gpu: add RenderPipeline.Descriptor

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

gpu/src/render_pipeline.zig

@@ -1,6 +1,25 @@
+const ChainedStruct = @import("types.zig").ChainedStruct;
+const DepthStencilState = @import("types.zig").DepthStencilState;
+const MultisampleState = @import("types.zig").MultisampleState;
+const VertexState = @import("types.zig").VertexState;
+const PrimitiveState = @import("types.zig").PrimitiveState;
+const FragmentState = @import("types.zig").FragmentState;
+const PipelineLayout = @import("pipeline_layout.zig").PipelineLayout;
+
 pub const RenderPipeline = enum(usize) {
     _,
 
     // TODO: verify there is a use case for nullable value of this type.
     pub const none: RenderPipeline = @intToEnum(RenderPipeline, 0);
+
+    pub const Descriptor = extern struct {
+        next_in_chain: *const ChainedStruct,
+        label: ?[*:0]const u8 = null,
+        layout: PipelineLayout = PipelineLayout.none, // nullable
+        vertex: VertexState,
+        primitive: PrimitiveState,
+        depth_stencil: ?*const DepthStencilState = null, // nullable
+        multisample: MultisampleState,
+        fragment: ?*const FragmentState = null, // nullable
+    };
 };

gpu/src/types.zig

@@ -461,7 +461,7 @@ pub const CopyTextureForBrowserOptions = extern struct {
     dst_alpha_mode: AlphaMode,
 };
 
-pub const MultisampleState = struct {
+pub const MultisampleState = extern struct {
     next_in_chain: *const ChainedStruct,
     count: u32,
     mask: u32,