renderer: create explicit sampler state for custom shaders

The GLSL to MSL conversion process uses a passed-in sampler state for
the `iChannel0` parameter and we weren't providing it. This magically
worked on Apple Silicon for unknown reasons but failed on Intel GPUs.

In normal, hand-written MSL, we'd explicitly create the sampler state as
a normal variable (we do this in `shaders.metal` already!), but the
Shadertoy conversion stuff doesn't do this, probably because the exact
sampler parameters can't be safely known.

This fixes a Metal validation error when using custom shaders:

```
-[MTLDebugRenderCommandEncoder validateCommonDrawErrors:]:5970: failed 
assertion `Draw Errors Validation Fragment Function(main0): missing Sampler 
binding at index 0 for iChannel0Smplr[0].
```

1 files changed, 12 insertions, 0 deletions

diff --git a/src/renderer/OpenGL.zig b/src/renderer/OpenGL.zig
index e572806d1..673f79501 100644
--- a/src/renderer/OpenGL.zig
+++ b/src/renderer/OpenGL.zig
@@ -20,6 +20,7 @@ pub const RenderPass = @import("opengl/RenderPass.zig");
 pub const Pipeline = @import("opengl/Pipeline.zig");
 const bufferpkg = @import("opengl/buffer.zig");
 pub const Buffer = bufferpkg.Buffer;
+pub const Sampler = @import("opengl/Sampler.zig");
 pub const Texture = @import("opengl/Texture.zig");
 pub const shaders = @import("opengl/shaders.zig");
 
@@ -364,6 +365,17 @@ pub inline fn textureOptions(self: OpenGL) Texture.Options {
     };
 }
 
+/// Returns the options to use when constructing samplers.
+pub inline fn samplerOptions(self: OpenGL) Sampler.Options {
+    _ = self;
+    return .{
+        .min_filter = .linear,
+        .mag_filter = .linear,
+        .wrap_s = .clamp_to_edge,
+        .wrap_t = .clamp_to_edge,
+    };
+}
+
 /// Pixel format for image texture options.
 pub const ImageTextureFormat = enum {
     /// 1 byte per pixel grayscale.