docs: Restructure FP docs (#1762)

docs/docs/guides/SKIA_FRAME_PROCESSORS.mdx

@@ -0,0 +1,67 @@
+---
+id: skia-frame-processors
+title: Drawing onto Frame Processors
+sidebar_label: Drawing onto Frame Processors
+---
+
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+import useBaseUrl from '@docusaurus/useBaseUrl';
+
+<div>
+  <svg xmlns="http://www.w3.org/2000/svg" width="283" height="535" style={{ float: 'right' }}>
+    <image href={useBaseUrl("img/frame-processors.gif")} x="18" y="33" width="247" height="469"  />
+    <image href={useBaseUrl("img/frame.png")} width="283" height="535" />
+  </svg>
+</div>
+
+### Drawing onto Frame Processors
+
+It is technically pretty difficult to draw onto a Camera Frame and have it rendered into the resulting photo or video in realtime, but I have built a working proof of concept of that using Metal/OpenGL and Skia straight in VisionCamera.
+
+This allows you to draw onto a Frame using simple JavaScript APIs:
+
+```ts
+const frameProcessor = useSkiaFrameProcessor((frame) => {
+  'worklet'
+
+  // Detect faces using GPU-accelerated ML API
+  const faces = detectFaces()
+
+  // Draw faces using GPU-accelerated Skia drawing API
+  for (const face of faces) {
+    const rect = Skia.XYWHRect(face.x, face.y, face.width, face.height)
+    const paint = Skia.Paint()
+    paint.setColor(Skia.Color('red'))
+    frame.drawRect(rect, paint)
+  }
+}, [])
+```
+
+..or even apply color-filters in realtime:
+
+```ts
+const invertColorsFilter = Skia.RuntimeEffect.Make(`
+  uniform shader image;
+  half4 main(vec2 pos) {
+    vec4 color = image.eval(pos);
+    return vec4((1.0 - color).rgb, 1.0);
+  }
+`)
+const paint = Skia.Paint(invertColorsFilter)
+
+const frameProcessor = useSkiaFrameProcessor((frame) => {
+  'worklet'
+
+  // Draw frame using Skia Shader to invert colors
+  frame.render(paint)
+}, [])
+```
+
+While this API was originally planned for V3, I decided to remove it again because VisionCamera got insanely complex with that code integrated (custom Metal/OpenGL rendering pipeline with intermediate steps and tons of build setup) and I wanted to keep VisionCamera lean so other users aren't affected by build issues caused by Skia or those GPU APIs. See [this PR for more information](https://github.com/mrousavy/react-native-vision-camera/pull/1740).
+
+In my agency, [Margelo](https://margelo.io), we have worked a lot with 2D and 3D graphics and Camera realtime processing (see the Snapchat-style mask filter on our website for example - that is running in VisionCamera/React Native!), if you need this feature [reach out to us](https://margelo.io#contact) and we'll build a customized/tailored solution for your company! :)
+
+<br />
+
+#### 🚀 Next section: [Zooming](/docs/guides/zooming) (or [creating a Frame Processor Plugin](/docs/guides/frame-processors-plugins-overview))

docs/sidebars.js

@@ -6,7 +6,13 @@ module.exports = {
       'guides/lifecycle',
       'guides/formats',
       'guides/capturing',
+      {
+        type: 'category',
+        label: 'Realtime Frame Processing',
+        items: [
           'guides/frame-processors',
+          'guides/frame-processor-plugin-list',
+          'guides/skia-frame-processors',
           {
             type: 'category',
             label: 'Creating Frame Processor Plugins',
@@ -17,7 +23,8 @@ module.exports = {
               'guides/frame-processors-plugins-final',
             ]
           },
-      'guides/frame-processor-plugin-list',
+        ]
+      },
       'guides/zooming',
       'guides/focusing',
       'guides/errors',