From f1cffea9448ac65735ccca35e49f5efe703117b6 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Fri, 1 Apr 2022 17:44:54 -0700
Subject: [PATCH] opengl: buffers

---
 src/main.zig               | 18 ++++--------
 src/opengl.zig             |  1 +
 src/opengl/Buffer.zig      | 56 ++++++++++++++++++++++++++++++++++++++
 src/opengl/VertexArray.zig |  5 ++++
 4 files changed, 68 insertions(+), 12 deletions(-)
 create mode 100644 src/opengl/Buffer.zig

diff --git a/src/main.zig b/src/main.zig
index cc0f1478c..69214a0ab 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -52,17 +52,11 @@ pub fn main() !void {
     };
     const vao = try gl.VertexArray.create();
     defer vao.destroy();
-    var vbo: c_uint = undefined;
-    c.glGenBuffers(1, &vbo);
+    const vbo = try gl.Buffer.create();
+    defer vbo.destroy();
     try vao.bind();
-
-    c.glBindBuffer(c.GL_ARRAY_BUFFER, vbo);
-    c.glBufferData(
-        c.GL_ARRAY_BUFFER,
-        @as(isize, @sizeOf(@TypeOf(vertices))),
-        &vertices,
-        c.GL_STATIC_DRAW,
-    );
+    try vbo.bind(c.GL_ARRAY_BUFFER);
+    try vbo.setData(c.GL_ARRAY_BUFFER, vertices[0..], c.GL_STATIC_DRAW);
 
     c.glVertexAttribPointer(
         0,
@@ -74,8 +68,8 @@ pub fn main() !void {
     );
     c.glEnableVertexAttribArray(0);
 
-    c.glBindBuffer(c.GL_ARRAY_BUFFER, 0);
-    c.glBindVertexArray(0);
+    try gl.Buffer.unbind(c.GL_ARRAY_BUFFER);
+    try gl.VertexArray.unbind();
 
     // Wait for the user to close the window.
     while (!window.shouldClose()) {
diff --git a/src/opengl.zig b/src/opengl.zig
index 65dc2284b..dbd5b39ad 100644
--- a/src/opengl.zig
+++ b/src/opengl.zig
@@ -9,6 +9,7 @@
 //! API is exposed via the `c` constant.
 
 pub const c = @import("opengl/c.zig");
+pub const Buffer = @import("opengl/Buffer.zig");
 pub const Program = @import("opengl/Program.zig");
 pub const Shader = @import("opengl/Shader.zig");
 pub const VertexArray = @import("opengl/VertexArray.zig");
diff --git a/src/opengl/Buffer.zig b/src/opengl/Buffer.zig
new file mode 100644
index 000000000..21b134f58
--- /dev/null
+++ b/src/opengl/Buffer.zig
@@ -0,0 +1,56 @@
+const Buffer = @This();
+
+const c = @import("c.zig");
+const errors = @import("errors.zig");
+
+id: c.GLuint,
+
+/// Create a single buffer.
+pub inline fn create() !Buffer {
+    var vbo: c.GLuint = undefined;
+    c.glGenBuffers(1, &vbo);
+    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 {
+    c.glBindBuffer(target, v.id);
+}
+
+pub inline fn setData(
+    v: Buffer,
+    target: c.GLenum,
+    data: []const f32,
+    usage: c.GLenum,
+) !void {
+    // Maybe one day in debug mode we can validate that this buffer
+    // is currently bound.
+    _ = v;
+
+    // Determine the per-element size. This is all comptime-computed.
+    const dataInfo = @typeInfo(@TypeOf(data));
+    const size: usize = switch (dataInfo) {
+        .Pointer => |ptr| switch (ptr.size) {
+            .Slice => @sizeOf(ptr.child),
+            else => unreachable,
+        },
+        else => unreachable,
+    };
+
+    c.glBufferData(
+        target,
+        @intCast(isize, size * data.len),
+        data.ptr,
+        usage,
+    );
+    try errors.getError();
+}
+
+pub inline fn destroy(v: Buffer) void {
+    c.glDeleteBuffers(1, &v.id);
+}
diff --git a/src/opengl/VertexArray.zig b/src/opengl/VertexArray.zig
index b78212013..718ec9b9f 100644
--- a/src/opengl/VertexArray.zig
+++ b/src/opengl/VertexArray.zig
@@ -11,6 +11,11 @@ pub inline fn create() !VertexArray {
     return VertexArray{ .id = vao };
 }
 
+// Unbind any active vertex array.
+pub inline fn unbind() !void {
+    c.glBindVertexArray(0);
+}
+
 /// glBindVertexArray
 pub inline fn bind(v: VertexArray) !void {
     c.glBindVertexArray(v.id);