From a5a2196d527ff348397d543c1753de16599616bf Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Fri, 1 Apr 2022 18:00:15 -0700
Subject: [PATCH] opengl: bound buffers

---
 src/main.zig          |   6 +--
 src/opengl/Buffer.zig | 106 +++++++++++++++++++++++-------------------
 2 files changed, 60 insertions(+), 52 deletions(-)

diff --git a/src/main.zig b/src/main.zig
index a882463d6..21ed0cba3 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -55,8 +55,8 @@ pub fn main() !void {
     const vbo = try gl.Buffer.create();
     defer vbo.destroy();
     try vao.bind();
-    try vbo.bind(c.GL_ARRAY_BUFFER);
-    try vbo.setData(c.GL_ARRAY_BUFFER, vertices, c.GL_STATIC_DRAW);
+    var binding = try vbo.bind(c.GL_ARRAY_BUFFER);
+    try binding.setData(&vertices, c.GL_STATIC_DRAW);
 
     c.glVertexAttribPointer(
         0,
@@ -68,7 +68,7 @@ pub fn main() !void {
     );
     c.glEnableVertexAttribArray(0);
 
-    try gl.Buffer.unbind(c.GL_ARRAY_BUFFER);
+    binding.unbind();
     try gl.VertexArray.unbind();
 
     // Wait for the user to close the window.
diff --git a/src/opengl/Buffer.zig b/src/opengl/Buffer.zig
index e5d47133c..c980669af 100644
--- a/src/opengl/Buffer.zig
+++ b/src/opengl/Buffer.zig
@@ -6,6 +6,61 @@ const errors = @import("errors.zig");
 
 id: c.GLuint,
 
+/// Binding is a bound buffer. By using this for functions that operate
+/// on bound buffers, you can easily defer unbinding and in safety-enabled
+/// modes verify that unbound buffers are never accessed.
+pub const Binding = struct {
+    target: c.GLenum,
+
+    /// Sets the data of this bound buffer. The data can be any array-like
+    /// type. The size of the data is automatically determined based on the type.
+    pub inline fn setData(
+        b: Binding,
+        data: anytype,
+        usage: c.GLenum,
+    ) !void {
+        // Determine the size and pointer to the given data.
+        const info: struct {
+            size: isize,
+            ptr: *const anyopaque,
+        } = switch (@typeInfo(@TypeOf(data))) {
+            .Array => |ary| .{
+                .size = @sizeOf(ary.child) * ary.len,
+                .ptr = &data,
+            },
+            .Pointer => |ptr| switch (ptr.size) {
+                .One => .{
+                    .size = @sizeOf(ptr.child) * data.len,
+                    .ptr = data,
+                },
+                .Slice => .{
+                    .size = @sizeOf(ptr.child) * data.len,
+                    .ptr = data.ptr,
+                },
+                else => {
+                    std.log.err("invalid buffer data pointer size: {}", .{ptr.size});
+                    unreachable;
+                },
+            },
+            else => {
+                std.log.err("invalid buffer data type: {s}", .{@tagName(@typeInfo(@TypeOf(data)))});
+                unreachable;
+            },
+        };
+
+        c.glBufferData(b.target, info.size, info.ptr, usage);
+        try errors.getError();
+    }
+
+    pub inline fn unbind(b: *Binding) void {
+        c.glBindBuffer(b.target, 0);
+
+        // By setting this to undefined, this ensures that any future calls
+        // error in safe build modes.
+        b.* = undefined;
+    }
+};
+
 /// Create a single buffer.
 pub inline fn create() !Buffer {
     var vbo: c.GLuint = undefined;
@@ -13,57 +68,10 @@ pub inline fn create() !Buffer {
     return Buffer{ .id = vbo };
 }
 
-// Unbind any active vertex array.
-pub inline fn unbind(target: c.GLenum) !void {
-    c.glBindBuffer(target, 0);
-}
-
 /// glBindBuffer
-pub inline fn bind(v: Buffer, target: c.GLenum) !void {
+pub inline fn bind(v: Buffer, target: c.GLenum) !Binding {
     c.glBindBuffer(target, v.id);
-}
-
-pub inline fn setData(
-    v: Buffer,
-    target: c.GLenum,
-    data: anytype,
-    usage: c.GLenum,
-) !void {
-    // Maybe one day in debug mode we can validate that this buffer
-    // is currently bound.
-    _ = v;
-
-    // Determine the size and pointer to the given data.
-    const info: struct {
-        size: isize,
-        ptr: *const anyopaque,
-    } = switch (@typeInfo(@TypeOf(data))) {
-        .Array => |ary| .{
-            .size = @sizeOf(ary.child) * ary.len,
-            .ptr = &data,
-        },
-        .Pointer => |ptr| switch (ptr.size) {
-            .One => .{
-                .size = @sizeOf(ptr.child) * data.len,
-                .ptr = data,
-            },
-            .Slice => .{
-                .size = @sizeOf(ptr.child) * data.len,
-                .ptr = data.ptr,
-            },
-            else => {
-                std.log.err("invalid buffer data pointer size: {}", .{ptr.size});
-                unreachable;
-            },
-        },
-        else => {
-            std.log.err("invalid buffer data type: {s}", .{@tagName(@typeInfo(@TypeOf(data)))});
-            unreachable;
-        },
-    };
-
-    c.glBufferData(target, info.size, info.ptr, usage);
-    try errors.getError();
+    return Binding{ .target = target };
 }
 
 pub inline fn destroy(v: Buffer) void {