draw/pt: adjust overflow calculations

gallium lies. buffer_size is not actually buffer_size but available
size, which is 'buffer_size - buffer_offset' so by adding buffer
offset we'd incorrectly compute overflow.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: José Fonseca <jfonseca@vmware.com>

2 files changed, 8 insertions, 2 deletions

diff --git a/src/gallium/auxiliary/draw/draw_pt_so_emit.c b/src/gallium/auxiliary/draw/draw_pt_so_emit.c
index 9b557733ddd..d624a990bc6 100644
--- a/src/gallium/auxiliary/draw/draw_pt_so_emit.c
+++ b/src/gallium/auxiliary/draw/draw_pt_so_emit.c
@@ -131,8 +131,7 @@ static void so_emit_prim(struct pt_so_emit *so,
    for (i = 0; i < draw->so.num_targets; i++) {
       struct draw_so_target *target = draw->so.targets[i];
       if (target) {
-         buffer_total_bytes[i] = target->internal_offset +
-            target->target.buffer_offset;
+         buffer_total_bytes[i] = target->internal_offset;
       } else {
          buffer_total_bytes[i] = 0;
       }
diff --git a/src/gallium/include/pipe/p_state.h b/src/gallium/include/pipe/p_state.h
index 28249d2261a..262078d09b3 100644
--- a/src/gallium/include/pipe/p_state.h
+++ b/src/gallium/include/pipe/p_state.h
@@ -465,6 +465,13 @@ struct pipe_constant_buffer {
  * have been written. The internal offset can be stored on the device
  * and the CPU actually doesn't have to query it.
  *
+ * Note that the buffer_size variable is actually specifying the available
+ * space in the buffer, not the size of the attached buffer. 
+ * In other words in majority of cases buffer_size would simply be 
+ * 'buffer->width0 - buffer_offset', so buffer_size refers to the size
+ * of the buffer left, after accounting for buffer offset, for stream output
+ * to write to.
+ *
  * Use PIPE_QUERY_SO_STATISTICS to know how many primitives have
  * actually been written.
  */