gpu: convert ExternalTexture from enum(usize) to *opaque

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

gpu/src/external_texture.zig

@@ -1,30 +1,25 @@
 const ChainedStruct = @import("types.zig").ChainedStruct;
 const TextureView = @import("texture_view.zig").TextureView;
 
-pub const ExternalTexture = enum(usize) {
-    _,
+pub const ExternalTexture = *opaque {};
 
-    // TODO: verify there is a use case for nullable value of this type.
-    pub const none: ExternalTexture = @intToEnum(ExternalTexture, 0);
-
-    pub const BindingEntry = extern struct {
-        chain: ChainedStruct,
-        external_texture: ExternalTexture,
-    };
-
-    pub const BindingLayout = extern struct {
-        chain: ChainedStruct,
-    };
-
-    pub const Descriptor = extern struct {
-        next_in_chain: *const ChainedStruct,
-        label: ?[*:0]const u8 = null,
-        plane0: TextureView,
-        plane1: TextureView = TextureView.none, // nullable
-        do_yuv_to_rgb_conversion_only: bool,
-        yuv_to_rgb_conversion_matrix: ?[*]const f32 = null, // nullable
-        src_transform_function_parameters: [*]const f32,
-        dst_transform_function_parameters: [*]const f32,
-        gamut_conversion_matrix: [*]const f32,
-    };
+pub const ExternalTextureBindingEntry = extern struct {
+    chain: ChainedStruct,
+    external_texture: ExternalTexture,
+};
+
+pub const ExternalTextureBindingLayout = extern struct {
+    chain: ChainedStruct,
+};
+
+pub const ExternalTextureDescriptor = extern struct {
+    next_in_chain: *const ChainedStruct,
+    label: ?[*:0]const u8 = null,
+    plane0: TextureView,
+    plane1: TextureView = TextureView.none, // nullable
+    do_yuv_to_rgb_conversion_only: bool,
+    yuv_to_rgb_conversion_matrix: ?[*]const f32 = null, // nullable
+    src_transform_function_parameters: [*]const f32,
+    dst_transform_function_parameters: [*]const f32,
+    gamut_conversion_matrix: [*]const f32,
 };