renderer/opengl: move opengl API to pkg/opengl

16 files changed, 833 insertions, 8 deletions

diff --git a/build.zig b/build.zig
index 6146f93f5..cb60aabb7 100644
--- a/build.zig
+++ b/build.zig
@@ -663,6 +663,7 @@ fn addDeps(
         .target = step.target,
         .optimize = step.optimize,
     });
+    const opengl_dep = b.dependency("opengl", .{});
     const pixman_dep = b.dependency("pixman", .{
         .target = step.target,
         .optimize = step.optimize,
@@ -730,6 +731,7 @@ fn addDeps(
     step.addModule("spirv_cross", spirv_cross_dep.module("spirv_cross"));
     step.addModule("harfbuzz", harfbuzz_dep.module("harfbuzz"));
     step.addModule("xev", libxev_dep.module("xev"));
+    step.addModule("opengl", opengl_dep.module("opengl"));
     step.addModule("pixman", pixman_dep.module("pixman"));
     step.addModule("ziglyph", ziglyph_dep.module("ziglyph"));
 
diff --git a/build.zig.zon b/build.zig.zon
index 580c8593e..309df74d1 100644
--- a/build.zig.zon
+++ b/build.zig.zon
@@ -32,6 +32,7 @@
         .harfbuzz = .{ .path = "./pkg/harfbuzz" },
         .libpng = .{ .path = "./pkg/libpng" },
         .macos = .{ .path = "./pkg/macos" },
+        .opengl = .{ .path = "./pkg/opengl" },
         .pixman = .{ .path = "./pkg/pixman" },
         .tracy = .{ .path = "./pkg/tracy" },
         .zlib = .{ .path = "./pkg/zlib" },
diff --git a/pkg/opengl/Buffer.zig b/pkg/opengl/Buffer.zig
new file mode 100644
index 000000000..b794ca4f0
--- /dev/null
+++ b/pkg/opengl/Buffer.zig
@@ -0,0 +1,218 @@
+const Buffer = @This();
+
+const std = @import("std");
+const c = @import("c.zig");
+const errors = @import("errors.zig");
+const glad = @import("glad.zig");
+
+id: c.GLuint,
+
+/// Enum for possible binding targets.
+pub const Target = enum(c_uint) {
+    ArrayBuffer = c.GL_ARRAY_BUFFER,
+    ElementArrayBuffer = c.GL_ELEMENT_ARRAY_BUFFER,
+    _,
+};
+
+/// Enum for possible buffer usages.
+pub const Usage = enum(c_uint) {
+    StreamDraw = c.GL_STREAM_DRAW,
+    StreamRead = c.GL_STREAM_READ,
+    StreamCopy = c.GL_STREAM_COPY,
+    StaticDraw = c.GL_STATIC_DRAW,
+    StaticRead = c.GL_STATIC_READ,
+    StaticCopy = c.GL_STATIC_COPY,
+    DynamicDraw = c.GL_DYNAMIC_DRAW,
+    DynamicRead = c.GL_DYNAMIC_READ,
+    DynamicCopy = c.GL_DYNAMIC_COPY,
+    _,
+};
+
+/// 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: Target,
+
+    /// 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: Usage,
+    ) !void {
+        const info = dataInfo(&data);
+        glad.context.BufferData.?(@intFromEnum(b.target), info.size, info.ptr, @intFromEnum(usage));
+        try errors.getError();
+    }
+
+    /// 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 setSubData(
+        b: Binding,
+        offset: usize,
+        data: anytype,
+    ) !void {
+        const info = dataInfo(data);
+        glad.context.BufferSubData.?(@intFromEnum(b.target), @intCast(offset), info.size, info.ptr);
+        try errors.getError();
+    }
+
+    /// Sets the buffer data with a null buffer that is expected to be
+    /// filled in the future using subData. This requires the type just so
+    /// we can setup the data size.
+    pub inline fn setDataNull(
+        b: Binding,
+        comptime T: type,
+        usage: Usage,
+    ) !void {
+        glad.context.BufferData.?(@intFromEnum(b.target), @sizeOf(T), null, @intFromEnum(usage));
+        try errors.getError();
+    }
+
+    /// Same as setDataNull but lets you manually specify the buffer size.
