[Mesa-dev] [PATCH 3/4] glsl: apply align layout qualifier rules to block offsets

[Timothy Arceri]

>From Section 4.4.5 (Uniform and Shader Storage Block Layout
Qualifiers) of the OpenGL 4.50 spec:

  "The align qualifier makes the start of each block member have a
  minimum byte alignment.  It does not affect the internal layout
  within each member, which will still follow the std140 or std430
  rules. The specified alignment must be a power of 2, or a
  compile-time error results.

  The actual alignment of a member will be the greater of the
  specified align alignment and the standard (e.g., std140) base
  alignment for the member's type. The actual offset of a member is
  computed as follows: If offset was declared, start with that
  offset, otherwise start with the next available offset. If the
  resulting offset is not a multiple of the actual alignment,
  increase it to the first offset that is a multiple of the actual
  alignment. This results in the actual offset the member will have.

  When align is applied to an array, it affects only the start of
  the array, not the array's internal stride. Both an offset and an
  align qualifier can be specified on a declaration.

  The align qualifier, when used on a block, has the same effect as
  qualifying each member with the same align value as declared on
  the block, and gets the same compile-time results and errors as if
  this had been done. As described in general earlier, an individual
  member can specify its own align, which overrides the block-level
  align, but just for that member.
---
 src/glsl/ast_to_hir.cpp | 51 ++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/src/glsl/ast_to_hir.cpp b/src/glsl/ast_to_hir.cpp
index f5da771..fd05fd7 100644
--- a/src/glsl/ast_to_hir.cpp
+++ b/src/glsl/ast_to_hir.cpp
@@ -6212,7 +6212,8 @@ ast_process_struct_or_iface_block_members(exec_list *instructions,
                                           ir_variable_mode var_mode,
                                           ast_type_qualifier *layout,
                                           unsigned block_stream,
-                                          unsigned expl_location)
+                                          unsigned expl_location,
+                                          unsigned expl_align)
 {
    unsigned decl_count = 0;
    unsigned next_offset = 0;
@@ -6466,6 +6467,34 @@ ast_process_struct_or_iface_block_members(exec_list *instructions,
             }
          } else {
             fields[i].offset = -1;
+         }
+
+         if (qual->flags.q.explicit_align || expl_align != 0) {
+            unsigned offset = fields[i].offset != -1 ? fields[i].offset :
+               next_offset;
+            if (align == 0 || size == 0) {
+               _mesa_glsl_error(&loc, state, "align can only be used with "
+                                "std430 and std140 layouts");
+            } else if (qual->flags.q.explicit_align) {
+               unsigned member_align;
+               if (process_qualifier_constant(state, &loc, "align",
+                                              qual->align, &member_align)) {
+                  if (member_align == 0 ||
+                      member_align & (member_align - 1)) {
+                     _mesa_glsl_error(&loc, state, "align layout qualifier "
+                                      "in not a power of 2");
+                  } else {
+                     fields[i].offset = glsl_align(offset, member_align);
+                     next_offset = glsl_align(fields[i].offset + size, align);
+                  }
+               }
+            } else {
+               fields[i].offset = glsl_align(offset, expl_align);
+               next_offset = glsl_align(fields[i].offset + size, align);
+            }
+         }
+
+         if (!qual->flags.q.explicit_offset) {
             if (align != 0 && size != 0)
                next_offset = glsl_align(next_offset + size, align);
          }
@@ -6590,7 +6619,8 @@ ast_struct_specifier::hir(exec_list *instructions,
                                                 ir_var_auto,
                                                 layout,
                                                 0, /* for interface only */
-                                                expl_location);
+                                                expl_location,
+                                                0 /* for interface only */);
 
    validate_identifier(this->name, loc, state);
 
@@ -6771,6 +6801,20 @@ ast_interface_block::hir(exec_list *instructions,
       }
    }
 
+   unsigned expl_align = 0;
+   if (layout.flags.q.explicit_align) {
+      if (!process_qualifier_constant(state, &loc, "align",
+                                      layout.align, &expl_align)) {
+         return NULL;
+      } else {
+         if (expl_align == 0 || expl_align & (expl_align - 1)) {
+            _mesa_glsl_error(&loc, state, "align layout qualifier in not a "
+                             "power of 2.");
+            return NULL;
+         }
+      }
+   }
+
    unsigned int num_variables =
       ast_process_struct_or_iface_block_members(&declared_variables,
                                                 state,
@@ -6782,7 +6826,8 @@ ast_interface_block::hir(exec_list *instructions,
                                                 var_mode,
                                                 &this->layout,
                                                 qual_stream,
-                                                expl_location);
+                                                expl_location,
+                                                expl_align);
 
    state->struct_specifier_depth--;
 
-- 
2.4.3