Add StackPreview basic version

frontend/src/App.svelte

@@ -3,6 +3,7 @@
   import Editor2D from './sections/Editor2D.svelte'
   import Importer from './sections/Importer.svelte';
   import PaletteSection from './sections/Palette.svelte'
+  import FloatingPanel from './components/FloatingPanel.svelte'
   import { Palette, PaletteEntry, defaultPalette } from './types/palette'
 
   import type { LoadedFile } from './types/file.ts'
@@ -14,6 +15,7 @@
   import { OverflowMenu, OverflowMenuItem } from "carbon-components-svelte"
 
   import { Close } from "carbon-icons-svelte"
+  import StackPreview from './sections/StackPreview.svelte'
   
   let theme: 'white'|'g10'|'g80'|'g90'|'g100' = 'g90'
   
@@ -84,6 +86,12 @@
         </svelte:fragment>
       </Tabs>
     </section>
+    <FloatingPanel
+      label="Stack Preview"
+      noPadding
+      >
+      <StackPreview files={files} />
+    </FloatingPanel>
   </section>
 </main>
 <ComposedModal bind:open={showImport} size="sm" preventCloseOnClickOutside on:click:button--primary={engageImport}>

frontend/src/components/FloatingPanel.svelte

@@ -0,0 +1,39 @@
+<script lang='ts'>
+  import {
+    ModalHeader,
+    ModalBody,
+    ModalFooter,
+  } from "carbon-components-svelte"
+  
+  export let title: string = "Untitled"
+  export let label: string = "Untitled"
+  
+  export let noPadding: boolean = false
+
+</script>
+
+<dialog>
+  <header class='bx--modal-header'>
+    <h2 class='bx--modal-header__label bx--type-delta'>{label}</h2>
+  </header>
+  <section class='bx--modal-content {noPadding?'-noPadding':''}'>
+    <slot/>
+  </section>
+</dialog>
+
+<style>
+  dialog {
+    position: fixed;
+    left: 100;
+    top: 100;
+    background-color: var(--cds-ui-01, #f4f4f4);
+    display: grid;
+    grid-template-columns: 100%;
+    grid-template-rows: auto 1fr auto;
+    outline: 3px solid rgba(0, 0, 0, 0);
+    outline-offset: -3px;
+  }
+  section.-noPadding {
+    padding: 0 !important;
+  }
+</style>

frontend/src/sections/StackPreview.svelte

@@ -0,0 +1,83 @@
+<script lang='ts'>
+  import { Grid, Row, Column, Checkbox, Slider } from "carbon-components-svelte"
+  import type { LoadedFile } from "src/types/file"
+  import { onMount } from "svelte";
+  
+  export let files: LoadedFile[]
+  let shownFiles: Record<string, boolean> = {}
+  
+  let rotation: number = 0
+  
+  let canvas: HTMLCanvasElement
+  function draw() {
+    if (!canvas) return
+    
+    let computedSize = getComputedStyle(canvas)
+    if (canvas.width !== parseInt(computedSize.width) || canvas.height !== parseInt(computedSize.height)) {
+      canvas.width = parseInt(computedSize.width)
+      canvas.height = parseInt(computedSize.height)
+    }
+
+    let ctx = canvas.getContext('2d')
+    if (!ctx) return
+    ctx.clearRect(0, 0, canvas.width, canvas.height)
+    ctx.fillStyle = '#222222'
+    ctx.fillRect(0, 0, canvas.width, canvas.height)
+    
+    let x = canvas.width/2
+    let y = canvas.height/2
+    for (let file of files) {
+      if (shownFiles[file.title]) {
+        // For now, just get the first frame of the first animation.
+        let done = false
+        for (let [groupName, group] of Object.entries(file.data.groups)) {
+          for (let [animationName, animation] of Object.entries(group.animations)) {
+            for (let frame of animation.frames) {
+              for (let layer of frame.layers) {
+                ctx.save()
+                ctx.translate(x, y)
+                ctx.rotate(rotation * Math.PI / 180)
+                ctx.drawImage(file.image, layer.x, layer.y, group.width, group.height, -group.width/2, -group.height/2, group.width, group.height)
+                ctx.restore()
+                y -= 1
+              }
+              done = true
+              if (done) break
+            }
+            if (done) break
+          }
+          x += group.width
+          y = canvas.height/2
+          if (done) break
+        }
+      }
+    }
+  }
+  
+  onMount(()=>{
+    let frameID: number = 0
+    let frameDraw = () => {
+      draw()
+      frameID = requestAnimationFrame(frameDraw)
+    }
+    frameID = requestAnimationFrame(frameDraw)
+    return () => cancelAnimationFrame(frameID)
+  })
+</script>
+
+<Grid narrow condensed fullWidth>
+  <Row narrow condensed>
+    <Column sm>
+      {#each files as file, i}
+        <Checkbox bind:checked={shownFiles[file.title]} labelText={file.title.length>20?'…'+file.title.substring(file.title.length-20):file.title}></Checkbox>
+      {/each}
+    </Column>
+    <Column>
+      <canvas bind:this={canvas}></canvas>
+      <Slider labelText="Rotation" min={0} max={360} step={1} bind:value={rotation} fullWidth></Slider>
+    </Column>
+  </Row>
+</Grid>
+
+<style>
+</style>