examples/snake can set grid square to change color from main

examples/snake/src/main.zig

@@ -87,7 +87,7 @@ pub fn main() !void {
 
     var snake: [GRID_SIZE * GRID_SIZE]u32 = undefined;
     for (0..snake.len) |i| snake[i] = @intFromBool(false);
-    snake[0] = @intFromBool(true);
+    snake[0] = @intFromBool(true); // set head to active
 
     const snake_buffer = try device.CreateBuffer(&.{
         .label = wgpu.StringView.fromSlice("snake buffer"),
@@ -116,9 +116,10 @@ pub fn main() !void {
             .entryPoint = wgpu.StringView.fromSlice("vs_main"),
             .bufferCount = 1,
             .buffers = &[1]wgpu.VertexBufferLayout{
+                // grid?
                 wgpu.VertexBufferLayout{
                     .stepMode = .Vertex,
-                    .arrayStride = 0,
+                    .arrayStride = 2 * @sizeOf(f32),
                     .attributeCount = 1,
                     .attributes = &[1]wgpu.VertextAttribute{
                         wgpu.VertextAttribute{
@@ -127,7 +128,7 @@ pub fn main() !void {
                             .shaderLocation = 0
                         },
                     }
-                }
+                },
             }
         },
         .multisample = .{
@@ -172,13 +173,18 @@ pub fn main() !void {
     const bind_group = try device.CreateBindGroup(&.{
         .label = wgpu.StringView.fromSlice("bind group"),
         .layout = layout,
-        .entryCount = 1,
-        .entries = &[1]wgpu.BindGroup.Entry {
+        .entryCount = 2,
+        .entries = &[2]wgpu.BindGroup.Entry {
             wgpu.BindGroup.Entry{
                 .binding = 0,
                 .buffer = uniform_buffer._impl,
                 .size = uniform_buffer.GetSize()
             },
+            wgpu.BindGroup.Entry{
+                .binding = 1,
+                .buffer = snake_buffer._impl,
+                .size = snake_buffer.GetSize()
+            },
         }
     });
     defer bind_group.Release();

examples/snake/src/shaders/square.wgsl

@@ -1,24 +1,48 @@
 
 @binding(0) @group(0) var<uniform> grid: vec2f;
-//@binding(1) @group(0) var<storage, read> snake: array<u32>;
+
+// If buffer isn't used one get the following error
+// https://www.reddit.com/r/wgpu/comments/xhqxrk/number_of_bindings_in_bind_group_descriptor_2/
+//Number of bindings in bind group descriptor (2) does not match the number of bindings defined in the bind group layout (1)
+@binding(1) @group(0) var<storage> snake: array<u32>;
+
+
+struct VertOut {
+    @builtin(position) position: vec4f,
+    @location(0) color: vec3f
+}
 
 @vertex
 fn vs_main(
     @location(0) pos: vec2f,
     @builtin(instance_index) instance: u32
-) -> @builtin(position) vec4f {
+) -> VertOut {
     let i = f32(instance);
 
+
+
     let cell = vec2f(i % grid.x, floor(i / grid.x));
     let cell_offset = cell / grid * 2;
     let grid_pos = (pos + 1) /  grid - 1 + cell_offset;
 
-    return vec4f(grid_pos, 0, 1); // (X, Y, Z, W)
-}
+    var output: VertOut;
+
+    output.position = vec4f(grid_pos, 0, 1);
 
-@fragment
-fn fs_main() -> @location(0) vec4f {
     let dark_grey = vec3f(27, 27, 27);
     let max = vec3f(255, 255, 255);
-    return vec4f(dark_grey / max, 1); // red
+
+    if (snake[instance] == 1) {
+        output.color = vec3f(1, 0, 0);
+    } else {
+        output.color = dark_grey / max;
+
+    }
+
+    return output; // (X, Y, Z, W)
+}
+
+@fragment
+fn fs_main(@location(0) in_color: vec3f) -> @location(0) vec4f {
+    return vec4f(in_color, 1);
 }