+    pub inline fn setDataNullManual(
+        b: Binding,
+        size: usize,
+        usage: Usage,
+    ) !void {
+        glad.context.BufferData.?(@intFromEnum(b.target), @intCast(size), null, @intFromEnum(usage));
+        try errors.getError();
+    }
+
+    fn dataInfo(data: anytype) struct {
+        size: isize,
+        ptr: *const anyopaque,
+    } {
+        return switch (@typeInfo(@TypeOf(data))) {
+            .Pointer => |ptr| switch (ptr.size) {
+                .One => .{
+                    .size = @sizeOf(ptr.child) * data.len,
+                    .ptr = data,
+                },
+                .Slice => .{
+                    .size = @intCast(@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;
+            },
+        };
+    }
+
+    pub inline fn enableAttribArray(_: Binding, idx: c.GLuint) !void {
+        glad.context.EnableVertexAttribArray.?(idx);
+    }
+
+    /// Shorthand for vertexAttribPointer that is specialized towards the
+    /// common use case of specifying an array of homogeneous types that
+    /// don't need normalization. This also enables the attribute at idx.
+    pub fn attribute(
+        b: Binding,
+        idx: c.GLuint,
+        size: c.GLint,
+        comptime T: type,
+        offset: usize,
+    ) !void {
+        const info: struct {
+            // Type of the each component in the array.
+            typ: c.GLenum,
+
+            // The byte offset between each full set of attributes.
+            stride: c.GLsizei,
+
+            // The size of each component used in calculating the offset.
+            offset: usize,
+        } = switch (@typeInfo(T)) {
+            .Array => |ary| .{
+                .typ = switch (ary.child) {
+                    f32 => c.GL_FLOAT,
+                    else => @compileError("unsupported array child type"),
+                },
+                .offset = @sizeOf(ary.child),
+                .stride = @sizeOf(T),
+            },
+            else => @compileError("unsupported type"),
+        };
+
+        try b.attributeAdvanced(
+            idx,
+            size,
+            info.typ,
+            false,
+            info.stride,
+            offset * info.offset,
+        );
+        try b.enableAttribArray(idx);
+    }
+
+    /// VertexAttribDivisor
+    pub fn attributeDivisor(_: Binding, idx: c.GLuint, divisor: c.GLuint) !void {
+        glad.context.VertexAttribDivisor.?(idx, divisor);
+        try errors.getError();
+    }
+
+    pub inline fn attributeAdvanced(
+        _: Binding,
+        idx: c.GLuint,
+        size: c.GLint,
+        typ: c.GLenum,
+        normalized: bool,
+        stride: c.GLsizei,
+        offset: usize,
+    ) !void {
+        const normalized_c: c.GLboolean = if (normalized) c.GL_TRUE else c.GL_FALSE;
+        const offsetPtr = if (offset > 0)
+            @as(*const anyopaque, @ptrFromInt(offset))
+        else
+            null;
+
+        glad.context.VertexAttribPointer.?(idx, size, typ, normalized_c, stride, offsetPtr);
+        try errors.getError();
+    }
+
+    pub inline fn attributeIAdvanced(
+        _: Binding,
+        idx: c.GLuint,
+        size: c.GLint,
+        typ: c.GLenum,
+        stride: c.GLsizei,
+        offset: usize,
+    ) !void {
+        const offsetPtr = if (offset > 0)
+            @as(*const anyopaque, @ptrFromInt(offset))
+        else
+            null;
+
+        glad.context.VertexAttribIPointer.?(idx, size, typ, stride, offsetPtr);
+        try errors.getError();
+    }
+
+    pub inline fn unbind(b: *Binding) void {
+        glad.context.BindBuffer.?(@intFromEnum(b.target), 0);
+        b.* = undefined;
+    }
+};
+
+/// Create a single buffer.
