From de0f707c96ecb46b4b03836023953555f1f9d635 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Fri, 1 Apr 2022 15:34:03 -0700
Subject: [PATCH] opengl: programs

---
 src/main.zig   | 23 +++++---------
 src/opengl.zig | 81 +++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 75 insertions(+), 29 deletions(-)

diff --git a/src/main.zig b/src/main.zig
index eac21cdc0..351d342ae 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -36,20 +36,13 @@ pub fn main() !void {
     defer fs.destroy();
 
     // Shader program
-    const program = c.glCreateProgram();
-    c.glAttachShader(program, vs.handle);
-    c.glAttachShader(program, fs.handle);
-    c.glLinkProgram(program);
-    var success: c_int = undefined;
-    c.glGetProgramiv(program, c.GL_LINK_STATUS, &success);
-    if (success != c.GL_TRUE) {
-        var msg: [512]u8 = undefined;
-        c.glGetProgramInfoLog(program, 512, null, &msg);
-        std.log.err("program fail: {s}\n", .{std.mem.sliceTo(&msg, 0)});
-        return;
-    }
-    c.glDeleteShader(vs.handle);
-    c.glDeleteShader(fs.handle);
+    const program = try gl.Program.create();
+    defer program.destroy();
+    try program.attachShader(vs);
+    try program.attachShader(fs);
+    try program.link();
+    vs.destroy();
+    fs.destroy();
 
     // Create our bufer or vertices
     const vertices = [_]f32{
@@ -90,7 +83,7 @@ pub fn main() !void {
         c.glClearColor(0.2, 0.3, 0.3, 1.0);
         c.glClear(c.GL_COLOR_BUFFER_BIT);
 
-        c.glUseProgram(program);
+        c.glUseProgram(program.id);
         c.glBindVertexArray(vao);
         c.glDrawArrays(c.GL_TRIANGLES, 0, 3);
 
diff --git a/src/opengl.zig b/src/opengl.zig
index 15ac6d78f..f6a3e8e3e 100644
--- a/src/opengl.zig
+++ b/src/opengl.zig
@@ -36,30 +36,30 @@ fn mustError() Error!void {
 }
 
 pub const Shader = struct {
-    handle: c.GLuint,
+    id: c.GLuint,
 
     pub fn create(typ: c.GLenum) Error!Shader {
-        const handle = c.glCreateShader(typ);
-        if (handle == 0) {
+        const id = c.glCreateShader(typ);
+        if (id == 0) {
             try mustError();
             unreachable;
         }
 
-        log.debug("shader created id={}", .{handle});
-        return Shader{ .handle = handle };
+        log.debug("shader created id={}", .{id});
+        return Shader{ .id = id };
     }
 
     /// Set the source and compile a shader.
     pub fn setSourceAndCompile(s: Shader, source: [:0]const u8) !void {
-        c.glShaderSource(s.handle, 1, &@ptrCast([*c]const u8, source), null);
-        c.glCompileShader(s.handle);
+        c.glShaderSource(s.id, 1, &@ptrCast([*c]const u8, source), null);
+        c.glCompileShader(s.id);
 
         // Check if compilation succeeded
         var success: c_int = undefined;
-        c.glGetShaderiv(s.handle, c.GL_COMPILE_STATUS, &success);
+        c.glGetShaderiv(s.id, c.GL_COMPILE_STATUS, &success);
         if (success == c.GL_TRUE) return;
-        log.err("shader compilation failure handle={} message={s}", .{
-            s.handle,
+        log.err("shader compilation failure id={} message={s}", .{
+            s.id,
             std.mem.sliceTo(&s.getInfoLog(), 0),
         });
         return error.CompileFailed;
@@ -73,13 +73,66 @@ pub const Shader = struct {
     // if we ever need it.
     pub fn getInfoLog(s: Shader) [512]u8 {
         var msg: [512]u8 = undefined;
-        c.glGetShaderInfoLog(s.handle, msg.len, null, &msg);
+        c.glGetShaderInfoLog(s.id, msg.len, null, &msg);
         return msg;
     }
 
     pub fn destroy(s: Shader) void {
-        assert(s.handle != 0);
-        c.glDeleteShader(s.handle);
-        log.debug("shader destroyed id={}", .{s.handle});
+        assert(s.id != 0);
+        c.glDeleteShader(s.id);
+        log.debug("shader destroyed id={}", .{s.id});
+    }
+};
+
+pub const Program = struct {
+    id: c.GLuint,
+
+    pub fn create() !Program {
+        const id = c.glCreateProgram();
+        if (id == 0) try mustError();
+
+        log.debug("program created id={}", .{id});
+        return Program{ .id = id };
+    }
+
+    pub fn attachShader(p: Program, s: Shader) !void {
+        c.glAttachShader(p.id, s.id);
+        try getError();
+    }
+
+    pub fn link(p: Program) !void {
+        c.glLinkProgram(p.id);
+
+        // Check if linking succeeded
+        var success: c_int = undefined;
+        c.glGetProgramiv(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;
+    }
+
+    /// 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 fn getInfoLog(s: Program) [512]u8 {
+        var msg: [512]u8 = undefined;
+        c.glGetProgramInfoLog(s.id, msg.len, null, &msg);
+        return msg;
+    }
+
+    pub fn destroy(p: Program) void {
+        assert(p.id != 0);
+        c.glDeleteProgram(p.id);
+        log.debug("program destroyed id={}", .{p.id});
     }
 };