setBackgroundCanvas

Sets an Image or GLSLFragmentShader as the background of any Element.

This functions allows you to apply a Image or GLSLFragmentShader behind all element children. By using this function you will have far more control. The main reason for this was to allow opacity over an still background image without effecting nested elements. Now each nested element can have its own alpha use setAlpha project for this. Use the opacity rule for the canvas.

Make sure your parent Element has the CSS rule position: relative;.

Demostration Site

Image Example

        /* create the image */
        var img1 = new Image();

    img1.onload = function () {
        
        document.getElementById("your_block_level_element").setBackgroundCanvas(img1);

    };
    img1.crossOrigin = "anonymous"; /* required removes: operation is insecure */
    img1.src = 'https://upload.wikimedia.org/wikipedia/commons/9/9b/The.Matrix.glmatrix.2.png';

GLSLFragmentShader Example

           let parentElement = document.getElementById("glslContainer");
           let glslFragmentShader = new GLSLFragmentShader(parentElement, "./shaders/triangle_grid_contouring_v100.glsl.json");
       
   /* create a function for Loaded event within parent element */
   parentElement.glslFragmentShaderLoaded = function(event){
   	/* set your size */
            glslFragmentShader.size = 4; // between .5 - 8
    
    /* add to the background */
     parentElement.setBackgroundCanvas(glslFragmentShader);

    
   }

Video Example

           No Longer Supported

Change Canvas Object

    /* create the image */
    var img1 = new Image();

    img1.onload = function () {
        /* destroy the old canvas first */
        document.getElementById("col_1").destroyBackgroundCanvas();
        document.getElementById("col_1").changeBackgroundCanvas(img1);
    };
    img1.crossOrigin = "anonymous";
    img1.src = 'https://upload.wikimedia.org/wikipedia/commons/thumb/9/97/The_Earth_seen_from_Apollo_17.jpg/1024px-The_Earth_seen_from_Apollo_17.jpg';

Canvas Element

You can access the canvas element directly by using

element.canvas.element

Refresh

You can access the reFresh function if you have any refreshing issues with

element.canvas.reFresh();

Events

BackgroundCanvasLoaded

document.getElementById("your_block_level_element").addEventListener("BackgroundCanvasLoaded", function(event){
           /* add the classes to the canvas element to effect the appearance */
           /* set position */
        
       /* set repeat */
        
       /* set opacity */
        
       /* set stretch */
       /* stretch both axis */
           event.target.canvas.element.classList.add("xy-xy");

           event.target.canvas.reFresh();
});

BackgroundCanvasChanged

Triggered when a change to the canvas object.

Requires

containsAll https://github.com/webciter/containsAll
arrayMin https://github.com/webciter/arrayMin

Optional

By including this module you will get an extra reFresh call.

classListMonitor https://github.com/webciter/classListMonitor
GLSLFragmentShader https://github.com/webciter/GLSLFragmentShader#2.0.0

Installation

npm i element-functions-set_background_canvas

Positioning

To reposition the image use two classes on the canvas element, both x and y classes are needed.

9 positions are possible

 xl yt, xc yt, xr yt
 xl yc, xc yc, xr yc
 xl yb, xc yb, xr yb
 

So for a center image use

/* center image */
 document.getElementById("your_block_level_element").canvas.element.classList.add("xc yc");
 

Stretch

The object ether image, video can be stretched over the element, using the following classes. aspect ratio is ignored.

 x-x - x axis only
 y-y - y axis only
 xy-xy - both axis
 

Opacity

Use the opacity rule, inheritance will not be effected as it's on it own branch.

  /* 50% Opacity */
  document.getElementById("your_block_level_element").backgroundCanvas.opacity = 0.5;

 

Repeat

/* only on the x axis */
 document.getElementById("your_block_level_element").canvas.element.classList.add("xx");

/* only on the y axis */
 document.getElementById("your_block_level_element").canvas.element.classList.add("yy");

/* both axis, essentially tile cover */
 document.getElementById("your_block_level_element").canvas.element.classList.add("xx yy");

Levels

Levels were added for manipulation of pixels just in case there is some chroma pixels remaining. The class of levels must be added to the Element or it will be ignored

document.getElementById("your_block_level_element").canvas.element.levels.red = 1; /* 0.0 - 2.0 */
document.getElementById("your_block_level_element").canvas.element.levels.green = 1; /* 0.0 - 2.0 */
document.getElementById("your_block_level_element").canvas.element.levels.blue = 1; /* 0.0 - 2.0 */

Chroma Key

Apply a color of chroma key to the GLSLFragmentShader or Image the class of chromaKey must be added to the canvas element to function, make sure you slect the exact colour of the chroma key.

document.getElementById("your_block_level_element").canvas.element.chromaKey = {red: 0, green: 255, blue:0};

Chroma Variance

Apply an amount of chroma variance to the GLSLFragmentShader or Image the class of chromaKey must be added to the canvas element to function

document.getElementById("your_block_level_element").backgroundCanvas.chromaVariance = 300;