+pub inline fn create() !Buffer {
+    var vbo: c.GLuint = undefined;
+    glad.context.GenBuffers.?(1, &vbo);
+    return Buffer{ .id = vbo };
+}
+
+/// glBindBuffer
+pub inline fn bind(v: Buffer, target: Target) !Binding {
+    glad.context.BindBuffer.?(@intFromEnum(target), v.id);
+    return Binding{ .target = target };
+}
+
+pub inline fn destroy(v: Buffer) void {
+    glad.context.DeleteBuffers.?(1, &v.id);
+}
diff --git a/pkg/opengl/Program.zig b/pkg/opengl/Program.zig
new file mode 100644
index 000000000..d266bd226
--- /dev/null
+++ b/pkg/opengl/Program.zig
@@ -0,0 +1,128 @@
+const Program = @This();
+
+const std = @import("std");
+const assert = std.debug.assert;
+const log = std.log.scoped(.opengl);
+
+const c = @import("c.zig");
+const Shader = @import("Shader.zig");
+const errors = @import("errors.zig");
+const glad = @import("glad.zig");
+
+id: c.GLuint,
+
+const Binding = struct {
+    pub inline fn unbind(_: Binding) void {
+        glad.context.UseProgram.?(0);
+    }
+};
+
+pub inline fn create() !Program {
+    const id = glad.context.CreateProgram.?();
+    if (id == 0) try errors.mustError();
+
+    log.debug("program created id={}", .{id});
+    return Program{ .id = id };
+}
+
+/// Create a program from a vertex and fragment shader source. This will
+/// compile and link the vertex and fragment shader.
+pub inline fn createVF(vsrc: [:0]const u8, fsrc: [:0]const u8) !Program {
+    const vs = try Shader.create(c.GL_VERTEX_SHADER);
+    try vs.setSourceAndCompile(vsrc);
+    defer vs.destroy();
+
+    const fs = try Shader.create(c.GL_FRAGMENT_SHADER);
+    try fs.setSourceAndCompile(fsrc);
+    defer fs.destroy();
+
+    const p = try create();
+    try p.attachShader(vs);
+    try p.attachShader(fs);
+    try p.link();
+
+    return p;
+}
+
+pub inline fn attachShader(p: Program, s: Shader) !void {
+    glad.context.AttachShader.?(p.id, s.id);
+    try errors.getError();
+}
+
+pub inline fn link(p: Program) !void {
+    glad.context.LinkProgram.?(p.id);
+
+    // Check if linking succeeded
+    var success: c_int = undefined;
+    glad.context.GetProgramiv.?(p.id, c.GL_LINK_STATUS, &success);
+    if (success == c.GL_TRUE) {
+        log.debug("program linked id={}", .{p.id});
+        return;
+    }
+
+    log.err("program link failure id={} message={s}", .{
+        p.id,
+        std.mem.sliceTo(&p.getInfoLog(), 0),
+    });
+    return error.CompileFailed;
+}
+
+pub inline fn use(p: Program) !Binding {
+    glad.context.UseProgram.?(p.id);
+    try errors.getError();
+    return Binding{};
+}
+
+/// Requires the program is currently in use.
+pub inline fn setUniform(
+    p: Program,
+    n: [:0]const u8,
+    value: anytype,
+) !void {
+    const loc = glad.context.GetUniformLocation.?(
+        p.id,
+        @ptrCast(n.ptr),
+    );
+    if (loc < 0) {
+        return error.UniformNameInvalid;
+    }
+    try errors.getError();
+
+    // Perform the correct call depending on the type of the value.
+    switch (@TypeOf(value)) {
+        comptime_int => glad.context.Uniform1i.?(loc, value),
+        f32 => glad.context.Uniform1f.?(loc, value),
+        @Vector(2, f32) => glad.context.Uniform2f.?(loc, value[0], value[1]),
+        @Vector(3, f32) => glad.context.Uniform3f.?(loc, value[0], value[1], value[2]),
+        @Vector(4, f32) => glad.context.Uniform4f.?(loc, value[0], value[1], value[2], value[3]),
+        [4]@Vector(4, f32) => glad.context.UniformMatrix4fv.?(
+            loc,
+            1,
+            c.GL_FALSE,
+            @ptrCast(&value),
+        ),
+        else => {
+            log.warn("unsupported uniform type {}", .{@TypeOf(value)});
+            unreachable;
+        },
+    }
+    try errors.getError();
+}
+
+/// getInfoLog returns the info log for this program. This attempts to
+/// keep the log fully stack allocated and is therefore limited to a max
+/// amount of elements.
+//
+// NOTE(mitchellh): we can add a dynamic version that uses an allocator
+// if we ever need it.
