[Mesa-dev] [PATCH] i965: fix MakeCurrent when switching a context between multiple drawables.

[Iago Toral Quiroga]

Commit 11baad35088dfd4bdabc1710df650dbfb413e7a3 produces a regression when
switching a single context between multiple drawables.

The problem is that we check whether we have a viewport set to decide if we
need to generate buffers for the drawble, but the viewport is initialized
with the first call to MakeCurrent for that context, so calling MakeCurrent on
the same context with a different drawable will have the viewport already
initialized and will not generate buffers for the new drawable.

This patch fixes the problem by reverting to the previous solution implemented
in commit 05da4a7a5e7d5bd988cb31f94ed8e1f053d9ee39 with a small fix to suppport
single buffer drawables too. This solution checks if we have a renderbuffer for
the drawable to decide if we need to generate a buffer or not. The original
implementation, however, did this by checking the BACK_LEFT buffer, which is
not a valid solution for single buffer drawables. This patch modifies this
to check the FRONT_LEFT buffer instead, which should work in both scenarios.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=74005
---
 src/mesa/drivers/dri/i965/brw_context.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
index c9719f5..c593286 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -926,6 +926,7 @@ intelMakeCurrent(__DRIcontext * driContextPriv,
 {
    struct brw_context *brw;
    GET_CURRENT_CONTEXT(curCtx);
+   struct intel_renderbuffer *rb = NULL;
 
    if (driContextPriv)
       brw = (struct brw_context *) driContextPriv->driverPrivate;
@@ -950,6 +951,7 @@ intelMakeCurrent(__DRIcontext * driContextPriv,
       } else {
          fb = driDrawPriv->driverPrivate;
          readFb = driReadPriv->driverPrivate;
+         rb = intel_get_renderbuffer(fb, BUFFER_FRONT_LEFT);
          driContextPriv->dri2.draw_stamp = driDrawPriv->dri2.stamp - 1;
          driContextPriv->dri2.read_stamp = driReadPriv->dri2.stamp - 1;
       }
@@ -961,10 +963,9 @@ intelMakeCurrent(__DRIcontext * driContextPriv,
       intel_gles3_srgb_workaround(brw, fb);
       intel_gles3_srgb_workaround(brw, readFb);
 
-      /* If the context viewport hasn't been initialized, force a call out to
-       * the loader to get buffers so we have a drawable size for the initial
-       * viewport. */
-      if (!brw->ctx.ViewportInitialized)
+      /* If we don't have buffers for the drawable yet, force a call to
+       * getbuffers here so we can have a default drawable size. */
+      if (rb && !rb->mt)
          intel_prepare_render(brw);
 
       _mesa_make_current(ctx, fb, readFb);
-- 
1.8.3.2