gl-shader

gl-shader

A wrapper for WebGL shaders. Part of stack.gl

Example

Try it out now in your browser: http://stackgl.github.io/gl-shader/

var shell = require('gl-now')()
var createShader = require('gl-shader')
var shader, buffer

shell.on('gl-init', function() {
  var gl = shell.gl

  //Create shader
  shader = createShader(gl,
    'attribute vec3 position;\
    varying vec2 uv;\
    void main() {\
      gl_Position = vec4(position, 1.0);\
      uv = position.xy;\
    }',
    'precision highp float;\
    uniform float t;\
    varying vec2 uv;\
    void main() {\
      gl_FragColor = vec4(0.5*(uv+1.0), 0.5*(cos(t)+1.0), 1.0);\
    }')

  //Create vertex buffer
  buffer = gl.createBuffer()
  gl.bindBuffer(gl.ARRAY_BUFFER, buffer)
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
    -1, 0, 0,
    0, -1, 0,
    1, 1, 0
  ]), gl.STATIC_DRAW)
})

shell.on('gl-render', function(t) {
  var gl = shell.gl

  //Bind shader
  shader.bind()
  
  //Set attributes
  gl.bindBuffer(gl.ARRAY_BUFFER, buffer)
  shader.attributes.position.pointer()

  //Set uniforms
  shader.uniforms.t += 0.01

  //Draw
  gl.drawArrays(gl.TRIANGLES, 0, 3)
})

Here is the result:

Install

npm install gl-shader

API

var createShader = require('gl-shader')

Constructor

There are two main usages for the constructor. First,

var shader = createShader(gl, vertexSource, fragmentSource[, uniforms, attributes])

Constructs a wrapped shader object with shims for all of the uniforms and attributes in the program.

• gl is the webgl context in which the program will be created
• vertexSource is the source code for the vertex shader
• fragmentSource is the source code for the fragment shader
• uniforms is an (optional) list of all uniforms exported by the shader program
• attributes is an (optional) list of all attributes exported by the shader program

The optional uniforms and attributes arrays have the following format. This will be extracted at run-time from the shader, so you can typically omit the uniforms and attributes arguments.

{
  uniforms: [
    { type: 'mat4', name: 'projection' },
    { type: 'sampler2D', name: 'texture0' }
  ],
  attributes: [
    { type: 'vec3', name: 'position' }
  ]
}

You can specify a default location number for each attribute, otherwise WebGL will bind it automatically.

Returns A compiled shader object.

var shader = createShader(gl, opt)

The same as above, but takes an object instead of a parameter list.

• gl is a WebGL context
• opt.vertex a vertex shader source
• opt.fragment a fragment shader source
• opt.uniforms (optional) a list of uniforms
• opt.attributes (optional) a list of attributes

Returns A wrapped shader object

Methods

shader.bind()

Binds the shader for rendering

shader.update(vertSource,fragSource[,uniforms,attributes])

Rebuilds the shader object with new vertex and fragment shaders (same behavior as constructor)

shader.update(opt)

Rebuilds the shader object with new vertex and fragment shaders (same behavior as constructor)

shader.dispose()

Deletes the shader program and associated resources.

Properties

gl

The WebGL context associated to the shader

program

A reference to the underlying program object in the WebGL context

vertShader

A reference to the underlying vertex shader object

fragShader

A reference to the underlying fragment shader object

Uniforms

The uniforms for the shader program are packaged up as properties in the shader.uniforms object. The shader must be bound before the uniforms are assigned. For example, to update a scalar uniform you can just assign to it:

shader.bind()
shader.uniforms.scalar = 1.0

While you can update vector uniforms by writing an array to them:

shader.uniforms.vector = [1,0,1,0]

Matrix uniforms must have their arrays flattened first:

shader.uniforms.matrix = [ 1, 0, 1, 0,
                           0, 1, 0, 0,
                           0, 0, 1, 1,
                           0, 0, 0, 1 ]

You can read the value of uniform too if the underlying shader is currently bound. For example,

shader.bind()
console.log(shader.uniforms.scalar)
console.log(shader.uniforms.vector)
console.log(shader.uniforms.matrix)

Struct uniforms can also be accessed using the normal dot property syntax:

shader.uniforms.light[0].color = [1, 0, 0, 1]

It is also possible to initialize uniforms in bulk by assigning an object:

shader.uniforms = {
  model:  [1, 0, 0, 0,
           0, 1, 0, 0,
           0, 0, 1, 0,
           0, 0, 0, 1],
  color:  [1, 0, 1, 1]
}

The contents of uniform values are lost when a shader is unbound.

Attributes

The basic idea behind the attribute interface is similar to that for uniforms, however because attributes can be either a constant value or get values from a vertex array they have a slightly more complicated interface. All of the attributes are stored in the shader.attributes property.

attrib = constant

For non-array attributes you can set the constant value to be broadcast across all vertices. For example, to set the vertex color of a shader to a constant you could do:

shader.attributes.color = [1, 0, 0, 1]

This internally uses gl.vertexAttribnf. Setting the attribute will also call gl.disableVertexAttribArray on the attribute's location.

attrib.location

This property accesses the location of the attribute. You can assign/read from it to modify the location of the attribute. For example, you can update the location by doing:

attrib.location = 0

Or you can read the currently bound location back by just accessing it:

console.log(attrib.location)

WARNING Changing the attribute location requires recompiling the program. This recompilation is deferred until the next call to .bind()

attrib.pointer([type, normalized, stride, offset])

A shortcut for gl.vertexAttribPointer/gl.enableVertexAttribArray. See the OpenGL man page for details on how this works. The main difference here is that the WebGL context, size and index are known and so these parameters are bound.

• type is the type of the pointer (default gl.FLOAT)
• normalized specifies whether fixed-point data values should be normalized (true) or converted directly as fixed-point values (false) when they are accessed. (Default false)
• stride the byte offset between consecutive generic vertex attributes. (Default: 0)
• offset offset of the first element of the array in bytes. (Default 0)

Matrix attributes

Matrix attributes are also supported, however there are a few subtle difference. Due to WebGL limitations, d-dimensional matrix attributes require d separate attribute locations. If matrix is a matrix attribute, then the rows of the matrix can be accessed independently using:

//First row of matrix
shader.attributes.matrix[0]

//Second row
shader.attributes.matrix[1]

// ... etc.

The interface for these attributes is identical to the above interfaces for vector attributes (support constant setters, .pointer(), and .location).

There is also a bulk interface which simplifies working with the matrix as a whole unit. For example, it is possible to update the location of each row of the matrix simultaneously by assigning it a vector value:

shader.attributes.matrix.location = [1, 2, 3, 4]

Similarly, if the matrix attribute is stored as a contiguous range in memory, the pointer for each row can be set using .pointer(). For example, if matrix is a 4x4 matrix attribute then,

shader.attributes.matrix.pointer(gl.FLOAT, false, 16, 0)

is equivalent to,

shader.attributes.matrix[0].pointer(gl.FLOAT, false, 16, 0)
shader.attributes.matrix[0].pointer(gl.FLOAT, false, 16, 4)
shader.attributes.matrix[0].pointer(gl.FLOAT, false, 16, 8)
shader.attributes.matrix[0].pointer(gl.FLOAT, false, 16, 12)

Reflection

Finally, the library supports some reflection capabilities. The set of all uniforms and data types are stored in the "type" property of the shader object,

console.log(shader.types)

This reflects the uniform and attribute parameters that were passed to the shader constructor.

Acknowledgements

(c) 2013-2015 Mikola Lysenko. MIT License