line Styles

Property	Description
lineCap	Sets or returns the style of the end caps for a line
lineJoin	Sets or returns the type of corner created, when two lines meet
lineWidth	Sets or returns the current line width
miterLimit	Sets or returns the maximum miter length

Rectangles

Method	Description
rect()	Creates a rectangle
fillRect()	Draws a "filled" rectangle
strokeRect()	Draws a rectangle (no fill)
clearRect()	Clears the specified pixels within a given rectangle

Paths

Method	Description
fill()	Fills the current drawing (path)
stroke()	Actually draws the path you have defined
beginPath()	Begins a path, or resets the current path
moveTo()	Moves the path to the specified point in the canvas, without creating a line
closePath()	Creates a path from the current point back to the starting point
lineTo()	Adds a new point and creates a line from that point to the last specified point in the canvas
clip()	Clips a region of any shape and size from the original canvas
quadraticCurveTo()	Creates a quadratic Bézier curve
bezierCurveTo()	Creates a cubic Bézier curve
arc()	Creates an arc/curve (used to create circles, or parts of circles)
arcTo()	Creates an arc/curve between two tangents
isPointInPath()	Returns true if the specified point is in the current path, otherwise false

Transformations

Method	Description
scale()	Scales the current drawing bigger or smaller
rotate()	Rotates the current drawing
translate()	Remaps the (0,0) position on the canvas
transform()	Replaces the current transformation matrix for the drawing
setTransform()	Resets the current transform to the identity matrix. Then runs transform()

Text

Property	Description
font	Sets or returns the current font properties for text content
textAlign	Sets or returns the current alignment for text content
textBaseline	Sets or returns the current text baseline used when drawing text

Method	Description
fillText()	Draws "filled" text on the canvas
strokeText()	Draws text on the canvas (no fill)
measureText()	Returns an object that contains the width of the specified text

Image Drawing

Method	Description
drawImage()	Draws an image, canvas, or video onto the canvas

Pixel Manipulation

Property	Description
width	Returns the width of an ImageData object
height	Returns the height of an ImageData object
data	Returns an object that contains image data of a specified ImageData object

Method	Description
createImageData()	Creates a new, blank ImageData object
getImageData()	Returns an ImageData object that copies the pixel data for the specified rectangle on a canvas
putImageData()	Puts the image data (from a specified ImageData object) back onto the canvas

Compositing

Property	Description
globalAlpha	Sets or returns the current alpha or transparency value of the drawing
globalCompositeOperation	Sets or returns how a new image are drawn onto an existing image

Other

Method	Description
save()	Saves the state of the current context
restore()	Returns previously saved path state and attributes

Dan ini contoh sederhana dari sebuah <canvas> untuk menggambar sebuah persegi :

1.  Buat file .html kemudian ketikkan code seperti berikut :
   
   
   Code:

   <!DOCTYPE html>
   <html>
   <body>
   
   <canvas id="myCanvas" width="200" height="100" style="border:1px solid #c3c3c3;">
   Your browser does not support the HTML5 canvas tag.
   </canvas>
   
   <script>
   
   var c = document.getElementById("myCanvas");
   var ctx = c.getContext("2d");
   ctx.fillStyle = "#FF0000";
   ctx.fillRect(0,0,150,75);
   
   </script>
   
   </body>
   </html>
2. Simpan file.html kemudian jalankan, dan berikut tampilannya :
   
   
   
   
   
   
   
   
   
   
   Dan ini contoh kedua dari sebuah <canvas> untuk menggambar seperti aplikasi paint :
   

   1. Buat file .html baru dan ketikkan code seperti berikut : 
      
      
      Title of Spoiler:

      <!DOCTYPE html>
      <html>
      <body>
      
      <div id="sketch" border=1>
        <canvas id="paint"></canvas>
      </div>
      
      <script>
      var canvas = document.querySelector('#paint');
      var ctx = canvas.getContext('2d');
      
      var sketch = document.querySelector('#sketch');
      var sketch_style = getComputedStyle(sketch);
      canvas.width = parseInt(sketch_style.getPropertyValue('width'));
      canvas.height = parseInt(sketch_style.getPropertyValue('height'));
      var mouse = {x: 0, y: 0};
      
      /* Mouse Capturing Work */
      canvas.addEventListener('mousemove', function(e) {
        mouse.x = e.pageX - this.offsetLeft;
        mouse.y = e.pageY - this.offsetTop;
      }, false);
      
      /* Drawing on Paint App */
      ctx.lineWidth = 5;
      ctx.lineJoin = 'round';
      ctx.lineCap = 'round';
      ctx.strokeStyle = 'blue';
      
      canvas.addEventListener('mousedown', function(e) {
          ctx.beginPath();
          ctx.moveTo(mouse.x, mouse.y);
      
          canvas.addEventListener('mousemove', onPaint, false);
      }, false);
      
      canvas.addEventListener('mouseup', function() {
          canvas.removeEventListener('mousemove', onPaint, false);
      }, false);
      
      var onPaint = function() {
          ctx.lineTo(mouse.x, mouse.y);
          ctx.stroke();
      };
      
      </script>
      
      </body>
      </html>  

       
      
       
      Ini hasilnya hahahaha :3