From b048f6b6ff1dfb8d553015d3d45749aaa812a772 Mon Sep 17 00:00:00 2001
From: Lactozilla <jp6781615@gmail.com>
Date: Tue, 28 Nov 2023 15:28:50 -0300
Subject: [PATCH] Implement I_ReadScreenTransposed

---
 src/android/i_video.c |  5 +++++
 src/dummy/i_video.c   |  5 +++++
 src/i_video.h         |  8 ++++++++
 src/m_anigif.c        |  4 ++--
 src/m_misc.c          |  4 ++--
 src/sdl/i_video.c     | 19 +++++++++++++++++++
 6 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/src/android/i_video.c b/src/android/i_video.c
index bf0decb74..b4e1d979f 100644
--- a/src/android/i_video.c
+++ b/src/android/i_video.c
@@ -87,6 +87,11 @@ void I_ReadScreen(UINT8 *scr)
   (void)scr;
 }
 
+void I_ReadScreenTransposed(UINT8 *scr)
+{
+  (void)scr;
+}
+
 void I_BeginRead(void){}
 
 void I_EndRead(void){}
diff --git a/src/dummy/i_video.c b/src/dummy/i_video.c
index bb796b676..7d5884728 100644
--- a/src/dummy/i_video.c
+++ b/src/dummy/i_video.c
@@ -75,6 +75,11 @@ void I_ReadScreen(UINT8 *scr)
 	(void)scr;
 }
 
+void I_ReadScreenTransposed(UINT8 *scr)
+{
+	(void)scr;
+}
+
 void I_BeginRead(void){}
 
 void I_EndRead(void){}
diff --git a/src/i_video.h b/src/i_video.h
index 8efca5f9a..1b0720d3c 100644
--- a/src/i_video.h
+++ b/src/i_video.h
@@ -143,6 +143,14 @@ void I_WaitVBL(INT32 count);
 */
 void I_ReadScreen(UINT8 *scr);
 
+/**	\brief	The I_ReadScreenTransposed function
+
+	\param	scr	buffer to copy screen to
+
+	\return	void
+*/
+void I_ReadScreenTransposed(UINT8 *scr);
+
 /**	\brief Start disk icon
 */
 void I_BeginRead(void);
diff --git a/src/m_anigif.c b/src/m_anigif.c
index 5bc7717e0..a44f28629 100644
--- a/src/m_anigif.c
+++ b/src/m_anigif.c
@@ -565,7 +565,7 @@ static void GIF_framewrite(void)
 
 		// blit to temp screen
 		if (rendermode == render_soft)
-			I_ReadScreen(movie_screen);
+			I_ReadScreenTransposed(movie_screen);
 #ifdef HWRENDER
 		else if (rendermode == render_opengl)
 		{
@@ -594,7 +594,7 @@ static void GIF_framewrite(void)
 		// Copy the first frame into the movie screen
 		// OpenGL already does the same above.
 		if (gif_frames == 0 && rendermode == render_soft)
-			I_ReadScreen(movie_screen);
+			I_ReadScreenTransposed(movie_screen);
 
 		movie_screen = screens[0];
 	}
diff --git a/src/m_misc.c b/src/m_misc.c
index d4b272f1d..42534a92b 100644
--- a/src/m_misc.c
+++ b/src/m_misc.c
@@ -1280,7 +1280,7 @@ void M_SaveFrame(void)
 				{
 					// munge planar buffer to linear
 					linear = screens[2];
-					I_ReadScreen(linear);
+					I_ReadScreenTransposed(linear);
 				}
 #ifdef HWRENDER
 				else
@@ -1590,7 +1590,7 @@ void M_DoScreenShot(void)
 	{
 		// munge planar buffer to linear
 		linear = screens[2];
-		I_ReadScreen(linear);
+		I_ReadScreenTransposed(linear);
 	}
 
 	if (!freename)
diff --git a/src/sdl/i_video.c b/src/sdl/i_video.c
index 46b6ee9b3..42db204fc 100644
--- a/src/sdl/i_video.c
+++ b/src/sdl/i_video.c
@@ -1306,6 +1306,25 @@ void I_ReadScreen(UINT8 *scr)
 			vid.rowbytes, vid.rowbytes);
 }
 
+//
+// I_ReadScreenTransposed
+// The screen buffers in SRB2 are transposed, meaning they are ordered by columns instead of rows.
+// This function copies the buffer transposed so that it's arranged by rows, for things that expect the buffer to be that way.
+//
+void I_ReadScreenTransposed(UINT8 *scr)
+{
+	if (rendermode != render_soft)
+		I_Error("I_ReadScreenTransposed: called while in non-software mode");
+
+	UINT8 *buffer = screens[0];
+
+	size_t dest_rowbytes = vid.width * vid.bpp;
+
+	for (int y = 0; y < vid.height; y++)
+		for (int x = 0; x < vid.width; x++)
+			scr[(y * dest_rowbytes) + x] = buffer[(x * vid.rowbytes) + y];
+}
+
 //
 // I_SetPalette
 //