+pub inline fn getInfoLog(s: Program) [512]u8 {
+    var msg: [512]u8 = undefined;
+    glad.context.GetProgramInfoLog.?(s.id, msg.len, null, &msg);
+    return msg;
+}
+
+pub inline fn destroy(p: Program) void {
+    assert(p.id != 0);
+    glad.context.DeleteProgram.?(p.id);
+    log.debug("program destroyed id={}", .{p.id});
+}
diff --git a/pkg/opengl/Shader.zig b/pkg/opengl/Shader.zig
new file mode 100644
index 000000000..beaae9e94
--- /dev/null
+++ b/pkg/opengl/Shader.zig
@@ -0,0 +1,56 @@
+const Shader = @This();
+
+const std = @import("std");
+const assert = std.debug.assert;
+const log = std.log.scoped(.opengl);
+
+const c = @import("c.zig");
+const errors = @import("errors.zig");
+const glad = @import("glad.zig");
+
+id: c.GLuint,
+
+pub inline fn create(typ: c.GLenum) errors.Error!Shader {
+    const id = glad.context.CreateShader.?(typ);
+    if (id == 0) {
+        try errors.mustError();
+        unreachable;
+    }
+
+    log.debug("shader created id={}", .{id});
+    return Shader{ .id = id };
+}
+
+/// Set the source and compile a shader.
+pub inline fn setSourceAndCompile(s: Shader, source: [:0]const u8) !void {
+    glad.context.ShaderSource.?(s.id, 1, &@as([*c]const u8, @ptrCast(source)), null);
+    glad.context.CompileShader.?(s.id);
+
+    // Check if compilation succeeded
+    var success: c_int = undefined;
+    glad.context.GetShaderiv.?(s.id, c.GL_COMPILE_STATUS, &success);
+    if (success == c.GL_TRUE) return;
+    log.err("shader compilation failure id={} message={s}", .{
+        s.id,
+        std.mem.sliceTo(&s.getInfoLog(), 0),
+    });
+    return error.CompileFailed;
+}
+
+/// getInfoLog returns the info log for this shader. This attempts to
+/// keep the log fully stack allocated and is therefore limited to a max
+/// amount of elements.
+//
+// NOTE(mitchellh): we can add a dynamic version that uses an allocator
+// if we ever need it.
+pub inline fn getInfoLog(s: Shader) [512]u8 {
+    var msg: [512]u8 = undefined;
+    glad.context.GetShaderInfoLog.?(s.id, msg.len, null, &msg);
+    return msg;
+}
+
+pub inline fn destroy(s: Shader) void {
+    assert(s.id != 0);
+    glad.context.DeleteShader.?(s.id);
+    log.debug("shader destroyed id={}", .{s.id});
+}
diff --git a/pkg/opengl/Texture.zig b/pkg/opengl/Texture.zig
new file mode 100644
index 000000000..91a65b565
--- /dev/null
+++ b/pkg/opengl/Texture.zig
@@ -0,0 +1,163 @@
+const Texture = @This();
+
+const std = @import("std");
+const c = @import("c.zig");
+const errors = @import("errors.zig");
+const glad = @import("glad.zig");
+
+id: c.GLuint,
+
+pub inline fn active(target: c.GLenum) !void {
+    glad.context.ActiveTexture.?(target);
+    try errors.getError();
+}
+
+/// Enun for possible texture binding targets.
+pub const Target = enum(c_uint) {
+    @"1D" = c.GL_TEXTURE_1D,
+    @"2D" = c.GL_TEXTURE_2D,
+    @"3D" = c.GL_TEXTURE_3D,
+    @"1DArray" = c.GL_TEXTURE_1D_ARRAY,
+    @"2DArray" = c.GL_TEXTURE_2D_ARRAY,
+    Rectangle = c.GL_TEXTURE_RECTANGLE,
+    CubeMap = c.GL_TEXTURE_CUBE_MAP,
+    Buffer = c.GL_TEXTURE_BUFFER,
+    @"2DMultisample" = c.GL_TEXTURE_2D_MULTISAMPLE,
+    @"2DMultisampleArray" = c.GL_TEXTURE_2D_MULTISAMPLE_ARRAY,
+};
+
+/// Enum for possible texture parameters.
+pub const Parameter = enum(c_uint) {
+    BaseLevel = c.GL_TEXTURE_BASE_LEVEL,
+    CompareFunc = c.GL_TEXTURE_COMPARE_FUNC,
+    CompareMode = c.GL_TEXTURE_COMPARE_MODE,
+    LodBias = c.GL_TEXTURE_LOD_BIAS,
+    MinFilter = c.GL_TEXTURE_MIN_FILTER,
+    MagFilter = c.GL_TEXTURE_MAG_FILTER,
+    MinLod = c.GL_TEXTURE_MIN_LOD,
+    MaxLod = c.GL_TEXTURE_MAX_LOD,
+    MaxLevel = c.GL_TEXTURE_MAX_LEVEL,
+    SwizzleR = c.GL_TEXTURE_SWIZZLE_R,
+    SwizzleG = c.GL_TEXTURE_SWIZZLE_G,
+    SwizzleB = c.GL_TEXTURE_SWIZZLE_B,
+    SwizzleA = c.GL_TEXTURE_SWIZZLE_A,
+    WrapS = c.GL_TEXTURE_WRAP_S,
+    WrapT = c.GL_TEXTURE_WRAP_T,
+    WrapR = c.GL_TEXTURE_WRAP_R,
+};
+
+/// Internal format enum for texture images.
