mesa: refactor _mesa_compute_max_transform_feedback_vertices from i965.

Previously, the i965 driver contained code to compute the maximum
number of vertices that could be written without overflowing any
transform feedback buffers.  This code wasn't driver-specific, and for
GLES3 support we're going to need to use it in core mesa.  So this
patch moves the code into a core mesa function,
_mesa_compute_max_transform_feedback_vertices().

Reviewed-by: Ian Romanick <[email protected]>

v2: Eliminate C++-style variable declarations, since these won't work
with MSVC.

Reviewed-by: Jordan Justen <[email protected]>
Reviewed-by: Brian Paul <[email protected]>

1 files changed, 29 insertions, 0 deletions

diff --git a/src/mesa/main/transformfeedback.c b/src/mesa/main/transformfeedback.c
index 22060c34c97..d9c6e514e8f 100644
--- a/src/mesa/main/transformfeedback.c
+++ b/src/mesa/main/transformfeedback.c
@@ -34,6 +34,7 @@
 #include "bufferobj.h"
 #include "context.h"
 #include "hash.h"
+#include "macros.h"
 #include "mfeatures.h"
 #include "mtypes.h"
 #include "transformfeedback.h"
@@ -246,6 +247,34 @@ _mesa_init_transform_feedback_functions(struct dd_function_table *driver)
 
 
 /**
+ * Compute the maximum number of vertices that can be written to the currently
+ * enabled transform feedback buffers without overflowing any of them.
+ */
+unsigned
+_mesa_compute_max_transform_feedback_vertices(
+      const struct gl_transform_feedback_object *obj,
+      const struct gl_transform_feedback_info *info)
+{
+   unsigned max_index = 0xffffffff;
+   unsigned i;
+
+   for (i = 0; i < info->NumBuffers; ++i) {
+      unsigned stride = info->BufferStride[i];
+      unsigned max_for_this_buffer;
+
+      /* Skip any inactive buffers, which have a stride of 0. */
+      if (stride == 0)
+	 continue;
+
+      max_for_this_buffer = obj->Size[i] / (4 * stride);
+      max_index = MIN2(max_index, max_for_this_buffer);
+   }
+
+   return max_index;
+}
+
+
+/**
  ** Begin API functions
  **/