glsl: use bitmask of active xfb buffer indices

This allows us to print the correct binding point when not all
buffers declared in the shader are bound.

For example if we use a single buffer:

layout(xfb_buffer=2, offset=0) out vec4 v;

We now print '2' when the buffer is not bound rather than '0'.

Reviewed-by: Dave Airlie <airlied@redhat.com>

src/compiler/glsl/link_varyings.cpp

@@ -872,6 +872,11 @@ store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
                      unsigned num_tfeedback_decls,
                      tfeedback_decl *tfeedback_decls, bool has_xfb_qualifiers)
 {
+   /* Make sure MaxTransformFeedbackBuffers is less than 32 so the bitmask for
+    * tracking the number of buffers doesn't overflow.
+    */
+   assert(ctx->Const.MaxTransformFeedbackBuffers < 32);
+
    bool separate_attribs_mode =
       prog->TransformFeedback.BufferMode == GL_SEPARATE_ATTRIBS;
 
@@ -904,6 +909,7 @@ store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
                     num_outputs);
 
    unsigned num_buffers = 0;
+   unsigned buffers = 0;
 
    if (!has_xfb_qualifiers && separate_attribs_mode) {
       /* GL_SEPARATE_ATTRIBS */
@@ -913,6 +919,7 @@ store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
                                        has_xfb_qualifiers))
             return false;
 
+         buffers |= 1 << num_buffers;
          num_buffers++;
       }
    }
@@ -949,6 +956,7 @@ store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
          } else {
             buffer = num_buffers;
          }
+         buffers |= 1 << num_buffers;
 
          if (!tfeedback_decls[i].store(ctx, prog,
                                        &prog->LinkedTransformFeedback,
@@ -956,12 +964,11 @@ store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
                                        has_xfb_qualifiers))
             return false;
       }
-      num_buffers++;
    }
 
    assert(prog->LinkedTransformFeedback.NumOutputs == num_outputs);
 
-   prog->LinkedTransformFeedback.NumBuffers = num_buffers;
+   prog->LinkedTransformFeedback.ActiveBuffers = buffers;
    return true;
 }
 

src/mesa/drivers/dri/i965/gen6_sol.c

@@ -256,7 +256,7 @@ brw_begin_transform_feedback(struct gl_context *ctx, GLenum mode,
     * overflowing any of the buffers currently being used for feedback.
     */
    unsigned max_index
-      = _mesa_compute_max_transform_feedback_vertices(xfb_obj,
+      = _mesa_compute_max_transform_feedback_vertices(ctx, xfb_obj,
                                                       linked_xfb_info);
 
    /* Initialize the SVBI 0 register to zero and set the maximum index. */

src/mesa/main/mtypes.h

@@ -1649,10 +1649,8 @@ struct gl_transform_feedback_info
 {
    unsigned NumOutputs;
 
-   /**
-    * Number of transform feedback buffers in use by this program.
-    */
-   unsigned NumBuffers;
+   /* Bitmask of active buffer indices. */
+   unsigned ActiveBuffers;
 
    struct gl_transform_feedback_output *Outputs;
 

src/mesa/main/transformfeedback.c

@@ -347,23 +347,25 @@ compute_transform_feedback_buffer_sizes(
  * enabled transform feedback buffers without overflowing any of them.
  */
 unsigned
-_mesa_compute_max_transform_feedback_vertices(
+_mesa_compute_max_transform_feedback_vertices(struct gl_context *ctx,
       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;
+   for (i = 0; i < ctx->Const.MaxTransformFeedbackBuffers; i++) {
+      if ((info->ActiveBuffers >> i) & 1) {
+         unsigned stride = info->BufferStride[i];
+         unsigned max_for_this_buffer;
 
-      /* Skip any inactive buffers, which have a stride of 0. */
-      if (stride == 0)
-	 continue;
+         /* 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);
+         max_for_this_buffer = obj->Size[i] / (4 * stride);
+         max_index = MIN2(max_index, max_for_this_buffer);
+      }
    }
 
    return max_index;
@@ -445,12 +447,14 @@ _mesa_BeginTransformFeedback(GLenum mode)
       return;
    }
 
-   for (i = 0; i < info->NumBuffers; ++i) {
-      if (obj->BufferNames[i] == 0) {
-         _mesa_error(ctx, GL_INVALID_OPERATION,
-                     "glBeginTransformFeedback(binding point %d does not have "
-                     "a buffer object bound)", i);
-         return;
+   for (i = 0; i < ctx->Const.MaxTransformFeedbackBuffers; i++) {
+      if ((info->ActiveBuffers >> i) & 1) {
+         if (obj->BufferNames[i] == 0) {
+            _mesa_error(ctx, GL_INVALID_OPERATION,
+                        "glBeginTransformFeedback(binding point %d does not "
+                        "have a buffer object bound)", i);
+            return;
+         }
       }
    }
 
@@ -470,7 +474,7 @@ _mesa_BeginTransformFeedback(GLenum mode)
        * feedback.
        */
       unsigned max_vertices
-         = _mesa_compute_max_transform_feedback_vertices(obj, info);
+         = _mesa_compute_max_transform_feedback_vertices(ctx, obj, info);
       obj->GlesRemainingPrims = max_vertices / vertices_per_prim;
    }
 

src/mesa/main/transformfeedback.h

@@ -50,7 +50,7 @@ extern void
 _mesa_init_transform_feedback_functions(struct dd_function_table *driver);
 
 extern unsigned
-_mesa_compute_max_transform_feedback_vertices(
+_mesa_compute_max_transform_feedback_vertices( struct gl_context *ctx,
       const struct gl_transform_feedback_object *obj,
       const struct gl_transform_feedback_info *info);