+pub const InternalFormat = enum(c_int) {
+    Red = c.GL_RED,
+    RGBA = c.GL_RGBA,
+
+    // There are so many more that I haven't filled in.
+    _,
+};
+
+/// Format for texture images
+pub const Format = enum(c_uint) {
+    Red = c.GL_RED,
+    BGRA = c.GL_BGRA,
+
+    // There are so many more that I haven't filled in.
+    _,
+};
+
+/// Data type for texture images.
+pub const DataType = enum(c_uint) {
+    UnsignedByte = c.GL_UNSIGNED_BYTE,
+
+    // There are so many more that I haven't filled in.
+    _,
+};
+
+pub const Binding = struct {
+    target: Target,
+
+    pub inline fn unbind(b: *Binding) void {
+        glad.context.BindTexture.?(@intFromEnum(b.target), 0);
+        b.* = undefined;
+    }
+
+    pub fn generateMipmap(b: Binding) void {
+        glad.context.GenerateMipmap.?(@intFromEnum(b.target));
+    }
+
+    pub fn parameter(b: Binding, name: Parameter, value: anytype) !void {
+        switch (@TypeOf(value)) {
+            c.GLint => glad.context.TexParameteri.?(
+                @intFromEnum(b.target),
+                @intFromEnum(name),
+                value,
+            ),
+            else => unreachable,
+        }
+    }
+
+    pub fn image2D(
+        b: Binding,
+        level: c.GLint,
+        internal_format: InternalFormat,
+        width: c.GLsizei,
+        height: c.GLsizei,
+        border: c.GLint,
+        format: Format,
+        typ: DataType,
+        data: ?*const anyopaque,
+    ) !void {
+        glad.context.TexImage2D.?(
+            @intFromEnum(b.target),
+            level,
+            @intFromEnum(internal_format),
+            width,
+            height,
+            border,
+            @intFromEnum(format),
+            @intFromEnum(typ),
+            data,
+        );
+    }
+
+    pub fn subImage2D(
+        b: Binding,
+        level: c.GLint,
+        xoffset: c.GLint,
+        yoffset: c.GLint,
+        width: c.GLsizei,
+        height: c.GLsizei,
+        format: Format,
+        typ: DataType,
+        data: ?*const anyopaque,
+    ) !void {
+        glad.context.TexSubImage2D.?(
+            @intFromEnum(b.target),
+            level,
+            xoffset,
+            yoffset,
+            width,
+            height,
+            @intFromEnum(format),
+            @intFromEnum(typ),
+            data,
+        );
+    }
+};
+
+/// Create a single texture.
+pub inline fn create() !Texture {
+    var id: c.GLuint = undefined;
+    glad.context.GenTextures.?(1, &id);
+    return Texture{ .id = id };
+}
+
+/// glBindTexture
+pub inline fn bind(v: Texture, target: Target) !Binding {
+    glad.context.BindTexture.?(@intFromEnum(target), v.id);
+    try errors.getError();
+    return Binding{ .target = target };
+}
+
+pub inline fn destroy(v: Texture) void {
+    glad.context.DeleteTextures.?(1, &v.id);
+}
diff --git a/pkg/opengl/VertexArray.zig b/pkg/opengl/VertexArray.zig
new file mode 100644
index 000000000..b86794042
--- /dev/null
+++ b/pkg/opengl/VertexArray.zig
@@ -0,0 +1,29 @@
+const VertexArray = @This();
+
+const c = @import("c.zig");
+const glad = @import("glad.zig");
+const errors = @import("errors.zig");
+
+id: c.GLuint,
+
+/// Create a single vertex array object.
+pub inline fn create() !VertexArray {
+    var vao: c.GLuint = undefined;
+    glad.context.GenVertexArrays.?(1, &vao);
+    return VertexArray{ .id = vao };
+}
+
+// Unbind any active vertex array.
