From b2ba15425ce41e134d7e1187e366374d9cb41a06 Mon Sep 17 00:00:00 2001
From: Daniel Gibson <metalcaedes@gmail.com>
Date: Wed, 3 Jul 2024 20:06:20 +0200
Subject: [PATCH] Hopefully fix screenshots on Wayland

- screenshots on native wayland (SDL_VIDEODRIVER=wayland) were black,
  at least on Gnome
  => fixed(?) by reading from the default (back) buffer instead of
     the front buffer
- after taking a screenshot, resizing the window (or switching to
  fullscreen) was broken (window remained black or became invisible
  or partly contained garbage), both with native wayland and xwayland
  => fixed by restoring the glReadBuffer state after reading the pixels
---
 neo/renderer/RenderSystem.h        |  1 +
 neo/renderer/RenderSystem_init.cpp | 18 ++++++++++++++++--
 neo/sys/glimp.cpp                  |  2 ++
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/neo/renderer/RenderSystem.h b/neo/renderer/RenderSystem.h
index 2972ba26..15a98645 100644
--- a/neo/renderer/RenderSystem.h
+++ b/neo/renderer/RenderSystem.h
@@ -93,6 +93,7 @@ typedef struct glconfig_s {
 	// DG: current video backend is known to need opaque default framebuffer
 	//     used if r_fillWindowAlphaChan == -1
 	bool				shouldFillWindowAlpha;
+	bool				isWayland; // DG: for other wayland-specific hacks.. (does *not* detect XWayland!)
 
 	// For some reason people decided that we need displays with ultra small pixels,
 	// so everything rendered on them must be scaled up to be legible.
diff --git a/neo/renderer/RenderSystem_init.cpp b/neo/renderer/RenderSystem_init.cpp
index d9a4a1cb..3a5fd169 100644
--- a/neo/renderer/RenderSystem_init.cpp
+++ b/neo/renderer/RenderSystem_init.cpp
@@ -1251,8 +1251,22 @@ void R_ReadTiledPixels( int width, int height, byte *buffer, renderView_t *ref =
 				h = height - yo;
 			}
 
-			qglReadBuffer( GL_FRONT );
-			qglReadPixels( 0, 0, w, h, GL_RGB, GL_UNSIGNED_BYTE, temp );
+			if ( glConfig.isWayland ) {
+				// DG: Native Wayland (=> not XWayland) doesn't seem to support reading
+				//     from the front buffer - screenshot is black then..
+				//     So just read from the default (probably back-) buffer
+				qglReadPixels( 0, 0, w, h, GL_RGB, GL_UNSIGNED_BYTE, temp );
+			} else {
+				// DG: It's probably better to restore the glReadBuffer mode after reading the pixels..
+				//     (at least with XWayland on GNOME changing resolutions is wonky when not doing this)
+				GLint oldReadBuf = GL_BACK;
+				qglGetIntegerv( GL_READ_BUFFER, &oldReadBuf );
+				qglReadBuffer( GL_FRONT );
+
+				qglReadPixels( 0, 0, w, h, GL_RGB, GL_UNSIGNED_BYTE, temp );
+
+				qglReadBuffer( oldReadBuf );
+			}
 
 			int	row = ( w * 3 + 3 ) & ~3;		// OpenGL pads to dword boundaries
 
diff --git a/neo/sys/glimp.cpp b/neo/sys/glimp.cpp
index dc4ca35b..afee28dc 100644
--- a/neo/sys/glimp.cpp
+++ b/neo/sys/glimp.cpp
@@ -579,10 +579,12 @@ try_again:
 
 		// for r_fillWindowAlphaChan -1, see also the big comment above
 		glConfig.shouldFillWindowAlpha = false;
+		glConfig.isWayland = false;
 #if SDL_VERSION_ATLEAST(2, 0, 0)
 		const char* videoDriver = SDL_GetCurrentVideoDriver();
 		if (idStr::Icmp(videoDriver, "wayland") == 0) {
 			glConfig.shouldFillWindowAlpha = true;
+			glConfig.isWayland = true;
 		}
 #endif