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[patch] Patch that adds a general hint for low-latency video in some drivers

double_buffer_hint001.diff (text/plain), 6.50 KB, created by Manuel Alfayate Corchete on 2017-11-06 00:36:44 UTC

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Description:

Filename:

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Creator: Manuel Alfayate Corchete

Created: 2017-11-06 00:36:44 UTC

Size: 6.50 KB

patch

obsolete

>diff -rupN SDL/include/SDL_hints.h SDL2/include/SDL_hints.h
>--- SDL/include/SDL_hints.h	2017-11-06 00:34:24.684285675 +0100
>+++ SDL2/include/SDL_hints.h	2017-11-06 00:51:39.525965000 +0100
>@@ -798,14 +798,22 @@ extern "C" {
> #define SDL_HINT_RPI_VIDEO_LAYER           "SDL_RPI_VIDEO_LAYER"
> 
> /**
>- * \brief Tell SDL the KMS/DRM video driver that we want double buffer only.
>+ * \brief Tell the video driver that we only want a double buffer.
>  *
>- * By default KMS/DRM will use a triple buffer solution that wastes no CPU
>- * time on waiting for vsync after issuing a flip, but introduces a frame of
>- * latency. Waiting for vsync immediately after issuing a flip on the other
>- * hand is recommended for cases where low latency is an important factor.
>+ * By default, most lowlevel 2D APIs will use a triple buffer scheme that 
>+ * wastes no CPU time on waiting for vsync after issuing a flip, but
>+ * introduces a frame of latency. On the other hand, using a double buffer
>+ * scheme instead is recommended for cases where low latency is an important
>+ * factor because we save a whole frame of latency.
>+ * We do so by waiting for vsync immediately after issuing a flip, usually just
>+ * after eglSwapBuffers call in the backend's *_SwapWindow function.
>+ *
>+ * Since it's driver-specific, it's only supported where possible and
>+ * implemented. Currently supported the following drivers:
>+ * - KMSDRM (kmsdrm)
>+ * - Raspberry Pi (raspberrypi)
>  */
>-#define SDL_HINT_KMSDRM_DOUBLE_BUFFER      "SDL_KMSDRM_DOUBLE_BUFFER"
>+#define SDL_HINT_VIDEO_DOUBLE_BUFFER      "SDL_VIDEO_DOUBLE_BUFFER"
> 
> /**
>  *  \brief  A variable controlling what driver to use for OpenGL ES contexts.
>diff -rupN SDL/src/video/kmsdrm/SDL_kmsdrmvideo.c SDL2/src/video/kmsdrm/SDL_kmsdrmvideo.c
>--- SDL/src/video/kmsdrm/SDL_kmsdrmvideo.c	2017-11-06 00:34:24.768335833 +0100
>+++ SDL2/src/video/kmsdrm/SDL_kmsdrmvideo.c	2017-11-06 00:53:04.762914794 +0100
>@@ -525,7 +525,7 @@ KMSDRM_CreateWindow(_THIS, SDL_Window *
> 
>     /* In case we want low-latency, double-buffer video, we take note here */
>     wdata->double_buffer = SDL_FALSE;
>-    if (SDL_GetHintBoolean(SDL_HINT_KMSDRM_DOUBLE_BUFFER, SDL_FALSE)) {
>+    if (SDL_GetHintBoolean(SDL_HINT_VIDEO_DOUBLE_BUFFER, SDL_FALSE)) {
>         wdata->double_buffer = SDL_TRUE;
>     }
> 
>diff -rupN SDL/src/video/raspberry/SDL_rpiopengles.c SDL2/src/video/raspberry/SDL_rpiopengles.c
>--- SDL/src/video/raspberry/SDL_rpiopengles.c	2017-11-06 00:34:24.772338221 +0100
>+++ SDL2/src/video/raspberry/SDL_rpiopengles.c	2017-11-06 00:38:39.979786509 +0100
>@@ -19,6 +19,8 @@
>   3. This notice may not be removed or altered from any source distribution.
> */
> #include "../../SDL_internal.h"
>+#include "SDL_hints.h"
>+#include "SDL_log.h"
> 
> #if SDL_VIDEO_DRIVER_RPI && SDL_VIDEO_OPENGL_EGL
> 
>@@ -40,8 +42,27 @@ RPI_GLES_LoadLibrary(_THIS, const char *
>     return SDL_EGL_LoadLibrary(_this, path, EGL_DEFAULT_DISPLAY, 0);
> }
> 
>+int
>+RPI_GLES_SwapWindow(_THIS, SDL_Window * window) {
>+    SDL_WindowData *wdata = ((SDL_WindowData *) window->driverdata);
>+
>+    if (!(_this->egl_data->eglSwapBuffers(_this->egl_data->egl_display, wdata->egl_surface))) {
>+        SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "eglSwapBuffers failed.");
>+        return 0;
>+    }
>+
>+    /* Wait immediately for vsync (as if we only had two buffers), for low input-lag scenarios.
