camera update and resetting with custom zoom/pan

[cornhundred]

Sometimes the camera and zoom object can get out of sync. They are reset when the user zooms all the way out (as a fail safe). We should ultimately prevent this mis-syncing from happening or add an additional fail safe that resets the camera when the user has finished interacting with the visualization.

[cornhundred]

Using the current camera system, resetting to a particular zoom/pan level might require initializing the camera with a single instantaneous zoom/pan interaction that represents the previous incremental zooming/panning.

https://github.com/ismms-himc/clustergrammer-gl/blob/master/src/cameras/camera_interaction.js

[cornhundred]

Also, slow down zooming a little by default (maybe allow this to be adjusted by users).

[cornhundred]

Camera update notes (paraphrased from gitter channel @rreusser comments):

Using d3-zoom

the main code is here: https://observablehq.com/@rreusser/regl-tools#persistentZoom

function persistentZoom (xScale, yScale, originalXScale, originalYScale, callback) {
  return d3.zoom().on('zoom', function () {
    let range
    let t = d3.event.transform;

    range = xScale.range().map(t.invertX, t);
    xScale.domain(originalXScale.domain())
    xScale.domain(range.map(xScale.invert, xScale));

    range = yScale.range().map(t.invertY, t);
    yScale.domain(originalYScale.domain())
    yScale.domain(range.map(yScale.invert, yScale));
  });
}

note, the scales are d3 scales (see scale definitions under sample usage)

  let xScale = d3.scaleLinear()
    .domain([-3, 3])
    .range([viewport.margin.l, viewport.width - viewport.margin.r])
    .clamp(true);

  let yScale = constrainLinearScaleAspectRatio(
    d3.scaleLinear()
      .domain([-1.5, 1.5])
      .range([viewport.height - viewport.margin.b, viewport.margin.t])
      .clamp(true),
    xScale, 1);

usage looks like this

  svg.call(
    persistentZoom(currentXScale, currentYScale, xScale, yScale)
      .scaleExtent([0.01, 10000])
      .on('zoom.plot', () => (dirty = true))
  );

Using the d3 scales with webgl is a different manner, the function below translates the scales into a 2d view matrix that can be used in webgl

https://observablehq.com/@rreusser/regl-tools#createReglViewportConfiguration

function createReglViewportConfiguration (regl) {
  const viewport3 = mat3create();

  let command = regl({
    scissor: {
      enable: true,
      box: { 
        x: (ctx, props) => ctx.pixelRatio * props.margin.l,
        y: (ctx, props) => ctx.pixelRatio * props.margin.b,
        width: (ctx, props) => ctx.framebufferWidth - ctx.pixelRatio * (props.margin.r + props.margin.l),
        height: (ctx, props) => ctx.framebufferHeight - ctx.pixelRatio * (props.margin.t + props.margin.b)
      }
    },
    viewport: {
      x: (ctx, props) => ctx.pixelRatio * props.margin.l,
      y: (ctx, props) => ctx.pixelRatio * props.margin.b,
      width: (ctx, props) => ctx.framebufferWidth - ctx.pixelRatio * (props.margin.r + props.margin.l),
      height: (ctx, props) => ctx.framebufferHeight - ctx.pixelRatio * (props.margin.t + props.margin.b)
    },
    uniforms: {
      viewportResolution: (ctx, props) => [ctx.viewportWidth, ctx.viewportHeight],
      framebufferResolution: ctx => [ctx.framebufferWidth, ctx.framebufferHeight],
      inverseViewportResolution: (ctx, props) => [1 / ctx.viewportWidth, 1 / ctx.viewportHeight],
      inverseFramebufferResolution: ctx => [1 / ctx.framebufferWidth, 1 / ctx.framebufferHeight],
    }
  });
  return function (viewport, callback) {
    command(viewport, callback);
  }
}