dri3: Track current Present swap mode and adjust buffer counts

This automatically adjusts the number of buffers that we want based on
what swapping mode the X server is using and the current swap interval:

        swap mode       interval        buffers
        copy            > 0             1
        copy            0               2
        flip            > 0             2
        flip            0               3

Note that flip with swap interval 0 is currently limited to twice the
underlying refresh rate because of how the kernel manages flipping. Moving
from 3 to 4 buffers would help, but that seems ridiculous.

v2: Just update num_back at the point that the values that change num_back
    change.  This means we'll have the updated value at the point that the
    freeing of old going-to-be-unused backbuffers happens, which might not
    have been the case before (change by anholt, acked by keithp).

Signed-off-by: Keith Packard <[email protected]>
Signed-off-by: Eric Anholt <[email protected]>
Reviewed-by: Eric Anholt <[email protected]>

1 files changed, 5 insertions, 19 deletions

diff --git a/src/glx/dri3_priv.h b/src/glx/dri3_priv.h
index 9d142cf5137..1d124f8abd7 100644
--- a/src/glx/dri3_priv.h
+++ b/src/glx/dri3_priv.h
@@ -143,25 +143,9 @@ struct dri3_context
    __DRIcontext *driContext;
 };
 
-#define DRI3_NUM_BACK   2
+#define DRI3_MAX_BACK   3
 #define DRI3_BACK_ID(i) (i)
-#define DRI3_FRONT_ID   (DRI3_NUM_BACK)
-
-static inline int
-dri3_buf_id_next(int buf_id)
-{
-   if (buf_id == DRI3_NUM_BACK - 1)
-      return 0;
-   return buf_id + 1;
-}
-
-static inline int
-dri3_buf_id_prev(int buf_id)
-{
-   if (buf_id == 0)
-      return DRI3_NUM_BACK - 1;
-   return buf_id - 1;
-}
+#define DRI3_FRONT_ID   (DRI3_MAX_BACK)
 
 static inline int
 dri3_pixmap_buf_id(enum dri3_buffer_type buffer_type)
@@ -172,7 +156,7 @@ dri3_pixmap_buf_id(enum dri3_buffer_type buffer_type)
       return DRI3_FRONT_ID;
 }
 
-#define DRI3_NUM_BUFFERS        (1 + DRI3_NUM_BACK)
+#define DRI3_NUM_BUFFERS        (1 + DRI3_MAX_BACK)
 
 struct dri3_drawable {
    __GLXDRIdrawable base;
@@ -182,6 +166,7 @@ struct dri3_drawable {
    uint8_t have_back;
    uint8_t have_fake_front;
    uint8_t is_pixmap;
+   uint8_t flipping;
 
    /* SBC numbers are tracked by using the serial numbers
     * in the present request and complete events
@@ -198,6 +183,7 @@ struct dri3_drawable {
 
    struct dri3_buffer *buffers[DRI3_NUM_BUFFERS];
    int cur_back;
+   int num_back;
 
    uint32_t *stamp;