SDL2-compat/SDL3 invisible mouse cursor with KSMDRM

[Lassebq]

OS: Arch Linux
SDL 3.4.2-1

Cursor appears invisible, but fully functional when running source engine games with SDL's KMSDRM backend.
Is there perhaps some way for a regular user to specify initial cursor image if the game doesn't use custom one?

[MichaIng]

We face this with native SDL3 usage. Not in v3.2.x, but in v3.4.2. Interestingly, while on x86_64 with OpenGL renderer, the cursor is entirely invisible, on aarch64 with OpenGLES it is visible, but just very tiny.

[Kontrabant]

Does setting the envvar SDL_KMSDRM_ATOMIC=0 make any difference? Atomic support being re-added and made the default is really the only large functional change to the KMSDRM backend between 3.2.x and 3.4.x.

[MichaIng]

Is this a runtime variable or cmake variable?

[Kontrabant]

It's an environment variable, so you would use it like SDL_KMSDRM_ATOMIC=0 ./myapp

[MichaIng]

Oh, yes, as runtime variable, it solves the issue, indeed. Tested with main branch, but will redo with 3.4.2.

[Lassebq]

With 3.4.2 and SDL_KMSDRM_ATOMIC=0 I can see a black mouse cursor with white outline in top left corner during the initial loading, after which the cursor is invisible anyway. The games I tested were: Insurgency 2014, and some of games from Valve such as HL2, Counter Strike: Source and Portal. All of which are source engine games with linux ports, so they should share mostly the same codebase.

I was able to see a moving mouse cursor with input feedback in Portal, but as soon as I tried changing resolution to native the cursor disappeared

[icculus]

So I don't know what's wrong with this yet, but turning off just the atomic mouse cursor lets the rest of the atomic version work, and fixes the missing cursor for me. It makes it work in things like testsprite, in that a usable cursor is suddenly available, but also testcustomcursor works correctly, too.

If this works for others, I'm willing to do this for 3.4.4 and read up on the kmsdrm API for proper fixes in 3.4.6.

diff --git a/src/video/kmsdrm/SDL_kmsdrmmouse.c b/src/video/kmsdrm/SDL_kmsdrmmouse.c
index df321031a..8f48df3e8 100644
--- a/src/video/kmsdrm/SDL_kmsdrmmouse.c
+++ b/src/video/kmsdrm/SDL_kmsdrmmouse.c
@@ -32,6 +32,9 @@
 
 #include "../SDL_pixels_c.h"
 
+// !!! FIXME: atomic cursors are broken right now.
+#define USE_ATOMIC_CURSOR 0
+
 static SDL_Cursor *KMSDRM_CreateDefaultCursor(void);
 static SDL_Cursor *KMSDRM_CreateCursor(SDL_Surface *surface, int hot_x, int hot_y);
 static bool KMSDRM_ShowCursor(SDL_Cursor *cursor);
@@ -40,10 +43,10 @@ static void KMSDRM_FreeCursor(SDL_Cursor *cursor);
 
 /**************************************************************************************/
 // BEFORE CODING ANYTHING MOUSE/CURSOR RELATED, REMEMBER THIS.
-// How does SDL manage cursors internally? First, mouse =! cursor. The mouse can have
+// How does SDL manage cursors internally? First, mouse != cursor. The mouse can have
 // many cursors in mouse->cursors.
 // -SDL tells us to create a cursor with KMSDRM_CreateCursor(). It can create many
-// cursosr with this, not only one.
+// cursors with this, not only one.
 // -SDL stores those cursors in a cursors array, in mouse->cursors.
 // -Whenever it wants (or the programmer wants) takes a cursor from that array
 // and shows it on screen with KMSDRM_ShowCursor().
@@ -68,7 +71,7 @@ void KMSDRM_DestroyCursorBO(SDL_VideoDevice *_this, SDL_VideoDisplay *display)
     // Destroy the curso GBM BO.
     if (dispdata->cursor_bo) {
         SDL_VideoData *viddata = (SDL_VideoData *) _this->internal;
-        if (viddata->is_atomic) {
+        if (USE_ATOMIC_CURSOR && viddata->is_atomic) {
             if (dispdata->cursor_plane) {
                 // Unset the the cursor BO from the cursor plane.
                 KMSDRM_PlaneInfo info;
@@ -99,7 +102,7 @@ bool KMSDRM_CreateCursorBO(SDL_VideoDisplay *display)
     SDL_VideoData *viddata = dev->internal;
     SDL_DisplayData *dispdata = display->internal;
 
-    if (viddata->is_atomic) {
+    if (USE_ATOMIC_CURSOR && viddata->is_atomic) {
         setup_plane(dev, dispdata, &dispdata->cursor_plane, DRM_PLANE_TYPE_CURSOR);
     }
 
@@ -141,7 +144,7 @@ static bool KMSDRM_RemoveCursorFromBO(SDL_VideoDisplay *display)
     SDL_VideoDevice *video_device = SDL_GetVideoDevice();
     SDL_VideoData *viddata = video_device->internal;
 
-    if (viddata->is_atomic) {
+    if (USE_ATOMIC_CURSOR && viddata->is_atomic) {
         if (dispdata->cursor_plane) {
             KMSDRM_PlaneInfo info;
             SDL_zero(info);
@@ -207,7 +210,7 @@ static bool KMSDRM_DumpCursorToBO(SDL_VideoDisplay *display, SDL_Mouse *mouse, S
         goto cleanup;
     }
 
-    if (viddata->is_atomic) {
+    if (USE_ATOMIC_CURSOR && viddata->is_atomic) {
         // Get the fb_id for the GBM BO so we can show it on the cursor plane.
         KMSDRM_FBInfo *fb = KMSDRM_FBFromBO(video_device, dispdata->cursor_bo);
         KMSDRM_PlaneInfo info;
@@ -400,7 +403,7 @@ static bool KMSDRM_WarpMouseGlobal(float x, float y)
         if (dispdata->cursor_bo) {
             SDL_VideoDevice *dev = SDL_GetVideoDevice();
             SDL_VideoData *viddata = dev->internal;
-            if (viddata->is_atomic) {
+            if (USE_ATOMIC_CURSOR && viddata->is_atomic) {
                 const SDL_CursorData *curdata = (const SDL_CursorData *) mouse->cur_cursor->internal;
                 drm_atomic_movecursor(dispdata, curdata, (uint16_t) (int) x, (uint16_t) (int) y);
             } else {
@@ -467,7 +470,7 @@ static bool KMSDRM_MoveCursor(SDL_Cursor *cursor)
             return SDL_SetError("Cursor not initialized properly.");
         }
 
-        if (viddata->is_atomic) {
+        if (USE_ATOMIC_CURSOR && viddata->is_atomic) {
             /* !!! FIXME: Some programs expect cursor movement even while they don't do SwapWindow() calls,
                and since we ride on the atomic_commit() in SwapWindow() for cursor movement,
                cursor won't move in these situations. We could do an atomic_commit() here

[slouken]

If this works for others, I'm willing to do this for 3.4.4 and read up on the kmsdrm API for proper fixes in 3.4.6.

This seems reasonable to me!

[icculus]

Okay, pushed and cherry-picked. Moving this to 3.4.6 for further investigation later.