+pub inline fn unbind() !void {
+    glad.context.BindVertexArray.?(0);
+}
+
+/// glBindVertexArray
+pub inline fn bind(v: VertexArray) !void {
+    glad.context.BindVertexArray.?(v.id);
+    try errors.getError();
+}
+
+pub inline fn destroy(v: VertexArray) void {
+    glad.context.DeleteVertexArrays.?(1, &v.id);
+}
diff --git a/pkg/opengl/build.zig b/pkg/opengl/build.zig
new file mode 100644
index 000000000..34e5a8ab1
--- /dev/null
+++ b/pkg/opengl/build.zig
@@ -0,0 +1,5 @@
+const std = @import("std");
+
+pub fn build(b: *std.Build) !void {
+    _ = b.addModule("opengl", .{ .source_file = .{ .path = "main.zig" } });
+}
diff --git a/pkg/opengl/c.zig b/pkg/opengl/c.zig
new file mode 100644
index 000000000..8f4a0f22f
--- /dev/null
+++ b/pkg/opengl/c.zig
@@ -0,0 +1,3 @@
+pub usingnamespace @cImport({
+    @cInclude("glad/gl.h");
+});
diff --git a/pkg/opengl/draw.zig b/pkg/opengl/draw.zig
new file mode 100644
index 000000000..ea6b63103
--- /dev/null
+++ b/pkg/opengl/draw.zig
@@ -0,0 +1,59 @@
+const c = @import("c.zig");
+const errors = @import("errors.zig");
+const glad = @import("glad.zig");
+
+pub fn clearColor(r: f32, g: f32, b: f32, a: f32) void {
+    glad.context.ClearColor.?(r, g, b, a);
+}
+
+pub fn clear(mask: c.GLbitfield) void {
+    glad.context.Clear.?(mask);
+}
+
+pub fn drawArrays(mode: c.GLenum, first: c.GLint, count: c.GLsizei) !void {
+    glad.context.DrawArrays.?(mode, first, count);
+    try errors.getError();
+}
+
+pub fn drawElements(mode: c.GLenum, count: c.GLsizei, typ: c.GLenum, offset: usize) !void {
+    const offsetPtr = if (offset == 0) null else @as(*const anyopaque, @ptrFromInt(offset));
+    glad.context.DrawElements.?(mode, count, typ, offsetPtr);
+    try errors.getError();
+}
+
+pub fn drawElementsInstanced(
+    mode: c.GLenum,
+    count: c.GLsizei,
+    typ: c.GLenum,
+    primcount: usize,
+) !void {
+    glad.context.DrawElementsInstanced.?(mode, count, typ, null, @intCast(primcount));
+    try errors.getError();
+}
+
+pub fn enable(cap: c.GLenum) !void {
+    glad.context.Enable.?(cap);
+    try errors.getError();
+}
+
+pub fn frontFace(mode: c.GLenum) !void {
+    glad.context.FrontFace.?(mode);
+    try errors.getError();
+}
+
+pub fn blendFunc(sfactor: c.GLenum, dfactor: c.GLenum) !void {
+    glad.context.BlendFunc.?(sfactor, dfactor);
+    try errors.getError();
+}
+
+pub fn viewport(x: c.GLint, y: c.GLint, width: c.GLsizei, height: c.GLsizei) !void {
+    glad.context.Viewport.?(x, y, width, height);
+}
+
+pub fn pixelStore(mode: c.GLenum, value: anytype) !void {
+    switch (@typeInfo(@TypeOf(value))) {
+        .ComptimeInt, .Int => glad.context.PixelStorei.?(mode, value),
+        else => unreachable,
+    }
+    try errors.getError();
+}
diff --git a/pkg/opengl/errors.zig b/pkg/opengl/errors.zig
new file mode 100644
index 000000000..86639a53a
--- /dev/null
+++ b/pkg/opengl/errors.zig
@@ -0,0 +1,33 @@
+const std = @import("std");
+const c = @import("c.zig");
+const glad = @import("glad.zig");
+
+pub const Error = error{
+    InvalidEnum,
+    InvalidValue,
+    InvalidOperation,
+    InvalidFramebufferOperation,
+    OutOfMemory,
+
+    Unknown,
+};
+
+/// getError returns the error (if any) from the last OpenGL operation.
