[Mesa-dev] [PATCH 3/6] glsl: Generalize compute_packing_order for varying structs.

[Paul Berry]

This patch paves the way for allowing varying structs by generalizing
varying_matches::compute_packing_order to handle any type of varying.
Previously, we packed in the order (vec4, vec2, float, vec3), with
matrices being packed according to the size of their columns.  Now, we
pack everything according to its number of components mod 4, in the
order (0, 2, 1, 3).

There is no behavioural change for vectors.  Matrices are now packed
slightly more sensibly (e.g. a mat2 is now packed with vec4's, which
guarantees that it will occupy a single varying slot, whereas it
previously was packed with vec2's, which meant that it might get split
across two adjacent slots).
---
 src/glsl/link_varyings.cpp | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/glsl/link_varyings.cpp b/src/glsl/link_varyings.cpp
index 5a3240b..d8f501c 100644
--- a/src/glsl/link_varyings.cpp
+++ b/src/glsl/link_varyings.cpp
@@ -804,16 +804,15 @@ varying_matches::compute_packing_order(ir_variable *var)
 {
    const glsl_type *element_type = var->type;
 
-   /* FINISHME: Support for "varying" records in GLSL 1.50. */
    while (element_type->base_type == GLSL_TYPE_ARRAY) {
       element_type = element_type->fields.array;
    }
 
-   switch (element_type->vector_elements) {
+   switch (element_type->component_slots() % 4) {
    case 1: return PACKING_ORDER_SCALAR;
    case 2: return PACKING_ORDER_VEC2;
    case 3: return PACKING_ORDER_VEC3;
-   case 4: return PACKING_ORDER_VEC4;
+   case 0: return PACKING_ORDER_VEC4;
    default:
       assert(!"Unexpected value of vector_elements");
       return PACKING_ORDER_VEC4;
-- 
1.8.1.1