From 38886de0c3e9ea5729ef23e4c653fa2822f52e8f Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Tue, 6 Apr 2021 14:43:39 +0200
Subject: xscreensaver 6.00

---
 README.hacking | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

(limited to 'README.hacking')

diff --git a/README.hacking b/README.hacking
index f2958b4..39f9e14 100644
--- a/README.hacking
+++ b/README.hacking
@@ -50,6 +50,11 @@ Requirements for inclusion with the XScreenSaver collection
     your name and the current year).  The GNU GPL is not compatible with
     the rest of XScreenSaver.
 
+  - No clocks! Just as time travellers always try to kill Hitler on their
+    first trip, everyone seems to think that their first screen saver
+    should be a clock of some kind.  Nobody needs to know what time it is
+    with such frequency.  Fight The Tyranny Of The Clock.
+
 
 ==========================================================================
 The XScreenSaver API
@@ -184,6 +189,10 @@ Programming Tips
     in long-lived processes where no such cleanup takes place.
     Consider Valgrind or gcc -fsanitize=leak to find memory leaks.
 
+  - Again, don't use global variables.  If you are doing your developent
+    under X11, test your saver from the command line with the "-pair"
+    argument.  If that crashes, you're using global variables!
+
 
 ==========================================================================
 macOS, iOS and Android
@@ -201,4 +210,30 @@ macOS, iOS and Android
   To check that an X11 saver will fit well on a mobile device, test it
   with -geometry 640x1136 and 640x960.  That's a good first step, anyway.
 
+
+==========================================================================
+Theory behind the ifdefs
+==========================================================================  
+
+  HAVE_ macros indicate that an API is available.
+  USE_ macros indicate that a feature is requested.
+
+  Some notable ones:
+
+  HAVE_GL	The OpenGL 1.3 API is available, natively or through emulation.
+  HAVE_GLES	The OpenGLES 1.x API is available.
+  HAVE_COCOA	The Cocoa API is available, meaning compiling for macOS or iOS.
+  HAVE_IPHONE	Compiling for iOS, including iPad.
+  HAVE_ANDROID	Compiling for Android.
+  HAVE_MOBILE	iOS or Android, typically used for things related to rotation
+		or screen size that apply to all phones and tablets.
+  HAVE_JWXYZ	Compiling on a system where the X11 API is emulated
+		(macOS, iOS or Android).
+  HAVE_JWZGLES	Compiling on a system where the OpenGL 1.3 API is emulated
+		(iOS, Android, possibly Linux).
+  HAVE_GLSL	Compiling against a library that supports the GL Shading
+		Language.  Note that using GLSL also requires a runtime check
+		to see which version of GLSL the *running* system supports.
+  HAVE_EGL	OpenGL interfaces with native windows via EGL instead of GLX.
+
 ==========================================================================
-- 
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