+pub fn getError() Error!void {
+    return switch (glad.context.GetError.?()) {
+        c.GL_NO_ERROR => {},
+        c.GL_INVALID_ENUM => Error.InvalidEnum,
+        c.GL_INVALID_VALUE => Error.InvalidValue,
+        c.GL_INVALID_OPERATION => Error.InvalidOperation,
+        c.GL_INVALID_FRAMEBUFFER_OPERATION => Error.InvalidFramebufferOperation,
+        c.GL_OUT_OF_MEMORY => Error.OutOfMemory,
+        else => Error.Unknown,
+    };
+}
+
+/// mustError just calls getError but always results in an error being returned.
+/// If getError has no error, then Unknown is returned.
+pub fn mustError() Error!void {
+    try getError();
+    return Error.Unknown;
+}
diff --git a/pkg/opengl/extensions.zig b/pkg/opengl/extensions.zig
new file mode 100644
index 000000000..ca8a4973d
--- /dev/null
+++ b/pkg/opengl/extensions.zig
@@ -0,0 +1,32 @@
+const std = @import("std");
+const c = @import("c.zig");
+const errors = @import("errors.zig");
+const glad = @import("glad.zig");
+
+/// Returns the number of extensions.
+pub fn len() !u32 {
+    var n: c.GLint = undefined;
+    glad.context.GetIntegerv.?(c.GL_NUM_EXTENSIONS, &n);
+    try errors.getError();
+    return @intCast(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 = glad.context.GetStringi.?(c.GL_EXTENSIONS, self.i);
+        try errors.getError();
+        self.i += 1;
+        return std.mem.sliceTo(res, 0);
+    }
+};
diff --git a/pkg/opengl/glad.zig b/pkg/opengl/glad.zig
new file mode 100644
index 000000000..4ee85c549
--- /dev/null
+++ b/pkg/opengl/glad.zig
@@ -0,0 +1,45 @@
+const std = @import("std");
+const c = @import("c.zig");
+
+pub const Context = c.GladGLContext;
+
+/// This is the current context. Set this var manually prior to calling
+/// any of this package's functions. I know its nasty to have a global but
+/// this makes it match OpenGL API styles where it also operates on a
+/// threadlocal global.
+pub threadlocal var context: Context = undefined;
+
+/// Initialize Glad. This is guaranteed to succeed if no errors are returned.
+/// The getProcAddress param is an anytype so that we can accept multiple
+/// forms of the function depending on what we're interfacing with.
+pub fn load(getProcAddress: anytype) !c_int {
+    const GlProc = *const fn () callconv(.C) void;
+    const GlfwFn = *const fn ([*:0]const u8) callconv(.C) ?GlProc;
+
+    const res = switch (@TypeOf(getProcAddress)) {
+        // glfw
+        GlfwFn => c.gladLoadGLContext(&context, @ptrCast(getProcAddress)),
+
+        // null proc address means that we are just loading the globally
+        // pointed gl functions
+        @TypeOf(null) => c.gladLoaderLoadGLContext(&context),
+
+        // try as-is. If this introduces a compiler error, then add a new case.
+        else => c.gladLoadGLContext(&context, getProcAddress),
+    };
+    if (res == 0) return error.GLInitFailed;
+    return res;
+}
+
+pub fn unload() void {
+    c.gladLoaderUnloadGLContext(&context);
+    context = undefined;
+}
+
+pub fn versionMajor(res: c_uint) c_uint {
+    return c.GLAD_VERSION_MAJOR(res);
+}
+
+pub fn versionMinor(res: c_uint) c_uint {
+    return c.GLAD_VERSION_MINOR(res);
+}
diff --git a/pkg/opengl/main.zig b/pkg/opengl/main.zig
new file mode 100644
index 000000000..79d32acea
--- /dev/null
+++ b/pkg/opengl/main.zig
@@ -0,0 +1,23 @@
+//! OpenGL bindings.
+//!
+//! These are purpose-built for usage within this program. While they closely
+//! align with the OpenGL C APIs, they aren't meant to be general purpose,
+//! they aren't meant to have 100% API coverage, and they aren't meant to
+//! be hyper-performant.
+//!
+//! For performance-intensive or unsupported aspects of OpenGL, the C
+//! API is exposed via the `c` constant.
+//!
+//! WARNING: Lots of performance improvements that we can make with Zig
+//! comptime help. I'm deferring this until later but have some fun ideas.
