vkd3d-shader: Introduce a function to build a varying map between sm1 stages.

Approved-by: Henri Verbeet (@hverbeet)
Approved-by: Alexandre Julliard (@julliard)
Merge-Request: https://gitlab.winehq.org/wine/vkd3d/-/merge_requests/280

include/vkd3d_shader.h

@@ -1743,6 +1743,8 @@ struct vkd3d_shader_next_stage_info
      * field is necessary to correctly match inter-stage varyings.
      * This mapping may also be necessary under other circumstances where the
      * varying interface does not match exactly.
+     *
+     * This mapping may be constructed by vkd3d_shader_build_varying_map().
      */
     const struct vkd3d_shader_varying_map *varying_map;
     /** The number of registers provided in \ref varying_map. */
@@ -2262,6 +2264,35 @@ VKD3D_SHADER_API int vkd3d_shader_serialize_dxbc(size_t section_count,
  */
 VKD3D_SHADER_API void vkd3d_shader_free_scan_signature_info(struct vkd3d_shader_scan_signature_info *info);
 
+/**
+ * Build a mapping of output varyings in a shader stage to input varyings in
+ * the following shader stage.
+ *
+ * This mapping should be used in struct vkd3d_shader_next_stage_info to
+ * compile the first shader.
+ *
+ * \param output_signature The output signature of the first shader.
+ *
+ * \param input_signature The input signature of the second shader.
+ *
+ * \param count On output, contains the number of entries written into
+ * \ref varyings.
+ *
+ * \param varyings Pointer to an output array of varyings.
+ * This must point to space for N varyings, where N is the number of elements
+ * in the input signature.
+ *
+ * \remark Valid legacy Direct3D pixel shaders have at most 12 varying inputs:
+ * 10 inter-stage varyings, face, and position.
+ * Therefore, in practice, it is safe to call this function with a
+ * pre-allocated array with a fixed size of 12.
+ *
+ * \since 1.9
+ */
+VKD3D_SHADER_API void vkd3d_shader_build_varying_map(const struct vkd3d_shader_signature *output_signature,
+        const struct vkd3d_shader_signature *input_signature,
+        unsigned int *count, struct vkd3d_shader_varying_map *varyings);
+
 #endif  /* VKD3D_SHADER_NO_PROTOTYPES */
 
 /** Type of vkd3d_shader_get_version(). */

libs/vkd3d-shader/vkd3d_shader_main.c

@@ -1891,3 +1891,41 @@ void shader_instruction_array_destroy(struct vkd3d_shader_instruction_array *ins
         vkd3d_free(instructions->icbs[i]);
     vkd3d_free(instructions->icbs);
 }
+
+void vkd3d_shader_build_varying_map(const struct vkd3d_shader_signature *output_signature,
+        const struct vkd3d_shader_signature *input_signature,
+        unsigned int *ret_count, struct vkd3d_shader_varying_map *varyings)
+{
+    unsigned int count = 0;
+    unsigned int i;
+
+    TRACE("output_signature %p, input_signature %p, ret_count %p, varyings %p.\n",
+            output_signature, input_signature, ret_count, varyings);
+
+    for (i = 0; i < input_signature->element_count; ++i)
+    {
+        const struct vkd3d_shader_signature_element *input_element, *output_element;
+
+        input_element = &input_signature->elements[i];
+
+        if (input_element->sysval_semantic != VKD3D_SHADER_SV_NONE)
+            continue;
+
+        varyings[count].input_register_index = input_element->register_index;
+        varyings[count].input_mask = input_element->mask;
+
+        if ((output_element = vkd3d_shader_find_signature_element(output_signature,
+                input_element->semantic_name, input_element->semantic_index, 0)))
+        {
+            varyings[count].output_signature_index = output_element - output_signature->elements;
+        }
+        else
+        {
+            varyings[count].output_signature_index = output_signature->element_count;
+        }
+
+        ++count;
+    }
+
+    *ret_count = count;
+}