>+     * Run your SDL2 program with "SDL_RPI_DOUBLE_BUFFER=1 <program_name>" to enable this. */
>+    if (wdata->double_buffer) { 
>+        SDL_LockMutex(wdata->vsync_cond_mutex);
>+        SDL_CondWait(wdata->vsync_cond, wdata->vsync_cond_mutex);
>+        SDL_UnlockMutex(wdata->vsync_cond_mutex);      
>+    }
>+
>+    return 0;
>+}
>+
> SDL_EGL_CreateContext_impl(RPI)
>-SDL_EGL_SwapWindow_impl(RPI)
> SDL_EGL_MakeCurrent_impl(RPI)
> 
> #endif /* SDL_VIDEO_DRIVER_RPI && SDL_VIDEO_OPENGL_EGL */
>diff -rupN SDL/src/video/raspberry/SDL_rpivideo.c SDL2/src/video/raspberry/SDL_rpivideo.c
>--- SDL/src/video/raspberry/SDL_rpivideo.c	2017-11-06 00:34:24.756328668 +0100
>+++ SDL2/src/video/raspberry/SDL_rpivideo.c	2017-11-06 00:53:49.936355050 +0100
>@@ -214,6 +214,16 @@ RPI_SetDisplayMode(_THIS, SDL_VideoDispl
>     return 0;
> }
> 
>+static void
>+RPI_vsync_callback(DISPMANX_UPDATE_HANDLE_T u, void *data)
>+{
>+   SDL_WindowData *wdata = ((SDL_WindowData *) data);
>+
>+   SDL_LockMutex(wdata->vsync_cond_mutex);
>+   SDL_CondSignal(wdata->vsync_cond);
>+   SDL_UnlockMutex(wdata->vsync_cond_mutex);
>+}
>+
> int
> RPI_CreateWindow(_THIS, SDL_Window * window)
> {
>@@ -289,6 +299,15 @@ RPI_CreateWindow(_THIS, SDL_Window * win
>         return SDL_SetError("Could not create GLES window surface");
>     }
> 
>+    /* Start generating vsync callbacks if necesary */
>+    wdata->double_buffer = SDL_FALSE;
>+    if (SDL_GetHintBoolean(SDL_HINT_VIDEO_DOUBLE_BUFFER, SDL_FALSE)) { 
>+        wdata->vsync_cond = SDL_CreateCond();
>+        wdata->vsync_cond_mutex = SDL_CreateMutex();
>+        wdata->double_buffer = SDL_TRUE; 
>+        vc_dispmanx_vsync_callback(displaydata->dispman_display, RPI_vsync_callback, (void*)wdata);
>+    }
>+
>     /* Setup driver data for this window */
>     window->driverdata = wdata;
>     
>@@ -304,7 +323,22 @@ void
> RPI_DestroyWindow(_THIS, SDL_Window * window)
> {
>     SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
>+    SDL_VideoDisplay *display = SDL_GetDisplayForWindow(window);
>+    SDL_DisplayData *displaydata = (SDL_DisplayData *) display->driverdata;
>+
>     if(data) {
>+	if (data->double_buffer) {
>+	    /* Wait for vsync, and then stop vsync callbacks and destroy related stuff, if needed */
>+	    SDL_LockMutex(data->vsync_cond_mutex);
>+	    SDL_CondWait(data->vsync_cond, data->vsync_cond_mutex);
>+	    SDL_UnlockMutex(data->vsync_cond_mutex);      
>+	    
>+	    vc_dispmanx_vsync_callback(displaydata->dispman_display, NULL, NULL);
>+	    
>+	    SDL_DestroyCond(data->vsync_cond);
>+	    SDL_DestroyMutex(data->vsync_cond_mutex);
>+	}
>+
> #if SDL_VIDEO_OPENGL_EGL
>         if (data->egl_surface != EGL_NO_SURFACE) {
>             SDL_EGL_DestroySurface(_this, data->egl_surface);
>diff -rupN SDL/src/video/raspberry/SDL_rpivideo.h SDL2/src/video/raspberry/SDL_rpivideo.h
>--- SDL/src/video/raspberry/SDL_rpivideo.h	2017-11-06 00:34:24.728311948 +0100
>+++ SDL2/src/video/raspberry/SDL_rpivideo.h	2017-11-06 00:38:39.979786509 +0100
>@@ -48,6 +48,12 @@ typedef struct SDL_WindowData
> #if SDL_VIDEO_OPENGL_EGL  
>     EGLSurface egl_surface;
> #endif    
>+
>+    /* Vsync callback cond and mutex */
>+    SDL_cond  *vsync_cond;
>+    SDL_mutex *vsync_cond_mutex;
>+    SDL_bool double_buffer;
>+
> } SDL_WindowData;
> 
> #define SDL_RPI_VIDEOLAYER 10000 /* High enough so to occlude everything */

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We are currently migrating Bugzilla to GitHub issues.Any changes made to the bug tracker now will be lost, so please do not post new bugs or make changes to them.When we're done, all bug URLs will redirect to their equivalent location on the new bug tracker.

We are currently migrating Bugzilla to GitHub issues.
Any changes made to the bug tracker now will be lost, so please do not post new bugs or make changes to them.
When we're done, all bug URLs will redirect to their equivalent location on the new bug tracker.