text: ﻿"use strict";
  
  function main() {
      // Get A WebGL context
      /** @type {HTMLCanvasElement} */
      var canvas = document.getElementById("canvas");
      var gl = canvas.getContext("webgl");
      if (!gl) {
          return;
      }
  
      // setup GLSL program
      var program = webglUtils.createProgramFromScripts(gl, ["2d-vertex-shader", "2d-fragment-shader"]);
  
      // look up where the vertex data needs to go.
      var positionLocation = gl.getAttribLocation(program, "a_position");
  
      // lookup uniforms
      var resolutionLocation = gl.getUniformLocation(program, "u_resolution");
      var colorLocation = gl.getUniformLocation(program, "u_color");
      var matrixLocation = gl.getUniformLocation(program, "u_matrix");
  
      // Create a buffer to put positions in
      var positionBuffer = gl.createBuffer();
      // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
      gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
      // Put geometry data into buffer
      setGeometry(gl);
  
      var translation = [100, 150];
      var angleInRadians = 0;
      var scale = [1, 1];
      var color = [Math.random(), Math.random(), Math.random(), 1];
  
      drawScene();
  
      // Setup a ui.
      webglLessonsUI.setupSlider("#x", { value: translation[0], slide: updatePosition(0), max: gl.canvas.width });
      webglLessonsUI.setupSlider("#y", { value: translation[1], slide: updatePosition(1), max: gl.canvas.height });
      webglLessonsUI.setupSlider("#angle", { slide: updateAngle, max: 360 });
      webglLessonsUI.setupSlider("#scaleX", { value: scale[0], slide: updateScale(0), min: -5, max: 5, step: 0.01, precision: 2 });
      webglLessonsUI.setupSlider("#scaleY", { value: scale[1], slide: updateScale(1), min: -5, max: 5, step: 0.01, precision: 2 });
  
      function updatePosition(index) {
          return function (event, ui) {
              translation[index] = ui.value;
              drawScene();
          };
      }
  
      function updateAngle(event, ui) {
          var angleInDegrees = 360 - ui.value;
          angleInRadians = angleInDegrees * Math.PI / 180;
          drawScene();
      }
  
      function updateScale(index) {
          return function (event, ui) {
              scale[index] = ui.value;
              drawScene();
          };
      }
  
      // Draw the scene.
      function drawScene() {
          webglUtils.resizeCanvasToDisplaySize(gl.canvas);
  
          // Tell WebGL how to convert from clip space to pixels
          gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
  
          // Clear the canvas.
          gl.clear(gl.COLOR_BUFFER_BIT);
  
          // Tell it to use our program (pair of shaders)
          gl.useProgram(program);
  
          // Turn on the attribute
          gl.enableVertexAttribArray(positionLocation);
  
          // Bind the position buffer.
          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(
              positionLocation, size, type, normalize, stride, offset);
  
          // set the resolution
          gl.uniform2f(resolutionLocation, gl.canvas.width, gl.canvas.height);
  
          // set the color
          gl.uniform4fv(colorLocation, color);
  
          // Compute the matrices
          var translationMatrix = m3.translation(translation[0], translation[1]);
          var rotationMatrix = m3.rotation(angleInRadians);
          var scaleMatrix = m3.scaling(scale[0], scale[1]);
  
          // Starting Matrix.
          var matrix = m3.identity();
  
          for (var i = 0; i < 5; ++i) {
              // Multiply the matrices.
              matrix = m3.multiply(matrix, translationMatrix);
              matrix = m3.multiply(matrix, rotationMatrix);
              matrix = m3.multiply(matrix, scaleMatrix);
  
              // Set the matrix.
              gl.uniformMatrix3fv(matrixLocation, false, matrix);
  
              // Draw the geometry.
              var primitiveType = gl.TRIANGLES;
              var offset = 0;
              var count = 18;  // 6 triangles in the 'F', 3 points per triangle
              gl.drawArrays(primitiveType, offset, count);
          }
      }
  }
  
  var m3 = {
      identity: function() {
          return [
            1, 0, 0,
            0, 1, 0,
            0, 0, 1,
          ];
      },
  
      translation: function (tx, ty) {
          return [
            1, 0, 0,
            0, 1, 0,
            tx, ty, 1,
          ];
      },
  
      rotation: function (angleInRadians) {
          var c = Math.cos(angleInRadians);
          var s = Math.sin(angleInRadians);
          return [
            c, -s, 0,
            s, c, 0,
            0, 0, 1,
          ];
      },
  
      scaling: function (sx, sy) {
          return [
            sx, 0, 0,
            0, sy, 0,
            0, 0, 1,
          ];
      },
  
      multiply: function (a, b) {
          var a00 = a[0 * 3 + 0];
          var a01 = a[0 * 3 + 1];
          var a02 = a[0 * 3 + 2];
          var a10 = a[1 * 3 + 0];
          var a11 = a[1 * 3 + 1];
          var a12 = a[1 * 3 + 2];
          var a20 = a[2 * 3 + 0];
          var a21 = a[2 * 3 + 1];
          var a22 = a[2 * 3 + 2];
          var b00 = b[0 * 3 + 0];
          var b01 = b[0 * 3 + 1];
          var b02 = b[0 * 3 + 2];
          var b10 = b[1 * 3 + 0];
          var b11 = b[1 * 3 + 1];
          var b12 = b[1 * 3 + 2];
          var b20 = b[2 * 3 + 0];
          var b21 = b[2 * 3 + 1];
          var b22 = b[2 * 3 + 2];
          return [
            b00 * a00 + b01 * a10 + b02 * a20,
            b00 * a01 + b01 * a11 + b02 * a21,
            b00 * a02 + b01 * a12 + b02 * a22,
            b10 * a00 + b11 * a10 + b12 * a20,
            b10 * a01 + b11 * a11 + b12 * a21,
            b10 * a02 + b11 * a12 + b12 * a22,
            b20 * a00 + b21 * a10 + b22 * a20,
            b20 * a01 + b21 * a11 + b22 * a21,
            b20 * a02 + b21 * a12 + b22 * a22,
          ];
      },
  };
  
  // Fill the buffer with the values that define a letter 'F'.
  function setGeometry(gl) {
      gl.bufferData(
          gl.ARRAY_BUFFER,
          new Float32Array([
              // left column
              0, 0,
              30, 0,
              0, 150,
              0, 150,
              30, 0,
              30, 150,
  
              // top rung
              30, 0,
              100, 0,
              30, 30,
              30, 30,
              100, 0,
              100, 30,
  
              // middle rung
              30, 60,
              67, 60,
              30, 90,
              30, 90,
              67, 60,
              67, 90,
          ]),
          gl.STATIC_DRAW);
  }
  
  main();
  