Opening a GL context with Win32 (#19)

* start

* wording.

* gl progress

* fix a freeing the box bug

* complete the transition.

* well now it doesn't make the window!

* works with an alternate window class, not sure why

* fake context stuff all done

* note update.

* gl for win32 complete

* copy main.rs to example

Author: Lokathor

Cargo.toml

@@ -4,3 +4,6 @@ version = "0.1.0"
 authors = ["Lokathor <zefria@gmail.com>"]
 edition = "2018"
 license = "Zlib OR Apache-2.0 OR MIT"
+
+[profile.release]
+lto = "thin"

book_src/SUMMARY.md

@@ -4,5 +4,7 @@
 * [Opening A Window](opening_a_window/index.md)
   * [Win32](opening_a_window/win32.md)
   * [Win32 Cleanup](opening_a_window/win32_cleanup.md)
+* [Loading OpenGL](loading_opengl/index.md)
+  * [Win32](loading_opengl/win32.md)
 * [Appendix](appendix/index.md)
   * [UTF-16 Literals](appendix/utf16_literals.md)

book_src/loading_opengl/index.md

@@ -0,0 +1,33 @@
+
+# Loading Open GL
+
+While the *usage* of Open GL is basically the same across platforms,
+the precise details of how to first initialize Open GL varies.
+
+The general idea is that we need to do two things:
+
+1) Create an [Open GL context](https://www.khronos.org/opengl/wiki/OpenGL_Context)
+  and make it "current".
+  A GL context is what holds all of the drawing state for GL.
+  Each GL Context must only be current in a single thread at a time,
+  otherwise you'll get undefined behavior.
+  Also, a thread's current context is a thread-local variable,
+  so you can't have more than one context current in a thread at a time.
+  Also, a context is associated with a particular window's drawing area.
+  Usually you have just one window,
+  and so you have only one GL context,
+  meaning that don't need to worry about any of that.
+  If you're trying to use GL with more than one window at a time,
+  things can get tricky.
+2) Load the GL function pointers.
+  Unfortunately, you can't access GL like it was a normal dynamic library.
+  At least, you can't on Windows and Linux.
+  We'll have a whole fun time
+  [loading function pointers](https://www.khronos.org/opengl/wiki/Load_OpenGL_Functions) manually.
+
+## Acknowledgements
+
+For this portion of the guide I'd like to give an incredible acknowledgement to
+[glowcoil](https://github.com/glowcoil), who wrote the
+[raw-gl-context](https://github.com/glowcoil/raw-gl-context)
+crate, which gives come very clean and clear examples of how you open a GL context on the major platforms.