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x11: Deal with difference in GLX_EXT_swap_control_tear behavior.

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Mesa and Nvidia handle it differently, and one or the other may fix their
implementation in the future, so test which way it works at runtime.

Reference Issue #8004.

(cherry picked from commit 74a25425646d64edeff508ec8e99622a41576905)
This commit is contained in:
Ryan C. Gordon 2023-11-23 13:47:13 -05:00
parent 489e9b69df
commit d8102bf660
No known key found for this signature in database
GPG key ID: FA148B892AB48044
3 changed files with 80 additions and 5 deletions
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61
src/video/x11/SDL_x11opengl.c
View file

@ -241,6 +241,8 @@ int X11_GL_LoadLibrary(_THIS, const char *path)
return SDL_SetError("GLX is not supported");
}
_this->gl_data->swap_interval_tear_behavior = SDL_SWAPINTERVALTEAR_UNTESTED;
/* Initialize extensions */
/* See lengthy comment about the inc/dec in
../windows/SDL_windowsopengl.c. */
@ -889,7 +891,6 @@ int X11_GL_SetSwapInterval(_THIS, int interval)
int currentInterval = X11_GL_GetSwapInterval(_this);
_this->gl_data->glXSwapIntervalEXT(display, drawable, currentInterval);
_this->gl_data->glXSwapIntervalEXT(display, drawable, interval);
status = 0;
swapinterval = interval;
} else if (_this->gl_data->glXSwapIntervalMESA) {
@ -912,6 +913,53 @@ int X11_GL_SetSwapInterval(_THIS, int interval)
return status;
}
static SDL_GLSwapIntervalTearBehavior CheckSwapIntervalTearBehavior(SDL_VideoDevice *_this, Window drawable, unsigned int current_val, unsigned int current_allow_late)
{
/* Mesa and Nvidia interpret GLX_EXT_swap_control_tear differently, as of this writing, so
figure out which behavior we have.
Technical details: https://github.com/libsdl-org/SDL/issues/8004#issuecomment-1819603282 */
if (_this->gl_data->swap_interval_tear_behavior == SDL_SWAPINTERVALTEAR_UNTESTED) {
if (!_this->gl_data->HAS_GLX_EXT_swap_control_tear) {
_this->gl_data->swap_interval_tear_behavior = SDL_SWAPINTERVALTEAR_UNKNOWN;
} else {
Display *display = ((SDL_VideoData *)_this->driverdata)->display;
unsigned int allow_late_swap_tearing = 22;
int original_val = (int) current_val;
/*
* This is a workaround for a bug in NVIDIA drivers. Bug has been reported
* and will be fixed in a future release (probably 319.xx).
*
* There's a bug where glXSetSwapIntervalEXT ignores updates because
* it has the wrong value cached. To work around it, we just run a no-op
* update to the current value.
*/
_this->gl_data->glXSwapIntervalEXT(display, drawable, current_val);
/* set it to no swap interval and see how it affects GLX_LATE_SWAPS_TEAR_EXT... */
_this->gl_data->glXSwapIntervalEXT(display, drawable, 0);
_this->gl_data->glXQueryDrawable(display, drawable, GLX_LATE_SWAPS_TEAR_EXT, &allow_late_swap_tearing);
if (allow_late_swap_tearing == 0) { /* GLX_LATE_SWAPS_TEAR_EXT says whether late swapping is currently in use */
_this->gl_data->swap_interval_tear_behavior = SDL_SWAPINTERVALTEAR_NVIDIA;
if (current_allow_late) {
original_val = -original_val;
}
} else if (allow_late_swap_tearing == 1) { /* GLX_LATE_SWAPS_TEAR_EXT says whether the Drawable can use late swapping at all */
_this->gl_data->swap_interval_tear_behavior = SDL_SWAPINTERVALTEAR_MESA;
} else { /* unexpected outcome! */
_this->gl_data->swap_interval_tear_behavior = SDL_SWAPINTERVALTEAR_UNKNOWN;
}
/* set us back to what it was originally... */
_this->gl_data->glXSwapIntervalEXT(display, drawable, original_val);
}
}
return _this->gl_data->swap_interval_tear_behavior;
}
int X11_GL_GetSwapInterval(_THIS)
{
if (_this->gl_data->glXSwapIntervalEXT) {
@ -924,6 +972,7 @@ int X11_GL_GetSwapInterval(_THIS)
unsigned int interval = 0;
if (_this->gl_data->HAS_GLX_EXT_swap_control_tear) {
allow_late_swap_tearing = 22; /* set this to nonsense. */
_this->gl_data->glXQueryDrawable(display, drawable,
GLX_LATE_SWAPS_TEAR_EXT,
&allow_late_swap_tearing);
@ -932,11 +981,19 @@ int X11_GL_GetSwapInterval(_THIS)
_this->gl_data->glXQueryDrawable(display, drawable,
GLX_SWAP_INTERVAL_EXT, &interval);
switch (CheckSwapIntervalTearBehavior(_this, drawable, interval, allow_late_swap_tearing)) {
case SDL_SWAPINTERVALTEAR_MESA:
return (int)interval; /* unsigned int cast to signed that generates negative value if necessary. */
case SDL_SWAPINTERVALTEAR_NVIDIA:
default:
if ((allow_late_swap_tearing) && (interval > 0)) {
return -((int)interval);
}
return (int)interval;
}
return (int)interval; /* shouldn't hit this, but just in case. */
} else if (_this->gl_data->glXGetSwapIntervalMESA) {
return _this->gl_data->glXGetSwapIntervalMESA();
} else {

