Textures

COS 350 - Computer Graphics

Show-and-Tell

http://dust.awevation.com/

texture mapping

links: wood, full

texture mapping

texture: night, globe, full

texture mapping

Texture mapping defines a mapping from a point on surface to a texture coordinate in an image.

texture mapping

prepare image to be mapped to geometric shape
specify image mapping method
load texture image and configure
fragment shader
- extract texture elements (texels) from image
- set gl_FragColor

texture mapping

texture mapping

texturedquad

Note: chrome -allow-file-access-from-files TexturedQuad.html

texturedquad

// TexturedQuad.js (c) 2012 matsuda and kanda
// Vertex shader program
var VSHADER_SOURCE =
  'attribute vec4 a_Position;\n' +
  'attribute vec2 a_TexCoord;\n' +
  'varying vec2 v_TexCoord;\n' +
  'void main() {\n' +
  '  gl_Position = a_Position;\n' +
  '  v_TexCoord = a_TexCoord;\n' +
  '}\n';

// Fragment shader program
var FSHADER_SOURCE =
  '#ifdef GL_ES\n' +
  'precision mediump float;\n' +
  '#endif\n' +
  'uniform sampler2D u_Sampler;\n' +
  'varying vec2 v_TexCoord;\n' +
  'void main() {\n' +
  '  gl_FragColor = texture2D(u_Sampler, v_TexCoord);\n' +
  '}\n';

function main() {
  // Retrieve <canvas> element
  var canvas = document.getElementById('webgl');

  // Get the rendering context for WebGL
  var gl = getWebGLContext(canvas);
  if (!gl) {
    console.log('Failed to get the rendering context for WebGL');
    return;
  }

  // Initialize shaders
  if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
    console.log('Failed to intialize shaders.');
    return;
  }

  // Set the vertex information
  var n = initVertexBuffers(gl);
  if (n < 0) {
    console.log('Failed to set the vertex information');
    return;
  }

  // Specify the color for clearing <canvas>
  gl.clearColor(0.0, 0.0, 0.0, 1.0);

  // Set texture
  if (!initTextures(gl, n)) {
    console.log('Failed to intialize the texture.');
    return;
  }
}

function initVertexBuffers(gl) {
  var verticesTexCoords = new Float32Array([
    // Vertex coordinates, texture coordinate
    -0.5,  0.5,   0.0, 1.0,
    -0.5, -0.5,   0.0, 0.0,
     0.5,  0.5,   1.0, 1.0,
     0.5, -0.5,   1.0, 0.0,
  ]);
  var n = 4; // The number of vertices

  // Create the buffer object
  var vertexTexCoordBuffer = gl.createBuffer();
  if (!vertexTexCoordBuffer) {
    console.log('Failed to create the buffer object');
    return -1;
  }

  // Bind the buffer object to target
  gl.bindBuffer(gl.ARRAY_BUFFER, vertexTexCoordBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, verticesTexCoords, gl.STATIC_DRAW);

  var FSIZE = verticesTexCoords.BYTES_PER_ELEMENT;
  //Get the storage location of a_Position, assign and enable buffer
  var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
  if (a_Position < 0) {
    console.log('Failed to get the storage location of a_Position');
    return -1;
  }
  gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, FSIZE * 4, 0);
  gl.enableVertexAttribArray(a_Position);  // Enable the assignment of the buffer object

  // Get the storage location of a_TexCoord
  var a_TexCoord = gl.getAttribLocation(gl.program, 'a_TexCoord');
  if (a_TexCoord < 0) {
    console.log('Failed to get the storage location of a_TexCoord');
    return -1;
  }
  // Assign the buffer object to a_TexCoord variable
  gl.vertexAttribPointer(a_TexCoord, 2, gl.FLOAT, false, FSIZE * 4, FSIZE * 2);
  gl.enableVertexAttribArray(a_TexCoord);  // Enable the assignment of the buffer object

  return n;
}

function initTextures(gl, n) {
  var texture = gl.createTexture();   // Create a texture object
  if (!texture) {
    console.log('Failed to create the texture object');
    return false;
  }

  // Get the storage location of u_Sampler
  var u_Sampler = gl.getUniformLocation(gl.program, 'u_Sampler');
  if (!u_Sampler) {
    console.log('Failed to get the storage location of u_Sampler');
    return false;
  }
  var image = new Image();  // Create the image object
  if (!image) {
    console.log('Failed to create the image object');
    return false;
  }
  // Register the event handler to be called on loading an image
  image.onload = function(){ loadTexture(gl, n, texture, u_Sampler, image); };
  // Tell the browser to load an image
  image.src = 'images/sky.jpg';

  return true;
}

function loadTexture(gl, n, texture, u_Sampler, image) {
  gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, 1); // Flip the image's y axis
  // Enable texture unit0
  gl.activeTexture(gl.TEXTURE0);
  // Bind the texture object to the target
  gl.bindTexture(gl.TEXTURE_2D, texture);

  // Set the texture parameters
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
  // Set the texture image
  gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGB, gl.RGB, gl.UNSIGNED_BYTE, image);

  // Set the texture unit 0 to the sampler
  gl.uniform1i(u_Sampler, 0);

  gl.clear(gl.COLOR_BUFFER_BIT);   // Clear <canvas>

  gl.drawArrays(gl.TRIANGLE_STRIP, 0, n); // Draw the rectangle
}

setting up textures

setting up textures

gl.activeTexture(gl.TEXTURE0);
gl.bindTexture(gl.TEXTURE_2D, texture)
// or gl.TEXTURE_CUBE_MAP  (type of texture image)

setting up textures

gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGB, gl.RGB, gl.UNSIGNED_BYTE, image);

setting up textures

gl.texParameteri(gl.TEXTURE_2D,
                 gl.TEXTURE_MIN_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D,
                 gl.TEXTURE_MAG_FILTER, gl.NEAREST);

setting up textures

gl.texParameteri(gl.TEXTURE_2D,
                 gl.TEXTURE_WRAP_T, gl.MIRRORED_REPEAT);
gl.texParameteri(gl.TEXTURE_2D,
                 gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);

texturedquad_clamp_mirror

texturedquad_repeat

multitexture

loading...