From 7c53d95c6f5a8a1d1f67a0eb9a358f579b031391 Mon Sep 17 00:00:00 2001
From: turret <turret@duck.com>
Date: Thu, 29 Jun 2023 17:20:42 -0500
Subject: donut: implement double buffering

---
 config.mk |  2 +-
 donut.c   | 12 +++++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/config.mk b/config.mk
index 6880dbe..436d9d9 100644
--- a/config.mk
+++ b/config.mk
@@ -2,6 +2,6 @@ PREFIX = /usr/local
 
 CPPFLAGS = -D_DEFAULT_SOURCE -D_BSD_SOURCE -D_XOPEN_SOURCE=700L -D_POSIX_C_SOURCE=200809L
 CFLAGS = -std=c99 -pedantic -Wall -Wno-deprecated-declarations -Os ${CPPFLAGS}
-LDFLAGS = -lm -lX11
+LDFLAGS = -lm -lX11 -lXext
 
 CC = cc
diff --git a/donut.c b/donut.c
index b136c36..36d7a19 100644
--- a/donut.c
+++ b/donut.c
@@ -28,6 +28,7 @@
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 #include <X11/Xos.h>
+#include <X11/extensions/Xdbe.h>
 
 char *argv0;
 #include "arg.h"
@@ -121,6 +122,12 @@ int main(int argc, char **argv) {
     XClearWindow(dis, win);
     XMapRaised(dis, win);
 
+    XdbeSwapInfo swap_info = {
+        win,
+        XdbeUndefined
+    };
+    XdbeBackBuffer back_buffer = XdbeAllocateBackBufferName(dis, win, swap_info.swap_action);
+
     // torus rotation floats
     float A = 0; // x-axis
     float B = 0; // z-axis
@@ -149,12 +156,15 @@ int main(int argc, char **argv) {
             for(int y = 0; height >= y; y++){
                 int color = (b[x + width * y] - 1 + M_SQRT2) / sqrt(8) * 255;
                 XSetForeground(dis, gc, color << 16 | color << 8 | color);
-                XFillRectangle(dis, win, gc, x * SCALE, y * SCALE, SCALE, SCALE);
+                XFillRectangle(dis, back_buffer, gc, x * SCALE, y * SCALE, SCALE, SCALE);
             }
         }
 
+        XdbeSwapBuffers(dis, &swap_info, 1);
+
         free(b);
 
+        XSync(dis, 1);
         double etime = utime();
 
         if(etime < stime + 1000/FPS_MAX)
-- 
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