opengl: support extension iteration, list in debug mode

src/Window.zig

@@ -124,6 +124,7 @@ const Cursor = struct {
         );
     }
 
+    /// Stop the timer. This is idempotent.
     pub fn stopTimer(self: Cursor) !void {
         try self.timer.stop();
     }
@@ -166,6 +167,12 @@ pub fn create(alloc: Allocator, loop: libuv.Loop, config: *const Config) !*Windo
         gl.glad.versionMajor(version),
         gl.glad.versionMinor(version),
     });
+    if (builtin.mode == .Debug) {
+        var ext_iter = try gl.ext.iterator();
+        while (try ext_iter.next()) |ext| {
+            log.debug("OpenGL extension available name={s}", .{ext});
+        }
+    }
 
     // Culling, probably not necessary. We have to change the winding
     // order since our 0,0 is top-left.

src/opengl.zig

@@ -15,6 +15,7 @@ pub const c = @import("opengl/c.zig");
 pub const glad = @import("opengl/glad.zig");
 pub usingnamespace @import("opengl/draw.zig");
 
+pub const ext = @import("opengl/extensions.zig");
 pub const Buffer = @import("opengl/Buffer.zig");
 pub const Program = @import("opengl/Program.zig");
 pub const Shader = @import("opengl/Shader.zig");

src/opengl/extensions.zig

@@ -0,0 +1,31 @@
+const std = @import("std");
+const c = @import("c.zig");
+const errors = @import("errors.zig");
+
+/// Returns the number of extensions.
+pub fn len() !u32 {
+    var n: c.GLint = undefined;
+    c.glGetIntegerv(c.GL_NUM_EXTENSIONS, &n);
+    try errors.getError();
+    return @intCast(u32, n);
+}
+
+/// Returns an iterator for the extensions.
+pub fn iterator() !Iterator {
+    return Iterator{ .len = try len() };
+}
+
+/// Iterator for the available extensions.
+pub const Iterator = struct {
+    /// The total number of extensions.
+    len: c.GLuint = 0,
+    i: c.GLuint = 0,
+
+    pub fn next(self: *Iterator) !?[]const u8 {
+        if (self.i >= self.len) return null;
+        const res = c.glGetStringi(c.GL_EXTENSIONS, self.i);
+        try errors.getError();
+        self.i += 1;
+        return std.mem.sliceTo(res, 0);
+    }
+};