webgl/webgl-2d-matrixstack-02.html

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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
<title>WebGL - 2D - DrawImage with MatrixStack rotation point in center of image</title>
<link type="text/css" href="resources/webgl-tutorials.css" rel="stylesheet" />
</head>
<body>
<canvas id="canvas"></canvas>
</body>
<!-- vertex shader -->
<script id="drawImage-vertex-shader" type="x-shader/x-vertex">
attribute vec4 a_position;
attribute vec2 a_texcoord;

uniform mat4 u_matrix;
uniform mat4 u_textureMatrix;

varying vec2 v_texcoord;

void main() {
   gl_Position = u_matrix * a_position;
   v_texcoord = (u_textureMatrix * vec4(a_texcoord, 0, 1)).xy;
}
</script>
<script id="drawImage-fragment-shader" type="x-shader/x-fragment">
precision mediump float;

varying vec2 v_texcoord;

uniform sampler2D texture;

void main() {
   gl_FragColor = texture2D(texture, v_texcoord);
}
</script>
<!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See https://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and https://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="resources/webgl-utils.js"></script>
<script src="resources/m4.js"></script>
<script>
"use strict";

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

  var matrixStack = new MatrixStack();

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

  // look up where the vertex data needs to go.
  var positionLocation = gl.getAttribLocation(program, "a_position");
  var texcoordLocation = gl.getAttribLocation(program, "a_texcoord");

  // lookup uniforms
  var matrixLocation = gl.getUniformLocation(program, "u_matrix");
  var textureMatrixLocation = gl.getUniformLocation(program, "u_textureMatrix");
  var textureLocation = gl.getUniformLocation(program, "u_texture");

  // Create a buffer.
  var positionBuffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

  // Put a unit quad in the buffer
  var positions = [
    0, 0,
    0, 1,
    1, 0,
    1, 0,
    0, 1,
    1, 1,
  ];
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

  // Create a buffer for texture coords
  var texcoordBuffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, texcoordBuffer);

  // Put texcoords in the buffer
  var texcoords = [
    0, 0,
    0, 1,
    1, 0,
    1, 0,
    0, 1,
    1, 1,
  ];
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(texcoords), gl.STATIC_DRAW);

  // creates a texture info { width: w, height: h, texture: tex }
  // The texture will start with 1x1 pixels and be updated
  // when the image has loaded
  function loadImageAndCreateTextureInfo(url) {
    var tex = gl.createTexture();
    gl.bindTexture(gl.TEXTURE_2D, tex);
    // Fill the texture with a 1x1 blue pixel.
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE,
                  new Uint8Array([0, 0, 255, 255]));

    // let's assume all images are not a power of 2
    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.LINEAR);

    var textureInfo = {
      width: 1,   // we don't know the size until it loads
      height: 1,
      texture: tex,
    };
    var img = new Image();
    img.addEventListener('load', function() {
      textureInfo.width = img.width;
      textureInfo.height = img.height;

      gl.bindTexture(gl.TEXTURE_2D, textureInfo.texture);
      gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, img);
    });
    img.src = url;

    return textureInfo;
  }

  var textureInfo = loadImageAndCreateTextureInfo('resources/star.jpg');

  function draw(time) {
    webglUtils.resizeCanvasToDisplaySize(gl.canvas);

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

    gl.clear(gl.COLOR_BUFFER_BIT);

    matrixStack.save();
    matrixStack.translate(gl.canvas.width / 2, gl.canvas.height / 2);
    matrixStack.rotateZ(time);
    matrixStack.translate(textureInfo.width / -2, textureInfo.height / -2);

    drawImage(
      textureInfo.texture,
      textureInfo.width,
      textureInfo.height,
      0, 0);

    matrixStack.restore();
  }

  var then = 0;
  function render(time) {
    time *= 0.001;
    var now = time;
    var deltaTime = Math.min(0.1, now - then);
    then = now;

    draw(time);
    requestAnimationFrame(render);
  }
  requestAnimationFrame(render);

