draw-scene.js

// draw-scene.js
// Code by the devs at Mozilla.org
// Once the shaders are established, the locations are looked up,
// and the square plane's vertex positions put in a buffer, we can
// actually render the scene.
function drawScene(gl, programInfo, buffers, cubeRotation) {
  gl.clearColor(0.0, 0.0, 0.0, 1.0); // Clear to black, fully opaque
  gl.clearDepth(1.0); // Clear everything
  gl.enable(gl.DEPTH_TEST); // Enable depth testing
  gl.depthFunc(gl.LEQUAL); // Near things obscure far things

  // Clear the canvas before we start drawing on it.

  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  // Create a perspective matrix, a special matrix that is
  // used to simulate the distortion of perspective in a camera.
  // Our field of view is 45 degrees, with a width/height
  // ratio that matches the display size of the canvas
  // and we only want to see objects between 0.1 units
  // and 100 units away from the camera.

  const fieldOfView = (45 * Math.PI) / 180; // in radians
  const aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
  const zNear = 0.1;
  const zFar = 100.0;
  const projectionMatrix = mat4.create();

  // note: glmatrix.js always has the first argument
  // as the destination to receive the result.
  mat4.perspective(projectionMatrix, fieldOfView, aspect, zNear, zFar);

  // Set the drawing position to the "identity" point, which is
  // the center of the scene.
  const modelViewMatrix = mat4.create();

  // Now move the drawing position a bit to where we want to
  // start drawing the square.
  mat4.translate(
    modelViewMatrix, // destination matrix
    modelViewMatrix, // matrix to translate
    [-0.0, 0.0, -6.0]
  ); // amount to translate

  //   mat4.rotate(
  //     modelViewMatrix, // destination matrix
  //     modelViewMatrix, // matrix to rotate
  //     squareRotation, // amount to rotate in radians
  //     [0, 0, 1]
  //   ); // axis to rotate around // 2D
  mat4.rotate(
    modelViewMatrix, // destination matrix
    modelViewMatrix, // matrix to rotate
    cubeRotation, // amount to rotate in radians
    [0, 0, 1]
  ); // axis to rotate around (Z)
  mat4.rotate(
    modelViewMatrix, // destination matrix
    modelViewMatrix, // matrix to rotate
    cubeRotation * 0.7, // amount to rotate in radians
    [0, 1, 0]
  ); // axis to rotate around (Y)
  mat4.rotate(
    modelViewMatrix, // destination matrix
    modelViewMatrix, // matrix to rotate
    cubeRotation * 0.3, // amount to rotate in radians
    [1, 0, 0]
  ); // axis to rotate around (X)

  // Tell WebGL how to pull out the positions from the position
  // buffer into the vertexPosition attribute.
  setPositionAttribute(gl, buffers, programInfo);

  setColorAttribute(gl, buffers, programInfo);

  // Tell WebGL which indices to use to index the vertices
  gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, buffers.indices);

  // Tell WebGL to use our program when drawing
  gl.useProgram(programInfo.program);

  // Set the shader uniforms
  gl.uniformMatrix4fv(
    programInfo.uniformLocations.projectionMatrix,
    false,
    projectionMatrix
  );
  gl.uniformMatrix4fv(
    programInfo.uniformLocations.modelViewMatrix,
    false,
    modelViewMatrix
  );

  {
    const vertexCount = 36;
    const type = gl.UNSIGNED_SHORT;
    const offset = 0;
    gl.drawElements(gl.TRIANGLES, vertexCount, type, offset);
  }
}

// Tell WebGL how to pull out the positions from the position
// buffer into the vertexPosition attribute.
function setPositionAttribute(gl, buffers, programInfo) {
  const numComponents = 3; // pull out 3 values per iteration
  const type = gl.FLOAT; // the data in the buffer is 32bit floats
  const normalize = false; // don't normalize
  const stride = 0; // how many bytes to get from one set of values to the next
  // 0 = use type and numComponents above
  const offset = 0; // how many bytes inside the buffer to start from
  gl.bindBuffer(gl.ARRAY_BUFFER, buffers.position);
  gl.vertexAttribPointer(
    programInfo.attribLocations.vertexPosition,
    numComponents,
    type,
    normalize,
    stride,
    offset
  );
  gl.enableVertexAttribArray(programInfo.attribLocations.vertexPosition);
}

// Tell WebGL how to pull out the colors from the color buffer
// into the vertexColor attribute.
function setColorAttribute(gl, buffers, programInfo) {
  const numComponents = 4;
  const type = gl.FLOAT;
  const normalize = false;
  const stride = 0;
  const offset = 0;
  gl.bindBuffer(gl.ARRAY_BUFFER, buffers.color);
  gl.vertexAttribPointer(
    programInfo.attribLocations.vertexColor,
    numComponents,
    type,
    normalize,
    stride,
    offset
  );
  gl.enableVertexAttribArray(programInfo.attribLocations.vertexColor);
}

export { drawScene };