renderer: start of fix to srgb framebuffer

the main test still fails, but this should fix some of them.

src/vrend_renderer.c

@@ -1236,8 +1236,23 @@ static void vrend_hw_emit_framebuffer_state(struct vrend_context *ctx)
    };
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, ctx->sub->fb_id);
 
-   if (ctx->sub->nr_cbufs == 0)
+   if (ctx->sub->nr_cbufs == 0) {
        glReadBuffer(GL_NONE);
+       glDisable(GL_FRAMEBUFFER_SRGB_EXT);
+   } else {
+      struct vrend_surface *surf = NULL;
+      int i;
+      for (i = 0; i < ctx->sub->nr_cbufs; i++) {
+	 if (ctx->sub->surf[i]) {
+	    surf = ctx->sub->surf[i];
+	 }
+      }
+      if (util_format_is_srgb(surf->format)) {
+	 glEnable(GL_FRAMEBUFFER_SRGB_EXT);
+      } else {
+	 glDisable(GL_FRAMEBUFFER_SRGB_EXT);
+      }
+   }
    glDrawBuffers(ctx->sub->nr_cbufs, buffers);
 }