  // Unlike images, textures do not have a width and height associated
  // with them so we'll pass in the width and height of the texture
  function drawImage(
      tex, texWidth, texHeight,
      srcX, srcY, srcWidth, srcHeight,
      dstX, dstY, dstWidth, dstHeight) {
    if (dstX === undefined) {
      dstX = srcX;
    }
    if (dstY === undefined) {
      dstY = srcY;
    }
    if (srcWidth === undefined) {
      srcWidth = texWidth;
    }
    if (srcHeight === undefined) {
      srcHeight = texHeight;
    }
    if (dstWidth === undefined) {
      dstWidth = srcWidth;
    }
    if (dstHeight === undefined) {
      dstHeight = srcHeight;
    }

    gl.bindTexture(gl.TEXTURE_2D, tex);

    // Tell WebGL to use our shader program pair
    gl.useProgram(program);

    // Setup the attributes to pull data from our buffers
    gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
    gl.enableVertexAttribArray(positionLocation);
    gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);
    gl.bindBuffer(gl.ARRAY_BUFFER, texcoordBuffer);
    gl.enableVertexAttribArray(texcoordLocation);
    gl.vertexAttribPointer(texcoordLocation, 2, gl.FLOAT, false, 0, 0);

    // this matirx will convert from pixels to clip space
    var matrix = m4.orthographic(0, gl.canvas.width, gl.canvas.height, 0, -1, 1);

    // this matrix moves the origin to the one represented by
    // the current matrix stack.
    matrix = m4.multiply(matrix, matrixStack.getCurrentMatrix());

    // this matrix will translate our quad to dstX, dstY
    matrix = m4.translate(matrix, dstX, dstY, 0);

    // this matrix will scale our 1 unit quad
    // from 1 unit to texWidth, texHeight units
    matrix = m4.scale(matrix, dstWidth, dstHeight, 1);

    // Set the matrix.
    gl.uniformMatrix4fv(matrixLocation, false, matrix);

    // Because texture coordinates go from 0 to 1
    // and because our texture coordinates are already a unit quad
    // we can select an area of the texture by scaling the unit quad
    // down
    var texMatrix = m4.translation(srcX / texWidth, srcY / texHeight, 0);
    texMatrix = m4.scale(texMatrix, srcWidth / texWidth, srcHeight / texHeight, 1);

    // Set the texture matrix.
    gl.uniformMatrix4fv(textureMatrixLocation, false, texMatrix);

    // Tell the shader to get the texture from texture unit 0
    gl.uniform1i(textureLocation, 0);

    // draw the quad (2 triangles, 6 vertices)
    gl.drawArrays(gl.TRIANGLES, 0, 6);
  }

}

function MatrixStack() {
  this.stack = [];

  // since the stack is empty this will put an initial matrix in it
  this.restore();
}

// Pops the top of the stack restoring the previously saved matrix
MatrixStack.prototype.restore = function() {
  this.stack.pop();
  // Never let the stack be totally empty
  if (this.stack.length < 1) {
    this.stack[0] = m4.identity();
  }
};

// Pushes a copy of the current matrix on the stack
MatrixStack.prototype.save = function() {
  this.stack.push(this.getCurrentMatrix());
};

// Gets a copy of the current matrix (top of the stack)
MatrixStack.prototype.getCurrentMatrix = function() {
  return this.stack[this.stack.length - 1].slice();
};

// Lets us set the current matrix
MatrixStack.prototype.setCurrentMatrix = function(m) {
  this.stack[this.stack.length - 1] = m;
  return m;
};

// Translates the current matrix
MatrixStack.prototype.translate = function(x, y, z) {
  if (z === undefined) {
    z = 0;
  }
  var m = this.getCurrentMatrix();
  this.setCurrentMatrix(m4.translate(m, x, y, z));
};

// Rotates the current matrix around Z
MatrixStack.prototype.rotateZ = function(angleInRadians) {
  var m = this.getCurrentMatrix();
  this.setCurrentMatrix(m4.zRotate(m, angleInRadians));
};

// Scales the current matrix
MatrixStack.prototype.scale = function(x, y, z) {
  if (z === undefined) {
    z = 1;
  }
  var m = this.getCurrentMatrix();
  this.setCurrentMatrix(m4.scale(m, x, y, z));
};

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