10
src/video/x11/SDL_x11opengl.h
View file

@ -27,6 +27,14 @@
#include "SDL_opengl.h"
#include <GL/glx.h>
typedef enum SDL_GLSwapIntervalTearBehavior
{
SDL_SWAPINTERVALTEAR_UNTESTED,
SDL_SWAPINTERVALTEAR_UNKNOWN,
SDL_SWAPINTERVALTEAR_MESA,
SDL_SWAPINTERVALTEAR_NVIDIA
} SDL_GLSwapIntervalTearBehavior;
struct SDL_GLDriverData
{
int errorBase, eventBase;
@ -48,6 +56,8 @@ struct SDL_GLDriverData
int minor;
} es_profile_max_supported_version;
SDL_GLSwapIntervalTearBehavior swap_interval_tear_behavior;
Bool (*glXQueryExtension)(Display *, int *, int *);
void *(*glXGetProcAddress)(const GLubyte *);
XVisualInfo *(*glXChooseVisual)(Display *, int, int *);

10
test/testgl2.c
View file

@ -205,6 +205,11 @@ Render()
ctx.glRotatef(5.0, 1.0, 1.0, 1.0);
}
static void LogSwapInterval(void)
{
SDL_Log("Swap Interval : %d\n", SDL_GL_GetSwapInterval());
}
int main(int argc, char *argv[])
{
int fsaa, accel;
@ -300,7 +305,9 @@ int main(int argc, char *argv[])
SDL_GetCurrentDisplayMode(0, &mode);
SDL_Log("Screen BPP : %" SDL_PRIu32 "\n", SDL_BITSPERPIXEL(mode.format));
SDL_Log("Swap Interval : %d\n", SDL_GL_GetSwapInterval());
LogSwapInterval();
SDL_GetWindowSize(state->windows[0], &dw, &dh);
SDL_Log("Window Size : %d,%d\n", dw, dh);
SDL_GL_GetDrawableSize(state->windows[0], &dw, &dh);
@ -408,6 +415,7 @@ int main(int argc, char *argv[])
SDL_GL_MakeCurrent(state->windows[i], context);
if (update_swap_interval) {
SDL_GL_SetSwapInterval(swap_interval);
LogSwapInterval();
}
SDL_GL_GetDrawableSize(state->windows[i], &w, &h);
ctx.glViewport(0, 0, w, h);