webgl/webgl-2-textures.html

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<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
    <title>WebGL2 - 2 Textures</title>
<link type="text/css" href="resources/webgl-tutorials.css" rel="stylesheet" />
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<body>
<canvas id="canvas" width="400" height="300"></canvas>
</body>
<script src="resources/webgl-utils.js"></script>
<script src="resources/webgl-lessons-helper.js"></script>
<script>
"use strict";

var vertexShaderSource = `#version 300 es

// an attribute is an input (in) to a vertex shader.
// It will receive data from a buffer
in vec2 a_position;
in vec2 a_texCoord;

// Used to pass in the resolution of the canvas
uniform vec2 u_resolution;

// Used to pass the texture coordinates to the fragment shader
out vec2 v_texCoord;

// all shaders have a main function
void main() {

  // convert the position from pixels to 0.0 to 1.0
  vec2 zeroToOne = a_position / u_resolution;

  // convert from 0->1 to 0->2
  vec2 zeroToTwo = zeroToOne * 2.0;

  // convert from 0->2 to -1->+1 (clipspace)
  vec2 clipSpace = zeroToTwo - 1.0;

  gl_Position = vec4(clipSpace * vec2(1, -1), 0, 1);

  // pass the texCoord to the fragment shader
  // The GPU will interpolate this value between points.
  v_texCoord = a_texCoord;
}
`;

var fragmentShaderSource = `#version 300 es

// fragment shaders don't have a default precision so we need
// to pick one. mediump is a good default. It means "medium precision"
precision mediump float;

// our texture
uniform sampler2D u_image0;
uniform sampler2D u_image1;

// the texCoords passed in from the vertex shader.
in vec2 v_texCoord;

// we need to declare an output for the fragment shader
out vec4 outColor;

void main() {
  vec4 color0 = texture(u_image0, v_texCoord);
  vec4 color1 = texture(u_image1, v_texCoord);
  outColor = color0 * color1;
}
`;

function loadImage(url, callback) {
  var image = new Image();
  image.src = url;
  image.onload = callback;
  return image;
}

function loadImages(urls, callback) {
  var images = [];
  var imagesToLoad = urls.length;

  // Called each time an image finished
  // loading.
  var onImageLoad = function() {
    --imagesToLoad;
    // If all the images are loaded call the callback.
    if (imagesToLoad == 0) {
      callback(images);
    }
  };

  for (var ii = 0; ii < imagesToLoad; ++ii) {
    var image = loadImage(urls[ii], onImageLoad);
    images.push(image);
  }
}

function main() {
  loadImages([
    "resources/leaves.jpg",
    "resources/star.jpg",
  ], render);
}

function render(images) {
  // Get A WebGL context
  var canvas = document.getElementById("canvas");
  webglLessonsHelper.setupLesson(canvas);
  /** @type {WebGLRenderingContext} */
  var gl = canvas.getContext("webgl2");
  if (!gl) {
    webglLessonsHelper.showNeedWebGL2(canvas);
    return;
  }

  // setup GLSL program
  var program = webglUtils.createProgramFromSources(gl,
      [vertexShaderSource, fragmentShaderSource]);

  // look up where the vertex data needs to go.
  var positionAttributeLocation = gl.getAttribLocation(program, "a_position");
  var texCoordAttributeLocation = gl.getAttribLocation(program, "a_texCoord");

  // lookup uniforms
  var resolutionLocation = gl.getUniformLocation(program, "u_resolution");
  var u_image0Location = gl.getUniformLocation(program, "u_image0");
  var u_image1Location = gl.getUniformLocation(program, "u_image1");

  // Create a vertex array object (attribute state)
  var vao = gl.createVertexArray();

  // and make it the one we're currently working with
  gl.bindVertexArray(vao);

  // Create a buffer and put a single pixel space rectangle in
  // it (2 triangles)
  var positionBuffer = gl.createBuffer();

  // Turn on the attribute
  gl.enableVertexAttribArray(positionAttributeLocation);

  // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

  // Tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER)
  var size = 2;          // 2 components per iteration
  var type = gl.FLOAT;   // the data is 32bit floats
  var normalize = false; // don't normalize the data
  var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
  var offset = 0;        // start at the beginning of the buffer
  gl.vertexAttribPointer(
      positionAttributeLocation, size, type, normalize, stride, offset)

  // provide texture coordinates for the rectangle.
  var texCoordBuffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, texCoordBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
      0.0,  0.0,
      1.0,  0.0,
      0.0,  1.0,
      0.0,  1.0,
      1.0,  0.0,
      1.0,  1.0]), gl.STATIC_DRAW);
  gl.enableVertexAttribArray(texCoordAttributeLocation);
  var size = 2;          // 2 components per iteration
  var type = gl.FLOAT;   // the data is 32bit floats
  var normalize = false; // don't normalize the data
  var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
  var offset = 0;        // start at the beginning of the buffer
  gl.vertexAttribPointer(
      texCoordAttributeLocation, size, type, normalize, stride, offset)

  // Create a texture.
  var texture = gl.createTexture();

  // create 2 textures
  var textures = [];
  for (var ii = 0; ii < 2; ++ii) {
    var texture = gl.createTexture();
    gl.bindTexture(gl.TEXTURE_2D, texture);

    // Set the parameters so we don't need mips
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);

    // Upload the image into the texture.
    var mipLevel = 0;               // the largest mip
    var internalFormat = gl.RGBA;   // format we want in the texture
    var srcFormat = gl.RGBA;        // format of data we are supplying
    var srcType = gl.UNSIGNED_BYTE  // type of data we are supplying
    gl.texImage2D(gl.TEXTURE_2D,
                  mipLevel,
                  internalFormat,
                  srcFormat,
                  srcType,
                  images[ii]);

    // add the texture to the array of textures.
    textures.push(texture);
  }

  // Bind the position buffer so gl.bufferData that will be called
  // in setRectangle puts data in the position buffer
  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

  // Set a rectangle the same size as the image.
  // Note: we're assuming both images are the same size.
  setRectangle(gl, 0, 0, images[0].width, images[0].height);

  // Tell WebGL how to convert from clip space to pixels
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  // Clear the canvas
  gl.clearColor(0, 0, 0, 0);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  // Tell it to use our program (pair of shaders)
  gl.useProgram(program);

  // Bind the attribute/buffer set we want.
  gl.bindVertexArray(vao);

  // set the resolution
  gl.uniform2f(resolutionLocation, gl.canvas.width, gl.canvas.height);

  // Tell the shader to get the texture from texture unit 0
  // set which texture units to render with.
  gl.uniform1i(u_image0Location, 0);  // texture unit 0
  gl.uniform1i(u_image1Location, 1);  // texture unit 1

  // Set each texture unit to use a particular texture.
  gl.activeTexture(gl.TEXTURE0);
  gl.bindTexture(gl.TEXTURE_2D, textures[0]);
  gl.activeTexture(gl.TEXTURE1);
  gl.bindTexture(gl.TEXTURE_2D, textures[1]);

  // Draw the rectangle.
  var primitiveType = gl.TRIANGLES;
  var offset = 0;
  var count = 6;
  gl.drawArrays(primitiveType, offset, count);
}

function randomInt(range) {
  return Math.floor(Math.random() * range);
}

function setRectangle(gl, x, y, width, height) {
  var x1 = x;
  var x2 = x + width;
  var y1 = y;
  var y2 = y + height;
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
     x1, y1,
     x2, y1,
     x1, y2,
     x1, y2,
     x2, y1,
     x2, y2]), gl.STATIC_DRAW);
}

main();
</script>
</html>