Design a Loading Screen

Its id in the pack.

Its name.

Whether it is the one the pack shows. A pack shows one.

Its first effect, or none.

Options: none, snow, rain, stars, embers, sparkles, fireflies, bubbles, petals, hearts, confetti

Every effect, in the order they are drawn.

How many words and pictures the logo has.

Whose logo: its own (custom), Minecraft's (vanilla) or none.

Options: custom, vanilla, none

The words of the logo's first words layer.

The ready-made look it started from, when it did.

ISO 8601.

The design, as layers: background {style solid|vertical|radial|diagonal|stripes|checker|sunburst, color (the whole screen, the top, the edges, or a pattern's first colour), color2 (the bottom, the middle, or the pattern's second), glow (a soft light behind the logo, or null)}; effects, up to 3 drawn in order: [{id, kind snow|rain|stars|embers|sparkles|fireflies|bubbles|petals|hearts|confetti, color, color2 (confetti's second paper, a bubble's glint, a petal's or heart's shading), amount 0-1}]; logo {kind custom|vanilla|none, layers, up to 6 stacked top to bottom: [{id, type text, text (up to 30 characters), font rank (chunky capitals, the default)|classic (square capitals)|tiny (has lower case), size 1-4 (a title is 2, a line under it 1), color, color2 (the bottom of a gradient, or null), outline (a 1px line round the letters, or null), bold, spacing 0-3} or {id, type picture, picture: {width up to 128, height up to 64, palette (up to 12 colours), pixels (one hex digit per pixel, row by row: 0 transparent, 1-c the palette)}}, two pictures at most], shadow (a shadow under every layer, or null), shadowDepth 1-4 (1 is a drop shadow, more a solid 3D edge), layout stacked|side (the pictures beside the words), offset -1 to 1 (the logo up or down from the middle), scale 0.5-2}; bar {style solid|gradient|stripes|segments, frame, fill, fill2 (the gradient's far end or the second stripe), track (the empty part, or null)}. Colours are #rrggbb. Send effects or logo.layers whole: a layer keeps its id from get_loading_screen. The older single effect and a logo's title, subtitle and picture fields are still accepted and change the first effect, the first two words layers and the first picture. Anything left out keeps its value (on a new screen, the default look); anything out of range is brought back into it. Send it back changed to update_loading_screen. Absent from the listing.