+
+pub const c = @import("c.zig");
+pub const glad = @import("glad.zig");
+pub usingnamespace @import("draw.zig");
+
+pub const ext = @import("extensions.zig");
+pub const Buffer = @import("Buffer.zig");
+pub const Program = @import("Program.zig");
+pub const Shader = @import("Shader.zig");
+pub const Texture = @import("Texture.zig");
+pub const VertexArray = @import("VertexArray.zig");
diff --git a/src/renderer/OpenGL.zig b/src/renderer/OpenGL.zig
index 32781a7eb..ce442ed48 100644
--- a/src/renderer/OpenGL.zig
+++ b/src/renderer/OpenGL.zig
@@ -7,6 +7,7 @@ const glfw = @import("glfw");
 const assert = std.debug.assert;
 const testing = std.testing;
 const Allocator = std.mem.Allocator;
+const ArenaAllocator = std.heap.ArenaAllocator;
 const apprt = @import("../apprt.zig");
 const configpkg = @import("../config.zig");
 const font = @import("../font/main.zig");
@@ -14,7 +15,7 @@ const imgui = @import("imgui");
 const renderer = @import("../renderer.zig");
 const terminal = @import("../terminal/main.zig");
 const Terminal = terminal.Terminal;
-const gl = @import("opengl/main.zig");
+const gl = @import("opengl");
 const trace = @import("tracy").trace;
 const math = @import("../math.zig");
 const Surface = @import("../Surface.zig");
@@ -226,8 +227,10 @@ const GPUCellMode = enum(u8) {
 /// configuration. This must be exported so that we don't need to
 /// pass around Config pointers which makes memory management a pain.
 pub const DerivedConfig = struct {
+    arena: ArenaAllocator,
+
     font_thicken: bool,
-    font_features: std.ArrayList([]const u8),
+    font_features: std.ArrayListUnmanaged([]const u8),
     font_styles: font.Group.StyleStatus,
     cursor_color: ?terminal.color.RGB,
     cursor_text: ?terminal.color.RGB,
@@ -238,17 +241,21 @@ pub const DerivedConfig = struct {
     selection_background: ?terminal.color.RGB,
     selection_foreground: ?terminal.color.RGB,
     invert_selection_fg_bg: bool,
+    custom_shaders: std.ArrayListUnmanaged([]const u8),
 
     pub fn init(
         alloc_gpa: Allocator,
         config: *const configpkg.Config,
     ) !DerivedConfig {
+        var arena = ArenaAllocator.init(alloc_gpa);
+        errdefer arena.deinit();
+        const alloc = arena.allocator();
+
+        // Copy our shaders
+        const custom_shaders = try config.@"custom-shader".value.list.clone(alloc);
+
         // Copy our font features
-        var font_features = features: {
-            var clone = try config.@"font-feature".list.clone(alloc_gpa);
-            break :features clone.toManaged(alloc_gpa);
-        };
-        errdefer font_features.deinit();
+        const font_features = try config.@"font-feature".list.clone(alloc);
 
         // Get our font styles
         var font_styles = font.Group.StyleStatus.initFill(true);
@@ -287,11 +294,15 @@ pub const DerivedConfig = struct {
                 bg.toTerminalRGB()
             else
                 null,
+
+            .custom_shaders = custom_shaders,
+
+            .arena = arena,
         };
     }
 
     pub fn deinit(self: *DerivedConfig) void {
-        self.font_features.deinit();
+        self.arena.deinit();
     }
 };
 
diff --git a/src/renderer/shadertoy.zig b/src/renderer/shadertoy.zig
index 45c225d85..92b340e76 100644
--- a/src/renderer/shadertoy.zig
+++ b/src/renderer/shadertoy.zig
@@ -335,5 +335,22 @@ test "shadertoy to msl" {
     defer alloc.free(msl);
 }
 
+test "shadertoy to glsl" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    const src = try testGlslZ(alloc, test_crt);
+    defer alloc.free(src);
+
+    var spvlist = std.ArrayListAligned(u8, @alignOf(u32)).init(alloc);
+    defer spvlist.deinit();
+    try spirvFromGlsl(spvlist.writer(), null, src);
+
+    const glsl = try glslFromSpv(alloc, spvlist.items);
+    defer alloc.free(glsl);
+
+    //log.warn("glsl={s}", .{glsl});
+}
+
 const test_crt = @embedFile("shaders/test_shadertoy_crt.glsl");
 const test_invalid = @embedFile("shaders/test_shadertoy_invalid.glsl");