[Mesa-dev] [PATCH mesa-demos] glxgears: Smooth animation with AIGLX

[Jon TURNEY]

Since commit 0b19fb0a5c6299baf28e26625e39773846f815b2 "improved animation rate"
glxgears computes the amount to turn the gears each frame by multipling the
angular velocity of the gears by the time since the last frame, rather than at a
constant amount per frame.

This gives a smooth animation with direct rendering, but is very bad for
accelerated indirect rendering, since glXSwapBuffers does not block and we can
queue many frames rapidly (i.e. with close to zero time between frames, and
hence no noticeable rotation) until we block on something else (perhaps the
socket buffer being full), but the server is still limited to swapping at the
vsync frequency.

(This is not an issue with indirect software rendering as there is no vsync)

One way to deal with this seems to be to check for indirect rendering and force
blocking until the swap is complete using glFinish().

This perhaps prevents glxgears from reporting the largest possible number for
fps when using indirect software rending, but since glxgears is not a benchmark,
perhaps that is not as big a problem as running glxgears and seeing an
apparently still image.

It's probable that other mesa demos suffer from the same issue, but I haven't
yet investigated that.

Signed-off-by: Jon TURNEY <jon.turney at dronecode.org.uk>
---
 src/xdemos/glxgears.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/xdemos/glxgears.c b/src/xdemos/glxgears.c
index 7a3b567..fdd6179 100644
--- a/src/xdemos/glxgears.c
+++ b/src/xdemos/glxgears.c
@@ -315,7 +315,7 @@ draw_gears(void)
 
 /** Draw single frame, do SwapBuffers, compute FPS */
 static void
-draw_frame(Display *dpy, Window win)
+draw_frame(Display *dpy, Window win, GLXContext ctx)
 {
    static int frames = 0;
    static double tRot0 = -1.0, tRate0 = -1.0;
@@ -336,6 +336,9 @@ draw_frame(Display *dpy, Window win)
    draw_gears();
    glXSwapBuffers(dpy, win);
 
+   if (!glXIsDirect(dpy, ctx))
+     glFinish(); /* if indirect, block until swap is complete */
+
    frames++;
    
    if (tRate0 < 0.0)
@@ -680,7 +683,7 @@ handle_event(Display *dpy, Window win, XEvent *event)
 
 
 static void
-event_loop(Display *dpy, Window win)
+event_loop(Display *dpy, Window win, GLXContext ctx)
 {
    while (1) {
       int op;
@@ -694,7 +697,7 @@ event_loop(Display *dpy, Window win)
             break;
       }
 
-      draw_frame(dpy, win);
+      draw_frame(dpy, win, ctx);
    }
 }
 
@@ -787,7 +790,7 @@ main(int argc, char *argv[])
     */
    reshape(winWidth, winHeight);
 
-   event_loop(dpy, win);
+   event_loop(dpy, win, ctx);
 
    glDeleteLists(gear1, 1);
    glDeleteLists(gear2, 1);
-- 
1.8.3.4