fix index triangle digram (#156)

webgpu/lessons/ko/webgpu-vertex-buffers.md

@@ -896,12 +896,12 @@ function createCircleVertices({
 +  let ndx = 0;
 +
 +  // 1st tri  2nd tri  3rd tri  4th tri
-+  // 0 1 2    2 1 3    4 5 6    6 5 7
++  // 0 1 2    2 1 3    2 3 4    4 3 5
 +  //
-+  // 0--2        2     4--6        6  .....
++  // 0--2        2     2--4        4  .....
 +  // | /        /|     | /        /|
 +  // |/        / |     |/        / |
-+  // 1        1--3     5        5--7  .....
++  // 1        1--3     3        3--5  .....
 +  for (let i = 0; i < numSubdivisions; ++i) {
 +    const ndxOffset = i * 2;
 +

webgpu/lessons/webgpu-bind-group-layouts.md

@@ -2,5 +2,52 @@ Title: WebGPU Bind Group Layouts
 Description: Explicit Bind Group Layouts
 TOC: Bind Group Layouts
 
-TBD
+Bind Group Layouts are used to make it easy and efficient
+for WebGPU to match Bind Groups to Compute and Render Pipelines.
+
+How it works: 
+
+A Pipeline, like a `GPUComputePipeline` or `GPURenderPipeline`
+uses a `GPUPipelineLayout` which defines 0 or more
+`GPUBindGroupLayout`s. Each `GPUBindGroupLayout` is assigned
+to a specific group index.
+
+Bind Groups are created with a specific `GPUBindGroupLayout`
+as well.
+
+When you go to `draw` or to `dispatchWorkgroups`, WebGPU only
+needs to check, does the `GPUBindGroupLayout` for each group index
+on the current pipeline's `GPUPipelineLayout` match the
+currently bound bind groups, the ones set with `setBindGroup`.
+This check is trivially simple. Most of the detailed checking
+happens when you create the bind group. That way, when you're
+actually drawing or computing, there's almost nothing left to
+check.
+
+Pipelines with generate their own `GPUPipelineLayout` and
+populate it with `GPUBindGroupLayouts` automatically if you
+create the pipeline with `layout: 'auto'` which is what
+most of the samples on this website do.
+
+There are 2 main reasons to **NOT** use `layout: 'auto'`.
+
+1. **You want to use a bind group with more than 1 pipeline**
+
+   You can not use a bind group made with from a bindGroupLayout
+   that was made from a pipeline with `layout: 'auto'` with a
+   different pipeline.
+
+2. **You want a layout that's different than the default `'auto'` layout**
+
+## Using a bind group with more than 1 pipeline
+
+--- need a good example - problem is, drawing twice in 2 different locations
+--- requires 2 different uniform buffers which means it requires 2 bind groups
+--- which means sharing doesn't matter.
+
+Let's made a toy example. We'll make 2 render pipelines and try
+to draw a cube with both pipelines.
+
+
+