WebGL 杂记

WebGL 2D RotationHow to rotate in 2Dhttps://webglfundamentals.org/webgl/lessons/webgl-2d-rotation.html

假设您有一个矩形，并且想要旋转它。在开始旋转之前，右上角是 3.0、9.0。让我们在单位圆上从 12 点顺时针方向选择一个点。

圆圈上的位置是 0.50 和 0.87

rotatedX = a_position.x * u_rotation.y + a_position.y * u_rotation.x;
rotatedY = a_position.y * u_rotation.y - a_position.x * u_rotation.x;

 顺时针 60 度也一样

3.0 * 0.50 + 9.0 * 0.87 = 9.3
9.0 * 0.50 - 3.0 * 0.87 = 1.9

您可以看到，当我们将该点顺时针向右旋转时，X 值变大而 Y 值变小。如果我们继续超过 90 度，X 会再次开始变小，而 Y 会开始变大。这种模式给了我们旋转。

单位圆上的点还有另一个名称。它们被称为正弦和余弦。因此，对于任何给定的角度，我们都可以像这样查找正弦和余弦。

-----------------------------------------扩展理解 ----------------------------------------

"use strict";

function main() {
  // Get A WebGL context
  /** @type {HTMLCanvasElement} */
  var canvas = document.querySelector("#canvas");
  var gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }

  // setup GLSL program
  var program = webglUtils.createProgramFromScripts(gl, ["vertex-shader-2d", "fragment-shader-2d"]);

  // 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 translationLocation = gl.getUniformLocation(program, "u_translation");
  var rotationLocation = gl.getUniformLocation(program, "u_rotation");

  // 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 rotation = [0, 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});
  $("#rotation").gmanUnitCircle({
    width: 200,
    height: 200,
    value: 0,
    slide: function(e,u) {
      rotation[0] = u.x;
      rotation[1] = u.y;
      drawScene();
    }
  });

  function updatePosition(index) {
    return function(event, ui) {
      translation[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);

    // Set the translation.
    gl.uniform2fv(translationLocation, translation);

    // Set the rotation.
    gl.uniform2fv(rotationLocation, rotation);

    // 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);
  }
}

// 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);
}

$(function(){
  main();
});

--------------------------------------扩展阅读：三角函数----------------------------------

感谢这位台湾老师，让我的三角函数在班中无敌手。数学入门基础教程中华科技大学公开课李柏坚教授_哔哩哔哩_bilibili

什么是弧度？

弧度是用于圆、旋转和角度的测量单位。就像我们可以用英寸、码、米等来测量距离一样，我们可以用度或弧度来测量角度。

您可能知道使用公制测量的数学比使用英制测量的数学更容易。从英寸到英尺，我们除以 12。从英寸到码，我们除以 36。我不了解你，但我无法在脑海中除以 36。使用公制就容易多了。从毫米到厘米，我们乘以 10。从毫米到米，我们乘以 1000。我可以在脑海中乘以 1000。

弧度与度数相似。学位使数学变得困难。弧度使数学变得容易。一个圆有 360 度，但只有 2π 弧度。所以一整圈是 2π 弧度。半圈是 1π 弧度。1/4 转，即 90 度是 1/2π 弧度。因此，如果您想将某些东西旋转 90 度，只需使用Math.PI * 0.5. 如果您想将其旋转 45 度，请使用Math.PI * 0.25等。

如果您开始以弧度思考，几乎所有涉及角度、圆或旋转的数学运算都非常简单。所以试试看。使用弧度，而不是度数，除非在 UI 显示中。

获取坐标----------------------

function click(ev, gl, canvas, a_Position, u_FragColor) {
  var x = ev.clientX; // x coordinate of a mouse pointer
  var y = ev.clientY; // y coordinate of a mouse pointer
  var rect = ev.target.getBoundingClientRect();

  x = ((x - rect.left) - canvas.width/2)/(canvas.width/2);
  y = (canvas.height/2 - (y - rect.top))/(canvas.height/2);

  // Store the coordinates to g_points array
  g_points.push([x, y]);
  // Store the coordinates to g_points array
  if (x >= 0.0 && y >= 0.0) {      // First quadrant
    g_colors.push([1.0, 0.0, 0.0, 1.0]);  // Red
  } else if (x < 0.0 && y < 0.0) { // Third quadrant
    g_colors.push([0.0, 1.0, 0.0, 1.0]);  // Green
  } else {                         // Others
    g_colors.push([1.0, 1.0, 1.0, 1.0]);  // White
  }

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

  var len = g_points.length;
  for(var i = 0; i < len; i++) {
    var xy = g_points[i];
    var rgba = g_colors[i];

    // Pass the position of a point to a_Position variable
    gl.vertexAttrib3f(a_Position, xy[0], xy[1], 0.0);
    // Pass the color of a point to u_FragColor variable
    gl.uniform4f(u_FragColor, rgba[0], rgba[1], rgba[2], rgba[3]);
    // Draw
    gl.drawArrays(gl.POINTS, 0, 1);
  }
}

webgl单点绘制-----------------------------------------

var g_points = []; // The array for the position of a mouse press
function click(ev, gl, canvas, a_Position) {
  var x = ev.clientX; // x coordinate of a mouse pointer
  var y = ev.clientY; // y coordinate of a mouse pointer
  var rect = ev.target.getBoundingClientRect() ;

  x = ((x - rect.left) - canvas.width/2)/(canvas.width/2);
  y = (canvas.height/2 - (y - rect.top))/(canvas.height/2);
  // Store the coordinates to g_points array
  g_points.push(x); g_points.push(y);

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

  var len = g_points.length;
  for(var i = 0; i < len; i += 2) {
    // Pass the position of a point to a_Position variable
    gl.vertexAttrib3f(a_Position, g_points[i], g_points[i+1], 0.0);

    // Draw
    gl.drawArrays(gl.POINTS, 0, 1);
  }
}